1985 Chevy 350 charge circuit question


#1

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…)


#2

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


#3

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?


#4

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.


#5

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


#6

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?


#7

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.

M


#8

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.


#9

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…