Alternator/charging issues

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g0thiac

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Sep 6, 2020
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So if I disconnect the negative cable it should die if it’s a bad alternator? Technically
You can disconnect both, and it should still run like I said.

Because, in terms of functions we are talking the relationship to the alternator, besides charging it it also serves kind of like an filter, easing off out huge spikes in amps, because generated power is not as a clean, as the sine waves at the local power plant man 😎👌
 

Built6spdMCSS

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Jun 15, 2012
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You can disconnect both, and it should still run like I said.

Because, in terms of functions we are talking the relationship to the alternator, besides charging it it also serves kind of like an filter, easing off out huge spikes in amps, because generated power is not as a clean, as the sine waves at the local power plant man 😎👌
DC has no sine waves.. ;)
 

ck80

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Feb 18, 2014
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So if I disconnect the negative cable it should die if it’s a bad alternator? Technically
Well, if you disconnect the battery it will tell you that the alternator isn't providing sufficient output.

Depending on what's been done to a car, there can be other issues. For example, if someone screwed with a pulley size, the alternator won't spin as fast as it should at idle, and, you'll put out less current than you should.

Someone could've swapped a weaker alternator on the car that isn't properly sized for everything you are running. A/C cars get bigger alternators than non-a/c but both 'fit' when installed. You could be running a bigger stereo/amp power drain than the factory Delco did, and the alt doesn't keep up.

I'm ignoring parasitic drain issues as well which can occur due to wiring issues. But, for 30 seconds of work, you CAN just disconnect an battery while the car is running and if all is good with the alternator itself functioning as it should, and, putting out enough juice to keep the engine running, you will be able to keep it running. I can jump my '77 truck and drive it around without a battery in it at all, and do, since it's used so seldom these days it doesn't make sense to keep a battery in it.
 
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g0thiac

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Street Sweeper22

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Nov 18, 2017
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Not really. Bad battery will kill an alternator.
Battery tested good just low. So I charged the battery and the alternator tested good. Since doing that with the car running it still only puts out 13.1v max and sometimes drops down to 12v. That’s without the fans or the stereo running.
 
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