The Stovebolt Site Forums The Shop Area The Electrical Bay regulator or alternator or .... ?

I have a problem with my ' 65 C10 . At idle , it shows a slight discharge . If you up the rpm's just a little bit , it shows a slight charge .If you turn the headlights on , even at the elevated rpm's , it shows a healthy discharge . Any electrical device turned on ( I.E. - turn signal ) gets a negative response on the gauge . The truck has a new solid state regulator and the alternator was checked at two different places and passed each time . The battery has been checked and pronounced good .I replaced the old ( circa - 1965 ) regulator because I thought it was causing the problem . The new one hasn't fixed the problem either . Any way the alternator could be the culprit even though it passes the test ? The old regulator had a screw , under the cover , that could be adjusted to increase the voltage output . The new solid state one does not have this screw or any other way to adjust the output . I think I'll reinstall the old one and see if that adjustment screw will do any good . Does anyone have any ideas what's going on here ? All help will be truly appreciated !

Do you have other means to check out what going on with your charging circuit? A voltmeter would help answer some questions and a clip-on ampmeter would answer most others. If you have access to at least one of these meters than a search of the forums most likely will pinpoint your problem or a repost with the meter readings will get you answers from the vast knowledge of the guys and gals here. Good luck.

Sounds like you have a shorted diode or shorted stater in the alt. although they should show up when tested. Make shure the fan belt is tight & in good condition. These can slip under high loads. Beltfed is right, a voltmeter would tell you more. With the battery well charged hook the voltmeter across the bat or junktion block to ground. Run the engine up a little & it should go up to about 14 volts. Turn the lights on & it still should show 14 volts. Don't try to adjust the regulator as they are set at the factory for approx. 14 volts & that is normal setting. There is a way to bypass the regulator but if you have 2 different ones & they both do the same it,s time to look at the curcuit or the alt. If you like to tinker with stuff yourself they are not hard to o-haul if you have a good book. Used ones are a dime a dozen if you want to get another one for parts. Remans arn't that expensive if you want to get going & get it over with.

May I ask a question ? I've always been told the fastest way to see if you have a bad alternator is to start your engine and then pull a battery cable off , if it quits , your alternator is bad . My question - is it true and does it matter which cable ( + or - ) you disconnect ? I pulled my negative cable off and it quit . Or is the positive cable the one to disconnect ? Yes , I am a jr. novice electrician and that's probably overrating my skills ! Thanks for all your help and advice !

I believe you are correct as to the test. If the alternator is outputing, then removing either lead to the battery will not be cause for the engine to quit. This is assuming that everything is 'wired' correctly.

While it might be possible to check the alternator for function that way, it's extremely hazardous to all the elecrtonic components in the circuit. The battery acts as a shock absorber in the curcuit, dampening out voltage spikes as components are turned on and off. As the connection to the battery is broken, the charging system, either generator or alternator, will spike the voltage up to extremely high levels, trying to maintain the current flow. It takes a moment for the voltage regulator to regain control of the circuit with the battery missing. I've monitored primary voltage on an oscilloscope at times, and seen spikes exceeding 100 volts occur just as the battery cable leaves the post.

If you've got NO solid state electronic components, such as diodes, transistors, computers, etc. on the vehicle, you'll probably get away with that test. Alternators have six high-current diodes, and most voltage regulators have very complex solid-state circuitry. Got a modern radio? There's all sorts of solid state electronics there. Radar detector? GPS unit? Cell phone charger? All those things are at severe risk if they're turned on, or even plugged in.

There are much better ways to check charging system output. A $10.00 digital multimeter from the FLAPS will tell you if the generator/alternator is producing a vlotage higher than the battery, without putting all your electronics in danger!
Jerry