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post #1 of 4 (permalink) Old 07-26-2018, 06:55 AM Thread Starter
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Charging System Inquiry

2005 Cobalt base model standard transmission

I was just doing some tests on my charging system. With the engine running I'm getting full amperage (about 30 amps) from the cable running between the starter and fusebox. I'm getting 3 amps from the positive cable at the battery in the trunk. Shouldn't the entire charging system have the same amperage? Is my battery not being fully charged?
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post #2 of 4 (permalink) Old 07-26-2018, 07:52 AM
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I don't know how you are measuring DC current but what you should be looking at is voltage . If you have approximately 14.3V at the battery with engine running at 1000rpm your alternator is working good. If you want to check your battery turn engine "OFF" and measuring at the battery with headlights "ON" your battery should read 12.3 volts for 30 seconds. If voltage drops suddenly below 11 volts you have a bad cell.

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post #3 of 4 (permalink) Old 07-27-2018, 07:47 AM Thread Starter
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Using a digital clamp style DC ammeter. Voltage is constant around the entire charging circuit however the Amperage seems to vary. The battery tests good and so does the alternator. Possibly the PCM modulates charge circuit amperage to optimize battery life??
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post #4 of 4 (permalink) Old 07-27-2018, 10:18 AM
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After you first start the car charging current will be high and gradually diminish to nothing as the battery charges. Then you should only read the current that the car is using at the time. So probably by the time you got in the trunk to the battery current had already dropped to 3 amp. I don't think there's anything wrong with your system.

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