Alternator not charging

Farmall Super A, AV, 1939 - 1954

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Alternator not charging

Postby papermaker » Fri Feb 08, 2008 1:12 pm

I have a 1941ish farmall A that has been converted to a single wire 12V alternator. I've nursing a weak battery for a while but seems to charge after the initial starting. Today the "A" started but didn't show that it was charging. Replaced both battery cables because they "looked" bad. Still not charging. Took the alternator to a local repair shop and had it tested. They found that the rotor was bad and replaced it. Alternator back on and still not charging. Could the battery be so far gone that the alternator can't charge it. The amp gauge normally shows a charge but not now.

Thanks in advance for any suggestions or input!!!
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Postby Eugene » Fri Feb 08, 2008 4:57 pm

Could be the battery but may be not if the battery will crank the engine. The alternator is externally excited. Meaning requires a voltage from the battery to initially start the alternator charging.

Check for an open in the other wires, amp gauge, etc., connecting the alternator to the battery. Just a thought.
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Postby beaconlight » Fri Feb 08, 2008 6:14 pm

Does the amp gauge show a discharge with the lights on while not running? Do you have a volt meter?
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Postby deputy jailer » Sat Feb 09, 2008 5:45 am

Try this. The Delco 10si is internally regulated. Their are 2 different types of regulators. One kicks in on battery voltage when the alternator starts turning and the other kicks in off magnetism. If you dont have the right rotor and stator combination the second type wont work too well. Take a jumper wire and momentarily arc the number 1 or 2 terminals on the regulator to the battery wire on the back of the alternator. If everything is like it should it will kick it in and charge. Problem is, if this is the case it requires getting the right combo of stator/rotor or arcing it each time you want to use which is a nuscence. Also rev the tractor up to see if it kicks in at higher rpms, if it works, you can put a smaller pulley on it if you have the adjustment on the bracket to compensate for the length of the belt. Some rotors are wound thicker than others and if not matched with the right ampereage stator they wont work. If this doesn't work let me know. I can fix you a plug with a diode in it to eliminate the problem, we experience this problem from time to time at the shop. I'll send it at no charge, DEAL :?:
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Postby papermaker » Sat Feb 09, 2008 11:44 am

Thanks for all of the input. You guys are all great. I just started the graveyard shift at the mill. I'll try this on Tuesday and see what happens.I'll let you know if I need any further assistance. Again, thanks!!!
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Postby papermaker » Fri Feb 15, 2008 6:06 pm

finally got around to trying the "A" again. This time the battery had been on the charger for a few days . Started right up and the amp guage showed that it was charging. Am I correct in assuming that the battery has to have some life in it to "excite" the alternator into charging? Thanks for all of the help and suggestions .
Looks like a new battery will be in the future. Again tahnks for the assistance..
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Postby deputy jailer » Fri Feb 15, 2008 6:32 pm

papermaker wrote:finally got around to trying the "A" again. This time the battery had been on the charger for a few days . Started right up and the amp guage showed that it was charging. Am I correct in assuming that the battery has to have some life in it to "excite" the alternator into charging? Thanks for all of the help and suggestions .
Looks like a new battery will be in the future. Again tahnks for the assistance..


You are correct. All the regulators I have installed usually wont kick in to charge unless there is about 10 volts in the battery. Some regulators will kick in at a much lower voltage but then there is the danger of burning the diode trio or rectifier bridge up very quickly.
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