Generator Troubleshooting Questions

madcat_1212

New User
Hi All,

I am new to the forums as a poster, but have been lurking around for a while.

I have been troubleshooting a generator issue with my 1958 Farmall 460 diesel and am hoping that someone can weigh in on what they think the issue may be. The tractor is not charging and the batteries will die out on it periodically. Here is the outline of things I have done so far.

1) Bench tested generator off of tractor using the motor test. Connected negative battery cable to case of generator and positive battery cable to A terminal. Generator spins freely.

2) Performed the same test with the F field grounded to the case. This slowed the rotation of the generator.

3) I removed both leads on generator and started the tractor. I warmed it up and then tested the voltage at different engine speeds. Seems to increase from 1.5V to 3.5V with engine speed.

4) With both leads still off generator, I connected the A post to the F post with alligator clips. The voltage between the A post and the ground of the generator still varied between 1.5V to 3.5V. I was expecting the output voltage to be higher than this.

5) With both leads connected to the voltage regulator, the voltage output seems to be even lower, ranging from .2V to 1V.

Does this indicate that the generator may be failing? In one of the troubleshooting guides I read, it seemed to indicate that it could be faulty field coils?

Thanks for any input.
 
Madcat, Good questions. OFTEN but NOT always if a genny passes BOTH motor tests as you performed above, it should charge. The gennys output is measured across its Armature which is between the ARM post and case/frame NOTTTTTTTTTT between ARM and FLD. It obviously has to be higher then battery voltage and rises as RPM increases.

For max charge condition YOU GROUND THE FLD NOT CONNECT IT TO ARM

The true test of a charging system is if it will raise the battery voltage !!! A full charged good battery should measure around 12.6 volts subject to temperature BUTTTTTTT if connected to a good charging system battery voltage should rise to at least 13 up to 14+ volts subject to RPM and VR.

When running at fast RPM if she's NOT charging temporarily ground the Gennys FLD post. If it charges then but NOT otherwise, that says the Genny itself is okay and the problem is the VR isn't well grounded or is bad. If no charge even with FLD grounded the genny is likely bad.

SEE WHAT HAPPENS WITH GENNYS FLD GROUNDED !!!! Charge or not ??? Ground the FLD for max charge instead of connecting to ARM.......Insure BOTH the Genny and VR are well grounded !!!!!!!

Work through my Charging Troubleshooting Procedure linked below for a step by step testing procedure, no use re inventing the wheel each time this question is asked.

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=jd&th=458743

John T
John Ts Troubleshooting
 
Hi John,

I actually did perform your recommended test as well, and can't believe I forgot to include the results as they we're quite strange.

I connected alligator clips from the F post to the case ground of the generator. When I did this, the voltage of the generator would range from 28V - 68V when measured across the A post and the case ground. It seemed to be approx the voltage of the other testx12. I am wondering if this means the tractor batteries are somehow hooked up in series to the generator? The tractor has 2 x 12V batteries hooked up in parallel. If I have the leads for the generator hooked up, then try to connect the F post to ground, the alligator clips start glowing red as if they are shorting.


I am just a backyard mechanic with a base line understanding of auto electrical. I just thought that those voltage ranges seems abnormally high. Is the alligator clip glowing when connected from F to ground concerning when the leads are hooked up?
 
Don't ground the F post with the A post disconnected. You can get zapped doing that and if allowed to continue to build arc inside the generator. The quick test is with the engine running at half throttle or higher, ground the F terminal. This should give maximum output. If you get that, check the F wire between the generator and regulator before just putting a regulator on it. A simple easy test is use the F wire in a simple circuit to light a headlight bulb. DO NOT use your meter for this test as one thin strand of wire will indicate low resistance on any meter. That one strand will never carry the current needed for the field circuit.
 
Wow. Something really wrong there. Are you sure your batteries are good? I'm not super familiar with Farmall 460 but assume negative ground? What make and model of voltmeter? Sometimes low cost meters can pick up outside interference and give wacky readings. With all leads connected "properly" and engine running, what voltage do you read at the battery terminals?

The alligator clip getting red hot is indicating too much current through a small wire and small clip. I've used a similar connection to a field-to-case ground and alligator clip didn't get hot. Seems your field winding is drawing too much current. As John T indicated, could be that the generator is bad even though it "passed" motor test.

Always a challenge to troubleshoot by "remote control"! But the advice is free. (smile)
 
(quoted from post at 08:57:58 06/19/18) Hi John,

I actually did perform your recommended test as well, and can't believe I forgot to include the results as they we're quite strange.

I connected alligator clips from the F post to the case ground of the generator. When I did this, the voltage of the generator would range from 28V - 68V when measured across the A post and the case ground. It seemed to be approx the voltage of the other testx12. I am wondering if this means the tractor batteries are somehow hooked up in series to the generator? The tractor has 2 x 12V batteries hooked up in parallel. If I have the leads for the generator hooked up, then try to connect the F post to ground, the alligator clips start glowing red as if they are shorting.


I am just a backyard mechanic with a base line understanding of auto electrical. I just thought that those voltage ranges seems abnormally high. Is the alligator clip glowing when connected from F to ground concerning when the leads are hooked up?
h, yeah! Fields generally draw around 4 amperes and that is not going to make test clips glow red. Unless something wiring related is terribly different than indicated, then the generator has problem.
 
With the F post grounded and 28-68 volts indicated at the A post, that tells me the A post had no load applied, no connection to the battery. 68 volts fed into fields that normally only see 12-14 volts would make the field coils flow 20+ amps which would explain your hot test lead and clips. Try it again with a known good regulator connecting the generator A post to the batteries through the ammeter. With a battery load on the generator, it should show 14-18 volts at the battery posts with the F post grounded and engine at 3/4 throttle.

Once that is working, remove the F post ground wire and connect the generator F post to the F or fld terminal of the regulator, the charging voltage should now be between 13.5 and 15 volts at 3/4 throttle and a charged battery.
 

Hey Ron,

The batteries are brand new last year, and all we have done is a full tractor pulls with the machine. Its a toy, not a work horse.

The multi-meter is a cheap one (MasterCraft -- Canada's HarbourFreight from what I understand). I've had good luck with these units in the past though. I am starting to think it may be the regulator as the tests seem to be passing for the generator.
 

Thanks Jon. The 68V does not indicate to you that the generator may be having issues / over producing? As soon as I hook up my regulator, the voltage seems to go to nothing.

I mean obviously its one of the three:

1) The tractor wiring is completely borked.

2) The regulator is bad

3) The generator is bad.



I think I may pick up a new regulator and double check all electrical connections in the process. If that still doesn't do it, we may be in to a new generator.

With the generator passing both bench tests, what are the chances that a rebuild would fix it? Or should I spring for an entire new generator. From what I understand, if I got it rebuilt, that would not fix any field coil issues, only replace brushes and bearings.

Thank you everyone for their help so far, I'll keep you posted.
 
Obviously I'm not Jon, but his observation on field current if armature was actually at 68 volts when clips turned red is a good one. I have worked with many generators and even open circuited, have not seen 68 volts. 20 to close to 30 occasionally. So my next recommendation would be to get a decent analog voltmeter, rather than chase ghost with perhaps bogus voltage readings. A reasonable fields test would be to connect a 12v battery with series ammeter between ARM and Field terminals of generator (not running) and measure the field current. Gen housing floating (not grounded). Most will not even see the 4 amperes that I mentioned earlier, perhaps half or less.
 
I have had alternators full fielded with 12V produce as much as 150 volts at the output stud with no load on the alternator. If your generator is really producing 68 volts, there has to be some problem not connecting generator output to the battery. Bad wiring, bad ammeter, bad regulator. A generator with the field grounded and it's output connected to a 12V battery should never get above 18 volts.
 
(quoted from post at 23:15:33 06/20/18) I have had alternators full fielded with 12V produce as much as 150 volts at the output stud with no load on the alternator. If your generator is really producing 68 volts, there has to be some problem not connecting generator output to the battery. Bad wiring, bad ammeter, bad regulator. A generator with the field grounded and it's output connected to a 12V battery should never get above 18 volts.
t is not correct to compare alternators with generators. Why introduce extraneous material? He is probably confused enough.
 
Hey all,

Giving a quick update on the successful outcome!

As a few have you had mentioned, since the generator was passing the bench motor test it would likely produce a charge. This turned out to be true.

I had ordered a voltage regulator as it seemed likely that it was acting up. I also decided that I better trace the wires to be sure that everything was wired correctly.

It turned out that the F and GEN wires were backwards on the VR :roll:. I corrected them, then tested with the old VR. The old VR didn't seem to work, but I could get 18V at the A post if I manually grounded the F post to the chassis.

I replaced the VR with the new one, and then tried again. At this point I was getting 15V at the A post, but only 12V at the batteries. I then polarized the generator and then I started seeing 15V at both the generator and batteries at around 1/2 throttle.

Thanks for all the help. I was ready to consider a generator rebuild / replacement, but the wiring fix + new voltage regulator did the trick.

Ready for the pulls this weekend!
 
Those mis-wires will get you. Glad to see you found the problem & got it fixed! Thanks for reporting results.
 

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