Mechanics

BURNING UP ALTERNATORS

2000 Chevrolet Silverado • 167,170 miles

I have a 2000 Chevy Silerado 1500 LT, 167,170 miles, 3 weeks ago my original alternator went out, since then I have replaced the alternator 3 times with 105 amps and it burned them all up, then I put a 145 amp in and it burned it up too. What is causing this Where do I look first?
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Mitchf
July 16, 2012.



Start with battery. It may be full fielding the alternators causing the failures.

What is the voltage at the battery when running? It should be 14 to 14, 5 volts

Roy

ASEMaster6371
Jul 16, 2012.
I also noticed the junction box from the positive cable of the battery to the litte red plastic box had got hot and started to melt also where the small black cable goes to the alternator.

Tiny
Mitchf
Jul 16, 2012.
The battery voltage was 14.3

Tiny
Mitchf
Jul 16, 2012.
What brand of alternator?

Roy

ASEMaster6371
Jul 16, 2012.
I forgot the brand, I think it started with an "O". Got all of them from a parts store called O'Reilly's. They're going to give me my money back on the one I still have in the truck but they won't sell me any more alternators. I do remember all the alternators had tags on them saying " made in mexico", which is sad.

Tiny
Mitchf
Jul 16, 2012.
Start with the very first reply unless the battery is less than two years old. It depends too on what you mean by "burning up". AC generators by their very nature are incapable of putting out more current than they're designed for. By installing a 145 amp generator you will not get any more current if the car doesn't need it, but if there is a defect that causes it to "full-field" or run wide open, you are likely to destroy the wire going from the output terminal to the battery. That wire size was chosen based on the generator the car was built with. Now it is capable of much higher current so you can expect more damage.

It is real common on 1987 and newer GM cars to go through four to six generators in the life of the vehicle and the way to reduce those repeat failures is to replace the battery at the same time. These generators develop huge voltage spikes that destroy the internal diodes and voltage regulator and can interfere with computer sensor signals. The battery is the main component that dampens and absorbs those spikes. As it ages, it loses its ability to do that, and you have numerous repeat failures. This assumes your term "burning up" simply means failing. If you mean wires are melting, the cause could be the same, meaning the voltage spikes are causing the voltage regulator to short and full-field the generator, or make it run wide open. That could result in wires melting, but if you have connections that are getting real hot, that is due to resistance. You solve that taking the electrical terminals off and shining all of them up to remove any corrosion.

Caradiodoc
Jul 16, 2012.
I have put two new batterys on my truck and I fully charged them to make sure. I found out thru research that the melting plastic came from putting that 145 amp alternator on. Should have stayed with the 105 amp but that's what I get from listening to parts people. When each alternator goes out they have a hotspot on them where the metal has gotten very hot in the alternator. All my terminals are brand new and clean. Where do I go now?

Tiny
Mitchf
Jul 16, 2012.
The larger generator will not cause higher output on its own. It only has a higher capacity, just like a hydraulic pump on a piece of construction equipment will only pump the volume of fluid needed, even though it has a higher capacity than the old one. To melt the plastic insulator at the output terminal you have to have current that is constantly very high, (which those parts are designed to handle), or there is excessive resistance which in this case can be way too small to measure accurately with an ohm meter. We can measure the RESULTS of that resistance in the form of "voltage drops", but one point we would need to put a meter probe is inside the generator and is not accessible. Voltage drop tests are commonly performed in starter circuits. Since your connections are new, we can assume excessive resistance in the connection is not the problem. That would leave a defect in the generator when it was rebuilt or something in the vehicle is drawing high current.

If the problem is with something the rebuilder did or overlooked, it is usually due a new inexperienced person doing the work and there will be a whole pile of them with the same problem until it comes to the company's attention. The failures will all occur the same way and in about the same time. You'll solve that by going to a different parts store.

If excessive current is the problem you can verify that with a load tester with an inductive amp probe but you would still have to know what "normal" is. If you have an obnoxious amplifier many kids use or if you've added a lot of lights or other accessories, those may draw high current.

If the voltage regulator is sensing low system voltage it will run the generator harder and that excessive current will go through the battery and overcharge it. Normally that is not a problem on GM systems because system voltage is monitored right inside the unit. The notable exception is on vehicles with digital instrument clusters. They are affected by minute changes in supply voltage so they tap off that point and run a circuit to one of the terminals in the generator's plug and monitor voltage there instead. A problem on the cluster or in that wire can cause overcharging. You'd find that by measuring battery voltage with the engine running and comparing that to the voltage on that terminal at the cluster. They should be the same.

Caradiodoc
Jul 16, 2012.
Well everbody I checked evrything that I could that yall said to and I could not find the problem so I took my truck to a generator shop that I had been knowing the owner for a while. He found the problem in about an hour. It was that red junction box where the battery cable and the alternator wire connect together. He said the nut was holding them together tight but over the years (2000 model) what was holding the bolt and box on had become loose and was causing a 2-volt voltage drop making the alternators put out more. He checked out the 145 amp alternator and said it was fine, no problems, thank god. I appeciate evrybody's help and effort in helping me get this problem resolved. I've leaned how to do a lot more stuuf thanks to yall. Oh yea, all he had to do was replace that red junction box. I am going to recommend this site to a lot of people. Talk to yall later.

Tiny
Mitchf
Jul 18, 2012.
VERY happy to hear it's solved. Things like that are hard to diagnose over a computer.

Caradiodoc
Jul 19, 2012.
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