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Sat Apr 25, 2009 11:16 am

Ok, I'm testing my electrical and charging system this morning and I wondered if anyone knew what voltage should be seen at the battery while the engine is running. With nothing on and the engine running, I get 13.75 volts at the battery. It's the same at idle and 2500 rpm. The battery is brand new and had 12.6 volts when measured.

Is 13.75 the correct output? Is this the function of the alternator or voltage regulator? I know my home charger floats up to 14.2-14.4 volts for a full charge. Is my charging system functioning properly? I see some others have measured upward of 14 volts at the battery when the engine is running.

Thanks in advance.

Sat Apr 25, 2009 11:45 am

13.75v measured at the battery is acceptable.

The condition of the voltage regulator that is attached to the alternator will determine how many volts the alt puts out.

With the motor running, go back and measure the voltage directly at the alternator. You will probably be at or a little above 14v. There is some voltage loss in the cable run up to the battery compartments.

My alt started putting out about 13v, which is still probably good enough if the rest of your electrical is in good shape and you don't run down your batteries often, but I decided to replace the voltage regulator anyway. After replacement, I am now showing 14.6v at the alt and 14.2v at the batteries with the motor running.

You're probably fine especially if you are using a home charger from time to time. Keep an eye on the voltages every once in a while to see if anything changes over time.

Sat Apr 25, 2009 6:40 pm

13.75 volts is probably fine for a place like Portland that doesn't see much of any really cold weather.

Sat Apr 25, 2009 8:05 pm

I also checked under load and it drops to 13.4 with the high beams on. Not the worst but not new either.