De-mystifying Boxer
Electrics
(including troubleshooting,
ETC.)
©
boxerelectrics.htm-14A
This is an article to furnish THREE types of information:
(1) Some BASIC and ADVANCED INFORMATION on electricity and Airhead problems. The approach used here is different than in manuals and troubleshooting guides that you might have, or are contemplating obtaining. Although some hints are given later in this article on some common faults, this article should be used in conjunction with other articles on this website.
(2) Common problem areas, explanations of some of the circuitry, etc. A discussion of such as batteries; starter motors, voltage regulators, etc.....a goodly amount of good technical information. Other articles will get deeper into some of these things.
(3) An addendum that may discuss some particular point that has come up, or some topic of interest. This is at the very END of this article
Available to you are certain helpful booklets, etc. Guides such as the ones from Motorrad Elektrik, Chitech, and your Haynes and/or Clymers manuals (and, perhaps, a schematic in the rear of your owners booklet), may well be necessary items for you, and are actually recommended...and if you are anal enough to get them all! In MY OPINION, the Chitech electrics manual and the owners book or factory schematic, 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.) Manual (BMW Electric School Manual) is
THE BEST manual for BMW electrics, from basics to full-blown technical details,
components, diagrams, etc., and includes the singles and all boxer airheads. It is VERY
complete. Only a few errors are in it, and I have an article I did on those
errors. Here is the link to my Critique of the Chitech BMW Electric School
Manual: chitechelmnl.htm
See my url.htm
page for more information on Chitech, and how to order their publication.
Some of the schematics are not reproduced well, that is the only problem with that manual. Get it anyway.
Much of the following on basic electricity and its use in the airheads is rather simplified.
Please, no flaming from fellow engineers!
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 (zillions) moving through a wire, and you have a flow of
CURRENT. Apply the flow through something like a
lamp, and if enough are flowing, the lamp will heat up, and will put out light. Too much flow, the lamp burns out just like a fuse
which blows for excessive current flow.
Current flow is measured in amperes, and in many cases, very tiny parts of an ampere, such as milli-amperes or micro-amperes. Milli- means thousandth of; and
micro- means millionth of.
It is still popular to use water pipes to explain electricity. I find that this often
VERY confusing for people. It is OK to think that water
pressure is the force, like voltage, that ALLOWS more flow from the faucet,
at A GIVEN faucet opening. That adjustable opening IS like
resistance (ohms). UNfortunatgely...the rest of the usual story is BAD. I won't get into it
further other than a passing mention.
In order to have a CURRENT FLOWING, electron flow must
begin someplace, travel 'through a circuit' AND BE RETURNED
to the source. Please do not think of that idly!
Many folks have a
problem realizing that a COMPLETE circuit is necessary. Circuit here
means the same thing as a closed racetrack, or some other analogy......you start at
one point, and must continue ALL the way around. A battery may have an excess of electrons at one terminal, compared to the other
terminal, but NO current (other than internal leakage) is flowing. You need to have the device to be powered, a lamp for instance, connected
somehow to BOTH battery terminals, for
electrons to flow THROUGH the device, and the battery too. Again...this idea of a complete circuit often eludes folks, and is just
one place the typical water pipes analogy fails to make things clear.
When electrons flow through something allowing such a flow, the properties of the CONDUCTOR [usually metallic, often a
'wire'] are such that the conductor itself offers SOME 'resistance' to the flow. A thinner wire would offer much more resistance to
a flow
to your starter motor, than a much thicker wire. Resistance is generally undesirable in our
motorcycle wiring, switches, and so on. You can't get away from it,
however. 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 electronics, devices such as 'RESISTORS' are used on purpose to restrict electron flow.
In your motorcycle you have resistances in the wires themselves, diodes,
contacts in switches and connectors, relay coils, lamps, ignition coils,
alternator rotor and stator windings...even the carbon brushes (close to 3/4 of
one ohm for both of the brushes together), internal parts
of some things like voltage regulators, ETC. In some instances,
there was unwelcome resistance between the timing chest and the engine case, due to
factory paint,
and there are other examples.
In our BMW Airheads, the resistance of the GEN lamp is used to
supply initial magnetization of the alternator rotor (via the
battery, ignition switch, and 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 is the OHM) of the
fixed physical size alternator 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. Both of these are impractical. If you are thinking ahead here, you will realize that to
get more WATTS of alternator output, at any given rpm, you need some conflicting changes...heavier wire, which means less turns, so you
need a larger physical alternator...etc. BTW. The only conductor that is better than
copper that could conceivably be considered is silver, a costly
metal.
So far I have mentioned amperes, volts, & ohms, and a brief mention above of
WATTS. 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. In other cases the heat is not desirable.
Semiconductor 'things' like diodes and transistors, 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 failures from molecular-sized
faults in the manufacturing process. Sub-microscopic cracks, if
you will. In many types of electronics equipment, excessive
heat causes the circuitry to fail, sometimes in intermittent
ways. This happens to the ignition module under the tank if it
overheats due to lack of regular replacement of the heat
conducting paste. USUALLY in THAT instance, fresh paste fixes things ..without replacing the $$
module, but letting it overheat a large number of times may well
lead to permanent failure.
Constant heating and cooling may be responsible for diode board failures. That heating is caused by the engine heat itself, as well as the
current flow through the diodes. Diodes have an internal
resistance, and the current flowing through them adds more heat, to the existing
engine heat. That was a problem on some early Wehrle-brand diode boards,
as they did not have the large diodes outer wires bent-over before soldering, so
the soldered small area got hot, the solder melted. That was in the early
1980's. The Bosch boards were always OK.
When current flows, heat, or maybe work, is done...whichever way YOU want to think about it.
Work being done is called WATTS. It just so happens
that there are some very specific, dyed-in-the-wool relationships between amperes, volts, ohms, watts:
volts multiplied by amperes equals watts.
746 watts is one horsepower.
If you divide volts by amperes, you get ohms.
From the above, any value can be obtained from any two known values.
A thousand watts is called a KILOWATT, often abbreviated as Kw. You may see, at times, engine output rated in Kw. NOW you know how to convert Kw to horsepower! Whilst there are some differences between horsepower measurement standards in various Countries, the relationship between watts, voltage, current and horsepower is fixed.
In the world of electricity, the Greek letter omega is used for
ohms. I won't try to show that symbol here, as some
computers will display it wrongly. Continuing: v or V for volts (sometimes an E for electromotive force); W for
watts (sometimes P= xxxW). Current itself is usuall
represented by the letter I...but....if current is expressed in a
value, such as amperes, it might be written as something like 12
A. 9 ma would mean nine milli-amperes, or 9 housandths of an ampere.
If the flow of electricity is restricted by such as a too thin wire
(like maybe some broken strands!), badly corroded connections,
sulfated battery...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 small amount of current to be diverted from a circuit under test, and 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 meters divert so little current that the voltage is not
hardly noticeably changed by
attaching the meter. This is usually 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. The older meters with
actual meter movements...a needle physically moving....usually draw far more
current, but it is still NOT a problem with almost all areas of vehicles.
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 another battery for higher resistance ranges, and possibly a 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.
Common types of simple diodes (which are one-way devices!) 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, the diode may well not 'turn on', in the so-called 'forward direction'. 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. 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.
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, and 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, called laser
diodes. Some forms of those laser diodes are specifically manufactured to be indicators. These emit a
beam of light. Laser diodes are used for all sorts of
things, including vehicle tail lights, backlighting on TV and
computer screens, etc. Besides the
small and and also quite large diodes in your Airhead's diode board, you may find, depending on year and model, other diodes in your motorcycle...in the
headlight relay, starter relay, connection board in the headlight shell,
and 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 inherent internal resistance. Hence, they can, with enough current flowing, develop a lot of heat.
The forward drop of a common silicon power diode is fixed by atomic properties at roughly 0.5 to 0.6 volt.
Therefore, at 10 amperes, that is about 5 or 6 watts of heat to somehow be gotten rid of.
There are 6 of those larger 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.
Very little is absorbed by the passing air. The RUBBER
mounted diode boards, that were used on some models of
Airheads, can NOT throw off this heat nearly as well to the
timing chest metal, it being already hot from the engine being run.
This is just ONE reason I recommend that the rubber mounts be changed to aftermarket metal ones from Motorrad
Elektrik, http://www.motoelekt.com or
Thunderchild, http://www.thunderchild-design.com
The other reason is that the necessary extra grounding wires are
not absolutely needed, and with solid mounts the alternator
almost always operates better.
Although your motorcycle may have a lamp marked GEN, it is really an
alternator lamp indicator. Generator, the
term/name, has been used for a very long time as sort of a
generic term for a source of energy, typically means any mechanical source, but not a
storage battery. There is a type of real 'generator',
typically using brushes and armatures windings with a commutator,
no need to get into that here.
A little aside story: When the world was first being electrified by Edison for street lamps and home lamps, current flowed in one
direction, this current was called DC, Direct Current. This was very limiting, as when you had enough homes and factories using electricity, the wires must get larger and larger, as
more and more current must pass in total, and more homes are connected to a pair of wires from the generating plant...and soon the wires are
very unwieldy. It is almost impossible to move lots of electricity if it is DC (direct current), for long distances. That is where Edison
personally failed, from stubbornness, insisting on DC. As a
matter of fact, Edison had his ego on the line so strongly in
this area, that he lied about the dangers of A.C., and was quite
a nasty guy in some respects over AC versus DC.
The electricity in your home is AC (alternating current). What this
means is that over a portion of time, the power at the wall socket is such that its VOLTAGE is constantly varying, going
up and down, and in fact becomes ZERO as it follows a CURVE that mathematically is called a SINE WAVE. When this 'WAVEFORM' goes from
zero to maximum positive, back down through zero and back to maximum negative, and
then back to zero, that is called 'ONE CYCLE'.
Of course, ONE CYCLE could mean starting at ANY place on that sine curve, and
advancing in TIME until it reaches the same place on the sine
curve that it started from.
Conventionally one just thinks of it starting and ending at the zero
points. Cycles per
second (cps) gave way many years ago to the term HERTZ (Hz), to honor Mr. Hertz. In your home, the number of Hertz
(cycles per second), is
60. This value is kept very accurately by your power company...so accurately that your
electro-mechanical and some other clocks, run
correctly. In many 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 usually be heavier.
Alternating current has a HUGE advantage over Direct Current, it can be EASILY
transformed.
There is a very widespread use of an electrical part called a
transformer. A transformer is a specially designed magnetic steel structure, with some turns of wire on it called a coil, and another
such 'COIL' of more (or less) turns of wire, the two generally being electrically separated;
but magnetically coupled. This 'transformer' can very
efficiently can change an A.C. voltage to a lower or higher
voltage.
Since you have learned that POWER (watts) is
voltage times amperes, this means that we can TRANSFORM the POWER of a power plant to a super high voltage, many thousands
(in fact up to
half a million is in use), and send that power someplace at a much lower CURRENT (amperes). 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, we can use THINNER wire to send the 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 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, or both. The exact voltage is not
critical, except for, perhaps Industry purposes, so 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.
It is common in the USA today to use 120, 240, 440, and 660
volts, the first two for homes, and other two for big machines in
industry.
A special form of this transformation idea is actually done in your
alternator, magnetically and mechanically, from the induced field from the rotor, and some other effects in the stator...but this is far too
complicated to explain in this article.
The only other place transformation is done fairly directly in your
Airhead, is in the ignition coil,
which by trickery, has a DC voltage
applied that is made to ultimately act like a form of AC. The DC from the battery is applied to a moderately low number of
PRIMARY winding turns of fairly reasonably thick low resistance
wire. The important thing is the low number of turns. The
current in those turns produces a large magnetic field. The SECONDARY winding has many thousands of turns
of much thinner wire, so it will fit in the coil enclosure. It is a
property of transformers that a one turn primary and a 1000 turn secondary is a multiplication of 1:1000 in voltage step up
(and a corresponding DROP in CURRENT). If the 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 cut and dried 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. The ignition coil(s) output may be MANY thousands of volts,
and 40,000 is NOT unheard of. Since a certain amount of power is being 'transformed'.
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. The secondary then must have wire that is much
thinner, in order to fit in the case, since so many thousands of
turns are needed. Since VERY high voltages are being developed, insulation 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.
Once the coil secondary
winding (that is the term used to mean the output winding) voltage rises to the point that it will jump
the spark plug gap, the spark begins and the voltage output of the coil does not
continue to increase, but starts
to decrease very rapidly. The spark itself having a very short duration.
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 (and reducing radiated radio energy). IF the spark plug cap was off the spark plug, just
laying there, the coil voltage might just rise high enough to cause an
insulation breakdown inside the coil...or someplace else....and in the
electronics ignition models (1981+), you could damage expensive items besides
the coil(s). Sparks jump easiest in low gas
pressures. The easiest jumping would be in outer space.
The next easiest, for our illustration purposes here, is for a
spark plug cap to be off the spark plug and just lying wherever
it might be. In our Airheads, one cylinder fires at a time.
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 spark
plug is in the engine with that cylinder under
compression....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 resistance of the spark plug
firing gap.
In your Airhead, the primary source of electricity is the
battery,
which has an INTERNAL RESISTANCE which is very low, a very
small fraction of an ohm. This low resistance is why dangerous
currents (like melting things type of currents) can flow with
short circuits at the battery, or in too low a resistance in
circuits connected to the battery. Your battery stores energy NOT
as electricity, but as CHEMICAL energy...or potential chemical
energy. Upon a circuit being connected and 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 voltage of ~2.2 volts per CELL at rest.
That is not the voltage you will be dealing with, necessarily,
consider that 2.2 volts as a sort-of value, for conversation.
You have, however, SIX cells in your battery, hence 2.2 x 6 is a
'nominal' 13.2 volts. In practical terms, the battery
voltage, fully charged, but the engine off, and no substantial
load on the battery, will be AROUND 12.6 volts.
When you are riding down the road, the alternator keeps
the battery fully charged, and the battery voltage will be in region of about 13.6-14.5
volts. About 14.2 is a good optimal value for most
batteries. I won't get into just why, as I do that in
a battery article.
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, the terminal voltage will be in that range
mentioned, and if the engine is then shut off, the battery voltage will decrease
rapidly to under 13, then fall very slowly, until it stabilizes at about
12.6....and will remain there, until, over time and any drain, it is
slowly discharged. The voltage drops during this discharge. For practical purposes, a battery that measures....in its
well-rested state.....below 12...has a rather low charge. 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 (13.7 or more is obtained), and then the voltage drops under about 10.5
during engine cranking....then the battery has little life left (assuming the
starter is not excessively drawing current). More information on
voltages later in this article.
"Flooded" batteries are
the type that you can see liquid sloshing around, so I call them SLOSH or flooded
batteries. These are the types of batteries you must add
distilled or purified water to occasionally. In
quite hot weather, this type of battery can self-discharge as much as 1/3 every month, unless recharged. If
not
recharged
fully during a ride, this type of battery tends to fail faster due to somewhat
IRreversible chemical
effects. NOTE, however, that this type of battery is
typically longer-lasting, than most sealed batteries (non-slosh).
A battery fails
chemically as well as
failing if INternal connections break or partially break. Once a battery fails chemically, it MAY be
impossible to recharge it very
much at all. Failure of any one or more cells can cause a type of failure that is
sometimes hard for amateurs to determine. There are other types of batteries, one interesting type is called Valve Regulated, typified by the
Panasonic brand version. I
prefer the original, more properly descriptive name, Absorbed Mat.
As a general rule you should automatically replace your Panasonic battery every 3
years, and your flooded battery at 4 or 5 years. This schedule
assumes you take care of the battery, and it is being charged properly.
A vast number of Airhead owners try to get every last usable day
from their batteries, and 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 and more
alternator power to maintain it at a reasonable charge.
That becomes harder and harder on the alternator. 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,
causing excessive wear. Consider also, 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. I
treat sudden battery failures elsewhere's.
The
Airhead Alternator...in more depth:
[[[First, a VERY nerdy, hardly known bit of
information:
Earliest alternator rotors were 73.4 mm in diameter. From approximately early
1975, they are generally mostly 73.0 mm in diameter. I prefer the
73.4, rewound for low ohms]]]
Earliest /5 type alternators were 180 watts, had 105 mm diameter stators where they fit into the engine case, and had Bosch part numbers on the outer housings that ended in -001 or -002. The R90S only had a -003 stator, it had a slightly larger inside diameter...with slightly reduced output. The later stators, such as -004 and -005, are all 107 mm, and do NOT fit the /5. The EARLY /6 also had a 105 mm stator, and thus a /5 180 watt system is easily changed to a 280 watt system, by simply changing the stator and the diode board.
BMW elected to use in the Airheads a type of generator called an alternator. The name means that its output is alternating current...that sine wave thing again. The output frequency (number of CYCLES per second, or Hz) varies with engine speed.
Another very nerdy bit of 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.
60
When the
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 and perfectly
converted to DC by your diode board. In fact, due to inefficiencies
in the diode 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, and especially the ignition
system.
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 [/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. 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 are
identified by numbers: 1N3659 and 1N3659R. 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'. As you
learned well above in this article, one speaks about single and
multiple cycles of waveform. 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 different (very simplified here).
Those waveforms are constantly rising
and falling in sine-wave form. Since, with overlapping waveforms
at 120°, there is more constantly an actual output of good
value...that is, much LESS time is at lower sine-wave levels,
then these three waveforms produce more power, than if there was
only ONE phase....and, the three phases are rectified by the three positive and three
negative large pressed-in-place diodes. (aside
note: If you have one of the EnDuralast alternator conversions,
that is a ONE phase alternator. It would be more efficient
if it was 3 phases, but that would complicate the system they
use)
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 lines below the crossovers, you would see a positive-going part of a sine
wave, and a lower-going part of a sine wave, each with three peaks. The
vast AREA between them is increased. 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.
Besides the /6 and later stators and diode boards
center tap connections and associated small diodes mentioned previously
that increase the stator output a bit, ALL the diode boards have
yet another set of 3 diodes, again these are small ones, 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
relatively small amount of current, which has special functions:
(1) for driving the voltage regulator's
'sensing' function; and, (2) to drive the several amperes
needed for the rotor; and, (3) to extinguish the GEN lamp after
the alternator spins up fast enough to need more rotor current
than that provided through the GEN lamp.
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, and perhaps charring/burning, and perhaps a gross failure. If,
instead of shorting, that diode 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. This type of failure is hard to diagnose with the diode board still in the motorcycle, and
still
connected. It is possible for a device called an oscilloscope to make a
definite determination, but few own those instruments. Symptoms might be a battery that MIGHT seem to
fully charge up, with correct voltages....yet, when enough load
is put on the bike's system...such as the headlight, or 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 rare event, but does happen.
Diodes boards are best checked when OUT of the
motorcycle. Using just an ohmmeter will give reasonable results, for
forward and reverse diode readings (BE SURE TO DISCONNECT THE
BATTERY!), but the best test is using an 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.
Specific diode and other problems in Airheads, OTHER THAN in the diode board:
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 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. 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). NOTE that
the headlight relay pin 85, a black wire, the grounding end of the headlight
relay COIL, returns to ground 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 DEenergizes, turning OFF
the headlight, but the mentioned relay's diode keeps the tail and instruments
lit. ALSO note that 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 switch
works without the key.
2. On models /6 and /7 and up through 1984, if your neutral light
has weird things going on, such as being OUT in neutral, ON in gear, unless clutch lever pulled in, and maybe ON at every clutch
usage....or some one or more of these indications, you have a bad
diode that is located on the BACKside of the board inside the
headlight shell. This applies to all twin shock models, EXCEPT the R45 and R65.
In those two models the diode is
plugged into the wiring below the starter relay (on pre-1981 R45/65, .....and inside the starter relay in post 1981
R45/65 models). NOTE that on MONOLEVER
models the diode is also inside the starter relay.
Some have not understood these differences, have installed the
wrong relay type.
If your bike will crank the starter ONLY if you also
pull in the clutch bar lever, you may
have a bad starter relay diode. Did you notice here that the starter relay MIGHT have a diode? So, what do you think may happen if you don't use the proper relay?? YEP.
4. There are some peculiarities in the BMW system here
and there. One is that from 1977 the starter relay has
two RED wires that are essentially jumpered via a link
inside the
relay. Corrosion here can cause the entire lights, etc., system to act
weird or act disconnected. This is a relatively COMMON
PROBLEM. Just exactly why BMW did that particular
wiring arrangement is open to conjecture, but I solve is
permanently by NEATLY joining the wires, but leaving them
connected to the relay!!
Batteries:
A LOT more can be said about batteries. Here are a few somewhat useful bits of information:
Voltage regulator settings:
The voltage regulator should not be checked unless the battery
has first been charged. Voltage regulator settings are BEST
checked with a thermometer on the voltage regulator. However,
what I do is to simply start the bike after sitting all day or
night at a roughly known air temperature, and then I rev the bike
up within two or three minutes,
and measure the voltage at the battery terminals, with a known accurate digital meter, BEFORE the regulator
can be heated by engine heat. With the battery previously being fully charged, it takes only a minute or so at 4000 rpm for the battery to recharge
from starting and reach its voltage regulator setting. Temperatures below are VOLTAGE REGULATOR temperatures. It is FAR better to have the voltage
regulator and the battery both at about the same temperature, which is why the testing should be done from a fully cooled off engine within
minutes of starting. Values below are for flooded batteries.
47°F 13.8-14.4 volts
68°F OPTIMUM setting for MAREG batteries at this temp. is 14.1
volts.
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 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. NOTE that the voltage you are interested in is at the
battery, not at some other place on your bike. NOTE that if
connections, especially to the voltage regulator, alternator, diode board, and battery, are not good, clean, solid, the readings and
performance will likely suffer. Note also that 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.
Charging:
There are a few things to know about
charging a battery. Initially, on a very weak battery (low
charge), you especially want to simply limit the current flow. Typically
and usually recommended maximum is a rate of charge equal to 10% of the battery capacity in ampere-hours. That is, a 28 ampere-hour
battery should normally not be charged at a rate over 2.8 amperes. On a practical bases, about twice that value is usually acceptable for
the short term, just do not allow the battery to get over a
slightly warmish feeling. After the battery voltage comes up to near 14 volts,
which charges it fully....then....the
battery can be 'floated' at a much lower level, to keep it fully charged, and the float charger
can be left on indefinitely if the voltage is 12.8 to 13.2 (at
nominal 77°F). This is what 'smart chargers' do, although some
are smarter than others in HOW they do it, and the exact voltage
they are set for.
Slosh batteries, often called FLOODED or conventional lead acid
batteries, 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
'floating charging' is NOT recommended by ME.
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
15.0.
Hydrometer readings on slosh (flooded) batteries, corrected for
temperature, are fairly accurate, but some battery faults are
such that readings
are NOT overly useful. Still, the test is useful at
times. Lower liquid capacity hydrometers for small batteries are
available cheaply.
If a battery has been charged fully, then let sit and stabilize
over time, the battery voltage will very slowly drop, after a
much larger initial drop from fresh charging. The following
information assumes 77°F, and that
the battery has sat for at least a few hours:
Fully discharged: 11.89 volts or less. NOTE that SOME books will say that this is 10.5 volts, SOME will say that a 10% charge is left at
11.31 volts; and 20% at 11.58 volts, 30% at 11.75 volts. These variances are due to the type of battery construction, and method of
measuring and the amount of capacity left.
The following are generally accepted 'official'
values:
100% of charge at 12.7 volts and 77°F [UNofficially, your battery is PROBABLY going to read about 12.6 volts for fully charged, at around 65°F, after it sits for some hours].
The below values are for 77°F:
75% of charge at 12.5 volts
50% of charge at 12.27 volts
25% of charge at 12.06 volts
Absorbed Mat (Valve Regulated) (Panasonic and other similar types) batteries need somewhat higher
charging voltages....and I like to see the voltage regulators set for
about 14.3 or even a tad more, at nominal 'room temperature', at
the VR.
Typical electrical usage in the STOCK airhead:
Headlight 55 or 60 watts; ignition 40 watts; miscl small
lamps, etc about 15 watts; charging after battery fully charged...about 10 watts.
Starting:
Problems with
starting can often be traced to a starter in need of replacement or overhaul or
lubrication of the Bendix drive, a
bad starter solenoid, and occasionally a problem in the starter relay
circuitry. Some stock relays have a diode
inside. Unconfirmed information is that some have substituted a
0-332-014-118 relay, perhaps a DF005 'Blazer' relay from AutoZone
stores. DO keep in mind what I have posted earlier in this
long article about diodes inside of starter relays! The Bosch starter relay uses two #87 terminals,
and may sub to Bosch 03 32 019 150 for 1977+ bikes. That is a common Bosch
accessory use relay. Connector, if you need one, is 0 334 485 007, while
the spring loaded terminals are 1 901 355 917.
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 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.
Valeo starters can be replaced with Bosch, you also need the forward end bracket that the Bosch used to secure it to the timing chest wall. There is an $$ aftermarket Denso starter available that is quite high powered. You can also replace a Bosch with a Valeo. Be careful when installing a Valeo in place of a Bosch, to be sure the Valeo fits properly...you may have to do a small amount of metal filing.
NOTE: 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 acehoutx@flash.net.
Mention account 700. The Valeo starters are available. The part was
D6RA15, Valeo changed it to 432586. The last 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 thought that the Bosch starters MIGHT be put back into production at some
point. The information in THIS paragraph was provided by Ken
Kirk kirkkw@yahoo.com.
NOTE:
See information in the URL section of this website for other electrical
sources!!!...including oversize alternators, parts and service for Bosch and
Valeo, ETC!! In particular, see Euro Motoelectrics; www.EuroMotoElectrics.com!...they
have the correct latest version of starters and parts!...at very
competitive prices! Highly recommended! They also
produce the EnDuraLast Alternator system.
Addendum:
1. Eddy Currents. Eddy currents are a phenomena, or characteristic, of some forms of magnetics. In our airheads, they are at two prominent places, the speedometer, and the alternator stator. An eddy current can be thought of as a particular type of electrical and magnetic energy that can be induced into a magnetic medium (steel laminations of the stator), or into a non-magnetic structure, such as the aluminum cup used in the speedometer. In the stator, eddy currents are UNdesirable. Eddy currents are often generated in transformers, and are generated in the steel laminations of the stator, and lead to power losses. To combat this, thin, laminated strips of metal are used in the construction of power transformers, and your stator, rather than making the transformer or stator out of one solid piece of metal. The thin strips are separated by insulating glue, which confines the eddy currents to the strips. This reduces the eddy currents, thus reducing the power loss. It is important to not scratch the laminations across, which might cause currents to flow between the laminations in a way that they were not designed for. Nerdy point: In mechanical speedometers that use eddy current technology, a rotating magnet induces eddy currents into an aluminum cup. The cup is spring loaded (usually a flat round hairspring). The faster the rotation, the higher the magnetic forces the aluminum cup experiences, causing it to rotate, and take the attached indicating speed needle with it. Thus, even though the aluminum itself is seemingly UNaffected by you bringing a magnet near it, and you certainly cannot turn the aluminum part into a permanent magnet, it will be affected.
Revisions:
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 redundency'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.