1993 GSPD charging system question


1993 GSPD with about 85,000 KM (50,000 miles). I just replaced the alternator rotor (for the third time: first time - replaced with a new one from BMW, second one was repaired from independent service here in Canada, this latest one is one that I picked up from a local dealer - looks like he repaired it himself). Prior to and after this most recent rotor replacement, I noticed that in the morning I start it up and as I drive the (aftermarket) voltmeter jumps back and forth indicating between 13 and 14.5 volts. It jumps quite a bit which I think is fine - indicates the alternator is putting out power and the regulator cuts in and out as required. After about 10 minutes of riding, the voltmeter needle stabilizes at 13 V. This generally corresponds with my arrival at a freeway on my morning commute. The needle stays pretty much rock solid on my 15 minute highway commute (4500 to 5000 RPM). When I get back into city traffic, stopping for lights,etc, lower RPMs (idle to 4000), the volt meter is indicating only about 11 volts. My total commute time is about 30 -40 minutes. My battery is about 1 yr old and I haven't had a problem with it dying. Could it be a regulator issue that only happens when the bike gets warm? I just added some water to the battery this morning and will keep an eye on it to see if its boiling the acid/water out. My concern is that perhaps my alternator is running full out all the time (once the engine warms up) and that is causing the premature failure of the rotor. I've had the bike since it had about 15,000 km on it (one year old). As stated, I replaced the battery last year (first time) and I've smoked three rotors. Could my regulator or Diode Board be faulty? Currently (pardon the pun), I'm not running any extra electrical stuff (I've got heated grips, vest, radar detector and aux lights but none of these have been switched on since I blew the last rotor and really started paying attention to what is going on). I also haven't done the brushes yet but anticipate updating them before fall/before my next little trip.
I followed the instructions in my Haynes Manual to test the regulator. Connecting my voltmeter (handheld but not digital) between the B+/30 diode board terminal and the D- or D+ terminal on the alternator, I was supposed to get a reading of 13.55 to 14.25 volts at just over idle speed. My reading was 12.5. There is no issue with my gen light being on when it's not supposed to be on or being off when it should be on.
Any ideas or advice would be greatly appreciated.
Don't really know if you've actually got a problem, but be aware that these charging systems are pretty poor at low rpm.
I would recommend a "Police Spec" regulator available from Motorworks. These bump up the charge to the battery at low rpm.
i'd recommend checking all connections/earths & making sure you have a decently sized and good condition wire from diode board to starter motor.
can someone answer this

Howard Millichap said:
Don't really know if you've actually got a problem, but be aware that these charging systems are pretty poor at low rpm.
I would recommend a "Police Spec" regulator available from Motorworks. These bump up the charge to the battery at low rpm.

Q. Is it true the R80/100 systems only charge above 3000 rpms

i used to ride a R80TIC and if we had the blinks flash flash blink & wah wahs and knees knees going to much the battery died.

to overcome this they installed 2 batteries

the michanic (a pom) told me they don't charge under 3000rpms

Rotor failure is a common problem on airhead boxers. And charging can be an issue particularly when commuting. Starting a big twin takes a heck of a belt out of the battery which the charging system takes a long time to replace. Especially when the thing won't actually start to recharge the battery until well over 3000 rpm. What can happen is that the battery goes progressively flatter each time the bike is used. Electrical accesssories and alarms just make the situation worse. A high-output police-spec regulator does seem to help.

Having said all this, there seems to be some anomaly with your bike in that the voltage at idle is different after your 'commute' from when measured with your handheld meter (11V vs 12.5V). How close do the two voltmeters read? I would not expect the charging voltage at tickover to vary signficantly due to temperature and this could indeed indicate a problem.

I would compare the meter and voltmeter readings to establish that both are similar. Then maybe fit a high-output regulator as these aren't expensive and a reasonable mod anyway and check the voltages before and after a run.
Ha! That toe rag got my web site address too! Cyclists? Missing something more than an engine IMHO.
Could anyone confirm that fitting the higher output regulator has NO disadvantage ? I note that with autocom on, but no engine running, a poor battery soon discharges. If NO disadvantages it sounds a worthy upgrade whatever. Ta ;)
PS Did Nobby post details with which wire is worth changing to a 'thicker' one on the charging system ? Useful to all us airheads
I understand that the high output regulator produces 14.3V.... so the battery should be fine. The main advantage comes from the fact that you get higher voltages at lower rpm

I have a high output unit on my bike and used it on my RTW trip without any problems - but used a spare rotor on my friend's bike in India.

However, I am also on my third battery in 5 years - but I think that this is more down to laziness, lack of maintenance in extreme temperatures and leaving it all winter with the alarm connected.

I now have an optimate connected whenever I'm not using the bike and have disconnected the alarm.

Also, the jury is out on Hawker batteries with the RTW mob giving mixed reports.

Lifted from motobins:

If Your Battery Fails to Charge, always ensure that the alternator brushes are making good contact with the sliprings, that their holder is clean, and 12 volts can be measured at the brush connected to the black wire. Should this not be so, the voltage regulator or connecting wiring should be examined. If 12 volts is present, lift the 'brown' brush with a piece of cardboard, and measure for 12 volts at its slipring - if this not is present, the rotor windings will be faulty. Remove the cardboard, and measure at the 'brown' brush - if this does not read zero volts, its earthing is faulty. If these tests are in order, use a multimeter to measure the AC output of the alternator at the red, yellow, and blue wires - if 12 to 14 volts AC is measured here, but the battery voltage does not rise at higher engine speeds, the rectifier (diode pack) is at fault, and must be replaced

Commuting on a Boxer with a dipped headlamp can leave you with a flat battery after a week or so - maybe less if you have a small battery - but a good answer is to use a 20 watt halogen bulb in the pilot lamp position. The 20 watt bulb is as bright as a headlamp, but does not dazzle other drivers. RS and RT owners will need to connect the existing (but unused) holder in their headlights to the parking lamp circuit. We also recommend replacing the standard voltage regulator with the higher output one. This is done by the Police because of all the extra electrical equipment on their BMW's.
Q. Is it true the R80/100 systems only charge above 3000 rpms

no. not on mine anyway.

charge light on my 94 PD goes out above 750 rpm. as i understand it, that indicates the balance point between charge & not charge.

voltage then increases until the standard regulator cuts in at about 13.8v which is pretty damn low (i've tried 2 & they were both the same). 14>14.5v is what i would consider more normal.
my bike has a re wound alternator rotor. i suspect it has not got as many turns as it should have on it. i got it from a guzzi dealer.

i suggest the "high output" regulator is of a type that is more usually fitted to other vehicles. guzzi's use an identical charging system except they use the older mechanical regs. that do allow higher voltage. they do not suffer from charging probs at all.
well ok, the rotors pack up at about 30,000miles + ;)

my bike does NOT suffer from flat batteries. it will happily turn the motor over for ages.
if it did not i would consider there was a failure in the system & not a design error. having said that i don't ride with lights on in daylight.

BTW i also modified a stadard solid state BM regulator as described in an airheads.org (i think) article. it was supposed to increase the voltage. it didn't work, so i put it back to std. again.
yo Frankie Warner

Paragon said:
or change the whole system for a pulley based system, (a guy in Oz or is it NZ) has one

Airhead threads are the ONLY interesting ones

yo Frank.

can ya post that site address Les has on his big powa output alternator

i lost it in a reformat

TIA Steve
Yes you could have a problem.

I'd be checking the diode board - specifically the 3 smaller diodes that feed the voltage regulator.

There is a blue wire (at least it is on mine - but that is an 1981 model) that goes from the warning light to the regulator - check the insulation is not damaged! It can rub through and give large and rapid variations in battery readings!

See http://www.uuhome.de/william.darden/
for the battery FAQ - lots of good info

http://www.uuhome.de/william.darden/carfaq5.htm has a graph that shows a smaller alternator is better than a larger alternator at lower speeds! I'd think there would be some rules and exceptions to this .. but cannot comment.

Lesses alternator mod.
Well I cannot find the page either. I've just had a upper level management change - same job, same desk .. but a new pc with new operating system - new network (yep along side the old one that I am now not allowed to use - and the 'old' system is faster !!!) and phone and pabx ...
Basically he puts a small car alternator where the diode board used to be - removes the top part of the cam chain cover to do it. This is no small job - you don't see it under the tank and you keep the standard front cover. Like the R11s you get a rubber belt drive to the alternator thus reducing the rotor failure rate. THere was a guy do lesses mod in 'merica too .. if your still interested i can try another source ...

However I think your standard system is faulty - read the battery FAQ for 'how it works' and try doing some tests on the diode board.
Paragon said:
Airhead threads are the ONLY interesting ones

When i get back in September maybe i will sell my ADV and buy the best Kalahari or Basic that I can find and put every sensible mod on it.

Ways to solve the problem are:
An upgraded alternator stator and rotor, (the start of everything)
An ungraded regulator
Upgrade all the wiring
ungraded Diode Board
Bigger battery

or change the whole system for a pulley based system, (a guy in Oz or is it NZ) has one

Airhead threads are the ONLY interesting ones

Bill, glad to see you've given the man some help answering his question !!, thats what makes airhead threads so interesting, the convoluted way it gets there (via future plans and intentions) in the end.

:D :D
Thanks all for the input and advise. I did send a note to the guys at motoelectric and here is their response:

I can see 3 major areas that are causing the problems: post-1990 alternator (marginal 17 amp,204 w. output), short run time with city driving,and buying used rotors.

There aren't many load scenarios that cause the rotor to fail more quickly,it's usually just because the rotor is the moving part in the system.And,since Bosch does a mediocre job at best with their rotor construction,failure is typically from mechanical issues with the wire winding inside coming loose and fracturing.

Attempts at externally repairing a rotor never last,period.
When we remanufacture the rotors, we take them completely apart and do a proper job of replacing the entire winding,secured between high-temp nylon insulators (instead of the brown paper Bosch uses),and dip the whole thing in aerospace polymer.An '"external" repair simply will not hold.Used rotors are always a total shot-in-the-dark,as they may fail at any moment.

Since the alternator is mounted on the crank,and turning at crank speed,engine RPM is THE most critical factor in charging output.The battery does not actually begin charging until at least 3-4000 RPM;below that,the system only barely meets the demands of the ignition and lights. A short run interval,combined with slow city driving,is not enough to recover the system after a startup and using the brake lights and turn signals.

The charging system on that bike also suffers from inefficiency of the diode board,specifically from poor ground path.The factory insists on using the goofy rubber mounts,and then supposes that the tiny external ground wires will be adequate-they are not.This causes the diode board to overheat,and reduces its efficiency and lifespan.

These factors are very well known to me,as I see the results and hear the reports daily.That's why,after some years,it became clear that what was needed was a higher-output alternator,which we introduced in 2002.The 400 w Omega system simply eliminates all the concerns of the stock system,once and for all.

Based on that response, I'm considering my options. I just purchased this repaired rotor (about 2/3 the cost of a new BMW rotor and likely about 1/2 the cost of an OMEGA system). One thing I hadn't mentioned is that when I started checking my system, I measured the resistance in the new rotor. It was a bit high for the new rotors but not as high as old rotors (can't remember the exact resistance right now...I think it was about 4 ohms or 4.75 ohms or something like that). The higher resistance now makes sense - not a new rotor and more resistance = less output right? So I'm not really impressed. I'm thinking, I'll need a spare anyway so either get another rewound (again) or buy a new one (again) or splurge and go for the Omega system. The 400W is really tempting. My concern is how easy it would be to switch back, if I had to, in the future (emergency, motoelectric out of business, whatever). If I carry a rotor and stator, can I just swap it or does the new system require modifications that amke swapping back a lot tougher. Also is this new system really that reliable or will I just be buying new/replacement rotors in a year or two anyway?

I'm open to ideas and appreciate the help thus far.

i got 2 photos of the ozzie modified aletrnator and they lok good.

i don't wanna post im due to the size.

i don't have a shrinking program at moment loaded. who can take im shrink im and post im on this thread

reply offline 2 stevebell@paradise.net.nz
Here's a guy in America who posted at http://www.bmwmoa.org/forum/showthread.php?s=&threadid=3215 having the same question.

a member by the name of Doug replies:::::
Have the Omega system from Motorrad Elec. in my 90 GSPD and it works as advertised. The original system just doesn't cut it, especially riding around town and in other low rpm situations with a sizeable load on the system. At the National in Spokane I also saw a charging system of significant wattage mounted on I believe an R80GS or maybe an ST. Well anyways, the system did away with the BMW rotor,stator,diode board,etc. A pulley was mounted where the original alternator used to be and a vbelt from there drove an alternator mounted in the area at and behind the original diode board location. The owner had a spare vbelt hanging on the with a tag saying the "only spare part needed". Here's the name and #'s I got off the bike:
Greg Hutchison

I'm about 95% sure I'm gonna buy the Omega system for my '92GS100.
Now,"How to figureout how to get this one by the wife":(
alt mode

these are exactly the same piccies I have

greg sent me them yesterday.

nice job done, worth a look
i checked mine out with a multi meter yesterday. all works fine, starts charging at 1250 rpm.

trouble starts when i put the lights on. as the man said earlier, no charge until 3000 rpm.

just don't ride with your lights on. simple :D

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