Farmall M with 12v conversion wont charge.

Jasen · Mar 15, 2011

Need a little help. I converted my M last summer to 12 volts with the parts and wiring schematics I found here. The tractor had a alternator on it when I got it but wouldn't charge. I put a new alt on and rewired the whole thing. It worked great last year and I only put about 3 hours on the tractor. I went to start it this year and now it wont charge. The battery was weak so I charged it and nothing. I double checked all the wiring and it was correct. Took the alt to NAPA and it checked out good. I rev it up and the light stays on and the ammeter still reads discharge. Any ideas because I've about run out.

Janicholson · Mar 15, 2011

Assuming you have a Delco 10SI alternator, If the system you used to make it charge was the standard three wire setup. It should not need to be reved up to make it charge.
The big stud terminal is connected to the amp meter (on the opposite terminal from the wire going to the starter switch)
The #2 spade terminal is connected to the stud terminal. The #1 terminal is connected to one side of the indicator light. The other terminal of the indicator light is connected to the ignition switch I terminal (goes to the coil). This is all that is needed. If it is a one wire system, I have no idea. It should charge, but ??? they are not as designed from delco. Jim

Lance_MF_180 · Mar 15, 2011

Do you have the little resistor diode in the line so it doesn"t back feed, perhaps that is bad? My M is converted to 12 volt also from diagrams also found here.. sometimes it charges to beat the band and other times it doesn"t charge much at all.

old · Mar 15, 2011

What happens if you remove the light from the system as in wire around the light?? If it then charges you need a new bulb since bulbs over time can get where they are more resistive and that will cause it to not let the excite circuit of the alternator to work. Also are you just going by the amp gauge and the fact the light does not go out or are you checking battery voltage at the battery both run and not running to make sure you have the 12 or so volts at the battery not running and around 14 volts running??

old · Mar 15, 2011

Lance just for your info A diode and a resister are 2 totally different electronic components. A diode is a check valve sort of thing for electricity as in lets current flow only one direction and a resister resist current flow and by doing so depending on the circuit lowers voltage

Shawn in PA · Mar 15, 2011

Did you check voltage at the battery (tractor running) with a voltmeter or multi-tester?

Bob M · Mar 15, 2011

I agree with old. If the resistance of the idiot light circuit (lamp + connecting wiring) exceeds about 40 ohms the alternator will not "turn on". Temporarily bypassing the lamp as old suggests can confirm.

However it may simply be the alternator is being spun too slow. The 10SI - even in "3-wire" configuration - must be spun considerably beyond normal low idle speed briefly at startup before it will start to charge. And sometimes as an alternator gets older, it may need to be spun up faster it turn on than when it was new. (This may be why it tested OK on the NAPA test stand but won't work on your M.

Consequently may need to replace the alternator pulley with a smaller one in order to spin the alternator faster.

Jon Hagen · Mar 15, 2011

Check your fan and generator belt, make sure they are tight.
I have worked on several IH tractors of that series with generator or alternator that under charged or would not charge, it turned out to be loose fan and generator belts that would not turn the generaator / alternator fast enough to charge.

Farmall M with 12v conversion wont charge.

Jasen

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Janicholson

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Lance_MF_180

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old

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old

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Shawn in PA

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Bob M

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Jon Hagen

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