The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Barry on March 12, 2011, 09:40:54 AM
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I noticed recently that my headlight pilot bulb and tail light bulb had gone quite black. Then when I looked at the battery it needed topping up with a lot of distilled water. Both are signs of the charging voltage being too high so I checked at the battery with a digital voltmeter and sure enough it quickly rose up to 14.65V at 2500 - 3000 rpm. Had the battery been a Gel or AGM type I would have accepted that the bulbs should be changed more often and let things be but 14.65V is too high for a wet cell which ideally should be in the range 13.8 - 14.2 volts.
It might be possible to adjust the regulator in situ but I preferred to remove it and carry out a bench test as described by Snowbum http://bmwmotorcycletech.info/boschmechreg.htm
All voltage regulators have 3 simple spade connections D+ D- and DF
(These designations are historical and stand for Dynamo + Dynamo - and Dynamo Field)
To do a bench test connect D+ to the +ve terminal of a variable DC voltage bench supply and connect D- to the -ve terminal. Connect a 21 watt bulb between D- and DF
Slowly raise the voltage and monitor across D+ and D- with a digital meter. The bulb will glow brighter and brighter then go out at the switching voltage. You might need to do it a few times but don't take too long as there are some resistors at the bottom of the can which get hot.
To adjust the voltage set point bend the adjustment tab with long nose pliers up to raise the voltage or down to lower. Bend the tab carefully by the smallest possible amount and then test again. What you are actually doing is changing the tension on the steel leaf spring which rests on the top of the tab. Reducing the tension allows the solenoid to switch the contacts sooner thereby lowering the set voltage. Be extra careful not to bend or damage the spring.
More detail (lots) on snowbums site.
I was lucky to have a good quality bench power supply but the adjustment could be done by trial and error on the bike just make sure to bend the tab by the very smallest possible amount.
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That regulator is not even close to what I have on the '81 .
After you remove the tape and cover, there is solid state circuitry inside, no mechanical parts .
Outside of the case on the bottom, there is a stud that is locked with a jamnut, with a groove cut into it to turn it with a screwdriver .
I wonder if this is a voltage regulation adjustment ?
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From what I can make out Bob the 78 -80 bikes had a mechanical regulator then the 81 - 85 had an electronic regulator in a shorter metal can like yours. Snowbum describes how to adjust an electronic regulator using a potentiometer inside the can on the circuit board but he also mentions that there might be some regulators that had a voltage adjustment under the can.