Voltage Regulator

[Julio A.]

I think my Voltage Regulator is shot. My old lead acid battery got dry in a week's worth of ride; burning it up to a useless pile of lead very fast.

I got a new maintenance free sealed type battery and it works fine. I used a tester to find out the voltages at work and found out that the battery peaks at 15.6V at 3000 RPM. My voltage regulator is a mechanical type commonly used in old Hot Rods and I have finished cleaning up the contacts but the voltage is still quite high. It was the past owner who did the questionable modification; that is why I am quite hesitant to tinker with it. I have a replacement BMW-Bosch solid state voltage regulator but since the original plugs and brackets have been unknowingly modified, I don't know what to do from there.

[Rob Valdez 79 R65]

I am pretty sure the mechanical-type that BMW used to use were adjustable.
I don't know if you have to open it up to adjust it (if, indeed, yours is adjustable), but it might be worth the attempt.

I would be hesitant to ride it with the new battery, if it is putting out that high of voltage.  Especially if the battery was expensive.

Hucky's indicates the electronic regulator to be 14.2v:
http://www.bmwhucky.com/010012.html

[Lucky_Lou]

Just a thought ...would it be possible to put a resistor on the output to drop the voltage ? maybe Barry will set me straight on this as he is a wiz on electrickery.  
Lou

[Julio A.]

The voltage regulator is not OEM BMW. But i think it is adjustable.
I'll try to tinker around with it. Wouldn't want my new battery to burn.
It took me a week's worth of lunch to buy that. Haha.  

[Barry]

Mechanical voltage regulators can usually be adjusted by bending a tab to change the on/off ratio though it can be a bit tricky which is maybe how Julio's ended up at 15.6 volts They are usually remarkably reliable but it could also have failed. Snowbum has a a good write up on adjusting mechanical regulators.

Lou putting a resistor in series might sort of work a bit like the old British bikes which instead of trying to control the output of the alternator just dumped the excess to earth via a zener diode and a big heat sink.

Julio, if you want to fit the new electronic regulator and can trace the wires there are only 3 terminations on a voltage regulator :-

D-  brown wire connects to one of the alternator brushes which is also earthed

D+ blue wire connects to the diode board and then the gen light

Df  black wire connects to the other alternator brush

[Rob Valdez 79 R65]

What a wonderful picto-graph, Barry!  I love it!

See that red wire going from the starter to the diode board?
Don't ever forget to hook that up, or you will only get as far as the charge on your battery will allow.

[Lucky_Lou]

I told you he is a wiz on Electrickery even i can follow that.
Lou

[Barry]

I told you he is a wiz on Electrickery even i can follow that.

....trickery it is Lou and not my work.  Just something from the archives. Id like to credit someone with the pictograph but can no longer find it on the net and if Tom Wiesbeck ever had a website I can't find that anymore either.

Simple diagrams are easy on the eye though aren't they.

[nhmaf]

15.6V is definitely too high a voltage for battery longevity - I would definitely try to get the peak charging voltage down to around 14.5V or replace the regulator.    A resistor could be used but it is really a "sticking plaster" type of approach.  And, if you pick too small a wattage and it burns out, you'll then have no charging at all.

[Rob Valdez 79 R65]

A resistor could be used but it is really a "sticking plaster" type of approach.And, if you pick too small a wattage and it burns out, you'll then have no charging at all.  

Oh yes - you would definitely need a "honkin' big" (ceramic) resistor (with heat sink).  Not hard to source, but I wouldn't want any plaster on my bike.

[Vegasrandall]

That diagram is very easy to understand.I suspect it wasn't drawn by a german.

[Bob_Roller]

Can you post a picture of the regulator you have, it may be very simple to do an adjustment to get the voltage down to an acceptable level .