Alternator Output Voltage. What should it be?

[eacyde]

95 MTX with 3.2 Swap

I went to go for a drive, started up the car and the battery light was on. Sometimes this happens so a wiggle of the single wire usually fixes the light. No deal

Out comes the meter and I get 15.2 volts at the battery. The battery is relatively new and I get 12.6V when the car is off.

I believe 15.2 v is too high and a rebuild of the alternator is in order.

Am I correct in this assumption?

 

[SHOdded]

What RPM is the engine at when it shows 15.2V? Idle is closer to 13.8V-14.0V, up to 14.5V or so when revving. If the lights on interior displays seem brighter than normal, probably a good idea to rebuild the alternator.

 

[eacyde]

15v is at idle and doesn't change when I rev it up

 

[SHOdded]

I would check the grounds and the cables also, just to eliminate a problem there. But it sure sounds like the alternator needs help!

 

[rubydist]

14.8V is the top end - over 15V is too much. However, you don't know if your meter is exactly correct, so before you do anything else, have the voltage checked by someone who has a calibrated meter.

 

[Off Road SHO]

Agreed. Double check with another meter. If the voltage doesn't change with differing rpm's, the regulator is probably shot. It's internal and not easily accessed. When you first start the car, it takes a lot of amps out of the battery, which is sensed by the regulator and it sends more than normal current to rebuild the battery's capacity relatively quickly. After a few minutes at the most, the voltage should return to just above battery voltage level. While running, the battery is always being drained and re-filled at the same time. An AMP probe attachment for a good VOM, clamped around the positive battery cables, will show you the charging rate, in amps.

Tom

 

[eacyde]

Here is something interesting. When I read the voltage a few days ago I had just taken my GENIUS charger off the battery.

Yesterday it had sat for a few days with no charger, I fired t up and and there was no battery light. The voltage was 14.8-14.9. It still seems high. I think I will have it looked at. It is going on at least 8 years old