Whats the deal with these alternators going toast? I'm on my 4th in 2 weeks. Have an alternator shop that tells me I'm drawing too many amps. Tests normal amp draw at idle and 2000 rpm. noticed today alternator failed at high rpm 5000 or so, got the battery light and only 11.9 volts max on the scan gauge at any rpm.

 

I'm assuming you have a gas motor based on the 5k rpms. Do you have any aftermarket electronics like subs or an amp? Also what brand alternator are you using. I suspect something is shorting out. How is your battery?

 

i had my local electrical shop build me a 200+ amp alternator when my stock 135 amp died because with the snow plow and all the lights on i am drawing rite around 160 amps.

it cost the same as buying a stock alternator from an auto parts store

 

Sorry bout that, Its a 2004 f250 5.4. have lights and elec fans on the radiator is all, no big amps. everything was turned off this last time anyway. have not checked current draw on the radiator fans. is there any known weak spot in the electric system? any common problems besides the alternator?

 

Sounds like its time to find a new place to buy them. It sounds like your voltage regulators are crapping out. I had my original stocker and a second used stocker rebuilt at a local shop that has an excellent reputation. The guy even explained to me about some of the weak points these alternators have. Go with Tom's idea and have it rebuilt at a local shop that knows what they're doing.

 

I also agree to find a shop to build one for your needs. FWIW my stock alt went 275,000 miles. My new autozone alternator is already getting weak after 5k miles. Glad I get a free lifetime replacement!

 

That's why I had the stock one rebuilt! All that went was the regulator. He replaced the bearings, regulator and upgraded the diodes. They both still charged actually, but only above 1200rpms. Got nothing at idle. The lifetime warranties are nice, but it sucks having to replace one every year.

 

I have a starter generator shop that has repaired it for me twice. Only had to pay once. I don't think he ever replaced the voltage regulator. I'll have him do that this time.
On those weak alternators, that's usually blown diods

 

How is your battery? Is it over 5 years old?