Powermaster 140 Amp Alternator problems

I installed the Powermaster alternator more than a year ago and have had excellent results...until a week ago. While on a ride, I noticed the voltmeter in the car was reading just over 12 volts instead of 13.8 volts. Soon, the alternator light started blinking on and off.
A check with a digital meter showed 12.1 to 13.1 volts swinging around at any rpm.

While removing the alternator, I noticed the power stud turned 10 or 20 degrees (easily) before the external nut holding the output wire came loose. To make a long story short, the internal nut on the stud had come loose and created a high resistance, high current junction between the stud and heatsink. It had gotten so hot, it melted the solder on one of the diodes, and the diode was laying loose by the heatsink. All the diodes checked out okay, so I simply resoldered the diode back to the heatsink, cleaned the stud/nut/heatsink junction, and reassembled. The alternator now puts out a solid 13.8 volts again.

I have written Powermaster to see if this is a common occurance or simply my bad luck.
At any rate, something to put in the back of your mind if you have a Powermaster with similar voltage problems.

Dave

Dave,

Sounds like you had luck on your side in that nothing else got fried and it was a simple fix. But, as you no doubt agree, it should have never happened in the first place. I am anxious to hear how Powermaster responds to your letter.

You can bet that I'll be checking the posts on my alternator in the meantime!

Regards,
Lynn

Glad it was a simple fix, and glad that you shared it ... will watch for the same issue.

Here's some interesting facts that John Brady from Powermaster emailed me before I removed the alternator from the car. I was a bit concerned at how hot the alternator seemed to run when installed and knew it would get hotter yet being in a mid engine car tucked that closely to the firewall. Whether it runs hotter than recommended is open for question because you can't even see it once the firewall is installed. I could jack up the car and get a reading on it from underneith.

From John Brady at Powermaster:
1) We do have a rebuild kit number 912 that will work on that.
2) A 140 amp unit will run 175-225 degrees. The fan on our unit will move more air than just about any fan out there.
3) Our units are no different in terms of checking them to make sure they are working than a stock unit.

It was out of warranty. Isn't that the way it always works!
I didn't price the rebuild kit and was glad I was able to salvage what was there. It's working like a champ again.

No reply from Powermaster as to the loosing stud as of yet.

Dave