voltage dropping

[76stepsidechevy]

Recently ive noticed my voltage gauge plummits if I try to use more then one thing for any extended legth of time with the worst offender being the headlights. This is a 76 k10 with a 350/465. I had the battery and alt checked at the parts store and both tested good today, the truck starts and runs good, battery stays charged ect. With the truck running and no acc. on ive got 14 volts at the battery verified with my fluke meter, turn on one thing (blower motor, wipers, lights) and the voltage drops to 13, I can run with the blower full blast using the wipers every now and then and be fine all day but try to use the lights and anything else is a joke, voltage drops to 12 Ive got dim lights, slow wipers, and a slow blower motor. Its a little better at highway speed 2500 rpm but still have to watch what I turn on.

The truck only had a ground from the battery to the alt bracket and a smaller 10 gauge wire from the alt bracket to the frame. I cleaned all those connection points and both headlight to rad support ground last week as well as added a 10 gauge ground from the battery to the rad support.

I did notice the headlight switch gets a bit warm but not hot so I was thinking maybe I should grab a new headlight and dimmer switch.

Also it seems like when the wipers are left on for a few mins they heat up and start to draw more power (voltage starts to drop)

Where do I go from here? Im afraid to start frying stuff with low voltage mainly my stereo, im sure lights and motors dont mind the low voltage but its annoying when your blower speed switch is like a dimmer switch for your headlights at night.

This truck should have a 63 amp alt in it which I think should be more then enough for everything im running. Only extras are a head unit and 400 watt amp, and a pair of 55 watt fog lamps under the bumper. battery is an older but still good optima red top.

[qu1cks1lver56]

Do the relay trick for the headlights, do the "Big 3" wire upgrade under the hood, and run a heavier wire to the junction block on the firewall. Should help you out some.

edit: and ditch the Optima for an XS Power battery :P I've had nothing but trouble out of the 2 Optima's we have.

[James McClure]

Make sure when they test the alternator they load it, not just hook a volt meter to it. An alternator can put out 13.5 volts and still be bad. Alternators are 3 phase units. Each phase has 2 output diodes, 6 in total, mounted in what is called a "rectifier bridge" which changes AC current to DC and is connected to the B+ terminal and grounded internally. A second diode assembly with 3 diodes "diode trio" feeds info to the voltage regulator. Now, if you loose 1 phase, a volt meter will still show 13.5 volts, but the amperage will be dropping and eventually will drag down voltage. You don't mention the belt, see if it's glazed. The hotter they get the more they stretch and will slip, sometimes without the squeel, especially if it's wet out. Replace your belts every year and keep a set behind the seat. Jim

[76stepsidechevy]

Any idea what size wire I should use for the big three? I have a couple of those optimas as well and have had nothing but good luck with them but they are getting older now and I hear the quality just isn't the same. I probably wont be buying another optima to replace this one but this one seems to be a good one.

[76stepsidechevy]

Originally Posted by James McClure

Make sure when they test the alternator they load it, not just hook a volt meter to it. An alternator can put out 13.5 volts and still be bad. Alternators are 3 phase units. Each phase has 2 output diodes, 6 in total, mounted in what is called a "rectifier bridge" which changes AC current to DC and is connected to the B+ terminal and grounded internally. A second diode assembly with 3 diodes "diode trio" feeds info to the voltage regulator. Now, if you loose 1 phase, a volt meter will still show 13.5 volts, but the amperage will be dropping and eventually will drag down voltage. You don't mention the belt, see if it's glazed. The hotter they get the more they stretch and will slip, sometimes without the squeel, especially if it's wet out. Replace your belts every year and keep a set behind the seat. Jim

I had no idea it was three phase thats pretty interesting. They did load test it and it passed but maybe they should have done it a few times to really stress it. The voltage drop isn't always right away, for instance with the windshield wipers they can be on for a few mins before the voltage starts to drop. I was assuming the motor was heating up and building resistance over a few mins.

Belts look decent and I have spares but maybe I should try changing them just for the sake of it. I was thinking next time I hit the junkyard I would like to grab a serpentine setup.

I have noticed the alt chirps a bit under load sometimes, should I pull it apart and lube the bearings reaplce them ?

[qu1cks1lver56]

Originally Posted by 76stepsidechevy

Any idea what size wire I should use for the big three? I have a couple of those optimas as well and have had nothing but good luck with them but they are getting older now and I hear the quality just isn't the same. I probably wont be buying another optima to replace this one but this one seems to be a good one.

I always use 1/0 wire for it, but if you're not pulling tons of current (like I always am, damn high power amplifiers :P) then you could get away with a 4 gauge and it'll be plenty.

[76stepsidechevy]

lol just a single old school fosgate 100 and an alpine 60x4 head that required its own feed from the battery. Actually the stereo seems to have the least effect on the voltage. Even back in the day running 3 big amps in a little fwd buick regal the stock alt and wiring help up to it, It also wasn't 35 years old though.

[qu1cks1lver56]

Haha yeah, all the old wiring just can't handle a lot of current flow anymore. I'd start with the headlight relay trick and big 3 wiring in 4ga or 1/0 and go from there on your truck. I don't see why just that wouldn't help you a decent amount.

[76stepsidechevy]

After going through all the wiring and finding some scary looking old splices I was almost positive were the problem it didn't fix the issue. After all that I ended up having a weak alternator, I took it apart and there was almost no brushes left in it. It was original to the truck.

[qu1cks1lver56]

That'll do it lol.

[76stepsidechevy]

yup, Im glad I found and fixed that rats nest though.