[Pete Casper]

My BMW 1984 R100 runs with a quartz halogen headlight bulb. Something is wrong somewhere. I just went thru to bulbs in two minutes. $20 bucks! The bulbs appear to be surging when I give it gas. The filaments (both low and high beam) burn out before the fuses pop. Any ideas on what is going on? Damn.

 

[JAM614]

Voltage regulator failure?

 

[Pete Casper]

quote:Originally posted by JAM614

Voltage regulator failure?

Yeah, that is what I was thinking, but I don't see any noticable surge in the tail light. That is why I am thinking I may have a bad ground or the circuit connections are dirty, loose, etc.

Oh well, it is always fun rummaging thru the jungle of a wiring harness.

 

[HackAsaw]

I have had voltage regulators fail......... even one bout of having the wire break off the zener on my flatty

and damn if it wouldn't take out a headlight bulb or three before I opened my eyes and saw the wire hanging unattached

I wondered why it never popped a tail too

now that being said

I'd pull that front cover and check the alternator components carefully

those particular excited field rotors can develop a intermittent flying ground that will cause all manners of mayhem

not a bad idea to have the field "growled" and visually inspected

then check the stator windings....... preferably under a load

you can also have a voltage drop in the sensing circuit that will result in the alternator over charging......

surely you have put a volt meter on it?

those systems are quite straight forward to diagnose and work very well

however, they can be painful enough that you can get a permanent magnet alternator bolt on kit for them from the after market

I've done one for the earlier pre-70 BMW's using a big italian alternator because I hate stupid stuff especially when it doesn't even have solid state voltage regulation

 

[Pete Casper]

Hack: Thanks. No, I lost my cheapo voltage regulator, so I went out and purchased a digital meter this afternoon after work. Yes, I will likely install the heavy-ever duty aftermarket alternator bolt on kit this winter after I save up the $575 dollars. The stock alternators on the /7 puts out only 280watts. I want to run some plug in gear this winter to extend the season. So I want a beefier alternator.

Well, interesting I ran the voltmeter at the headlight bulb...at idle it hovered around 12.5v. Upon increasing the throttle to 3,500 it shot up to 17.5 volts. I think that is enough to fry a 12V 55/60 halogen bulb, isn't it? The other issue is with the tail light I have an after market LED tail light. It is a 12V, but maybe that withstands voltage surge better than the filaments in the stock bulbs.

I order an aftermarket voltage regulator for $32. Well see if that helps.

 

[HackAsaw]

have you seen the nearly 400 watt permanent magnet unit I have on my ironhead sportster with an open belt primary?

17.5 is over the line for sure

 

[Pete Casper]

quote:Originally posted by HackAsaw

have you seen the nearly 400 watt permanent magnet unit I have on my ironhead sportster with an open belt primary?

17.5 is over the line for sure

Yeah, here is one of many options for upgrades to the airheads.
http://www.airheads.org/content/view/298/98/

New regulator should be here tomorrow. I am almost positive that is the issue given the peaks in voltage I am seeing. Just goes to show me I should install a volt meter. I don't know why the previous owner removed it anyway.

Pete