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Good day electrical smart guys

About a week after picking up my nova I noticed that the battery was dead, charged it up, worked for a couple of days and dead again. Did the following tests to determine what was going on.(not sure if these are best methods to verify what works)

  • Checked for a draw on the battery when everything was off and this checked good. In the dark with a charged battery I disconnected the battery cable and reconnected and there were no sparks. Turned on a low voltage light in the dash and same test and I had a spark
  • Checked the actual battery and it would not hold a charge. With the keys off, lights on and an external load placed on the battery it dropped from 12 to 8 volts in about 30 seconds. Replaced the battery but still have some concerns.
  • I disconnected the battery while the car was at idle and it didn’t stay running. The in dash battery meter (50 years old) will read negative and well below half way when the car is idling, when I get out for a drive where the tach reads 3000 RPM the gauge will show above the middle line 3/5 to ¾ of the full gauge. So to me it looks to be charging.
The alternator that had been installed is one of the chrome replacement models (not sure on model – part numbers).

That said is the alternator showing normal. Should I look at changing the alternator drive pulley to a smaller size to so that the alternator spins quicker or does the symptoms I listed point back to an alternator issue or something all together different

Any assistance would be greatly appreciated

Roger
 

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If you replaced the battery, you would think that would be fine but what you could do is charge it with it disconnected from the car and then after it's charged let it sit for a little but and take a voltage reading then let it sit a few days and see how much it's dropped. There are charts online that show battery voltage and the state of charge.

Even though you have a gauge that read's above the middle line 3/5 to ¾ of the full gauge, you have to wonder if it's really giving you any good info. I would get a good volt meter and with the car off and the battery charged, see what the battery voltage is, then start the car and ideally you want to see at least one volt more or higher up to a maximum of about 14.5 volts. See how it does at an idle and then at a higher highway RPM. Some alternators do not have a lot of low RPM output and maybe yours is like that.

Also if you do a lot of starting the car and not driving it, the battery doesn't have a chance of being recharged. I talked to a guy years ago that after a while he had to charge his battery and then it was fine for a while and I asked him how much he drove it and he said he only drove it on and off of the trailer at car shows. I suggested he drive it more than that and if everything is good with the electrical, then it would be better with some driving.

Jim
 

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Discussion Starter #3
Thanks Jim

I realize the original volt meter may not be functioning correctly so that could throw off what I think is right.

I had also been thinking that the alternator could be under-driven and not giving me the volts I need when the engine is at idle. Good to know that some do not produce any usable voltage at idle.

I will run a few of your suggested tests and see what I come up with

Cheers
 

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Measure the crank and alternator pulley size. The crank pulley should be 2.75 to 3 times the size of the alternator pulley in order to charge properly at low rpm.

Do you have a newer 10si style alternator? Is it wired as a 1 wire, just one wire off the alternator?

There are some easy changes you can make to greatly improve the charging system.

Never unhook the battery with the engine running, it can damage the regulator.
 

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Checking with a known volt meter is the place to start. As stated, check voltage at the battery with the car off. Then start and check again. It should read a higher voltage. I'd be looking for about 13+ volts at idle, but whatever it is, it needs to be showing more than with the engine off. Then you can raise the engine rpms and the voltage should raise a bit more. Alternators don't usually put out much voltage/ amperage at idle. I'm guessing you may have a low quality aftermarket alternator.
 
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