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Discussion Starter · #1 ·
Just installed a new cs 130 alt in my car, it bench tested 156 amps. My last alt couldnt keep up with the 50 amp fans and air conditioner. Any way, the new alt would not "turn on" so when the car was running the volt gague only read 12 volts.I checked the conections, and did a search on this site to confirm that it was wired correctly. I was about to return it for another check, when I realized that I had my Allen Grove bracket that holds it in place powder coated, including the spacers and bolts, so I ran a wire from the housing to the block, and shazam, 14 volts on the meter.
I removed the wire and the lower mounting bolt and spacer, ground the coating off the bolt,the ends of the spacer, and the inside of the bracket where the spacer contacts it, and all is well in the Chevelle. I believe this is what solved the problem, the alt housing has to be grounded to the block. But I havent seen this mentioned on any post I have read, and that has been a bunch. If John or Pete could responed to this post, and let us all know if this is right, it may spare someone else a lot of trouble.
 

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An alternator needs to be grounded to work. Normally the case has enough surface area touching and hold down bolts that there is no problem. Same is true for the stater.
Paint, power coating, black oxide all can act as insulators. Chrome alternators don't care that much because the threaded holes aren't usually chromed.
Some guys add a separate ground strap from the alternator case back to the block if they are having a problem. An original factory set-up doesn't need it.
 

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Discussion Starter · #3 ·
Thanks John, I was sure that my powdercoat was the problem. While Im here, do you think 8 gague wire from the alt to the horn relay is large enough? the guy at the alt shop wants me to install 2 gague.
 

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8 guage is way too small for an alternator that can produce 156A. I'd expect they are about right with the 2 gauge but you could probably get away with a 4 gauge wire. Make sure you get a welding cable or amp power wire which has the fine multistrand wire.

And yes, the alternator has to be grounded. First reason is that the case is the return path for the charging current. Second reason is that the regulator uses the case ground as the negative or ground reference to read the charging voltage. Like any automotive wiring, the ground is as important as the +ve wiring. If you ever had to run a ground wire to the alternator case, you'd need one as heavy as the main B+ lead.

Peter
 
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