Alternators hot and burning up

How many amps are you making it produce?

How well is the alternator grounded?

 

I'd suspect a bad battery or two is failing internally. Years back, had the battery on my pickup go bad internally, it caused the alternator to overheat and fail. The initial assumption was simply a failed alternator, replaced it with a new one, few days later it too was acting up. This was an aftermarket high capacity alternator, took the truck to a local alternator shop and had them test the system, on the vehicle it appeared the alternator was failing, when they took it off and bench tested it, all was fine. They checked all the wiring for shorts/grounds/etc., couldn't find anything. When they pulled and tested the battery, it took a couple tries but they determined that it had an internal fault and was causing the alternator to fail. Worst part was, on the way home, the battery exploded inside the engine compartment, I'd already talked to the battery manufacturer and they were going to warranty replace the battery, after it exploded, well, so much for the warranty replacement as they could no longer test the battery.

 

You need actually do a load test on all the ground wires. Too much resistance is the number one cause of excessive heat. A wire can still ohm out even when it's corroded but when the amperage increases it'll fail. Also check to see if you have any draws too.

 

I second the bad battery theory presented by Striker. Something has to be telling the electronic internal regulator to charge. This is based on the difference the regulator sees in battery voltage, and the preset voltage to be supplied by the alternator. If there is no great load on the system from an accessory of some sort, it only leaves the batteries to blame. Over 55% of alternators replaced under warranty where i worked, were found to have no faults when returned to the manufacturer over a measured time. We were instructed to do better.

 

I've seen ground cables with nice, clean ends be rotted out inside. Easiest way I've found to test is to run the truck, turn on every possible accessory and measure the voltage drop across the cable.

One of my pickups had a rotted ground cable. Alternator was throwing out 18-20 volts but the battery was only getting the standard 13.5 volts at the posts. It took 5-6 volts just to push the current through the rotted spot in the cable. New cable, no problem.

 

Unless you're a mechanic with schooling.

Most have no idea about voltage drops and how to test.

 

That's a great example. Voltage drop testing is a very useful tool. There could just be a few strands carrying low voltage but those same few strands can't handle the full amps because the rest of the bundle is gone.

 

What kind of trailer do you pull and is it hooked up when this happens?
And check the pigtail.