Killed two OEM alterators in 30 days... about to set my 4r on fire

[swapmeet]

Man I hate electrical gremilins.

So I burned up my OEM alternator a few weeks back. I assumed 120k of life was all it had in it. I got a take off from the salvage yard... documented 24k/miles on the take off.
Well its dead now and i'm banging my head against the wall.

I'm running a O'rileys brand AGM battery. I've considered swapping that out for a standard style battery, but I can't wrap my head around why that battery would kill an alternator?

The battery seems to hold a charge.


Is it possible that my take off just happened to be junk? Its just hard for me to believe that two OEM alternators died in such short time span.

But if its my truck, I can't imagine whats killing them.

 

[wadle5]

Is it possible that my take off just happened to be junk? Its just hard for me to believe that two OEM alternators died in such short time span.

But if its my truck, I can't imagine whats killing them.

I would think this. Eventhough is OEM, I would agree with the first due to miles, and the second I would respectively argue could be junk. There is reason the vehicle is sitting in a scrap yard, but you don't know the reason its there. Damages incurred from an accident you never truly know the extent until you get into it. Also the possibility of how long it has been sitting out exposed to the elements and what other demons the totaled vehicle had? Just my 2 cents

 

[philskeeter]

I agree with wadle5. I know AGM batteries aren't best suited for car style charging but it would effect the battery life before it took two alternators. I would buy a brand new one and try that. I just replaced mine two months ago with 95,xxx miles on it and if you're doing the work than I really hope this is the last repair because they're just a pain until you wiggle the right way

 

[Sungod]

My guess is you probably have something that is drawing a ton of amps and that is what killed your first and then your second alternator. It could be a number of things, but you will need to put another one in and carefully figure out what it is. It could be your battery, but if it has been in for a while, that probably isn't likely. Other devices are protected by fuses which should stop a bigger than expected draw, that along with burning wires. If you have added anything like a big amp, extra lights, etc., could cause a problem.

Troubleshooting is going to be tricky. First you should check the alternator. It is pretty standard (you can find lots of youtube videos to show you how if you are not familiar) and can be done so with a $4 multi-meter. If your alternator output is too high, that is probably why you burned up the two alternators.

If your replacement lasted a few days, you should be ok playing the pull a fuse game. Chances are it burned up from a period of high draw as opposed to burning from all at once from a massive draw like an improper ground. That usually would result in a fire or burnt wires at minimum. I would start by pulling all the fuses you can that are not needed to run the vehicle. Check the amp draw and voltage output. If it is good then start adding the fuses back one by one and turning on the accessory and taking measurements.

It is a slow and tedious process, but short of someone else having a similar problem with this that may know exactly what to look for, I don't think there is an easier way.

 

[BlackWorksInc]

How did the two alternators fail? Did you have them tested? I'm curious how they are failing as that may point you in the right direction.

 

[swapmeet]

How did the two alternators fail? Did you have them tested? I'm curious how they are failing as that may point you in the right direction.

Thanks for chiming in Blackworks, it's great knowing we have a pro on the forum.


So I go to start pulling Alt #2 off the truck and notice the little cap that covers the large wire is badly melted. I send a pic to a buddy who is a toyota tech and the first thing he asks is "is the nut tight?" So I pull on the cable and sure as shit, the cable is loose.

He said loose connection makes very high resistance which creates arcing, and that increases resistance further.
Voltage reg sees low voltage and tells alternator to put out more. And that's how you let the smoke out.

IDK if I cross threaded the nut on the stud or what, but it was welded on when I went to remove it. Snapped the stud off.

Getting another OEM take off Tuesday. And I'm gonna see if I can get the two OEM ones I have rebuilt tomorrow.

Lesson learned.

 

[BlackWorksInc]

That sounds about right.

The nut probably welded itself to the stud as a result of arcing, it can happen sometimes.

Glad you got it figured out.