What is correct voltage output from alternator?

[Garrett]

I just installed a new Optima battery. Off the shelf it's measuring 12.6 volts. Anyone know the correct voltage range with engine running, measured at the battery? I'm seeing 13.9 to 14.2 volts.

As my last battery exploded spectacularly (case cracked all four sides), battery posts gone limber, I'm suspicious of a malfunctioning voltage regulator overcharging the battery.

Garrett

 

[velocewest]

If that 13.9 to 14.2 is the range you're seeing at lower and higher revs, you are golden.

Tony

 

[Garrett]

Thanks Tony. I'll have to check higher revs. Highest I checked was about 1500 rpm, didn't notice any fluctuation.

 

[jhjacobs]

Sometimes a simple voltage test doesn't uncover all problems. I have seen a bad rectifier diode (inside alternator) produce voltage spikes which are only visible with a scope. This is not likely to cause a battery to explode but it will cause the battery to die very quickly. Normally a bad diode will show up as reduced voltage under load (electrical load), especially at lower RPM. If you have access to a scope the voltage should look like inverted ocean waves of equal size; a bad diode will show up as a spike every 6th wave. It will also usually produce annoying buzzing in the radio that varies with engine speed.

Good luck!