The Stovebolt Site Forums The Shop Area The Electrical Bay Ammeter Suddenly Pegged on Acceleration

Hi everyone,
So I finally got my 54 3100 restoration project driving, and all seems great. Unfortunately, I just noticed that when driving, the ammeter goes pegged to full charge. It drops to normal, between D and C when at idle, but as soon as I give it any gas, it pegs to full charge. I did a 12 volt conversion and am running an alternator, but everything else is original 6V, except for lights/bulbs and coil. When I first got it driving the ammeter read normal, and would only "jump" when I honed the horn. I'm thinking the battery may be bad, but don't want to spend $100+ to troubleshoot this issue, while also not wanting to burn up my wiring.

Another thing, is that I have a headlight suddenly out as well, could this be the culprit, or related to it?

Any ideas?
Thanks,

Nico

You've probably got a shorted voltage regulator (inside the alternator) that's allowing the rotor field current to go full-on. Put a voltmeter to the battery posts and have a helper accelerate the engine speed (gently). If the voltage goes above 15, replace the alternator. Don't delay- - - -more blown bulbs and damage to the battery from overcharging are coming- - - -soon! I've seen alternators spike voltage into the 30's and above under similar circumstances.
Jerry

Thanks Jerry, will give it a try and report back!

Can't you replace just the voltage regulator in at least some alternators?

Why bother? 10SI alternators are so inexpensive these days the labor to swap regulators isn't worth the cost saving if you count your time to be worth much.
Jerry

I agree with Jerry (it's not good for your future if you disagree) (grease on your door handles, potato in your tail pipe... that kind of stuff)

There are some parts on a truck that are so easy to replace and so inexpensive that it is a good idea to just get a new one rather than mess around.
It's time management, funds management, psycho management. I do like to figure out most problems, to learn and get satisfaction, but do resort to replacement sometimes just to get something to happen/change.

There are many issues that need testing, analyzing, bench refurbish to fix. That can be a rewarding part of the hobby.

Most ignition and some charging component replacements can be called "tune up" or "preventive maintenance" so as to make sense to the budget. Most FLAPS in my area will come out of the store with a pretty modern tester and tell you all kinds of things about your battery and charging system..FOR FREE! if you are not adept at checking/testing yourself.

You forgot the limburger cheese on the exhaust manifold or the laxative-loaded tomcat left in your car overnight! LOL! Unless someone has a pretty good bit of experience diagnosing alternator failures, picking one of the 3 or 4 possible causes for runaway voltage becomes a crapshoot, and most FLAPS don't like giving refunds for parts that have been used for troubleshooting that didn't fix the problem. A shorted regulator is the most likely cause, but problems with the brushes, the diode trio, or even the rotor can also factor into the problem. It doesn't take very many mistakes in diagnosis before the cost of a rebuilt alternator gets spent, and you still don't have a working charging system.
Jerry

OK guys,
So the FLAPS says my alternator tested perfect. I changed the battery, reinstalled the alt, and I still have the same issue. Any thoughts?

What is the output/rating of your alternator?

Hi Tim,
I believe its a 63 amp. What's puzzling is that the gauge was reading normally, and now suddenly goes pegged Charge when under acceleration?!?!
Thanks,

Nico