keeps killing alternators!

[HVAC SuperTech]

Ok, I just had the alternator replaced(again) like on the 20th of Oct, and the batteries replaced. the old alt was only putting out 10 V. So, I have noticed it cranking slower and slower. Well, I just barely made it into the driveway. not even all the way, and it was dead. On the way home, it was getting dark, and I couldnt run the lights cause there was no power. I had to jump it off with the work van to get enough juice to park it. SO, I have to replace the alt AGAIN!!! thats 4 bad in just over 6 months!! And it killed the batteries, so I will most likely have them replaced too. I dunno what kills my alt. It happens so quick! Any one have any ideas?

[cchase]

wow, I went threw 2 in the last 6 months. but 4 is crazy, I havent changed my batterys yet, they are about 2 years old, getting weak but still just enough, I would just charge yours.

I have no idea what you cause them to short, how are they grounded?

[HVAC SuperTech]

Normal grounds(factory)....I am thinkin of doing the dual set up, but I dont see why I am killing them. I never have heard of a vehicle doing this, let alone own one. I dont think it would be a short, cause that would just wear on the batteries, not kill the alternator.

[CAT797]

A couple of questions for you........

Are you having the alternators rebuilt or are you buying new ones? If rebuilt, what is actually defective, mechanical or electrical??? i.e. regulator, bearing, etc.....A good motor rebuild shop should be able to rebuild it for about $100 depending on what's wrong with it.

Are any of the aftermarket goodies that you have installed wired directly to the battery without fuses?

Have you checked the current draw on the alternator with all your accessories running?

My guess is, you have something installed electrical without a fuse that is becoming shorted, allowing excessive current draw which is frying the internals of the alternator and if it's drawing more current than supplied by the alt. it will kill batteries too.

FYI.......I know these things are insanely expensive if you have to buy new (mine was like almost $500 from Ford IIRC), but most of the internals are relatively common and a good repair shop can save you some jack. When mine went bad I couldn't find one at Autozone, NAPA, etc., so that's how I stumbled onto the motor rewind place.....

[mrnecsteve]

The most likely cause of repeated alternator failures is excess voltage frying one or more diodes. The most likely cause of over voltage conditions are open wiring connections...especially if you have a faulty ,high resistance chassis-ground connection.(An intermittant connection will result in repeated surges through the diodes)
I dont know if they're still available...but some automotive stores USED to sell the diodes in a kit....fairly easy to check and replace with an ohmmeter.

[HVAC SuperTech]

I am getting the alt from Advance. Its a new one, not a rebuild. They have all been new since I started with the first one. They see to be dying even faster now. he only aftermarket things I have put in are Stereo(fused) some lights(fused) and some running liights up front. I dont remember if those are fused or not. I will check. I am gonna have to try to get to Advance so they can check it again. will get one more, maybe. If fords are 500 thats double what I paid at advance. I dont have that kind of extra money right now.

I have not personally checked current draw. How exactly would you do that?

[regor]

You would need a D/C clamp meter to check the amp draw, thats what i use to check D/C circuits on our diesel refrigeration units.

[HVAC SuperTech]

well, I have a meter which does AC/DC amps and volts. So I will check that too! Thanks Roger!

[CAT797]

The easiest way to check is with the ohmmeter that has a clamp on induction lead(similar to what is on a timing light for the #1 spark plug).

These things don't have an external voltage regulator on the chassis anywhere do they?

[HVAC SuperTech]

no. Internal in the alt. I did hear of a box that sent signal to the PCM that was near the firewall that controlled the voltage output, but that would be a voltage regulator, and I dont think our trucks have em, maybe the OBS's do.