Hot alternator

Paul in SC · Jun 7, 2012

Need opinion as to why newly replaced remanufactured 10 SI alternator is heating up. Alternator is on 1950 Farmall M and is wired as per Bob M"s diagram. Tractor has operated on 12 volt neg. ground for several years with no problems. Alternator was replaced due to non-charging of old unit. New unit runs hot to touch (too hot to hold hand on) after running 10 minutes at fast idle. Charging function is fine, showing charge on ammeter with a output of 13.8 to 14 volts. Just runs too hot to touch. Battery is in good shape. Any ideas?

rhtx55 · Jun 7, 2012

Does the alternator have a "fan" (fins) behind the belt pulley?
I would think the close proximity to the radiator fan would certainly cool it, possibly the belt is a bit too tight. Sorry, not much help.

Bob M · Jun 7, 2012

Paul - A 10 SI alternator WILL run hot when operated at maximum amp output for more than a few minutes. And a low battery can cause this.

Try putting the battery on a charger overnight, then run the tractor again. A couple minutes after startup the ammeter should settle around 3 - 4 amps charge, and voltage across the battery should be between about 14.2 and 14.8 volts (lower temperature = higher volts)

If the voltage stays 13.8 to 14 and the ammeter reads high, problem is the battery not taking a charge and should be replaced. But if the voltage is within spec and the ammeter shows a few amps of charge there's a problem with the new alternator.

Paul in SC · Jun 7, 2012

Thanks, guys, and Bob M, thanks, I sort of suspected the battery. I will change out to new battery because your analysis is exactly what is happening in that the ammeter is showing a charge of about 20 or more amps. And rhtx55, there is a cooling fan on the alternator but I think the radiator fan may disturb what little air flow this fan creates.

Janicholson · Jun 8, 2012

Bob is, as usual, correct. A shorted stator winding will not appear to be an obvious fault. My son's CRX had one last month and it just didn't charge strongly. 20 or 30 amps should not heat the alternator. Check the battery then have the alt output checked. Jim

Brownie 450 · Jun 8, 2012

The #2 terminal on the 2-wire plug should read out battery voltage to control charge current. If it isn't reading voltage due to a bad connection or bad terminal, it would cause your problem. Stick a voltmeter on #2 terminal & see what the voltage reads.
If this checks out, I'd go along with 1/3 of the stator windings shorted/ rectifier bank shorted.

Brownie 450 · Jun 9, 2012

Paul---you'd be surprised how much air flow that "little" fan creates--even working against the radiator air flow.

Hot alternator

Paul in SC

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Paul in SC

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Brownie 450

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