When I turn my car on, the battery gauge shows about 16V. But when I only turn the key 1/2 way (ie: just electrical components on) it's right at 12.8V.

Also, after about a minute or two of the engine idling and the battery showing 16V, it will all of the sudden jump to battery red-line. I'm pretty sure it's not just the gauge b/c when the jump occurs, the engine starts idling faster and the tach also goes wild.

Is this a voltage regulator problem or what?

 

well, what is suppose to happen is the gauge should read a bit high when the car is first started, as the battery is low and the regulator knows it, then, as the battery is charged up, the regulator senses a voltage balance and begins to kind of squeeze off the current allowed through. this occurs until the battery and the alternator voltages are both about 14 volts or so. the alternator will always be slightly on the higher side of the voltage, as it is suppose to take the brunt of the load. if you shut the car off, the alternator quits charging, and the battery will fairly quickly drop off in voltage, from 14, until it reaches about 12.5 to 12.8v or so.

here is the weird thing you have going on, as the gauge maxes out, indicating that the alt is charging as hard as it can, it should pull the engine rpms down, i wouldnt think you would see an increase in rpms.

the tach going haywire can be caused by the increased voltage and/or ac current leak possibly.

you might check the voltage at the rear of the alternator, and at the battery. your voltage check at either one of these spots should be close to what the gauge reads.

you could also disconnect the red wire at the rear of the alternator, this is the wire that is charging the battery, (via the starter i believe) and see if your problem decreases of goes away. might help you isolate the problem, running the car on just the battery.

you might drive the car to a local parts store, some of them can check voltage output, amperage, and load test your battery for you, free of charge, and right there in the parking lot.

if that doesnt shed any light on things for you, just simply begin to isolate each component in the circuit until you find the culprit. i mean, it could be the gauge, a wire, the battery, the alternator, and/or anything else connected.

i mean, if its like an 80 with an electric choke, that could be your problem even, might explain the delay in voltage increase. the choke could short out as the heater warms. would take a few minutes before coil moves, and could allow a short at some point. im kinda grasping there, but, itsa option.

first of all, before you do anything, check all of your wires and connections at and anywhere around the alternator and battery.

but, with all that being said, its most likely just a bum alternator.

good luck.

 

Thanks!

 

Love the avatar! (BSEE '81)

 

Nice! Sadly, I didn't go there, but have been a lifelong fan. My alma mater is a disgrace in football anyways, so it wouldn't have made sense to change teams. Go Hawks!

 

Your battery voltage with the engine off is correct, dont worry about that figure. The 16+ voltage when running means the alternator is producing voltage except too much. Therefore the regulator is not working causing this condition. Two types of alternators were available depending on the year. Later models have built in regulators within the alternator. These can be replaced by taking the alternator apart. Or the early Vettes have a remote reg that can removed from the innerskirt and easliy replaced. Either way the regulator is causing the over charging.....

 

Do you know what year they started putting the regulator in the alternator? I know i have a regulator in my alternator, but maybe I shouldn't? Where would it be otherwise?

 

I believe that only early '68s had separate regulators. Your's is a 79 and will have the regulator built into the alternator. There is a diode set and a rectifier set inside the alternator which could be causing your problem. These can be purchased and replaced separately, if you want, or you can just buy a replacement alternator. The individual parts are pretty inexpensive.,

 

The key position suggests to me that your switched battery to regulator voltage is not present when charging at 16 volts.

Please check the small wire to the regulator for switched voltage. With the key on battery voltage must be present to the regulator, or else the regulator will tell the alternator to full Field and max charge.
If the voltage is correct, regulator is the possible problem.

Good luck

 

MY 1969 was the first year for the internal regulator. If you want to get into an argument, go to a young counter parts guy at a chain store and try to tell him you want an internal regulator for a '69 Corvette. HaHa, just kidding, but it happened to me.

 

You can test the voltage regulator and the doides to be sure, here's how.
http://www.4wheelnoffroad.com/alter.html PG.

 

So after a quick visual check of the wires leading to the alternator, I just decided to replace the whole thing, but still have the same problem, so I'm thinking that the fault must be in the wiring.

 

Hi,

I'm a learner and trying to understand the working of voltage regulators. Found various online articles explaining functioning, advantages, disadvantages, types etc. but I'm looking for a content which is simple to understand for a new learner. This article https://www.derf.com/an-overview-on-voltage-regulators/ is a good example. Any other help would be useful for me!

Cheers
Tom

 

Well, for starters don't believe what you read in this old thread. The voltage regulator in a 10SI alternator is pretty dumb. It's a simple linear regulator. It just attempts to output about 14.5V. No current control. No idea what state the battery is in. Feedback voltage comes from the output wire, the tap is just down the wire a bit.