Basic Electricity 101+ for BMW Airhead motorcycles
....and other vehicles.
© Copyright, 2014, R. Fleischer
Also see my other electrical articles; in particular
There is a large section on electrics on this website, MANY articles; including this one: http://bmwmotorcycletech.info/misclelectrical.htm
This article was written to furnish THREE types of information:
(1) CONSIDERABLE amount of BASIC & SLIGHTLY ADVANCED INFORMATION on electricity & Airhead problems. The approach used here is probably different than in manuals & troubleshooting guides that you might have, or are contemplating obtaining. Although some hints are given in this article on some common faults, this article should be used in conjunction with other articles on this website, particularly: http://bmwmotorcycletech.info/electricalhints.htm
(2) Common problem areas, explanations of some of the circuitry. A discussion of such as batteries; starter motors, voltage regulators, etc.....a goodly amount of good technical information. Other articles will get far deeper into these things.
(3) An addendum that may discuss some particular point that has come up, or some topic of interest. SOME is at the very END of this article.
Available to you are certain helpful booklets from such as Motorrad Elektrik, Chitech, Haynes and/or
Clymers manuals (and, perhaps, a schematic in the rear of your owners booklet or on this Snowbum website).
These, or some of them, may well be necessary items for you, and are actually recommended ...and
if you are anal enough, get them all. In MY OPINION, the Chitech electrics manual and the owners book or factory schematic, or schematics on this website (and some elsewhere's, and I have links to
these on this website), are THE BEST sources for electrical information for the Airheads.
I recommend you purchase at least the Chitech Electrics Manual. The Chitech (Chicago Region BMW Owners Assoc.) BMW Electric School Manual is THE BEST manual for BMW electrics, from basics to full-blown technical details, components, diagrams, etc., & includes the singles & all Airheads; even some on the /2 era. It is VERY complete. Only a few errors are in it; I have an article I wrote on those errors. Here is the link to my Critique of the Chitech BMW Electric School Manual: http://bmwmotorcycletech.info/chitechelmnl.htm
See http://bmwmotorcycletech.info/url.htm article for more information on Chitech, and how to order their publication. Some of the total-bike schematics are not reproduced well, that is the only substantial problem with that manual. Get it anyway.....as the diagrams you probably will need are on MY website, and ARE reproduced well-enough. On top of which, I can supply any schematic.
I can almost guarantee that if you read the following article; and, purchase and study the Chitech electrics manual, you will become very familiar with electricity, electrical problems, and how to think and go about maintaining and repairing electrical things...and hardly just for your motorcycle(s). If electricity and electronics has always been a sore point for you, why not fix that now?
Here is a link to a website that has NUMEROUS articles on basic electricity. It also has a lot of articles on Toyota repairs, but you will likely find that the basic articles are VERY good. If you are interested in having a working knowledge of how vehicle electrical systems operate; this is not a bad place to review, in-depth. Read all the basic articles, and maybe more. I suggest that you read my own article, below, and then come back at your leisure and read the articles at this link: http://autoshop101.com/. This link is to the best series of articles I presently know of.
Section 1, Basic Electricity...and then some!
Much of the following on basic electricity & its use for Airheads and other motorcycles
is rather simplified. I do get into some complex, nerdy things. Please,
no flaming from
fellow engineers due to my simplifications!
Electricity might be easiest to think of as a flow of atomic-sized particles called electrons. These little bits have a 'charge'. Get enough of these little charges moving through a wire, & you have a flow of CURRENT. Apply the flow through something like a lamp, & if enough are flowing, the lamp will heat up, & will put out heat and light. Too much flow, the lamp burns out just like a fuse which blows for excessive current flow.
Current flow is measured in amperes & in many instances very tiny parts of an ampere, such as milli-amperes or micro-amperes. Milli- means thousandth of; and micro- means millionth of. Current may be listed as A for amperes, ma for milliamperes, when some device has a current rating. If a diagram showed current flows to be expected, it might show something like 12 A for 12 amperes, or 12 ma, which stands for 12 milliamperes. 12 µa would stand for 12 microamperes.
It is still popular to use water pipes to explain electricity. I find that this often confuses people. In MY opinion, it is OK to for a FEW of these popular explanations:
(a) Water pressure is the force (voltage), that allows more flow from the faucet, at a given faucet opening.
(b) That adjustable faucet opening is like resistance (ohms). The symbol used to express resistance (ohms) is the omega sign. Resistance may also be shown as R; for instance, R = 12,000 ohms.
(c) As with voltage and current, abbreviations are often used. For example: 12Kv means 12,000 volts....the K meaning Kilo, or one-thousand. Power is generally shown in watts or Kw.
(d) Power can also be expressed in horsepower...more on that a bit downwards.
There are distinct relationships between amperes, ohms, voltage, power, horsepower, and several other things. The relationships can be
manipulated easily, so if you know any two of these items, you can usually calculate a third,,,,or even most of the others.
The first basic relationship is simply that resistance in ohms is equal to voltage in volts divided by current in amperes. Engineers and many others use the formula R=E/I. Why these letters? The background in symbols for electricity is a bit involved. Both V and E have been used for voltage. In the formula, E stands for voltage. The reason E is used is that the E means Electromotive Force (which you can now forget, unless you ever see EMF and want to know, then look it up on Google). I is used for current flow in amperes. Schematic diagrams use R, V or v, and A.
There are other relationships you might be interested in. Power, expressed as watts (W or w), is equal to voltage in volts multiplied by current in amperes.
If you think about this for a few moments, you might notice that Power, expressed in watts, is ALSO equal to amperes squared, multiplied by ohms.
Wee bit of nerdy-ness that might be actually usable for you: Electrical Power, that Watts stuff.... is related to horsepower. Officially, 746 watts is ONE horsepower. Often it is rounded to 750. Engines from Germany are often rated in kW or Kw or KW. All three mean kilowatts, one of which is 1,000 watts. If your Airhead engine is rated at 44 kW, that is 59 hp. Can you see how I got that figure? (44 kW is 44,000 watts. Divide that by 746). If your Airhead's starter motor is rated at 0.7 Kw, that is 700 watts. Thus, 700 divided by 750 is 0.933 Hp.
In order to have CURRENT FLOWING, electrons must begin someplace, travel 'through a circuit' AND BE RETURNED to the source. Please do not think of that idly! A great many folks have a problem realizing that a COMPLETE circuit is necessary. Here, "circuit" means the same thing as a closed racetrack, or some other analogy ....you start at one point, and must continue ALL the way around. If the electrons do NOT continue all the way around, there is NO CURRENT (amperes) FLOW and hence no work (watts) done. Simple example: You have a floor lamp in your living room. It requires TWO wires to the power plug. If you cut one wire, there can be NO 'circuit'. In your motorcycles, the engine metal, transmission metal, frame, etc.....are all connected together mechanically, and since the surfaces are bare, unpainted, etc., the entire structure is or can be part of a circuit. Thus, you will find BROWN wires (solid brown means GROUND, or EARTH, as used by Germany) at various places, connected to the metal structures.
A battery can be said to have an excess of electrons at one terminal compared to the other terminal, but NO current (other than a small internal leakage) is flowing. You need to have the device to be powered, a lamp for instance, connected somehow, which means directly or through other items, to BOTH battery terminals, for electrons to flow THROUGH the lamp & any other items, and through the battery too. This idea of a complete circuit often eludes folks.
When electrons flow through something allowing such a flow (usually metallic, and called a 'conductor'), the properties of the conductor are such that the conductor itself always (unless at or near absolute zero temperature...said here for those purist nerds out there reading this) offers SOME 'resistance' to the flow. A thinner wire would offer much more resistance to flow to your starter motor, than a much thicker wire. If the starter motor wire was effectively too thin, the starter would not even rotate. That could happen on a very large stranded wire cable because individual copper wires had broken. This can happen from a mechanical break or chemical corrosion. If you have a switch that makes poor electrical contact, you can have similar resistance to current flow. Resistance is generally undesirable in our motorcycle wiring, switches, etc. You can't get away from resistance at common temperatures.
As more & more electrons flow through a conductor, the conductor will get warmer. This is how a fuse works. If the connection is not good, a small amount resistance, a value not desirable, might allow enough heating to cause problems. This is quite often seen at the Ahead alternator output terminals and at the diode board output terminal; ...where the insulators or wire ends that push over the spade terminals are often seen overheated.
An 'insulator' can generally be thought of as something that has such a high resistance that
electricity in any appreciable amount does not flow through it.
In many electrical and electronics devices, a part called a RESISTOR is used on purpose to restrict electron flow. There are places in your motorcycle that this is also done on purpose; such as resistors in your tachometer electronics circuit, or in a /5 starter relay (the /5 starter relay is a special type), etc. The coil of wire in relays and the starter motor switch windings are selected to allow a sufficient magnetic field, yet not burn up. Resistance is added sometimes on purpose ...perhaps to OBTAIN heating, such as with heated grips. In your motorcycle you have resistance in the wires themselves, in diodes, contacts in switches and connectors, relay coils, lamps, ignition coils, alternator rotor & stator windings...even the rotor's carbon brushes (close to 3/4 of one ohm for both of the brushes measured together), ETC.
Resistance values can add up from various causes; if excessive, you will have problems with your motorcycle. You may get undesirable resistances from such as corroded connections, poor contacts in a switch, a few broken strands of a wire; loose connections, etc. Excessive resistance can come about in some strange ways, & cause problems. BMW had some problems with irregularities in battery charging voltage due to poor grounds at the diode board ...but also had some irregularities from the PAINT on the surface of the timing chest ....which affected the accuracy of the alternator voltage regulator!
A commonly seen problem is at the plug-in version of the STARTER relay, where even a fairly modest amount of corrosion causing poor connections at the relay male spades and/or the socket female connection would cause big electrical problems ...quite often the entire bike went dead electrically. I have a permanent fix for that, located in the Snowbum website, http://bmwmotorcycletech.info/
In our BMW Airheads, the resistance of the GEN lamp is used on purpose to not only let the lamp provide an indication of charging, but to supply the correct amount of current for the initial magnetization of the alternator rotor (via the circuit basically consisting of the battery, ignition switch, & voltage regulator internals).
Your alternator must have a certain number of turns of wire, in order to obtain proper VOLTAGE output. If we wanted to reduce the resistance (the unit of measurement of resistance is the OHM) to allow more CURRENT output (current times voltage is WATTS), we need either a lower resistance copper wire (via a larger diameter copper wire), or a metal that flows electrons with less resistance. Copper is far cheaper than silver, which is THE best conductor of electricity. Aluminum wire is far WORSE electrically, so is almost never considered for such things, although some homes, etc., had aluminum wire installed....which is OK if the end fittings are proper type and assembled properly, otherwise, major problems occur.
The existing alternator physical size is more or less fixed, so we can't pack a lot more volume of copper wire into the alternator. Increasing the wire size (which would give less turns, less voltage, not more turns of a larger thickness wire, which is desirable) is not possible. The aftermarket Omega alternator gets its higher output mostly by physical changes in the alternator part sizes, changes of winding turns, tolerance of the rotor to stator, and a number of such things, that, together, add up......as well as still the existing timing chest casting. There is a lot to this, so won't go deeper here.
So far I have mentioned amperes, volts, ohms, watts; and, that when current (amperes) is flowing through a resistance (ohms), due to being forced through the conductor by pressure (voltage), HEAT is produced. In some cases the heat is desirable or necessary, like in an incandescent lamp (or, is used to open a fuse if the current is excessive). In other cases heat is not desirable. Semiconductor 'things' like diodes & transistors, generally do NOT like heat. They particularly do not like excessive heat, and also do not like to be cycled, cold>>hot>>cold ...this cycling tends to bring about stress failures from molecular-sized faults created in the never perfect manufacturing process. Sub-microscopic cracks, if you will.
In addition, there is the problem of excessive heat. In many types of electronics equipment, excessive heat causes the circuitry to fail, sometimes in intermittent ways. This happens to the older style of mounting of the ignition module under the tank. If it overheats due to lack of regular replacement of the heat conducting paste, it may fail to work properly. Fresh paste fixes things ..without replacing the $$ module, but if you let it overheat a large number of times, that USUALLY leads to permanent failure.
Heating/cooling cycles can be responsible for diode board failures. The heating is caused by the engine heat itself, as well as the current flow through the diodes. Diodes have an internal resistance, & thus the current flowing through them adds more heat. That was a problem on some early diode boards, as they did not have the large diodes outer wires bent-over before soldering; the only part the solder contacted was the tiny wire, and the JUNCTION got too hot; the solder melted, and soon formed an electrical arc. That was in the early 1980's. It is fixable.
If the flow of electricity is restricted by such as a too thin wire (like maybe some broken strands!),
badly corroded connections, sulfated battery, poor switch connections, etc....then we can say that there is 'excessive
resistance'. That literally means that there is excessive resistance to current flow.
Voltage is typically measured by allowing a teensy-small amount of current to be diverted from the circuit being tested & applying that diversion to some sort of meter, in such a way as to have a calibrated reading. Depending on the circuit under test, most digital meters divert so little current that the voltage is not noticeably changed by attaching the meter. For many vehicle circuits, the same could be said for analog meters, which take a lot more current to operate, but the current is still miniscule, compared to the current flowing or available in the tested point. This is usually universally true for situations where the source being measured is of low internal resistance, such as almost every area of a vehicle. This is NOT quite so true of the electronic ignition, which has some areas you should not even try to measure with a meter (the Hall device, as example).
Resistance in ohms, or kilo-ohms (thousands of ohms) or meg-ohms (millions of ohms) is typically measured by applying a small voltage to the part under test by internal meter circuitry in such a way that the current flow is indicated on the meter, but the meter is marked or displays for the effective resistance in the circuit. That is why ohmmeters contain at least one battery, to produce that small current flow through the part under test. Some meters contain a second battery for higher resistance ranges, and possibly a third battery for powering the digital display, if it is that type. Some devices, such as diodes, are often quick-tested by means of an ohmmeter. NEVER EVER connect a meter, on the resistance function(s), to a circuit that is powered. You will likely damage the ohmmeter extensively.
Common types of simple diodes (which are one-way devices as far as electron flows are concerned) must pass current in one direction, and not in the other (or, very very little). If the ohmmeter does not apply enough voltage and also current to the diode being tested, the diode may well not 'turn on' in the so-called 'forward direction'. Not 'turning on' means the diode acts like a VERY high resistance. This DOES happen on some, usually expensive, digital meters THAT ON PURPOSE use super-low currents to avoid damaging extra-sensitive devices that might be connected to the meter. There is hardly any use for such a meter on your Airhead motorcycle. Do not purchase a meter unless it tests diodes adequately. The readings on a meter that do NOT turn on diodes properly might be so weird as to be unusable. I will be getting into this deeper in the next few paragraphs.
It is common practice to use an ohmmeter to check diodes for forward & backwards resistance. Back resistance, or reverse resistance, is also called reverse leakage. Many digital meters will have a specific diode-testing function. In that function, the meter, proper polarity connected, reads the voltage drop the diode exhibits in the FORWARD CONDUCTION DIRECTION from a small meter-supplied voltage (via a resistor inside the meter to limit current flow). This usually is a approximately a half of one volt. This test is useful to those with some electrical/electronics knowledge....but what YOU are likely to be more concerned with is NOT that voltage, NOR is it what you may see in various literature about "the ratio of forward to backwards resistance of the diode". Most of your diode testing on your motorcycle will be on POWER diodes, which have a fairly LOW forward conduction mode & resistance. The forward resistance (the conducting direction) of such a diode should simply show a very low resistance. The exact value depends on your meter design & the type of diode. It might be 30 ohms or it might be a couple hundred. In the reverse direction the resistance on the meter should be VERY much higher....in the millions of ohms is not unusual. Thus, ratios and voltage are not really important, what is important is that the forward conduction resistance is VERY LOW, and the reverse connection shows the resistance to be VERY high. Any voltage test (if your meter has a diode testing function), should be approximately half a volt. If you REALLY wanted to test the diode thoroughly, the test needs to be with at least one end of the diode disconnected from anything; and both ohmmeter tests in both leads directions and a dynamic test, with a transformer and lamp, need to be performed. If the diode passes those tests, you can be 99% confident the diode is OK. But, you can be 90% confident just testing the diode FULLY CONNECTED IN ITS CIRCUIT....this is especially so for nearly every diode in your AIRHEADS motorcycle.
If anything else is connected to
the diode, the readings might be faulty. It may take some experience & knowledge to know
exactly what you should expect. I suggest you try testing some diodes that are not connected
to anything. Test large & small power diodes for sure. Use both ohmmeter and diode test
functions if you have both. Disconnect the battery in your Airhead, and test the diode board....while it is still in the bike, and connected. If you have a board out of the bike, test it too, and compare readings. Get a feel for testing results.
The applied voltage to the diode must be at least half a volt for most common diodes to 'turn on' in this 'forward' direction. Some types of diodes are specifically made for some 'strange' functions. A Zener diode is used in your electronics type voltage regulator, & some tachometers, to regulate a voltage to some set value...or provide a reference for that type of function. There are diodes used in your CD or DVD player or laser pointer pen, called laser diodes. Some types of laser diodes are specifically manufactured to be indicators. These emit a beam of light. In some, the light is invisible to our eyes. Laser diodes are used for all sorts of things, including vehicle tail lights, backlighting on TV & computer screens, etc. Besides the small & large diodes in your Airhead's diode board, you may find, depending on year & model, other diodes in your BMW Airhead motorcycle...in the headlight relay, starter relay, underside of the connection board in the headlight shell, & in the wiring harness near the coils if a R45 or R65.
Diodes, in the forward, turned-on direction, can be thought of as having an internal resistance; which causes a relatively constant voltage drop as current passes through the diode. With enough current flowing, diodes can develop a lot of heat. That is seen from the formulas you learned about earlier in this article. The forward voltage drop of a common silicon power diode is fixed by atomic properties at approximately 0.5 volt. Therefore, at 10 amperes, there is about 5 watts of heat to somehow be gotten rid of. There are 6 of those large power diodes in your diode board. Thus a goodly amount of heat must be cast off, which is done by the L metal ends of the diode board, to which the power diodes are pressed into. Some is also absorbed by the passing air. However, the hot engine also radiates to the diodes. The RUBBER-MOUNTED diode boards, that were used on some models of Airheads, can NOT remove the heat all that well to the timing chest metal, it being already hot from the engine being run. This is JUST ONE of the SEVERAL reasons I HIGHLY recommend that rubber mounts be changed to aftermarket metal ones from Motorrad Elektrik, http://www.motoelekt.com or Thunderchild, http://www.thunderchild-design.com, etc. Other reasons to get rid of the rubber mounts is that they deteriorate and then cause problems; AND, use of solid mounts eliminates the need for most of the extra grounding wires. Refer to BMW bulletins and my article on this: http://bmwmotorcycletech.info/diodebds&grdgwires.htm.
With solid metal diode board mounts the alternator almost always operates better as far as output power and slightly better on voltage regulation! You won't have rubber mounts failing in the future either. There are NO PROBLEMS using solid mounts....except for the modest hassle of installing them. They cost about $10 to $20 for a full set of 4. VERY worthwhile modification, if your bike did not come with solid mounts.
Although your motorcycle may have a lamp marked GEN, it is really an ALTERNATOR (ALT) indicator. Generator, the name, has been used for a very long time as a generic term for most any source of energy from a mechanical-electrical source (not a storage battery). In actual fact, a generator can be a source of something NOT involved with electricity at all! A REAL old-term Generator typically uses carbon brushes & an armature winding with a commutator. Yes, that means similar to a starter motor. In fact, most electric generators can be used as a starter, and vice-versa. Note that the Alternator in our bikes GENERATES electricity. So, it is perfectly OK for the alternator lamp to be a GEN lamp as marked.
A little story:
When the world was first being electrified by Edison (for street lamps, home lamps & industrial motors), electric current flowed in one direction, this current was called DC, Direct Current. This is in your motorcycle, at low voltage, in the BATTERY circuits. DC was very limiting. When you had enough homes & factories using electricity, the wires needed to supply all of them became larger & larger, as more and more current must pass in total. Soon the wires are very unwieldy. This was particularly so because the voltages used in homes was typically 110 & 220, & industry used as much as 660. It is almost impossible...or totally outrageous in cost.... to move lots of electricity, if it is low voltage DC, over long distances. A DC generator can be made that produces almost any voltage, but that voltage needs to be very high for efficient transmission to someplace...but there is no good way to drop the voltage to usable levels, such as in your home, for lighting, or mostly anything else. If you used a resistor, it uses up electricity, producing heat. If the generator uses lower voltage, it cannot be changed to a much higher voltage with any sort of efficient method....at least back in Edison's time.
This is where Edison personally failed, from stubbornness, insisting on DC. Edison had his ego on the line so strongly in this area, that he lied about the dangers of A.C., & was quite a nasty guy in some respects regarding AC versus DC. Edison lost, as we all know, since our homes, factories, etc., are all run on A.C. The major exceptions are in vehicles, at least in the battery circuits.
Note that moving A.C. over long distances would have the same problems if the voltage was low, it would require massive wire size.....but for A.C., we can TRANSFORM voltage/current (actually, we can transform D.C. these days easily). POWER is, as you have already learned in this article, a product of voltage & current, so for any given amount of power, you can raise the voltage & lower the current. Since the capacity of a wire is determined by CURRENT, raising the voltage and using better insulation (if required) is very economical, compared to using D.C. Thus we use the same size of wires, but they carry more power. Enormous amounts of alternating current power is moved about by using extremely high voltages. Half a million volts is NOT unusual anymore. That is why you see very tall towers with very big insulators here and there.
Summing up: Alternating Current has a HUGE advantage over Direct Current, it can be EASILY and cheaply transformed. There is a very widespread use of an electrical item called a transformer. There is probably a large one on a power pole near your home. Typically the very top wires on the pole might carry 12,000 volts, with the output side of the pole transformer being 120/240 for your home.
Just what IS a transformer? (no, I don't mean a childs toy):
A transformer is a specially designed magnetic steel structure, with some turns of copper wire on it called a coil, and another such 'COIL' of more (or less) turns of wire, the two generally being electrically separated (that means insulated from each other) but magnetically coupled. This 'transformer' can VERY efficiently can change an A.C. voltage to a lower or higher voltage...and there are NO moving parts to wear out. Transformers CAN be built in which there is only one winding, with multiple taps, but that usage offers NO isolation between input and output. That could be VERY dangerous for homes, so is not used on neighborhood power poles.
NOTE: Power, these days, can be transformed/converted, from DC to AC to DC, relatively efficiently (perhaps 92% or more) by means of relatively complicated transistorized circuits. This is done in all
sorts of electronics devices such as laptop computers, smart phones, & every sort of small device,
some larger ones, only rarely in massively large ones (for industry). It is beyond the scope of
this article to get deeply into these applications & how it is done. The bottom-line is, that in
general, the extreme reliability of wound transformers, where applicable, is the preferential way
to go to move electric power, or change from low voltage AC to high voltage AC, & vice versa, & has been, for a VERY long time: http://www.edisontechcenter.org/Transformers.html. What is particularly interesting about that article, to me, an electronics engineer, is the failure to discuss
Mr. Edison's stubbornness about AC/DC.
Since you have learned that POWER (watts) is voltage times amperes, this means that we can TRANSFORM the electrical energy output of a power plant to a super high voltage, & send that power someplace ...which is obviously at a much lower CURRENT (amperes) than if the voltage was less. Remember, the current carrying capacity of a wire is a primary function of the wire physical size (cross-section actually). Thus, for a given WATTAGE of power plant (major power plants are typically in the many millions, megawats, mw), we can use THINNER wire to send the SAME power plant output hundreds if not many thousands of miles... if the VOLTAGE is high enough. This thinner wire might still be very thick for large power plants, but it can carry a lot of power at half a million volts. That high voltage can be AND IS, TRANSFORMED downwards...usually in steps...first at a local power distribution center...and then dropped farther in your neighborhood by a transformer on a power pole...until it enters your home at 115 or 230 volts. On most homes, both voltages are supplied. Whether or not your house is said to have 110, or 115, or 120 volts, the actual value is about the same, or, as we say, a NOMINAL value (probably around 118; plus twice that on another wire connection). It is common in the USA today to use a nominal 120, 240, 440, and 660 volts, the first two for homes, and the last two for big machines used in industry.
Electricity in your home is A.C. (Alternating Current). Over a portion of time, the voltage at the wall socket is constantly varying, going up & down from a reference of ZERO as it follows a CURVE that mathematically is called a SINE WAVE. A sine wave looks something like an S, laying on its side. Draw a line through the middle, and you have equal curve above (+) and below (-). Much further down this page I have sketches of single waveforms & 3 phase waveforms. A sine curve is a very specific type of curve, that can be described mathematically. I shall spare you of that discourse here.
When this 'WAVEFORM' goes from zero to maximum positive, back down through zero & to maximum negative & then back to zero, that is called 'ONE CYCLE'. Of course, ONE CYCLE could mean starting at ANY place on that sine curve, & advancing in TIME until it reaches the same place on the sine curve that it started from (later in time, of course). Conventionally one just thinks of it starting & ending at zero. Cycles per second (CPS) gave way many years ago to the term HERTZ (Hz), to honor a Mr. Hertz who was a famous scientist involved in the study of magnetic fields. In your USA home, the number of Hertz (cycles per second), is 60. This value is kept very accurately by your power company...so accurately that electro-mechanical clocks run accurately. In things like some TV sets, it is critical that the 60 Hz be proper. In some areas of the world 50 Hz is used. For technical reasons dealing with magnetic fields, 50 Hz devices will often be heavier. This article will not deal with frequencies involved with sound, radio, TV, etc.
A special form of "transformation" is actually done in by your motorcycle alternator. Mechanical power is changed to electrical power.
Electrical-magnetic transformation is done in your Airhead in the ignition coil, which, almost by trickery, has a DC voltage applied that is made to ultimately act like a form of AC. I suppose one could argue that the electronic tachometer works by transformation; and some types of mechanical tachometers and speedometers work by transformation, using a property called Eddy Currents. I may get into eddy currents later here. While you cannot magnetize aluminum, you can induce current flow by means of a thing called eddy currents, which can apply force, and make the needle of your speedometer work. This SAME eddy current is what causes the ALUMINUM disc of your household electric use measuring device to spin, driving gears, that make small hands/dials show electrical use!!
Regarding the ignition coil:
DC from the battery is applied to a moderately low number of winding turns of reasonably large copper wire. This is called the PRIMARY winding. The resistance is fairly low & thus the proper level of current passes through it. The current in those turns, from applied battery voltage, produces a large magnetic field, very quickly after being applied. The magnetic field is stored in the winding & iron core so long as the power still is applied. The SECONDARY winding has many thousands of turns of much thinner wire, so the required number of turns will fit into the coil enclosure. It is a property of transformers that TURNS RATIOS have specific properties. As an example, a one turn primary & a 1000 turn secondary gives a multiplication of 1:1000 in voltage step up (with a corresponding DROP in CURRENT). If the secondary voltage is high enough, it can break down the resistance of human skin, and pass into the body, dangerously in some cases. It is hard to give absolute values, but generally you will not get an electrical shock if your skin, even if wet, comes in contact with a voltage under perhaps 30 volts. However, sometimes circuits have strange effects, and an applied voltage can be multiplied in strange ways. An example is in Airheads up through year 1980, where the ignition points may have no voltage across them, when the points are closed, and 12 volts when open, but may have many times that number during actual engine operation, so you could get a mild electrical shock if you touched the points or points circuit.
Our ignition coil(s) output can be MANY thousands of volts; as much as 40,000 is possible on 1981+ models.
So you have the primary winding of your ignition coil (the one with the spade lugs) having a relatively
small number of turns of a wire that is relatively thick, and the current is relatively high (at least 4
amperes, and can be higher)..
STOP!!....>>>did you happen to think: ""12 volts, 4 amperes...that's 48 watts needed from the alternator/battery"". NO? Why did you not think of this?
Since VERY high voltages are being developed in the ignition coil in order to have a high enough voltage to jump the spark plug gap in a cylinder under air/gas pressure, insulation in the coil and connecting wire must be quite good. The voltage coming out the high voltage terminal(s) of your ignition coil(s) will do all sorts of bad things if the wire insulation is not good, if the spark plug cap is not in good condition, if the 'tower(s)' of the ignition coil(s) are not in good condition....and you can RUIN the coil by having the secondary circuit OPEN (NEVER remove a spark plug cap from the grounded spark plug with the ignition powered)! DISREGARD any books/literature that say it is OK! You want a detailed explanation: ask me.
So, the coil structure is 'charged'...that is, it has a strong magnetic field. This occurs when the ignition points (nothing more than a switch) are
closed; or, the electronics module is turned ON by the Hall device trigger in the canister (1981+ models). It takes TIME for the magnetic charging, which is NOT
of any concern unless the rpm is extreme, or number of cylinders supplied by one coil is very high. NONE
of these conditions occur on a 2 cylinder boxer engine like our Airheads.
Properties of a coil with a magnetic structure are such that charging starts at a very low current & then builds on a mathematical curve to the point where simple ohms law (where resistance & applied voltage determines current) applies. It is a type of exponential curve. Thus, after a certain very short period of time, the coil current is constant, based on ohms law. At the instant of time this is reached, the coil is as fully charged magnetically as it can be by the applied voltage. The amount of time, as degrees of rotation of the ignition cam wherein current can flow, is called the DWELL TIME. This name came about from the days where there was only points types of ignition...dwell time meant the number of degrees the current flowed (points dwelled-closed). If you think about this, for engines of many cylinders, & one ignition cam, you can see that there is less & less time for charging of the coil, as rpm & number of cylinders rises. V-8 automobiles generally had one coil & a rotary switch directing the high voltage to the correct spark plug; so the cam driving the points had EIGHT positions of charging...and discharging. It can be more complex on some engines, this is a simplified explanation. For REAL nerdy-ness, the condenser (capacitor) used on points ignitions has a matching reverse function to coils. That is, when voltage is applied, the initial current flow is very high, tapering on the same curve, in the opposite direction. An even more nerdy point is that the condenser provides a short circuit on the coil primary when the points OPEN, and that not only has the commonly accepted function of minimizing points etching/burning; but, has the effect of increasing the efficiency of the coil's transformation abilities. The coil uses a decaying oscillatory waveform; and THAT is why the coil, supplied with D.C., can operate something like a coil driven by A.C.
When the PRIMARY current is interrupted by opening that battery circuit (points or module), the magnetic field collapses. Collapsing current, and a moderate voltage, goes into the condenser, which, for a very short period of time before it charges-up, acts like the points have closed...but in a very special way, that causes an oscillatory waveform. This is quite nerdy. Main thing is, that when the primary winding electricity is interrupted, it is THEN that the trickery really begins. That coil magnetic field collapse "induces" a very high voltage in the secondary winding of many thousands of turns. The TIME for the voltage to rise high enough to allow the jump-the-spark-plug-gap can be very short. The shorter, generally, the better. The voltage will generally rise only to the point that the electricity jumps the spark plug gap, or a bit higher, as the voltage must pass through any resistances, such as the coil resistance and the spark plug cap resistor...and there is a VERY nerdy thing about the points gap fuel mixture ionization resistance, which we will not get into here. The required voltage, to jump the spark plug gap, is much lower if the spark plug is in a cylinder NOT under compression pressure at that moment; and, conversely, the voltage required is much higher if the cylinder IS under compression pressure. This fact allowed BMW to use, on later models, a single coil, with TWO towers, so that the electricity is supplied by one coil to BOTH spark plugs at the same instant. Just in case of any confusion, the spark at the spark plug gap CAN be thought of as providing a bit of heat that starts the combustion process, although that is not really true....the combustion starts from other properties of an electrical spark in a combustible mixture...but, no need to get into that; this is supposed to be a simplified article! SO: A higher voltage is needed to jump the spark plug gap with a rise in cylinder air-fuel mixture pressure. Conversely, a lower pressure means the electricity has an easier time of jumping any gap. Yes, this means that insulation needs for electrical items located in the vacuum of outer space may be higher. What it means for your motorcycle is that very good insulation is needed for the coil and the high voltage wire and caps to the spark plug.
Once the coil secondary
winding voltage rises to the point that it will nearly jump the spark plug
gap, the fuel-air mixture begins to do something called "ionize" (curious?...look it up), and then the spark begins and the voltage output of
the coil starts to decrease very rapidly. The spark itself has a very short over-all duration.
While I personally think that the resistance cap (do not use resistance plugs in an Airhead) has
an effect of somewhat LENGTHENING the TIME that the spark exists, helping ignition (&
reducing radiated radio energy), this is not universally believed by all "guru's". In any event,
whether I am correct or not, adding series resistance makes things worse if the resistance is large enough. That is why the intensity of the spark is DEcreased by the use of
the necessary spark plug cap resistances. Actually, there is more to this. Because of the
ionization that occurs just immediately before the spark, a high voltage with little current will
easily ignite the mixture; the ionization is a large effect,
one can think of it as a pre-conditioning of the spark. This is all very nerdy to absorb....could not resist throwing it in here....for reasons I may explain some time. All I will say at this
point is that the ionization can be utilized as a 'signal' for an anti-pinging retardation of spark.
That does not happen in Airheads, but it is being experimented with for very modern engines...even Harley Davidson is using the idea: http://bmwmotorcycletech.info/nerdy-stuff.htm; see item
#18. The ionization event is being used to help control the engine.
OK...back to the discussion of ignition for Airheads (and other BMW bikes....).
There is an optimum value of resistance, that includes the resistance of the Secondary coil
winding & spark plug cap resistor. It is not critical, but needs to be within certain parameters.
There are very complicated reasons for the resistance to be within certain parameters, far
too complicated to explain here. It has to do with inductive-resistive-capacitive time constants. You REALLY don't want to read through the theory & mathematics on that! Enough said!
So, sparks jump easiest in low gas pressures. The easiest jumping would be in a vacuum chamber or in outer space. The next easiest, for our illustration purposes here, is for a spark plug cap to be off the spark plug & dangerously just lying wherever it might be. In our Airheads, one cylinder fires at a time (but both cylinders get sparks). There is compression pressure of the air-fuel mixture in the cylinder about to be fired (gases ignited) by the spark plug. It takes LOTS more VOLTAGE to jump the spark plug gap if the firing spark plug is the cylinder under compression pressure....than if the spark plug was NOT under compression pressure. Hence the ignition must be capable of producing a lot of voltage to overcome the spark plug firing gaps when the cylinder is pressurized. Some airheads use TWO coils, one for each cylinder; and some airheads use ONE coil, with two outputs. In those with ONE coil with two outputs, the output must jump TWO spark plug gaps....that is, the voltage/current from one end of the single coil goes to one spark plug, jumps that plug, returns to the engine case, travels to the other spark plug, jumps that gap, & returns to the other tower of the coil....remember, you must have a COMPLETE circuit for current to flow. Note that the cylinder NOT being 'fired' will be much easier to have the spark jump across the spark plug gap, since there is no compressed gas pressure.
The dual-output coil does have both a negative & positive output terminal. The spark plug connected to the negative terminal will have an easier time producing the spark when the electrodes are red hot. Because the coil output does not reverse during operation, the coil must be powerful enough to jump two gaps, at the same time. This was accommodated by using an electronic ignition that better handles the higher primary current in the more powerful coil. The primary resistance of the very last of the Airheads coils was only 0.5 ohm!!!...theoretically over 20 amperes could flow for a short term.
Section 2, Battery& Voltage Regulator:
In your Airhead, the primary source of electricity is the battery. It has an INTERNAL RESISTANCE which is VERY low, a very small teensy fraction of an ohm. This is why dangerous currents (like melting things type of currents) can flow with short circuits at the battery, or elsewhere's. Your battery stores energy NOT as electricity, but as CHEMICAL energy. Upon a circuit being connected & completed to the battery, the chemical relationship changes in a way that produces electricity. The type of parts inside the battery determine the nominal voltage of the battery. Lead-acid batteries have a nominal industry-speak rated fully-charged voltage of ~2.1 volts per CELL at rest. You have SIX cells in your battery, hence 2.1 x 6 is a 'nominal' 12.6 volts. The battery voltage, after fully charging, but the engine now off, and no substantial load on the battery, will be ~12.6 volts, after some minutes of resting. Due to inefficiency of the chemical reaction for recharging, the recharging voltage, for practical reasons, such as speed of recharging, etc., be higher than 12.6.
When you are riding down the road, the alternator keeps the battery fully charged (hopefully!), by reversing the chemical reaction from the battery being discharged, & the battery voltage will be about 13.6-14.6 volts. That is often called the float voltage value. About 14.2 is a good value for most batteries. I won't get into just why, as I do that in other articles. As soon as the alternator output is below that needed to 'float' the battery voltage at the voltage regulator set value, the battery voltage will drop. If the battery was 100% charged & if the engine is then shut off, the battery voltage will decrease rapidly to under 13, then fall less rapidly, until it stabilizes at about 12.6, usually within seconds if a substantial load, or minutes to an hour if not....and will remain there, only very slowly decreasing....until, over time and any drain, it is slowly discharged. The voltage drops initially rather slowly during that discharge. For practical purposes, a battery that measures....in its well-rested state.....below 12...has a rather low charge and damage is being done. There are published tables of battery charge level for all types of batteries, for voltage and temperature. If the battery will seem to charge properly & then the voltage drops under ~~ 10.5 during engine cranking....then the battery has little life left (assuming the starter is not excessively drawing current). The battery's chemical processes have become much less efficient, and the battery has developed a much higher internal resistance, therefore it can not deliver enough current. More information on voltages later in this article. Some types of batteries have a very small change in voltage as they discharge, & when a critical voltage is reached during discharge, the voltage starts to drop off extremely fast. Lithium batteries are like that, so are silver cells & also nickel-cadmium batteries. Another way of looking at those batteries is that there is a very narrow voltage range between charged and discharged. There are a number of types of lead-acid batteries. There are small differences in lead-acid batteries in terminal voltage, and, some have steeper drop offs than others.
"Flooded" batteries are the type where you can see liquid sloshing around, so I may call them SLOSH batteries. MOST of these are the types of batteries where you must add
distilled or purified
water occasionally. In very hot weather, some common types of these batteries can self-discharge, as you will read in some literature, "as much
as" 1/3 every month, unless recharged. What you are seldom told is what the more typical MONTHLY self-discharge is: 3% at 32°F &
18% at 100°F temperatures.
As the temperature drops, the battery has less chemical activity available, and will deliver less electricity, particularly if demand is high, such as for starting the engine.
If not recharged fully during a ride, any type of lead-acid battery tends to age and thus fail faster due to somewhat irreversible chemical effects; and repetitions will decrease battery life more and more. NOTE, however, that the flooded type of battery can, if maintained properly, exhibit somewhat longer-lasting characteristics, than most sealed batteries (non-slosh).
A battery fails chemically as well as failing if INternal connections break or partially break.
Lead acid batteries mostly fail from use, abuse, and old age, in which the most common mode of 'aging' (and failure) is sulfation, in which a chemical is developed inside the battery that coats the various plates that contain the active elements, and the coating acts like an electric barrier. That is very simplified. Once a battery ages enough, it MAY be impossible to recharge it very much at all, no matterwhat the smart battery charger makers advertise about de-sulfation modes. Failure of any one or more cells can cause a type of failure that is sometimes hard for amateurs to determine.
There are many types of lead-acid batteries, one interesting type is called Valve Regulated, typified by the high quality Panasonic brand version. I prefer the original, more properly descriptive name, Absorbed Mat. However, Valve Regulated batteries are a category that encompasses all vehicle type storage batteries that are sealed. The term, Valve Regulated, is really poor. These batteries are not really 'regulated' (except, broadly-speaking, for excessive gas pressure, should that happen).....that is, they are is sealed, with an included over-pressure valve. They use a chemical process similar to the flooded batteries, except the chemistry allows a recombining of gases generated in the battery from charge & discharge. That same process is used in SOME flooded batteries that are Low-Maintenance, or some that are No-Maintenance.
As a general rule you should automatically replace your VRLA or Absorbed Matt, or Panasonic or similar battery every 3 or 4 years, & your flooded battery at 4 or 5 years. This schedule assumes you take reasonable care of the battery, & it is being charged reasonably properly, and are likely to hardly ever have a sudden battery failure in your lifetime. "Reasonably" here means typical normal MILD abuse!!! A vast number of motorcycle owners try to get every last usable day from their batteries, & may brag about it. Stories are legion with owners getting 7 to 9 years of service. That can be penny-wise, pound foolish.
As the battery ages without catastrophic problems, it requires more & more alternator power to maintain it at a reasonable charge. That increases the heat; and it also increases wear on the alternator & diode board. If the battery is barely usable, the engine may be harder to start, that is, it may require longer (due to slower) cranking, particularly when it is cold. All this is harder on lots of things, battery, charging system, starter motor, etc.....all causing excessive wear. Consider if you are willing to have a battery 'suddenly' fail on you, if you are a long way from where you can obtain a replacement....and, perhaps it is a cold rainy night! Any battery can have a catastrophic failure of course, even if nearly new; it is just vastly less likely. I treat sudden battery failures elsewhere's. No matter what I say here, there will be PLENTY of vehicle owners priding themselves on getting every last bit of usage from their batteries. Battery life is a long involved subject.
Be sure you do not let the fluid level
(on a flooded battery) get below the proper indication line for fluid level, and secure ANY battery
so it does not bounce around on the motorcycle....vibration and sharp knocks will reduce its life,
as will quite high temperatures....all of which will possibly lead to a sudden catastrophic battery
failure. Stiffer-sprung, stiffer-riding motorcycles are harder on batteries. If you test your
battery, perhaps every 6 months to a year, on a REAL load tester that returns specific
data, then you might safely use your battery much longer than I have mentioned.
Harbor Freight Company sells (often on sale!) two types of real
load-testers. The HF 2-meters type is better, although both work OK. The two meter type is OK for cars AND BIKES, and, as noted, is better, and it gives much more information.
For much deeper information about batteries:
Somewhat nerdy hint: For a SMALL boost in battery life, recharge it manually every month, & leave it disconnected from the bike, & do not use a smart charger constantly. I am aware that this is not widely understood.
Slosh batteries, officially called FLOODED or "conventional lead acid batteries", have liquid you can see in them, & can endure a sustained charge of their rated ampere-hours, divided by 18. They will, however, need the water replenished more often...and this type of maintenance charging is NOT recommended by ME. In other words, do not use a NON-smart charger for long periods of time. Actually, constant use of a Smart Charger is ALSO not a good idea, but the damage is less. The better-designed chargers (not necessarily smart chargers!) of low charging rate, under 2 amperes, can have them left connected to the battery, charging, for a fair amount of time, as noted. Using quite low capacity chargers (especially below 1 ampere rating) can work rather well, even compared to a smart charger.
Never allow the voltage to exceed 15.5. Some batteries can handle this, short-term, others can NOT. In fact, I advise against going over 14.9 volts on ANY battery, and probably best not to exceed 14.5, even lower in warm to hot climates.
Hydrometer readings on slosh (flooded) batteries, corrected for temperature, are fairly accurate, but some battery faults make such readings NOT overly useful. Still, the test is useful at times. Lower liquid capacity hydrometers for small batteries are available cheaply. If you purchase a hydrometer for battery checking, be sure it has a temperature correction scale and incorporates a thermometer.
If a battery has been charged fully, then sits & stabilizes over a bit of time, the battery voltage will very slowly drop, after a much larger initial drop from fresh charging. The following information assumes 77°F; an open circuit (that is, NO LOAD, except for the measuring meter, & the battery sat for at least a few hours after being fully charged. The following are generally accepted values at 77°F for a common flooded style lead-acid battery:
100% of charge at 12.7 volts and 77°F. UNofficially, your battery is PROBABLY going to
read 12.55 to 12.75 volts for fully charged, at around 65°F, after it sits for a few hours
AFTER fully being charged.
The rest of these figures are official ones at 77°F:
75% of charge at 12.5 volts
50% of charge at 12.27 volts (some books say only 10% charge is left at 11.31 volts and 20% at 11.58 volts; 30% left at 11.75 volts.
Fully discharged: 11.89 volts or less. (some books say 10.5). No matter, because at less than 11.8, there is almost no charge left...maybe the battery would light up DIMLY, a small bulb. NOTE, again, that these are RESTING voltages, NOT CHARGING VOLTAGES, & NOT loaded voltages. The differences between various books on these voltages is due to types of batteries, temperatures, etc., that were not specified in detail. My figures are fairly accurate for real world situations.
Absorbed Mat (Valve Regulated) (Panasonic & other similar types) batteries need somewhat higher charging voltages....and I like to see the voltage regulators set for at least 14.3 at nominal 'room temperature', at the VR case. Those slightly higher voltages give a better charge, but have other effects, so I often may say to use 14.15 to 14.4. It is NOT critical. You can read up on your particular battery type, on the manufacturer's detailed specification sheet....MAYBE!....some makers just don't have such information available. Panasonic DOES.
"Smart Chargers" vary a lot in what voltages, for how long; how many 'stages', and so on. Smart chargers quite often have circuitry built-in that creates a problem you SHOULD know about. This particular problem MIGHT happen to you: You put a Smart Charger on a dead or nearly so battery, and it won't charge AT ALL. What has happened is that the existing battery voltage is too low to TRIGGER the Smart Charger ON. You need to, by some other means, perhaps a trickle charger or a somewhat faster charging method, get the battery voltage up over PERHAPS 8 volts. That voltage varies by smart charger manufacturer. Then put on the smart charger. Smart chargers GENERALLY have multiple STAGES of initial charging before reaching the amount used as a maintenance or float charge. A typical example is that the first stage of charging does charging up to 85% of full charge. Some makers call this the Bulk Charging Stage. The Smart Charger may have current & voltage limiters for this Stage. The next Stage might be what is commonly called the Absorption Stage, and it brings the battery to perhaps 14.2 to 15.5 volts. This Stage is to make sure that 100% of the plates surfaces is fully charged. The next Stage may be called the Float or Maintenance Stage, and is typically 12.8 to 13.2 volts, at 77°F, adjusted a bit for temperature by the charger. DO NOT misunderstand the floating voltage or charging voltage, and this maintenance or float voltage. ONCE the battery has been properly fully charged for a period of time necessary to try to ensure the ENTIRE battery plates surfaces are in that fully-charged condition; THEN, a much lower voltage can be used to MAINTAIN the 100% charge, without excessive gas pressure or water evaporation, ETC.
Voltage regulator settings:
The voltage regulator should not be checked, for serious values nor adjusted, unless the battery has first been charged and the battery needs to be KNOWN GOOD; preferably from a REAL Load Tester. Voltage regulator settings are BEST checked with a thermometer on the voltage regulator. However, what I do is to simply start the bike after it has been sitting all day or night at a roughly known air temperature, and after 2 maximum minutes I rev the bike up and measure the voltage at the battery terminals, with a known accurate digital meter. With the battery previously being fully charged, it takes only a minute or even less, at 3500 to 4000 rpm, for the battery to recharge from starting and reach its voltage regulator limit setting. Temperatures below are VOLTAGE REGULATOR temperatures. If inconvenient to measure, use the battery case temperature. It is FAR better to have the voltage regulator and the battery both at about the same temperature, and best not hot from the engine having been run, from a road run, etc.......which is why the testing should be done from a cool engine, but shortly after starting. Values below are for flooded batteries but are OK for other types. The values shown are compromise values, but quite good ones. For best life and results, I suggest using the high end of the values shown.
47°F 13.8-14.4 volts
68°F OPTIMUM setting for MAREG batteries at this temp. is 14.1 volts. This is factory information, hard to find, and I agree with it.
70°F 13.7-14.3 volts
93°F 13.6-14.2 volts
117°F 13.5-14.1 volts
140°F 13.4-14.0 volts
163°F 13.3-13.9 volts
NOTE: voltage regulators are supposed to be internally temperature compensated...and you can expect your fairing or other voltmeter to DEcrease in reading as the engine warms up and radiates heat to the voltage regulator. Voltage you are interested in is at the battery, not at some other place on your bike. DO NOT USE THE FAIRING VOLTMETER. If connections, especially to the voltage regulator, alternator, diode board, and battery, are not good, clean, solid, the readings and performance will likely suffer. The stock fairing or dash area voltmeters will normally read a bit lower than the battery terminal voltage, perhaps 0.3 volt lower. In excess of 0.5 lower means that you should check that voltmeter for accuracy, and if it is accurate, start looking for poor connections, etc....as you will have charging and other electrical problems soon enough. The fairing voltmeter reading is NOT the battery terminal reading that you use for adjustments of the VR, etc.
NOTE: if your dash voltmeter is swinging wildly upon using the flashers, and you HAVE
already gone through the many connections, and even a bad key switch has been tested for,
yet you find no reason, you either have a bad voltmeter, OR, a poor internal resistance battery.
Section 3, Alternators & Diode Boards:
(Airhead motorcycles...and...others.......in depth)
See http://bmwmotorcycletech.info/altbrushotor.htm for a very full treatment of stators, rotors and bushes
I have data on this website from REAL WORLD testing, on a known perfect system, a 1983 R100RT, that I personally owned. http://bmwmotorcycletech.info/altcapability.htm
BMW elected to use in the Airheads a type of generator called an alternator. The name means that its output is alternating current. The output frequency (number of CYCLES per second, or Hz) varies with engine speed.
information: The frequency output of an alternator is a function of the number of
pole-pairs, and the rpm. The formula is:
F = P x N Where P is the number of pole pairs; F is frequency in Hertz; N is rpm.
When the rpm/frequency is high enough, and your attached radio is not filtered well, some of the alternator noise may show up on your radio as a whine that rises and falls with rpm (and may get louder as you load the system more), as the alternating current is not totally & perfectly converted to DC by your diode board. In fact, due to inefficiencies in the diode's actions, the diodes themselves can create some types of radio noise, that can be difficult to filter out. There are other sources of radio type electrical noises in your airhead....switched contacts, relays, mechanical voltage regulator, & especially the ignition system. The contact noise is often heard in a radio as clicking, the ignition as static varying with rpm, and the alternator by a whining that varies with rpm. All can be filtered out, with some effort.
In order to charge the battery, the AC must be RECTIFIED, that is, converted to DC (Direct current), which is done PRIMARILY by the six large diodes in the diode board. The /6 and later have some additional small diodes connecting to a center tap of the stator winding, and have SLIGHTLY improved output, and SLIGHTLY smoother waveform, due to them. One diode section of three large diodes, the LOWER set, allows only the positive half of the AC to go to the battery positive post, and the other diode section of three large diodes, the TOP set, allows only the negative half of the AC to go to the battery negative post, via the engine structure metal. Because of this, the engine structure must be electrically solid...of very low resistance due to the large currents that will flow. The only known problem with the engine structure in this regards is that some engines have a black painted inner timing chest that in some instances has caused slight charging irregularities in voltage regulation....that is cured by addition of a grounding wire. Additionally, in some models which HAD rubber diode board mounts, changing to metal mounts helps, and needs some additional grounding. BMW themselves had bulletins on adding grounding wires, but never admitted that the rubber mounts were a faulty design change that made things worse. The original reason for the rubber mounts was to 'fix' supposed diode board problems from 'vibration'. The problems were NOT AT ALL from vibration, however. I highly recommend all rubber mounts be changed to metal types, using aftermarket mounts from such as Motorrad Elektrik or Thunderchild, or Euromotoelectrics. I prefer ROUND metal mounts over hex types.
The two rows of 3 large diodes are NOT the same part, although they look identical. One set of three diodes is internally reversed in direction of current flow from the other set. These 6 large press-fitted diodes used on the boards not identified, but they are industry numbers 1N3659 and 1N3659R. The R means reversed from normal polarity inside the diode structure. YOUR diodes may not have these generic numbers printed on them. All six are PRESS-fitted to aluminum heat sink material.
The alternator does not produce just one sine wave output; but, for efficiency, is designed to have THREE....'THREE PHASES'. Let us call one cycle as being 360 degrees on a linear time chart. The alternator produces, via its three phases, overlapping outputs. Each phase is 120 degrees offset. Those waveforms are constantly rising and falling in sine-wave form. With overlapping waveforms at 120°, there is more constantly actual output...that is, much LESS time is at lower sine-wave levels. The result is more power. If you have one of the EnDuralast permanent magnet alternator conversions, that is a ONE phase alternator. It would be more efficient if it was 3 phases, but that would complicate them. One of the reasons the EnDuraLast PM system does not produce very much additional output over stock, and produces its output at lower rpm, is due to this one phase design.
Let me state this 3 phase idea a bit differently: If you were to draw these three phase waveforms on a piece of paper, and eliminate the area below the waveform crossovers (towards the middle horizontal zero voltage line, from negative going and positive going), you would see three curvy peaks. Compare the power to just ONE of the colored phases, where a substantial area has no power. If you think about the AREA of the waveform, you can easily see that more OVER-ALL power, per unit of TIME, is available with THREE phases.....compared to ONE phase.
Here is a sketch of one cycle of one-phase electricity. NOTE that there is NO electricity flowing, at all, in the positive direction, for half of every cycle, and same for the negative direction.
Below is a sketch of 3 phase electricity. Note the ~average level, as marked in red, of the EQUIVALENT D.C. output, with the partial half-waves of a.c. riding at that level. In either the positive or negative going direction, there is NEVER a time when there is no electricity flowing.
Below is a sketch of 3 phase electricity presented another way. Note that no matter if the horizontal axis is degrees of rotation, or time, it is the same.
There is a large difference in efficiency between single and three phase generation. There is also a big difference in size and weight. A three phase alternator also has an effective frequency output that is much higher than single phase for the same RPM, which is MUCH easier to filter for hum/whine type noises. When you combine the electrical efficiency, ease of filtering, and the size efficiency, three phase is MUCH better.
All diode boards have three small diodes which do exactly the same thing as the
three very large positive-going ones. However, these particular small three diodes are used
to provide a smaller amount of current, which have these functions: (a) for driving the
voltage regulator's 'sensing' function; (b) providing the ROTOR current the several amperes needed for the
rotor after the alternator begins to produce electricity; and, (c) to extinguish the GEN lamp
after the alternator spins up fast enough to need more rotor current than that provided through
the GEN lamp (which happens at quite low RPM...hardly much above idle rpm.
If a large diode in the diode board shorts ["short-circuits"], it allows the AC waveform applied to it, to pass through it, causing a huge current flow, & perhaps charring/burning, and perhaps a gross failure. If, instead of shorting, 1 of the 6 large diodes OPENS, you will lose somewhat more than just 1/6th of the alternator output, due to complex interaction of the waveforms, diodes, and magnetic fields. An ohmmeter or diode tester section of a multimeter can usually do an adequate job of determination. Small diodes failures will reduce output, and possibly cause very strange symptoms.
Besides bad solder joints on some diode boards, the other common failure is an open large diode. NOTE that an open diode can ALSO be caused by the mentioned bad solder joint! An open large diode causes a MUCH reduced output from the alternator. The symptom, typically, is that the system seems to charge the battery nicely...>>until the headlight is turned on...then the voltage drops and charging is not maintained at even higher RPM. USUALLY an ohmmeter or meter with a diode test function will find the problem It is possible for a device called an oscilloscope to make a definite determination, but few own those instruments, and a multimeter works pretty good. When enough load is put on the bike's system...such as the headlight, heated clothing...etc....the voltage will not come up nearly far enough. Since other faults can mimic this one, it takes some sleuthing. It is a relatively rare event, but does happen. USUALLY when it does happen, it is not a bad diode, but a bad diode solder joint!...THAT can be seen visually most of the time.
Diode boards can usually be checked with an ohmmeter when still in the motorcycle and still connected. Using just an ohmmeter or multimeter diode test function will give reasonable results, for forward and reverse diode
readings (BE SURE TO DISCONNECT THE BATTERY if in the bike!). Diodes boards are best checked when OUT of the motorcycle, as more definitive tests can be done. The very best test is
using AC (Alternating Current voltage source) with a lamp. See Oak's June 1999 article on
Diode Boards, in Airmail, which deals extensively with the diode board OUT of the bike. On
a practical basis, since diodes can act funny if hot or cold, a really anal person would check
them at room temperature, and then repeat all measurements around boiling water temperature,
and at freezer temperature. I am NOT quite that anal, but admit to doing this a time or two when
faced with a seemingly intractable problem. There is no problem with dipping a diode board into hot water, just dry it when you remove it from the water. An air hose to blow away excessive water and then natural drying in the sun works fine; just do not wait.
Here is a sketch I did of a AC tester for diodes. You simply remove the diode board and connect the test leads (big arrows in the below sketch) of this test apparatus to the diode. No need to reverse the leads for a second reading. FIRST you short the two test leads together, and note the lamp brightness. Then you connect the leads to the diode you wish to test. If same brightness, the diode is SHORTED. If around half brightness the diode is OK. If no illumination the diode is OPEN. Use a lamp that is rated something near the voltage of the transformer, perhaps a 12 volt tail running lamp. For the BIG diodes, you can use an old headlamp bulb; don't use a high drain like a headlight bulb to test the small diodes. This test method is really superb. Combined with an ohmmeter and diode test function on a multimeter, and, heated, it is 99+% accurate.
Section 4, Specific diode and other problems in Airheads, OTHER THAN the diode board.
Description of the function of the headlight relay regarding the starter motor.
1. If a single diode in the headlamp relay shorts, the motorcycle engine will not turn off with the key switch, only by stalling the engine or by disconnecting a battery wire. The process repeats after the next start. Later headlight relays may contain TWO diodes. The function of the other diode inside this relay, at pin 85, which is in series with the coil, is NOT well understood by me, I've only seen one, it was 1.244.411, and I have proposed that it might be in case the starter locks up. The original diode, still there, is between pins 86 and 87b. The pin 86-87b diode's purpose is to leave the tail and dash lamps on during starting. This diode is found whether or not there is a second diode. Probably a German requirement.
In the monolever bikes, from 1987, if the lights come on when the starter is used, or PARK is selected, you have a bad diode in the lighting relay (one of those two in there).
The headlight relay pin 85 (has a black wire), this connects internally to the grounding end of the headlight relay COIL, providing the 'complete circuit', in this case it returns the coil to ground ...BUT... via the starter motor hot terminal. This 'clever' arrangement means that when the starter is energized, the headlight relay has +12 on BOTH sides of its coil, and the relay COIL DEenergizes, turning OFF the headlight, but the mentioned relay's first diode keeps the tail and instruments illuminated.
2. BMW has used TWO arrangements for the wiring to the 3 position left bar headlight switch. Most
schematic diagrams show the green wire going to the key switch, but some have it to the hot always
side, some do not. Thus, on some bikes the momentary HI FLASH switch works without the key.
3. On models from 1974 through 1984 (except the R45 and R65 & Monolever bikes).....regarding a diode on most bikes being mounted on the UNDERSIDE of the board inside the headlight shell:
PRE-1981 R45 and R65 have the diode plugged into the wiring below the starter relay. Monolever bikes, the diode is INside the starter relay (do NOT install wrong type of relay!)
Symptoms of a shorted diode in those various places:
Pulling the clutch lever towards the handlebars will cause the neutral lamp to illuminate.
Symptoms of an open diode in those places:
The starter motor will not operate if the transmission is in neutral.
Be sure to read #4, above the horizontal line, ...that's just above!
Bosch starters up through 1974 were 8 tooth 0.001.157.007, rated 0.5 hp and 290 A. The /6 bikes for 1975 and most of 1976 used an 8 tooth 0.001.157.015 rated 0.6 hp and 320 A. The 8 tooth starters are used ONLY with the 93 tooth flywheels.For 1977 and later, the starter has to be 9 tooth, for use with the 111 tooth flywheels (or later clutch carrier). The starter is 0.001.157.023, rated 0.7 hp and 320 A. Solenoids, unconfirmed, seem to be the same as EARLY air cooled VW.
The "Airheads Beemer Club" has an account with Ace Houston Warehouse, a
wholesaler/importer/remanufacturer, ETC. The Club account is #700. Call Bob Spencer at
1-800-392-3332 or e-mail to
email@example.com. Mention account 700. The Valeo starters
are available. The part was D6RA15, Valeo changed it to 432586. Quite some time ago the price for these
from Ace was $172.50 plus shipping. This is a brand NEW starter. 5 or more are cheaper.
There is no core charge, but they will probably pay shipping to get your old one. They have
rebuilt Bosch starters, last price was $200 and a $100 core charge and shipping (core charge
refunded). Bob Spencer thought that the Bosch starters MIGHT be put back into production at some point.
The information in THIS paragraph was provided by Ken Kirk
firstname.lastname@example.org. I don't
know of anyone buying from them lately. Frankly, I see no reason to. Overhaul your own, or, See my article on substituting starters!
Section 6, Addendum:1. Eddy Currents:
I personally use test lights A LOT. They can greatly speed up diagnosis. Takes only a
small amount of effort to understand how versatile a test lamp can be. I have a couple of typical commercial types, with a sharp prod at one end and a pigtail wire with an alligator clip.
They pull very little current, but are very useful, where a multimeter might give highly erroneous
readings. For larger current drains than that tiny lamp in the test lamp, I have old headlight bulbs.
Headlights always burn out one side first, so the other side is available. The one at my workbench
is an old 12 volt sealed beam headlamp which is exceptionally convenient for me due to its terminals, and ruggedness.
I also have a few previously burned-out push-in fuses, with leads attached for use with Classic K-bikes...and I have ones with small alligator clips for substituting for Airheads fuses. I might connect the old sealed beam to the fuse, and plug the fuse into the vehicle; or, use the airhead burned-out fuse with the test lamp or larger lamp. Since only ~ 5 amperes maximum can flow in a stock headlight lamp, & also the lamp can be used as an indicator, it can really save time in figuring out a problem, almost always without passing enough current to damage things. In other words, it is like a self-protecting, current-limiting fuse, but with an indicator function (the glowing lamp). A test lamp is very particularly excellent at finding pesky short circuits in your turn signals, rear run and brake light circuits, ETC.
There are plenty of unique uses for test lamps. I may use a test lamp between the battery + and the alternator brush holder terminal Df (Df wire connector pulled off). I don't need an ohmmeter to tell me what the rotor & brushes condition are, & the advantage of the lamp method is, in addition to no meter being needed, that this method will 100% turn on the alternator AND almost always 'show up' that nasty situation when a rotor is acting-up only at some rpm, as opposed to engine not rotating. Many a digital meter gets confused when trying to measure alternator output under that kind of intermittency.
One can even use a test lamp at the stator terminals....although stator problems are rare. It will check equality, engine running, and will also let you know that the stator has output on all three phases (and centertap, if 1975 /6 and later)...as well as you can use the lamp to test the diode board output versus the stator, VERY easily.
One can 'test' a voltage regulator by using the Df wire itself (the VR output wire) (removed from rotor
Df terminal) to run the test lamp (to ground). If the VR is faulty, the lamp will not work properly.
A slightly trickier method is to jumper the Df brush terminal to the battery + terminal, and then have the lamp connected from the Df wire that was pulled off, to ground. Then the lamp monitors the output of the VR, indirectly, as it runs from the regulator. As the lamp dims, the alternator is putting out more and more, as the regulator is telling the lamp, instead of the rotor, to produce less magnetism.
3. Key-off battery drain (Also known as parasitic battery draw, excessive resting current, quiescent current consumption, etc.):
There is ALWAYS a very small current flowing from the battery into some motorcycle electrical items. I am NOT speaking about the self-discharge current of a battery. Various items cause these small currents to flow, which discharge the battery somewhat...and in bad circumstances, a lot. Electric clocks. Keep-Alive or other memory things for radios, etc. Back-current (AKA Reverse Current) in diodes, such as on the diode board. ETC. The Airheads have almost no 'fancy' electronics. There are no electronics modules for fuel injection or other things like ABS, stability controls, etc. But, the Airheads CAN have excessive battery drain with the key OFF. Once in a great while it is due to corrosion that connects to ground from a battery powered connection. That is fairly rare. If the current is excessive, the battery may run down over a day or a month. Modern cars have extremely complicated electricals. No longer is excessive drain on a battery found to be a trunk light that is on due to a faulty switch. Dozens of electronics modules are in modern cars. FURTHER, after a vehicle's key is turned OFF, there may be up to a half-hour OR MORE, before the various modules shut down completely, or nearly, to "sleep mode". This is normal behavior! We have NONE of those things in the Airheads, early Oilheads nor Classic K bikes.
If your battery runs down rather fast, you need to LOAD TEST the battery (after fully charging it). Make sure the battery is OK!
There are standard/classical ways of measuring these (usually small) currents, and finding the electric drain problem(s).
One method uses a small low wattage lamp, connected so that it is inserted between battery negative post and the chassis (disconnect or use the battery negative lead). BE SURE no other leads are connected to the battery negative terminal!..if any are, connect them to the chassis. If the lamp glows, then the current is large enough to light it. Some books ERRONEOUSLY tell you to use a voltmeter into this lead...NOT CORRECT...you need an ammeter or milliampmeter.
Disconnect one fuse at a time, and/or connection....find out which causes the lamp or current flow to greatly diminish. I suggest you AVOID measuring ACROSS a fuse or ACROSS a ground wire, to try to measure current amount...although such testing is OK to find out where electricity is flowing, or stopping. It is easy to get confused, so best to insert a multimeter set for the current range, into the battery negative circuit as described. START with the highest current range, typically 10 or 20 amperes. Your meter may use a separate + terminal for such high currents.
How about some values?
Typically, battery flow with key off, is less than 1 milliampere (0.001 ampere); with values up to 5 ma not uncommon. Much more can be drawn by a clock. Some Rectifier-Regulator of Permanent Magnet aftermarket alternators may draw a milliampere. What does, for example, a total drain of 2 milliamperes mean to YOU?
In 24 hours, you will drain 2 x 24, or 48 milliampere-hours from the battery. That is 0.048 Ampere-hour; a very small amount, in one day, compared to a battery rated at, perhaps, 17 or 28 ampere-hours. But, in 20 days it is nearly 1 ampere-hour....still not all that much, but coupled with self-discharge, over a Winter's storage, and you can see why use of an occasional charger is a good idea.
As you can see, if you have a drain of 10 or 20 or more milliamperes, the battery can discharge fairly fast. In hot weather, the battery self-discharges faster too....so these things can add-up. If you, in addition, have a charging system that is not fully recharging the battery during riding, things can go south quickly.
02/03/2003: Add typical electrical usage values
02/04/2003: add information on starting and starters; headlight circuitry; (2) at top; add to #1 in problems area; simplify some explanations, eliminate some redundancy's.
04/03/2003: editing for clarity
01/05/2004: update the URL for Chicago Region club.
02/06/2004: clarifications only
05/26/2004: update contact information for Chicago Region Club
03/01/2005: revise including hyperlinks, for the chitech electrics manual, as article 80 is now done
04/12/2005: Add (3) at very top, add Addendum, and explain eddy currents
08/06/2006: Revised and updated entire article
02/23/2009: clarify rotors and stators
11/18/2009: Revise article for better clarity, and a few changes to keep up with latest tech.
12/03/2009: Try to clarify more details
09/14/2010: Clean up article, many places.
12/10/2010: Clarify some basics
05/20/2011: More clarifications, nothing at all major
06/03/2011: Add Addendum item #2
09/21/2012: Completely go through article & update it. Includes photos & sketches & descriptions & making things clearer & easier to understand. Add QR code. Change Google code.
10/18/2012: Add two more sketches of single & three phase A.C.
01/16/2012: Add info/link to http://autoshop101.com/
03/30/2013: Add information about replacing a bad diode in the neutral and clutch circuit
11/02/2013: Remove information on rotor sizes, etc., as the altbrushrotor.htm article has now been expanded for such things.
03/11/2014: Update a bit to improve clarity.
01/18/2016: Updated meta-codes, narrowing article, larger fonts, clarifying details. Both simplify & expanding information. Revise entire article; combine sections, eliminate redundancies, etc.
05/13/2016: Final update on metacodes, layout, fonts and colors, scripts. Make improvements for clarity and understanding; fix typos.
06/19/2016: Add 3. to Addendum section.
06/09/2017: Clean up fonts, colors, etc.
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