12 volt alternator discharge
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Category: Allis Chalmers
Forum Name: Farm Equipment
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=30853
Printed Date: 06 Mar 2025 at 7:08pm
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Topic: 12 volt alternator discharge
Posted By: WhiskeySup
Subject: 12 volt alternator discharge
Date Posted: 16 May 2011 at 3:46pm
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My WD45 had been converted to 12 volt sometime in the past. This weekend I noticed that the ampmeter shows discharge when the tractor is running. The battery is brand new and the tractor starts very easily. The alternator has just one wire from a terminal marked "BAT" . There are no other wires to or from the alternator which is different from other alternators I have worked with. I am assuming that the alternator is "self exciting"-no jokes please, and that maybe the ampmeter was wired incorrectly. There is no key start, just an on / off switch and the factory starter rod. Do I need to run a lead from the switched hot side of the switch to the input side of the ampmeter? I did not have my volt meter with me to check output from the alternator.
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Replies:
Posted By: Tedin NE-OH
Date Posted: 16 May 2011 at 4:21pm
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If the amount of discharg varies with engine speed, suspect ampmeter is wired backwards. Use a volt meter on the battery. If charginging at 1/2 throtle the battery voltage should be 13+ volts.
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Posted By: Brian Jasper co. Ia
Date Posted: 16 May 2011 at 5:58pm
Those 1 wire alternators require some pretty good engine speed to excite. Check it with your volt meter before you decide its not working. A new replacement ammeter I put in my D17D decided to show -15A with no battery or generator from the time I pulled the engine to when I started putting it back together. Could be the meter.
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"Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford
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Posted By: Steve in NJ
Date Posted: 16 May 2011 at 8:26pm
One wire Alternators are not a good choice for early Tractors. These units need 1200-1400 rpms in order to excite the VR to put the Alt in a charging mode. The problem is, its tough on the early engines to reach high rpms to turn the regulators on. You may have to rev the engine quite high to get it to charge. Depending on the mfr of the Alt, one wire Alts can sometimes be turned into a 3 wire unit by installing the VR plug and installing a circuit from the key switch to send 12V's to the VR. HTH
Steve@B&B
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Posted By: Gerald J.
Date Posted: 16 May 2011 at 9:12pm
It can help to install the smallest possible diameter pulley on the alternator. I did that on my gas 4020 and it still takes 1600 RPM at the engine to get the alternator started. I should make it a three wire, but I haven't yet.
Gerald J.
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