1985 Chevy 350 charge circuit question

I have a 1985 Chevy 350 with a charge circuit problem.

The symptoms are:

1- the 50Amp main breaker opens when the engine revs get to about 2000 rpms.

2- the amp meter on the dash reads 40+ amps.

3- nothing else seems wrong… the batteries are charged, the other systems seem to be working okay, mechanincal fuel pump, oil pump and such.

4-No AC compressor or anything…

Oh I should mention it’s in a boat, but I disconnected all of the other systems from the engine and charge circuits…

I think it’s the Regulator/rectifier in the Alternator (this engine doesn’t have a discrete RR so I’m guessing it’s solid state in the alternator…)

What is the voltage across the battery terminals when the engine is running at 2000 rpm. Could be you have no voltage regulation.

Yeah, 13+ VDC… I’m thinking that I’m overcharging the batteries… I just can’t get my head around that idea, but it can happen, right? Hydrolicize he liquid? Ruins tha battery thought right?

13+ VDC is OK … I would accept anything up to 15 VDC. You must have some circuit on board that is drawing excess current … normally the dash gauge should show almost zero current.

Assuming the battery is good (no shorted cells) … it’s time to start pulling fuses and disconnecting wires to locate the current thief.

Most likely the internal voltage regulator has a problem. Replacing the alternator should fix it up.

Oh … I reread your post and you already tried isolating the problem. So you have only the battery and alternator as a current load. You could try starting the engine and then disconnecting the battery to see if the current drops (run the engine at speed so it doesn’t stall) … if the current stays high that would leave a faulty alternator as the problem . I’ve never seen an alternator that draws 40 amps … but that doesn’t mean it can’t happen.

Are you sure you don’t have other circuits on board that may be loading the alternator?

Man, I can’t believe I forgot that step… I’ve done that before to isolate the alternator… oh well, getting old… Thanks for the intel…

I’ll let you know what happens.


You mention a dual battery set-up. I suggest you revert to a single battery set-up and see what is the result. Do you have some type of battery isolator device in use? perhaps this is where the problem lies.

Yeah, roger that. Actually this is what makes the missing the troubleshooting step sorta funny, all I have to do is turn the select to “none” I don’t have to disconnect anything…