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Alternator issues

P

Pete in Holland MI

Member
Hey all -

Bought a Farmall Cub this past winter. Previous owner converted it to 12 volt with a 3 wire alternator. Everything seemed to be working well. This Fall now, the amp meter shows that it isn't charging on a regular basis, other than once in a while (based on the am meter showing charge or dis-charge). Battery was near flat a few weeks ago and needing external charging, affirming the alternator isn't doing it's job. Outside of my wheelhouse on this one. Where do I start diagnosing?

Also, what RPM should an alternator be set up to run at? Alternator pulley is not much smaller than the engine pulley. Reving up the engine to full speed for a few minutes doesn't start any charging. Belt is the right size and tight.

Thanx !

Pete

Thanx !

Pete
 
Start with checking the wiring.

With the engine off, you should have battery voltage at the BAT stud and #2 terminal on the side of the alternator. With the engine off, ignition on, there should be some voltage or at least dimly burn a test light on the #1 terminal.

Start the engine, at full governed throttle, there should be around 14-15 volts at all three terminals, and across the battery. If there is good voltage at the alternator, but not across the battery, there is a connection problem between the alternator and the battery, possibly at the amp meter connection.

The RPM may be too low to initiate a charge. If all the wiring checks out, try a one time "cheat" on the governor, manually bring the RPM up above the governed speed just for a second to see if it starts charging. If it does the pulley can be changed out for the smallest pulley you can find. Pulleys can be bought at many sources, speed shops carry them. Be sure to get the correct width.

If all checks out, and still no charge, take the alternator to the auto supply and get it tested.
 
He stated three wire alternator. It doesn't need increased RPM's to excite and start charging. Only a one wire without an excite terminal wire needs that.
 
see if it will charge with a screwdriver stuck in the "D" hole, assuming it is a 10SI alt
 
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