Farm Equipment - M3 charging system

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M3 charging system

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=131399
Printed Date: 30 May 2025 at 3:08pm
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Topic: M3 charging system

Posted By: plummerscarin
Subject: M3 charging system
Date Posted: 15 Nov 2016 at 9:04pm

Fired up the M3 to pick corn yesterday and the alternator didn't seem to want to charge the batteries. Removed alt, took it in to be tested and only putting out 11 volts. Installed replacement unit and still no charging. Pulled one out of the other M3 that worked fine when combining beans and IT wont work either. After reading the book I tried a few checks to see what else might be wrong. The green output and blue volt sensor wire show 12 volts. The yellow exciter wire is 0 with key off and 2.4 volts with key on. That wire has an inline resistor. Is this normal? Am I missing something else? Your thoughts will be greatly appreciated,thanks.

Replies:

Posted By: DougS
Date Posted: 15 Nov 2016 at 9:07pm

The exciter wire should have 12 volts on it with the ignition turned on.

Check for a blown fuse, wring problem such as a loose connection, corroded terminal, bad ignition switch, etc. I doubt the problem is in the alternator unless the original alternator has a problem and blew a fuse.

Posted By: plummerscarin
Date Posted: 16 Nov 2016 at 8:03pm

Posted By: plummerscarin
Date Posted: 16 Nov 2016 at 8:11pm

Update:

I had considered the possibility of loose connector in the harness or possibly a short so after I got home from work I went to check and found that my uncle took it for a spin during the daylight. After while the voltage came up to 14 and now can run with the lights on. Didn't get to test exciter wire yet but I'm thinkin that a short could could be suspect? Thanks for the help Doug and I'll keep updating.

Posted By: Kevin in WA
Date Posted: 16 Nov 2016 at 9:45pm

Could be that the alternator self started on its own at high rpm when your uncle drove it and that the exciter wire is still low on voltage.

Posted By: DougS
Date Posted: 17 Nov 2016 at 5:02am

Probably what happened there, Kevin.

Posted By: plummerscarin
Date Posted: 17 Nov 2016 at 8:32pm

Got back out to it tonight. Uncle ran it for a while before I got there and it never kicked on for him. Checked the voltage again and it was up to 6 volts. Pulled the access panel off the cab and have 12 volts off the ignition switch. Wiggled some wires and harness around and got the exciter up to 10 volts (exciting!). Fired up the machine but still not charging until I took a short piece of fence wire and touched it from the power to fuel solenoid and exciter wire terminal.That got the alternator to go.

Posted By: DougS
Date Posted: 18 Nov 2016 at 9:03am

Go back to my original post. Check the items I mentioned. Beware of voltage readings that are made in an open circuit. This smells like a loose connection or corroded wire at a terminal or splice.