Possible Alternator Problems '82SC

[Rodney Nelson]

I think I may be having an alternator problem. My car would not start the other day and left me stranded.

I went and got my trusty Snap-on Digital Battery/Alt/Starter tester. Well it told me that I needed to charge the battery before testing. I went home charged it and tested it and it passed. So, the battery seems to be good.

Last time my alternator went bad the Alt light came on right away. This time no light. I talked to my mechanic and he told me that if it is a negative diode that goes bad then the alt light won't come on when I turn the key. So, I checked that and it does come on.

So, I tested my Alternator with the same Snap-on Tester. The directions state to run it at 1500 rpm, so I did that and the tester is showing "LO", so it seems that my alternator is still working and giving me a low charge????

What do you guys think?
Is this tester set up to accurately read a '82SC charging system? Do alternators some time start charging low or do they just totally fail?

Thanks for your input.

[Kraftwerk]

Mine was a sudden failure. Is it a loose belt? also the battery could still be a suspect in this...

[vash]

rodney, "LO" isnt accurate enough for me. why not just get a regular volt meter and measure how much the battery sees at idle, and reved up a bit?

my alt gave up all of a sudden when my battery ran low, and i elected to drive it home. i think i taxed it too much. the red light came on, by the time i got it home. good luck. easy fix, if it is an alt.

[Rodney Nelson]

Kraftwerk,

Thank you for your response. Yeah, mine were sudden failures as well. So, you think that the tester is not giving me the right answer?

[Rodney Nelson]

Vash,

Thank you for your reply. Exactly what you said "Lo isn't good enough for me" either. So if I measure my battery with a volt meter and base line it, then measure it when it is rev'd up, what should the change be?

Thanks for you help,

[TerryH]

The battery should measure ~12.5v with motor off and ~13-14v with it running and charging. But don't quote me on this...

[Rodney Nelson]

So, last night I tested the alternator and at 1800 rpms it was putting out 13.5 - 13.2

Then I turned on the high beams and the blower and the output was 12.5.

So, it seems that the alternator is just barley working and most likely if I am playing the stereo and driving with the lights on I am slowly losing juice.

So, I have a new alternator on order. Is this the right corse of action???

[Jadams1]

Yes, could be the internal voltage regulator is faulty or the brushes or slip rings are worn. Voltage should be 14-14.5 VDC even with a load.