FAQ - How do I know if my generator is generating

MNAirHead · Post by **MNAirHead** » Thu Dec 07, 2006 3:19 pm

It's common for all of us to just throw new parts at our old car. I'm convinced I've retired perfectly healthy generators. My thought has always been that as long as the engine is out, get a new generator?

1-How can I tell if my genrator is generating?
2-Do I test differently if it's a pre 67 6 volt radio?

MedicTed · Post by **MedicTed** » Thu Dec 07, 2006 3:45 pm

There is an "old school" test for a generator. With the engine running, disconnect a battery cable. If the engine dies, genny is bad.

Post by **Marc** » Thu Dec 07, 2006 3:51 pm

Not recommended to do that if you have an alternator, though - with no battery in the circuit for a reference they can run away and fry.
http://www.vw-resource.com/generator.html
http://www.nls.net/mp/volks/htm/gen.htm

SUbuggy · Post by **SUbuggy** » Thu Dec 07, 2006 8:28 pm

easiest way is to measure battery voltage with a multimeter with the engine off. shoudl be around 12.4.

start engine. once running, re-measure. if voltage is less than 12.4 you can bet you are pulling down the battery and not charging.

NOTE
sometimes big stereos, lights fans whatever may at idle cause your voltage reading to be low unless you have a BIG alternator. just rev it up a little and you shoudl see system voltage go ABOVE 12.4. this proves your alt is charging.

Badbugtwo · Post by **Badbugtwo** » Sun Dec 10, 2006 8:54 am

With the engine running around about 2,000 rpms, most cars should be able to maintain above 13.5 volts with every accessory turned on. Some cars could be as high as 15 volts. (This most likley wouldn't be an air cooled bug!)

blacktruck · Post by **blacktruck** » Wed Dec 27, 2006 8:10 pm

what about the reverse the leads and apply current thing?
I bench tested the gen on my 62(12 volt conversion)it spun when I applied
juice from a battery,I forget how the lead for the ground wire fits in this
story tho
gen light goes out,battery hasn't died on me yet

Post by **Marc** » Wed Dec 27, 2006 9:22 pm

That takes the same connections as polarizing (positive to B+, negative to DF) and the generator should spin smoothly - no jerkiness from dead spots or brush-hopping from an out-of-round commutator. I've yet to meet one that didn't work fine as a generator if it motorized OK.

...do not attempt with an alternator!