how many poles does my alternator have?

[MLind]

Hello

Recently picked up a surplus marine tachometer that can run off a 4,8,10,12, or 20 pole alternator. How do I tell how many poles my alternator has? I am guessing I can count the "lumps" that go by one of the air openings as I turn one revolution, but I don't now if I have to multiply by two for the north/south, etc.

Any help?

Cheers,
Myron

[Mark Krieger]

A tachometer?

So it measures the output frequency of the alternator?

Wouldn't you need to know how many poles AND the pulley ratio between the crank-shaft and the alternator?

[MLind]

Hi Mark

Yes, I will/would need to know both. I bought the thing with minimal detail and thought it would have a "metering" screw so I could dial it into the exact rpm as measured with a optical or measruing tach. This is how my VW diesel tachs (they tie into the alternator) are. This one does not have the metering adjustment but I thought I would at least keep forging ahead. With the various pole adjustments I thought perhaps I could set the pole number very close to the pulley ratio. At any rate, thats the story. Not too much invested--$16-18 or so.
Cheers
Myron

[TimK]

I thought the GM alternator is a 3 pole unit.

TimK

[Hye]

I suppose you could just hook up the tach and try each setting to see which one gives the right reading. There is probably enough difference between the right setting and any wrong setting that you'd know which is which. Please tell the rest of us what you found.

[CareyWeber]

I don't know, but here is some info that might help you tell how many it has.

http://members.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm

Carey