Alternator amps

[longbeach]

Is there a way to tell what alternator came on the truck originally. It's an 86 K20 Silverado with A/C. Nothing else unusual. I've put a couple of Generic brand 78 amp alternators in and they drop off voltage when running lights, Heater on #3, wipers. I've replaced the blower motor, resistor and relay. Also the the headlight switch. Do I need more amps or a higher priced alternator. Thanks

 

[F-64]

what rpm does the voltage drop at?? idle??
I put a smaller pulley on mine to increase voltage at idle.

 

[Turbo4whl]

The 78 amp would be standard w/AC. Is the alt. pulley large, smaller pulley will spin it faster? Old wires could have more resistance. You can check them with a voltage drop test to each component.

Aftermarket anything can be a problem. Rockauto lists a 94 amp for your truck as one of the replacements. I don't know if it is any better than what you have.

Do you have an alternator test meter? Many auto parts stores will run the test free.

 

[longbeach]

Yes, mostly at idle. Sometimes drips right off to like 8 volts. Turn things off it will come back up. I replaced it probably a year and a half ago and seemed okay. Just started acting up again. I'll take it down to Oreilly's let them test it. Good ideas. The smaller pulley might do the trick. It's a crate engine was installed before I bought the truck. Has a mini serpentine pulley on it. So, who knows if that's right or not.

 

[F-64]

I think this is the smaller pulley that I got.

MechMan 24-0005S46 MechMan Alternator Pulleys | Summit Racing

Free Shipping - MechMan Alternator Pulleys with qualifying orders of $109. Shop Alternator Pulleys at Summit Racing.

www.summitracing.com

My idle voltage with the high beams on is 14.2v. I've also increased my wire sizes going to my starter, alternator, ground and bulkhead buss bar.

 

[AuroraGirl]

Is there a way to tell what alternator came on the truck originally. It's an 86 K20 Silverado with A/C. Nothing else unusual. I've put a couple of Generic brand 78 amp alternators in and they drop off voltage when running lights, Heater on #3, wipers. I've replaced the blower motor, resistor and relay. Also the the headlight switch. Do I need more amps or a higher priced alternator. Thanks

Switching to a CS130 (stock option on 1987 trucks, not sure about 1986) would almost certainly fix your issue and give you a better alternator. Do you have V belts or a small "serpentine like" belt or a serpentine belt?

 

[longbeach]

Thanks for the info on Pulley. I have a small serpentine like belt.

 

[AuroraGirl]

Thanks for the info on Pulley. I have a small serpentine like belt.

You must be registered for see images attach

Does your alternator look like this
And does your belt for that only go around the crank, water pump, and is tensioned by the alternator?

 

[Snoots]

The newer AD230 is great for keeping everything charged at low RPM's. You'll need an adapter from Powermaster tho.

 

[AuroraGirl]

The newer AD230 is great for keeping everything charged at low RPM's. You'll need an adapter from Powermaster tho.

Fully agree. If it wasnt for the added weight on the v belt style brackets could potentially cause twisting on tbe brackets, id say go right for a ad244 lol. If one decides to do that, probably best to include a 3rd way to brace the alternator from the rear to the head/block/water pump lol

 

[longbeach]

Aurora Girl, my alternator does look like that and belt goes around alternator, crank, water pump..

 

[AuroraGirl]

Aurora Girl, my alternator does look like that and belt goes around alternator, crank, water pump..

So unfortunaterly, slighhtly, you have a rarer belt setup. Could you send a picture of your belt drive, I want to see if its the narrow looking serpentine like belt or if its the normal width kind.

 

[longbeach]

Sorry been busy last few days. I really feel like the alternator has some sort of dead spot. Gonna have it tested. If I need a new one probably go with 94 amp. Also I need to measure diameter of pulley.

 

[Bextreme04]

Sorry been busy last few days. I really feel like the alternator has some sort of dead spot. Gonna have it tested. If I need a new one probably go with 94 amp. Also I need to measure diameter of pulley.

Nobody really makes a good readily available option. I would recommend that you look around and see if you can find a motor rewinder locally. They are usually right around the same cost as buying a new one, but they actually care about doing a good job and using quality parts. Not sure where you are located in Maine, but I see several with a Quick google search with great reviews. Clements Starter and Alternator repair, Buko, G & E, etc...

Your symptoms sound like a bad battery or bad connections BTW. The battery shouldn't be dropping below 12 volts regardless of what the alternator is doing for at least several minutes.

 

[longbeach]

So, after checking a bunch of connections and testing the battery and alternator which both tested good. still had problem. I really felt it was an intermittent problem with alternator and it just wasn't happening when they tested it. Luckily, I convinced the staff at O'reilly's and they warrantied it and gave me a new one. Problem solved. Thanks to all for replies.