From: robert@Xenon.Stanford.EDU (Robert Kennedy)
Subject: How do voltage regulators get fried?
Originator: robert@Xenon.Stanford.EDU
Organization: Computer Science Department, Stanford University.
Date: Sun, 30 Aug 1992 19:31:27 GMT

So my sob story goes like this: I bought a beautiful, used 1985 Honda
Nighthawk 650 a few days back as my second bike. The idea was that I
would buy a bike that didn't need so much maintenance as my first one.
So far, I'm off on the wrong foot. Even though I checked the steering
head bearings for notchiness before I bought it, I must have
overlooked their problems because I got it home and the steering was
notchy. So I bit the bullet, bought tapered bearings, and tore the
front end apart on Friday night. Got it all back together with the new
bearings in yesterday, and it rides NICE. But the voltage regulator
seems to be shot now.

Relevant fact 1: When I started to tear the bike down to replace the
bearings, I noticed that the headlight high beam filament was burned
out. This was a minor bummer, but it didn't seem untoward. I got
another bulb and got ready to install it when I put the bike back
together.

Relevant fact 2: I had the front end almost all together mechanically
after replacing the bearings, and had just reconnected all the wiring
behind the headlight. SOP is to turn the ignition switch on and make
sure the turn signals, horn, idiot lights, etc. work, and that's what
I did. Everything checked out perfectly, and all seemed fine, until I
turned the kill switch to run and then back to kill again. I can't
remember whether it happened when I switched it to run or when I
switched it back, but I heard a "pop" sound, sort of like pressure
being released through a valve, or maybe like letting all the smoke
out of a voltage regulator.

Relevant fact 3: I thought, "Hmmmm," and continued putting the bike
back together. Once it was together with the new headlight bulb in
place, I took it out and rode it. After about 30 minutes of riding,
switching back and forth from high beam to low much of the time, the
high beam filament on the new bulb burned out.

Relevant fact 4: Suspecting that this meant voltage regulator trouble,
I tested the charging system, and sure enough, I can get over 17 volts
across the battery terminals at moderate revs. I do not believe the
regulator was bad when I bought the bike, because I checked the
charging before buying it, and I am almost sure I revved the engine
high enough for the regulator to kick in. The charging voltage was
something just under 15 volts, I think.

(Possibly) Relevant fact 5: My bike has capacitive discharge ignition.

Relevant fact 6: The schematics for the charging system show a fourth
coil in the alternator in addition to the usual Y-connected
three-phase stator windings. This fourth coil is drawn running
horizontally at the bottom of the symbol representing the alternator.
I don't understand what this coil does or what kind of signal it picks
up. It definitely seems related to charging and chassis electrical,
NOT to ignition.

Relevant fact 7: The bike does not vibrate excessively, and I am
nearly certain the second high beam failure was caused by the failed
regulator.

Relevant fact 8: There are no burn marks or visible signs of failure
anywhere on the body of the voltage regulator. I have never heard an
electrical component make the type of noise I heard when I flipped the
kill switch without also marking itself as failed (by burning or
whatever).

AND NOW, the whole point. Several questions:

When did my voltage regulator burn out? Was it when I flipped the kill
switch, or could the initial high beam filament failure indicate that
there was trouble before then? If flipping the kill switch did it, how
is this possible, i.e., where in the chassis electrical system could
there be a voltage high enough to fry the regulator? How do regulators
normally burn out? Are they just defective, or is there some other
component whose failure could fry the regulator? What other problems
should I look for before I fire the bike up with a new regulator and
headlight bulb in place? Why did my voltage regulator burn out? How
can I keep this from happening again?

Thanks for any and all info!

	-- Robert Kennedy

Robert Kennedy					(415) 723-4532 (office)
robert@cs.stanford.edu				(415) 322-7367 (home voice)
Computer Science Dept., Stanford University	(415) 322-7329 (home tty)
Newsgroups: rec.motorcycles