Amp meter reading on 12V alternator

mngreen

mngreen

Senior Member
I've had a 12V Delco alternator with regulator setup running in my Model A without an ammeter connected for the last 35 years. I decided last month to connect the ammeter for the first time. It shows about a 20 amp charge right after startup then decreases to near zero as a correct charging circuit should. It shows a charge to compensate when turning on headlights, etc. while running, so it mostly seems okay. However...

But then sometimes the meter intermittently fluctuates wildly at certain RPMs and then evens out at speed.

Anything that I should be concerned about? I have the circuit fused.

Thanks.
 
It would appear to me that your electrical system is working properly. My two cars work the same way, one is 6v, the other 12v. Both are equipped with an alternator. The regulator circuit in the alternator is constantly looking at the condition of the battery. When it is fully charged the ammeter should sit at zero when out on the road. With an undamped ammeter you might see fluctuation around zero as the the regulator tries to determine if the battery is fully charged.

When you turn on the headlights the ammeter should flicker and then return to zero. This tells you the alternator has picked up the load. Blow the ahooguh horn and you should see the ammeter doing a rain dance around zero.

Should you ever have a situation where the ammeter does not return to zero after a nominal period of driving, and shows charging, it could mean you have a bad cell in the battery and it will not take a full charge. The ammeter is telling you to have the battery checked.

Tom Endy
 
Is it harmonic vibrations causing the needle to jump erratically? If not, it could be a regulator or possibly dirty connection? As long as it is not over-charging, I would not get too excited.
 
BRENT in 10-uh-C said:
Is it harmonic vibrations causing the needle to jump erratically? If not, it could be a regulator or possibly dirty connection? As long as it is not over-charging, I would not get too excited.
Click to expand...


What's harmonic vibrations?? :o

If you mean needle moving from the car shaking, then no, that's not causing it. When the meter wasn't connected it didn't shake like that.
 
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