Aftermarket
Alternators: Installation, Capability, Performance
AftrMrktAlt.htm
15-C
©
Note:
Read 15-A and 15-B first!!!
Discussion: (much of this discussion is pertinent to ALL
charging systems!!):
Unless the output voltage of the alternator system is specified for the rated wattage, it is possible for the output voltage to sag from a large load (big headlamp, driving lights,heated clothing, whatever), while at the same time the output current could possibly be high.....OR NOT. If the output voltage was too low to keep the battery fully charged; yet the current availability was high, this would be false wattage. The reason is that what is really important is the real output with a "reasonable" voltage at the battery.
Most, if not all riders, want the battery to remain charged; yet the alternator system to supply adequate electricity to operate everything. If the battery terminal voltage is 12.7, that is enough for a rider's purpose. However, that is not enough voltage to truly maintain the battery really well...and you need a higher charging voltage to enable the battery, due to inefficiencies in the battery itself, to be FULLY charged. This is probably the most critical part of in-city commuting.
A major purpose of an aftermarket system should be to not only have MORE TOTAL WATTS available, but that they be truly usable watts; and that the system will properly maintain the battery under typical operating circumstances. This includes idling for periods of time in stop and go traffic (even if the voltage sags then at a stop light, the alternator desirably should be capable of fast recharging, by the next stop light).
The system must be capable of handling all the electrical items likely to be in use at the same time for reasonable periods of time. Idle output, or slightly above idle rpm output, should be sufficient for normal use, as this is one of the complaints about the stock system, in commuting use.
I
did a careful installation & testing to evaluate the practicality of the EnDuraLast system.
A known perfect battery was used. Firstly the system used at light loading
to fully charge the battery according to the system voltage
regulation (14.24 in my conversion), and then the battery loaded
moderately for awhile until a known value of battery DEcrease in
voltage was noted. At this point the output was measured by
starting the engine, which slightly drained the battery, and then using various rpm, rather quickly.
That is a simplification of the various tests I did.
The charging characteristics of batteries of
different types varies moderately widely. For MOST types of
lead-acid batteries, if one applies a voltage of about 12.8,
constantly, eventually the battery would require very little current,
from the charger or system, to
maintain that stabilized voltage. For most batteries, 12.8
volts at room temperature is very close to a full charge (but not
what is called a higher 'surface charge', which is unimportant
here). If the applied
voltage is raised, within reason (not exceeding a maximum
value, often nearly 15 volts), the battery will usually eventually reach the new applied voltage,
or close to it;
and the charging current needed to maintain that voltage will be
higher than at a lower voltage...that is, the charging current
needed will be
progressively higher for a stabilized higher
voltage.
Batteries vary rather WIDELY as to the current needed from the voltage source for any one specific voltage. Generally speaking, a typical 'flooded' type of battery of motorcycle size (I will use the larger size, about 28AH as illustration), will need about 2 or 3 amperes to maintain about 14.1 volts AT the battery TERMINALS. Some Gel and AGM type batteries are quite different.
The EnDuraLast voltage regulator is internally fixed at about a 14-14.26, and hence a bit more of the EnDuraLast output is used to keep the battery charged, than with the stock voltage regulator setup. That is because BMW's original VR settings for the stock bikes is closer to 13.8. I have always felt that BMW was WRONG in selecting 13.8, but understand why; which has to do with water use from the flooded batteries, and some minor other things. The Authorities (Police) VR is set higher than the EnDuraLast, however....nearly 14.5, depending on temperature! Most voltage regulators have a voltage versus temperature effect, purposely built-in. This is because the voltage needed to maintain any given charge percentage on a lead-acid battery will vary with temperature. The COLDER the battery, the more voltage is needed from the system. The voltage regulator, ideally, is mounted in the same airflow as the battery. Generally, only a few tenths of a volt is the temperature compensation, from perhaps 120°F down to perhaps 20°F.....the typical range of temperatures seen by the battery and VR. Some higher temperatures (and lower) are seen sometimes, and one can add a few tenths of a volt if going lower, subtract a few if going higher. Motorcyclists rarely ride where battery temperature will exceed 140°F (typically from engine heat blown over the battery); nor, under perhaps 10 below zero.
The
STOCK 280 Watt Bosch Alternator:
The following is the TRUE ACTUAL USABLE OUTPUT of the stock 280
watt Bosch alternator, using the 3.7 or 2.8 ohm later model rotor
and known good connections, wiring, battery, switch, etc.
RPM
OUTPUT in Amperes
1050
2.5
1550
10.0 (Approximately the point of equilibrium with stock system drain
of stock lights and ignition)
2100
15.0 (5 amperes is available for
charging, approximately)
2850
20.0 Maximum available, battery at 13.5v. and rising. This is 270
watts. Very slightly more will be available
as voltage rises a bit more.
NOTE: Watts = voltage, multiplied by amperes
The ORIGINAL Omega Alternator, as sold by Motorrad Elektrik:
Testing was with a known accurate ammeter with relatively
short heavy gauge leads in series with the Omega diode board
output. The battery was drained somewhat to begin
with (on purpose); and, a digital voltmeter was placed across the
battery terminals. Readings were taken well before
the battery was fully recharged, with heated grips, accessory
lights, and headlight all turned on. Readings were
repeated with lights off, and also with the battery fully
charged. The "set point" of the VR appeared
to be close to 13.8 volts.
NOTE that the chart below is a summary, and where you see a
higher rpm with lower voltage, that was due to battery charge
condition, and there are small deviations from expectations, due
to, I think, heating effects.
RPM
VOLTAGE AT BATTERY
OUTPUT IN AMPERES
WATTS
1550
11.70
2
23.4
1700
12.5
5
62.5
1750
11.83
8
95.6
1750
12.5
5
62.5
2200
12.8
12.5
160
4000
12.64
28
354
4000
13.5
20
270
5000
13.2
31.5
415.8
NOTE CAREFULLY,
the two 4000 rpm tests. Note how the wattage varies with the
voltage. I specifically loaded the system in order to get
these readings.
Can you see that the battery would be marginally fully charged
(not quite), at 4000 rpm, if 28 amperes of load was used.
Increasing rpm beyond 5000 did not yield increased output?
Thus, one would want to keep the load a bit less, if cruising at
4000 for long distances.
NOTE: output
might be better if the VR was set higher, the voltage
regulator was NOT the adjustable version on this tested
bike... and if a fresh battery had been used. Note also, that
the ammeter and its leads and connections add a very slight
series resistance, and thus would have the effect
of moving the output higher up in rpm (although slight). This also applies to the Bosch and
EnDuraLast when tested. While voltage multiplied by
amperes is how one converts to watts, it is
entirely possible, under some circumstances, for a battery not
100% charged, to have a lesser or greater current input at a
particular terminal voltage....and as such, the USABLE system
wattage is a bit difficult to interpret to the
layperson.
It is interesting to compare these figures with the stock Bosch system. While it is possible that there are some anomalies present that I did not go into, especially the stock Bosch equipped bike I tested had perfect electrical connections, etc.....still, the Omega output seemed low at low rpm, and then rapidly overcame the stock system as rpm into the cruising area was attained.
NOTE: The weight of the Omega is nearly identical with
the stock Bosch....differences are so small as to be of no
concern.
The
'new' higher powered '450 watt' Omega:
This unit has a 81 mm rotor (instead of the original Omega's 76 mm)
and a larger stator to match.
Tests will eventually be run on a 450 system and when such are done, they will be posted
here.
The EnduraLast Alternator, as sold by Euromotorsports:
The weight of all removed stock components: diode board, stator, rotor, housing, regulator, some wiring, etc., is 87 ounces; all the EnDuraLast items as installed will weigh almost exactly the same. For the Omega, as noted, things are also about the same as the stock Bosch.
Leakage current: under 1.5 MICROamperes, worst conditions.
Rotor diametrical clearance to stator:
0.006-0.008". This can vary some with the components,
as well as the exact fitment of the inner timing chest to the
engine casting, which is adjusted slightly during a timing chain
or other similar R/R job.
Rotor runout, axial: negligible.
Rotor lateral runout (side to side): 0.00075" maximum.
Special note on the EnDuraLast Rectifier/Regulator: In a normal system in a motorcycle, the regulator is USUALLY, purposely, mounted in an area that allows some engine heat (comparable to battery temperature in a modest way), to influence it. This is not universally true. In most modern cars the placement of the regulator is usually PART OF the alternator ITSELF, and thus as the alternator warms up, the regulating voltage DEcreases some purposely, to match battery temperature characteristics. This is not necessarily so on this conversion; depending on where the regulator is mounted, and HOW (it generates heat internally). From my testing, the EnDuraLast RR unit is OK over a normal temperature range.
ACTUAL results for the
EnDuraLast:
RPM current output
TO BATTERY
Watts
900
6A
1000 7.5A,
13.12V
98.3
1000 8A
1200 12.5A
13.39V
167.4
1500 15A
1600 16A
1900 18A
and
14.24V
256.3
2050 20A and
12.81V
256.2
MAX 26.5A
and
12.8V
339.2
I was UNable to obtain more watts,
no matter the rpm. Over 3500 rpm was NOT needed.
Note that for
the otherwise stock motorcycle, no additional electrical loads,
the EnDuraLast alternator will maintain a reasonable charge at
about 1050-1100 rpm. This means that commuting is no longer
an appreciable problem. Note that the EnDuraLast has
more usable wattage output at low rpm, compared to the stock
Bosch, or the Omega. However, the Omega has higher absolute
maximum output wattage.
***The EnDuraLast is better for in-city stop and go, than the stock or Omega alternators.
It was
noted that the Regulator
set point for the EnDuralast at 84°F was 14.48-14.50 volts,
which is more to my liking than the Omega.
1981 and later BMW airhead motorcycles; and some earlier models with aftermarket ignitions, are sensitive to electrical noise in the battery supply. That is ONE reason, of several, that the original MECHANICAL VR was changed to an electronic type. BUT, some electronics, including diodes and a RR regulating transistor, can CREATE high-frequency spiking type of noise. Thus, tests with an oscilloscope are going to be run on the system eventually; one trace monitoring the battery, and one trace monitoring the ignition pulses. This has NOT YET been done.
NOTE: My results did not duplicate the specifications/information on output. I made some minor changes, eliminating some very TINY voltage drops, that helped some. I have thought about this at some length. I have an IDEA of what may be PART of the problem...again, this is theoretical. The stator output is via TWO wires, with NO grounding reference. As such, then, the Rectifier/Regulator unit MUST have a circuit that involves a type of multiple-diode rectifier called a "Bridge Rectifier" ((Whilst a half-wave rectifier could be used, I am 99% sure THAT is not the design....and would be MUCH worse anyway)). A property of a two-wire source to a bridge rectifier, is that the IMPEDANCE (nearly the same thing as resistance) of the STATOR and connecting wires from that stator, can be MUCH higher, with little deleterious effect, than the same increase in EFFECTIVE output resistance. THUS, the STATOR wires....the YELLOW wires...can have more resistance in them and still get decent output; but, the RED wires output, and the CASE ground output, will need VERY heavy gauge wires, and negligible voltage drop in connectors and connections. I WAS able to get a modest improvement (about 1.3 amperes, nearly 18 watts) by simply repairing just the bullet connector of the RED wires. I think that FURTHER improvement, I know not how much, might be possible....and that mounting the RR unit next to the battery will offer the BEST performance, in this particular regard....due to the very short wires possible, the elimination of some connections/interfaces, and so on. As such, my recommendations to the makers of the EnDuraLast was to mount their VR/diode assembly next to the battery, perhaps on the battery box itself....which would be a decent heat sink also. I have not yet tested such an installation...but I anticipate that it could only be an improvement upon mine.
In the real world, lab tests aside, the OVERALL best performance from all the various alternators and for typical usage and conditions..., is LIKELY to be with a battery terminal voltage of about 14.4 volts. When one considers lamps life, battery life (most batteries 'prefer' a terminal voltage under VEHICLE charging conditions of close to 14.4 volts or higher), and many other factors, one PROBABLY should have a VR set for 14.4 volts (perhaps 14.6 cold, 14.3 hot, or around these values, with perhaps closer to 14 under very hot conditions). Temperature here means VR temperature. VR's are deliberately designed to increase voltage output when they are colder. If one has an adjustable VR, it should be adjusted on a fully charged battery, with all the accessories turned off, and after some engine running time at cruise; or, done at room temperature, with a slightly higher voltage as I have noted in this article.
Conclusions:
1. The stock 280 watt Bosch system is adequate for most Airhead riders. If driving lights and heated grips and other accessories are contemplated, one may well be marginal or negative on electricity generation. It depends on how much additional load is being actually used, for how long, and what the average rpm is, peak rpm, and idle time. Very difficult to make a definitive statement, as riders differ in how they ride and use the engine. If you want some estimates for the type of loads and your usage, I can do that for you, upon request.
2. For COMMUTERS with reasonably high electrical loads who do a lot of short distance stop and go, I recommend the EnDuraLast over the Omega. For those with similar electrical loads, or higher, but who do mostly open highway riding, the Omega will produce the additional electricity that might be needed. There is no question that the EnDuraLast is better for in-town short distance stop and go riding.
EITHER of these systems will perform adequately enough for those that just need more electricity for cruising. The Omega has the maximum output edge.
rev: 01/27/2008...checked for clarity
02/06/2009: mention of the Omega 450
09/16/2009: update article for clarity, numerous places