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Aftermarket Alternators
Installation, Capability, Performance

Copyright, 2014, R. Fleischer

Note:  Read 15-A and 15-B, first!!!


NOTE!    This article is due for major revision sometime in 2016.

This article was begun quite a few years ago, and has been added-to in a not well-integrated fashion for a long time.  Some tests were purposely run in extreme modes, and conclusions from looking at the figures may be difficult to understand.  When I revise the article, I will put it in much better and ordered format. 

There is nothing wrong with the design of the stock Bosch alternators as installed in the Airheads.  But, they get old, they age, they are sometimes abused, they fail, they are very often never maintained until there is a failure.  ETC.

I am not promoting aftermarket alternators; nor, am I saying to not get them.  I am reporting only facts and testing information, with conclusions that anyone with electrical knowledge can reasonably assume is correct.

You may well do fine with the stock system.  But, if you have special needs, such as big city stop and go commuting; or need more watts...perhaps you are approaching the stock alternator limits (which decreases reliability)...or, need even more watts....or; perhaps just want to upgrade....there is plenty of food for thought in this article.

Snowbum, June 15, 2016.

There is a lot of technical information in this article. This article includes information on charging the motorcycle battery that is far beyond what simple advertisements for alternators will provide.   Charging a battery in a vehicle like your Airhead is NOT as simple as you may think; nor, is interpreting the alternator ratings, typically simply wattage. This article presents a huge amount of information.  The article also presents information that allows you to select an aftermarket alternator, if you so desire.    I suggest you read through this article completely, to get an over-view, then, if you are confused, re-read more slowly.  If still confused, please inquire on Snowbum's favorite forum for such, which is actually an E-mailing LIST, the Airheads List, as hosted by  Input will help others, rather than my answering individual inquiries.

Discussion:  (much of this discussion is pertinent to ALL charging systems!):

Measuring or specifying output in watts is not as simple as it may seem for charging systems.   The simple part is that watts is equal to voltage multiplied by amperes.   So, if the output of the alternator can be measured in amperes and in voltage, multiplying those together would give you watts.  BUT, there are MANY complications.

The output of the alternator system should be AT LEAST specified and measured at a practical usable rated voltage.  It is wrong to JUST specify an alternator sales brochure or other information, in which voltage, perhaps not even stated, is not high enough to keep the battery charged; or, at least close to fully charged.  It is possible for the system output voltage to sag from a large load (big headlamp, driving lights, heated clothing, POOR BATTERY, etc). If the output voltage was too low to keep the battery fully charged; yet the current availability was high, it is possible for false wattage advertising.  What is important is the real output with a "reasonable & usable" charging voltage at the battery, that keeps the battery charged enough to have good battery life AND to be able to restart the bike over and over.  You want a reasonable fast recharging, after such as starting, or being at a traffic signal for awhile, etc.   The "reasonable & usable" battery voltage can be argued about.   In MY opinion, it is acceptable to publish possible battery performance AND performance at less than a fully charged battery.  But, both.  This means that if a battery is fully charged at a resting voltage of 12.8, and the system is so heavily loaded that only 12.4 volts is at the battery during vehicle operation, that is acceptable, if the purchaser/owner is informed, and understands...because if the battery is over ~ 11, the bike WILL RUN OK....but the battery should be charged by whatever means, before the next use.  This is not an easy concept to really understand.  

Stating some of this differently:  The owner should be informed if the alternator specification does not allow for a full charge during extended cruising.  The specification should, and seemingly never is, also specify as continuous output. If you cannot go on a trip knowing the alternator will CONTINUOUSLY produce the wattage you need, then you have a problem....right?  You also want to arrive at your destination with the battery fully charged....right?


OK...lets get into another area:

If the voltage is too high, the battery could deteriorate from too much voltage being applied, which also means too much current, which means wattage (HEAT) being MADE by all that electricity flowing INTO the battery.  The battery could overheat & warp; or use water too fast, or if a sealed type it might have enough internal pressure to open the safety valve (VRLA types and other sealed batteries).  These things have NOT been any problem in any of the systems tested....within the testing parameters.

You want the battery to recharge quickly after starting the bike or perhaps from long periods of waiting at stop lights... and then riding off.   If the battery terminal voltage falls to 12.6 (or below) while on the highway, that is not enough voltage to truly maintain the battery at a full charge.  In fact, if the battery terminal is below approximately 12.5, the battery is beginning to be drained.    Another consideration is that if the alternator capability is really very high, the excessive recharging current could damage the battery.

You need considerably higher charging voltage than 12.7, to enable the battery, due to inefficiencies in the battery chemistry itself, to REACH full charge in a reasonable amount of time.  It becomes more critical when doing stop and go riding in city traffic.  

When you stop where you are going, be it work or home or other, you want the battery to be fully charged...or nearly (or, reasonable...or, take your pick of words here).   If you ride to work, in stop and go city traffic, and the battery does not get over perhaps 12.3 or 12.4, at the time you park the bike for the day....then the battery is not fully charged, and IS deteriorating that day.  It may well start the bike.  It may well fully charge on the way home if traffic is lighter, but SOME damage was done.

If your battery is poor, and here I mean it's internal resistance has increased a fair amount, then the battery might still start your bike, and might still show a full charge as far as VOLTAGE is concerned (during charging)....but the battery terminal voltage will SAG, often quite a bit, and measurements for alternator output/performance will be TRICKY to accomplish accurately.   The INITIAL testing on the Omega 450 and 600 were done on the SAME bike, with the SAME poor battery, which happened to be the popular Odyssey type.  LATER, a brand-new Panasonic battery was used, and the performance is ALSO noted in this article.

There are three basic reasons for an aftermarket system; (1) you need more usable watts; & (2) you want more reliability, perhaps; & (3) you'd like the additional watts to be available at idle RPM, or, not much above it, which is helpful for stop and go riding in big city traffic.
There are other reasons, but those cover the basics.

An aftermarket system should not only have MORE TOTAL REAL WATTS ...RELIABLY....available, ...but the system should 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 'some' at a stop light, the alternator should be capable of fast recharging.....this is especially important in stop and go in city traffic.   A question might arise now, that if the battery is slightly damaged from excessively fast charging, and you are in stop and go traffic, and stopping every few city blocks for traffic damage being done to the battery.  YES...but it is not much, usually.  So...the primary thing is that you want the battery charge to remain high enough so the engine does not quit, and considerably more charge than THAT, actually.  There are a lot of variables.      

The system should be capable of handling all the electrical items likely to be in use at the same time for reasonable periods of time. 

Idle rpm 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 stop and go commuting use.

The idle rpm of Airhead motorcycles should not be set below 900 rpm, no matter what you read elsewhere's, and no matter what alternator, stock or otherwise.  I recommend a typical target of 1000 to 1050 rpm for idle rpm, after a full engine warm-up (5 miles or 6 minutes perhaps) at the normal altitude and temperature you ride in.    As much as 1500 is OK.  These figures were selected by me for a variety of factors, including carburetor performance & synchronization, and good timing chain compartment lubrication....and potential for some alternators to provide actual usable output at 1200 RPM under some circumstances. There is an effect I will call hysteresis:

What is this hysteresis that I just mentioned?   Due to untested factors, but believed to be the minimal but notable (?)magnetic memory of the rotor, with the rotor current turn-on characteristics of the voltage regulator (in conjunction with the GEN lamp current-passing ability), you will find, that to INITIATE usable current from the alternator, you need a certain RPM.  Once that RPM, or higher, is obtained, you will get some sort of output from the alternator as you lower RPM BELOW what was needed originally.  This is not a necessarily totally and always repeatable situation, depending on how low the RPM might reach now and then during the ride....but the effect IS notable. The hysteresis of the 600 watt alternator from Emerald Island (Omega) was fairly pronounced.  This characteristic allows this alternator to operate in the RPM area usually reserved for the permanent magnet alternators.

The charging characteristics of batteries of different types varies a considerable amount.   For MOST types of lead-acid batteries, if one applies a voltage of about 12.8, constantly, eventually...and this could take a LONG TIME... the battery would reach approximately full charge and then require very little current, from the charger or system, to maintain that stabilized voltage. UNfortunately, that voltage is vastly too low for practical on-road recharging. The battery needs a much higher APPLIED voltage to quickly, or reasonably quickly, re-charge.   Some battery types, notably the AGM/VRLA types, are quicker to convert chemically to a full charge, but still need much more than 12.8 volts of alternator output.   

Batteries vary rather WIDELY as to the current needed from the alternator to maintain a specific voltage.   Generally a typical 'flooded' type of battery of motorcycle size (I will use the larger motorcycle size, about 28AH, as illustration), will need about 1 to 3 amperes to maintain about 14.1 volts AT the battery TERMINALS.   Some Gel and AGM type batteries are quite different.   This 1 to 3 amperes has NOTHING to do with what the rest of the motorcycle will require for ignition, lights, etc. 1 to 3 amperes at 14.1 volts means that just maintaining the battery AFTER it reaches full charge will require 14 to 42 watts from the alternator! 

A battery requires more voltage to re-charge at lower temperatures. For the voltage regulator at room temperature, the motorcycle's system will try to keep the battery at a high floating charge level, perhaps around 14.2 volts (this could be 13.7-14.7, depending on VR and other things), when the rpm is high enough & assuming enough alternator output capability.  As temperature drops, the VR output should increase SLIGHTLY, and vice-versa.  A tenth or three tenths of a volt is typical, with maybe another tenth if the temperature is near freezing or somewhat below. 

BMW's original VR settings for the stock bikes is ~13.8 volts.  I have always felt that BMW was WRONG in selecting 13.8 volts but I understand why; which has to do with keeping water use low from the flooded batteries, and some minor other things.  The Authorities (Police) VR is set to approximately 14.4 depending some 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, AND, the chemical conversion works faster with an even slightly higher charging supply voltage when the battery is COLD.  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, there is only a few tenths of a volt compensation, from perhaps 120F down to perhaps 20F...the typical range of temperatures seen by the battery and VR.   Motorcyclists may ride where battery temperature will exceed 140F (typically from engine heat blown over the battery).  Some ride when the weather is below freezing. 

As the battery temperature falls towards freezing and below, the battery has a much more difficult time (it is, at its core, a chemical reaction device) producing the current needed to start the engine.  The engine has higher friction due to cold/thick oil and decreased clearances from metal shrinkage. THUS the starter motor is going to pull a LOT more battery current.  The chemical conversion in the battery to produce electricity ALSO gets more sluggish, and this is not only in battery delivery of electricity, but in re-charging, hence the higher charging voltage.  So, in cold weather, everything is much harder on the electrical system.

Schematic diagram of test circuit that was used for all alternators; with few differences.  Note that wires were of very large gauge to avoid errors.


The STOCK Bosch Alternators:

BMW has used several versions of the 'stock' Bosch alternator in its various Airhead motorcycles.  The highest output was 280 watts rated, used in the /6 and well into the eighties. The R90S had 238 watts.  The last of the Airheads had 240 or 250 watts but began charging somewhat lower in rpm.   The following is TRUE ACTUAL USABLE OUTPUT of the stock 280 watt Bosch alternator, using 3.7 or 2.8 ohm later model rotor; known perfect connections, wiring, battery, switch, etc.  NOTE that you CAN REALLY expect to get VERY close to the RATED output from Bosch Alternators.  This is NOT necessarily so with some aftermarket ones.  You will be able to see that in this article.


Output, amperes







Approximately the point of equilibrium with the stock system drain of lights and ignition



see above.  5+ amperes is available for charging after considering the ignition, basic lamps, etc.



MAXIMUM available, battery at 13.5 v, and rising.  This is 270 watts.  Very slightly more will be available as the voltage rises a wee bit more.



watts = voltage multiplied by amperes

13.5 volts is enough to maintain 100% of battery charge.

NOTE that the stock alternator produces what Bosch specified.  Note also that the voltage is a decent value, & above the minimum needed by the battery, to maintain a FULL CHARGE, even at maximum output.

Note also that 1550 RPM equilibrium point.  Theoretically, this means that the battery will, if already fully charged, not be discharging at a constant 1550 RPM.  You would likely never be riding in this situation.

The first generation "400" Omega Alternator, as sold by Motorrad Elektrik:
There are two sources (in the USA) for the GENUINE  "Omega" Alternators, mfr by Jeff Lee of Emerald Island.  These are products of high quality.  Those sources are:
Ted Porter's Beemershop:
Motorrad Elektrik

The tests on the original 400 watt Omega were not as extensively done as on the temperature, oscilloscope, stress gauges, hot/cold differences, etc.  What follows for the 400 watt early Omega is probably what YOU could actually expect of it.
  The new 450 and 600 watt Omega's are in the next section.

Testing was with a known accurate ammeter setup with short heavy gauge leads, connected in series with the Omega diode board output.   The good 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 charged, with heated grips, accessory lights, and headlight... all turned on.   Readings were repeated with lights off, & also with the battery fully charged.   The "set point" of the VR appeared to be close to 13.8 volts. I consider that somewhat too low for best battery life and system performance, but it does extend intervals between adding water on flooded type batteries.

The chart below is a summary, & where you see two instances of a higher rpm with lower voltage, that was due to battery charge condition at the instant of measurement, & small deviations from expectations, due to, I think, heating, etc.

OMEGA "400" alternator

NOTE:  Battery was loaded with a resistance box (carbon pile type) to obtain those 'less than fully charged' voltages.    If not so loaded, the alternator would show usable output at 1550...note the 1750 tst1 versus 1750 test.  This effect is much more prominently shown in the test of the 450 and 600 watt alternators, further down this article, due to a higher internal resistance battery to begin with.


Voltage at battery

Output in amperes


1550 11.70 2 23.4
1700 12.5 5 62.5
1750 11.83 8 95.6
1750  tst 2 12.5 5 62.5
2200  tst 2 12.8 12.5 160
4000  tst 1 12.64 28 354
4000  tst 2 13.5 20 270
5000 13.2 31.5 415.8









 You would need ~2400 rpm to enable the output of the stock 280 Bosch at 2100.  THUS, you can rightly assume that this alternator is not any better for constant stop and go in town, unless you have a bit of distance between stops....wild guess would be a half mile or more.   But, this alternator DOES produce considerably more total wattage than the stock 280 Bosch, out on the road.

NOTE CAREFULLY, the two 1750 & the two 4000 rpm tests. Note how the wattage varies with the voltage.  I specifically loaded the system in order to enable these readings.   What especially interests ME, Mr. Nerd, is that at 1750 rpm, a heavy load that dragged the system to 12.5 volts produced 95.6 watts, but the voltage was too low to fully charge the battery.  Compare carefully to the two 4000 rpm tests...and to my extensive comments early-on in this article.

You can see that the battery would be MARGINALLY CHARGED at 4000 rpm if 28 amperes of load was used.   This resulted in 354 watts.   If the load was DEcreased, the voltage rose to 13.5 volts.  That is STILL not enough floating voltage...I'd prefer to see 14 volts or even a bit more; but OK.    Increasing rpm beyond 5000 did not yield increased output. 
If using this alternator, performance WILL BE enhanced by using a voltage regulator set point of 14.2 to 14.5 volts.

To be FAIR about all these things,
I note that this alternator WILL keep the battery charged more than enough to enable you to use WELL OVER the maximum wattage that the Bosch in typical cruising mode.

Output might be better for the battery if the VR was set higher, see above note. The voltage regulator was NOT the adjustable type on this tested bike.   The battery was also not new.   The ammeter & its leads & connections add a small series resistance; this would have the effect of moving the output higher up in rpm (although slight, and mostly at highest outputs).   This also applies to the Bosch and EnDuraLast during tests.   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 figures with the stock Bosch system.   While it is possible that there are some anomalies present that I did not go into, especially noted is that the stock Bosch-equipped bike I tested had perfect electrical connections, etc.....still, the Omega output was low at low rpm, but it rapidly overcame the stock system as rpm into the cruising area was attained. 

It is important for those with considerable need for more wattage, to understand that the output of THIS Omega is ultimately HIGHER than the EnDuraLast.....but that the EnDuraLast has much higher output at truly low rpm, thusly, is PROBABLY better for COMMUTERS, especially if their electrical needs are modest.  NOTE, again, I am speaking of THIS PARTICULAR Omega system, the 400.

The weight of the Omega is nearly identical with the stock Bosch; differences are so small as to be of no concern.

Omega 450 watt and 600 watt alternators (400 looks almost identical to the 450).
NOTE:  Scot Marburger has written up what and how we, together, did the testing, etc., in April, 2016.  He will have further information in his article, eventually, now that we have finished final testing in June, 2016.   You may be interested in reading his article...and it has a lot more information about the installation, why's, how's, etc....and photos!

NOTE the MUCH increased number of magnetic poles on the 600W Omega (Emerald Island Co.) stator, in the below photo.

If your battery is poor, and here I mean it's internal resistance has increased a fair amount, then the battery might still start your bike, and might still show a full charge as far as VOLTAGE is concerned (during charging)....but the battery terminal voltage will SAG, often quite a bit, and measurements for alternator output/performance will be TRICKY to accomplish accurately.   The testing on the Omega 450 and 600 were done on the SAME bike, with the SAME poor battery, which happened to be the popular Odyssey battery.  Testing was done with a laboratory grade 50 Mv 500A commercial shunt, with a quality digital meter connected to it for ampere output testing. The shunt was connected in the diode board output lead, so measurements were of ACTUAL alternator output ONLY. A digital meter was connected across the battery terminals.   A carbon-pile type adjustable load resistance was connected across the battery in such a manner that the digital meter connection at the battery was NOT affected by the load connections at the battery from the bike, nor, the carbon pile adjtusable resistance.  BOTH alternators were tested by using the same diode board, same motorcycle.  Dates of testing:  04/16/2016, 04/17/2016.   Figures include repeated testing at same RPM, but differing loads and state of battery charge.  NOTE!  Testing was done with alternator parts relatively cool, that is, the front cover was OFF, and the bike had NOT be ridden before testing.  I would expect some DEcrease in performance in actual on-road testing, or 'garage' testing after a full warmup.

OMEGA "450" alternator.  Tests were run at a variety of conditions, on a 'weak' battery, that had moderately high internal resistance.  The battery was loaded to a variety of high normal, normal, and several voltages below 12.7 (12.7 is considered fully charged), to find out what the maximum output was.  To obtain the output we saw at 1550 rpm is exceptionally good.


Battery Voltage


1550     208,194
1700     246, 263, 269
2100     306.5
2200     352.3
2850     420
4000     515
5000 13.0 41 546
5000 13.66 39 533


Omega "600" alternator.  The first series of tests were run in April, 2016, at a variety of conditions, on a 'fairly weak' Odyssey battery, that had moderately high internal resistance.  The battery was loaded to a variety of high normal, normal, and several voltages below 12.7 (12.7 is considered fully charged), to find out what the maximum output was.  To obtain the output we saw at 1700 rpm and above is exceptionally good.  Testing was also done on the "600" alternator at 1700 RPM with various VERY substantial loads (far beyond normal use even with large extra headlights, etc); with battery voltage drained/loaded to give 11.79 and 10.58, both of which are well below that needed to maintain any full battery charge. Testing was done for same purpose/reasons at 2200, 2850.   Conclusion:  Even with a bad battery or exceptionally large loads, the engine would stay running and get you home.  It is difficult, even normally with a very good battery, to do these tests, as the load needed across the battery would be huge in order to reduce the battery voltage quickly. Luckily, we had a somewhat poor battery, making it easy to use a Harbor Freight two-meter battery load tester for the adjustable load...but making it twitchy and somewhat difficult to take quick readings. That meant one person at the throttle watching the tachometer and one person with two meters AND the load adjustment!   Note also, that the method of testing will over-rate the alternator normal use output; but it IS real-world for cold conditions and absolute maximum performance.  The performance of the Omega alternators is VERY GOOD.
A second series of tests was run on the same bike months later, same alternator, same basic conditions, except that the bike was equipped with an almost brand-new battery.  The results are in the SECOND table, below.

Below table is for the original tests with poor battery.





idle 12.6   4.9
1700 14.2 15 213
2200 11.6 38 440
2850 12 54 648
4000 12.6 67 844
5000 13.76 61 839
5000, max output test


12.35 73 901

Second series of tests, NEW battery.
  These tests were done June 12th and June 13th, 2016.  Besides an identical setup and the NEW Panasonic battery, various other tests were made, including a look at the alternator A.C. output at the alternator itself (pre-shunt) as well as at the battery (after shunt), using a dual-channel oscilloscope.  Testing was more extensive on voltage and current and RPM.  Repeated tests, engine hot and engine just warmed were done, in multiple tries.  Scot had set the voltage regulator some time ago, and my dynamic measurements showed that the set point for cut-back was ~14.08 volts.  I believe Scot uses ~14 volts to extend lamps life.  I would have preferred 14.4 at 70F as measured at the regulator metal case. 

Note that a considerable amount of the much earlier discussed hysteresis was seen.   This was looked-into several times. 
It required about 1600 RPM for output to which time the RPM could be backed off (!!)...and output would continue to be quite usable down to about 1200 RPM!....although battery voltage sagged somewhat below that necessary to maintain a full charge.   Testing was done at 1500, 1600, 1650, 1700 RPM to see what type of battery voltage could be maintained.  This was done with the headlight on....and off.  Tachometer was read ABP, and had not been calibrated.
NOTE that battery was purposely loaded heavily in some tests to obtain a low voltage for maximum alternator output measurements.  Such low voltage would, in cruising conditions, mean considerably less than full charge...but totally usable to get to a destination, ....even a very considerable distance!

Some tests may be difficult for you to understand.   This is because the battery was heavily loaded (typically 40, 50, and 90 amperes).






1500 12.1 24 290
1600 13.64 22 300
1700 12.16 35 426


48 593
2500 13.4 54 724
2850 12.34 57 703
2850 13.36 48 641





3000 14.09 34 480
3000 14.12 32 452
3000 13.4 62 831
3000 13.6 61 830
3000 13.85 59 817
3000 13.85 60 831
4000 13.87 65 902






Conclusions:  For all practical purposes, and I make NO conclusions as to long term reliability, the 600 Omega (600 watt alternator from Jeff Lee of Emerald Island Company) produces enough electricity to keep most anyone happy, in MOST ANY circumstances that are likely, such as in-City commuting and on-road cruising.

The stator is beautifully machine-made, and has MANY more magnetic poles (it is NOT just a larger alternator) than the stock Bosch alternator.  I would love to see what would be the results of a re-designed rotor (additional pole pieces).

The EnDuraLast Alternator (the original, with the PERMANENT MAGNET ROTOR):
I did a careful installation & very complete and full testing to evaluate the practicality of the ORIGINAL EnDuraLast permanent magnet alternator system.  A known perfect battery was used, as was the condition of all the connections/wiring/etc. in the electrical system (prepared carefully, before the tests). The system used light electrical loading & was allowed to fully charge the battery according to the system voltage regulation (14.24 in this conversion instance).  Then the battery was loaded moderately for a while until a known value of battery DEcrease in voltage was noted.  At this point the output was measured by starting the engine (which additionally slightly drained the battery), & then I used, quickly, various rpm during immediate measurements.  That is a simplification of the various tests I did.  My method for testing other alternators, whether aftermarket or stock, is the same, although the voltage noted above might be different, depending on if a fixed setting, or if it was adjustable...and if so, if I adjusted it.  I also use a heavy duty commercial millivolt shunt and lab quality metering....and carbon pile type loads.  I also test using the motorcycle's own lamps, ignition, etc.....and if large aftermarket headlights have been added, also add testing with them both on and off.

The weight of all removed stock Bosch 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 above, weight is 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.

EnDuraLast Rectifier/Regulator:  In a normal system in a motorcycle, the regulator is USUALLY mounted in an area that allows some engine heat (comparable to battery temperature in a modest way), to influence it.  In most modern cars the the regulator is usually PART OF the alternator ITSELF, and thus as the alternator warms up, the regulating voltage DEcreases slightly, on purpose, 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).  However, from my testing results, the EnDuraLast RR unit is OK over a normal temperature range, and I do NOT consider its location to be of importance, EXCEPT that it should be kept away from areas of high heat, to extend its life.  This means to NOT mount it to engine metal parts.

Note that there have been reports of RR unit failures when high levels of alternator output are consistently-continually used. Best that it be mounted where relatively cool air is on it.


The EnDuraLast voltage regulator is supposedly internally fixed at about 14-14.26, and hence a small amount more of the EnDuraLast output is used to keep the battery charged, once charged, than with the stock voltage regulator setup, this is truly a minor thing. A very good thing is that voltage at the battery is high enough to keep a full floating charge on the battery, during most uses.  Anything over about 1500 to 1600 rpm is QUITE adequate to supply the stock motorcycle, or, with one with an added headlamp.  That means that an RPM that is much lower than cruising RPM is going to produce plenty of wattage. 

ACTUAL results for the EnDuraLast (but, see information much further downwards about later tests on a different bike and different type of installation).

RPM Current, Voltage Watts
900 6 amperes  
1000 7.5 amperes, 13.12 volts 98.3
1000 8 amperes  
1200 12.5 amperes, 13.39 volts 167.4
1500 15 amperes  
1600 16 amperes  
1900 18 amperes, 14.24 volts 256.3
2050 20 amperes, 12.81 volts 256.2


26.5 amperes, 12.8 volts 339.2

I was UNable to obtain more watts, no matter the rpm.   This is a characteristic of permanent magnet alternators.  Another characteristic is larger voltage sag percentages [compared to the Bosch & Omega...basically any WOUND ROTOR types] as you reach top output levels.

Note that for the otherwise stock motorcycle, & no additional electrical loads, the EnDuraLast alternator will maintain a reasonable charge at about 1100 rpm.  This means that keeping the battery charged during stop and go big-city-type-commuting is no longer an considerable problem.  THIS is where the EnDuraLast is really good.

Re-said, differently:
The EnDuraLast has more usable wattage output at very low rpm, compared to the stock Bosch, or the 400 Omega.  However, the Omega has higher absolute maximum output wattage. Note also that the voltages at high watts output is not actually all that much different, and sometimes worse, than the stock 280 watt Bosch. Compare very carefully!  The advantage of the EnDuraLast is at low rpm....and, it does NOT give any huge amount more wattage at its maximum output, compared to the stock Bosch.

The EnDuraLast is, in SOME conditions, better for in-city stop and go, than the stock or Omega alternators.   The Omega is better for maximum output, and for maintaining the preferred higher battery voltage AT such a higher output....a DUAL benefit. Best performance of the Omega units is with a bit over 14 volts setpoint of the voltage regulator.  The 450, and particularly the 600 Omega, in practical use, will be MUCH better than the EnDuralast Permanent Magnet alternator.

It was noted that the Regulator set point for the EnDuralast that was tested, at 84F, was 14.48-14.50 volts, which is higher than expected, and somewhat more to my liking than the Omega.  Since the set-point is slightly affected by where the regulator is mounted;... due to LEAD LENGTHS between stator and regulator this voltage may be a bit different if you have your regulator mounted next to the battery (which is a good place, and was my suggestion to the developers). MY installation had the regulator mounted in the R100RT fairing air inlet area...where I could control temperature by controlling the air flow, etc, for my testing.  I suggested to John Rayski, that his literature reflect my findings.  He did so, with SOME of my findings.

1981 & later BMW airhead motorcycles; & earlier models with aftermarket electronic ignitions, are somewhat 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 in 1981.  Some electronics, including diodes and a RR regulating transistor, can CREATE high-frequency spiking type of electrical noise.   Thus, tests with an dual-trace type of oscilloscope were going to be run on the system; one trace monitoring the battery, and one trace monitoring the ignition pulses. 

Somewhat nerdy:
As you have seen, the EnDuraLast did not do what its advertisements seemed to say, regarding output, performance curve, etc. advertised specifications, certainly NOT in a meaningful and USABLE manner.  Considering that my EnDuraLast was provided to me for FREE, and for me to KEEP; in return for my comments, technical advice, etc, all this from the manufacturer of the system; rest assured that my negativity in some areas certainly DOES reflect my independent thought.
My results did not duplicate the specifications/information on output performance.  I did try to improve the installation (one of what I promised to John Rayski).  I made some minor changes, eliminating some quite small voltage drops... that helped some.  I have thought about these things at some length.    I have an IDEA of what may be PART of the problem... & this is theoretical:    The stator output is via TWO wires, with NO grounding reference. That is, the output is single phase, which is much less efficient than the 3-phase output of the other alternator systems in this article.  Because the output is just TWO wires, this has to be so.  The EnDuralast Rectifier/Regulator unit  COULD, and probably does, have a circuit that involves a type of multiple-diode rectifier called a "Bridge Rectifier".  That can be done with special transistors acting like controlling diodes (and, hence, act as regulators); or, by power diodes. Makes no real difference as to what type.  I did not test the output of the RR unit for type of waveform for determining the type of rectification.  For my own curiosity, I should have....although the end result would mean nothing for performance, that is fixed by the inherent design.  While a half-wave rectifier could be used, I am 90% sure THAT is not the design...because that is illogical, as output would greatly suffer; and, the extra parts for the bridge-type are cheap.    This discussion of rectifier types is really nerdy here. 

What is still nerdy, but actually of some importance, is this:

A property of a two-wire source to any type of rectifier, is that the IMPEDANCE (nearly the same thing as resistance) of the STATOR, and connecting wires from that stator, can be relatively higher (than the rectifier's wire size/length in the output to the battery), with little deleterious effect.   THUS, the STATOR wires....the EnDuraLast 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 heavy gauge wires, and negligible voltage drop in connectors and connections.
 The electrical reasons are not easy to explain to someone without serious knowledge of impedance/resistance and magnetic coil characteristics.  

NOT nerdy:
I WAS able to get a modest improvement (about 1.3 amperes, nearly 18 watts) by simply repairing just the bullet connectors of the RED wires, as furnished by the manufacturer, EuroMoto Electrics. This was reported to the manufacturer, so that the KIT could be upgraded/improved.  I think that FURTHER improvement will be possible by mounting the RR unit next to the battery due to the very short output-side wires then possible.  As such, my recommendations to the makers of the EnDuraLast was to mount their RR assembly next to the battery, which would be a decent heat sink also.  At the time, I had not tested my idea, but I have, since, & there IS a small improvement.  Additionally, the mounting of the RR was placed onto the frame downtube on the left side of the battery area, which exposes it to cooler air....this will lengthen its life.   SEE NEXT SECTION!

In June, 2015, I tested a permanent magnet EnDuraLast alternator in a 1995 R100RT, MY OWN!    Installation was of the 'new method' of the type I had recommended; with some additional mounting improvements also, & the RR unit was mounted on the left rear downtube frame member next to the battery.  I made sure all connections, etc., were solid and proper, before I load tested the Odyssey battery (yes, an Odyssey, which is a not recommend type for the EnDuraLast), and then ran the battery down a few ampere-hours more, before doing tests.  These were simple tests, with a digital voltmeter at the battery; and an ammeter in series with the RR unit's output by replacing the fuse with jumpers, which were nearly a foot long overall, and not of heavy enough gauge to give absolute maximum possible performance values but adequate for older installations, with some years on them, etc..  These are, then, real-world representative numbers; what YOU might really expect.  If large gauge wires were used, or a clamp-on/over meter, and a more discharged battery, particularly if not an Odyssey, I believe the output would have been slightly higher.  NOTE that this installation proved out my previous work and suggestion that the RR unit be mounted next to the battery for slightly higher performance.
8 amperes output at 900 rpm
10 amperes output at 1000 rpm (and, 12.42 volts)
13 amperes output at 1200 rpm
17 amperes output at 1500 rpm
17.5 amperes output at 1600 rpm
18 amperes output at 1900 rpm
21 amperes output at 2050 rpm
I did a further test as the battery began to recharge, but still was not fully charged.  That test was at 2500 rpm, and I got 19 amperes at 13.95 volts (265 watts)....and, after several minutes, noted the RR unit was getting fairly hot. This was with NO forced air cooling.  I did not try for an absolute maximum wattage output, which would have required discharging the battery again, and this time more considerably.

The various testing results reinforce my statements, condensed here, that the EnDuraLast is the alternator to use if you are doing stop and go city-commuting; but NOT the alternator to purchase if you really need lots more maximum wattage.

Note:  The permanent magnet rotor in the EnDuraLast alternator has fan blades at the forward end.  Due to the fan proximity to the cover, ETC., the fan makes a small amount of whirring noise during operation, that varies with engine RPM.  This has been remarked upon now and then, but is not annoying, unless you have 'just' noticed it.



1.  The stock 238 to 280 watt Bosch systems are adequate for most Airhead riders.   If driving lights, heated grips, and other accessories are contemplated, the stock alternator will 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 to the Airheads LIST on the Internet.

2.  For CITY COMMUTERS with reasonable to modestly high electrical loads who do a lot of very short distance stop and go, you might consider the EnDuraLast PERMANENT MAGNET SYSTEM over any of the Omega's.   The later 450 and 600 Omega alternators are MORE THAN quite adequate for most any type of commuting or cruising/tours/etc., even with substantial added electrical devices.   With the 450 or 600 watt Omega, there is now no really good reason for the EnDuraLast PM alternator, on a performance basis, even for city commuting situations.  That said, I want to be fair, and the permanent magnet EnDuraLast alternator has better performance at quite low RPM (compared to even the 600 watt Omega-Emerald Island)....and there is NO hysteresis effect of any note.  But, the EnDuraLast PM has much less maximum output.

I make NO statements here on longevity/reliability.


Reliability is improved, if one has a /5 (in particular), by using a later, better ventilated, front metal engine cover.

Reliability is improved, if one has a RS or RT, with NON-louvred front fiberglass cover, by installing a louvred one, or by making slots in the solid fiberglass cover.

rev:  01/27/2008...checked for clarity
02/06/2009:  mention of the Omega 450
09/16/2009:  update article for clarity, numerous places
05/07/2011:  Clarifications for comprehension, entire article
09/17/2012:  Minor updates. QR code added; Google ad layout changed.
2013:            Remove language button, due to problems on some browsers.
10/22/2014:  Minor updates, nothing substantial....but I did include some commentary about real-world usage, at equilibrium and slightly above, that I had not emphasized previously.
06/16/2015:  Addendum
12/26/2015:  Increase font size.  Update meta-codes.  Justify left for everything.  Clarify a few things.
04/18/2016:  Latest format and meta-codes.  Add results of testing, 450 & 600 Omega type alternators, done yesterday. Re-write the article to improve clarity, less confusion.
04/19/2016:  Clarify a few details between all the Omega alternators.  
04/21/2016:  Add testing schematic diagram and photo and information on Omega 400/450 and 600.
04/22/2016:  Clarified the testing at below fully charged battery status, and why.  Added commentary in 3 places regarding the Omega's, which now outshine the EnDuraLast PM in many respects, add photo, etc.
06/14/2016:  Update the article for clarity (in all sections) and add detailed testing information on the "600". 06/15: Note added on revising this year, and some minor clarifications of basic ideas near the beginning of the article.


Copyright, 2014, R. Fleischer

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Last check/edit: Wednesday, June 15, 2016