AC voltage at the battery (Alternator test)

[Infinitiguy19]

I read in a Motor Age magazine that if you put a Digital Volt Ohm Meter (DVOM) (in the AC volts setting) on the battery when the vehicle is running. If there is any AC volts showing up then a diode 9 or more inside the alternator is bad. If no AC voltage shows up then all is well as far as that test goes.

Using a Harbor Freight DVOM I got the number 30 on the screen. The DVOM was set to 200 AC Volts and the Q was fully warmed up.

[Q451990]

I can assure you that if you have a bad diode on a Q45 alternator, it just won't charge. There are 6 of them in the diode assembly...

So if you have 14.x VDC at the battery at idle, your diodes are fine.

Heath

[elwesso]

Yeah thats kind of what I was thinking.. if your voltage reads good and increases when you give it some throttle then everything is probably OK. Alternators don't really seem to work partially, they either work all way or none....

[Skibane]

Using a Harbor Freight DVOM I got the number 30 on the screen. The DVOM was set to 200 AC Volts and the Q was fully warmed up.

Some meters don't give a meaningful display of AC volts whenever there is also some DC voltage present.

For the record, there is no way that an honest 30 volts of AC could have been present on your battery terminals, even if every diode in your alternator was blown.

0.3 volts? Maybe.

30 volts? No.