# 1975 SS16 Charging circuit problem



## mdroll7780 (Apr 26, 2017)

Hello tractor wizards!

I have a 1975 SS16 that has been giving me some trouble. Here are symptoms:

The battery has been dying several times. Thought it was a separate problem, but now think maybe related. The tractor will start fine, run for an hour or less (with full batter charge), and then it will die. It quits similar to a kill switch. No coughing, no sputtering, just quits. The battery at this point is dead, but it will take a jump and start back up. It then will die a few minutes later in the same fashion as described above. The amp meter on the dash shows a constant discharge of -2 amps. A quick chek of the meter by having key on, engine off, and light switch on shows a quick jump to the negative, so seems like meter is telling the truth. I also checked across battery terminals when off, and read 12 volts. Check across same terminals with tractor running at WOT, and same 12 volts. Seems like its not charging battery.

First question: Does the tractor need the battery to run? My assumption was this whole system is mechanical, and can disconnect the battery while running with no real issue. I may be wrong. An easy test obviously, but I have not yet done it.

Second question. Is there a simple way to test my charging coil/alternator? I can see there are three wires on a small harness from the votage regulator, one goes to the ignition, while the other two drop down somewhere behind the flywheel. I assume these go to some sort of coil. I have been trying to check grounds, and so far seem ok. Although I have not taked all wires off yet and cleaned to make sure. Is it possible the charging coil could be bad? Is there a typical ohm reading across those two wires from the voltage regulator I can expect?

Trying to get a headstart on troubleshooting from you guys to save me some time. If you have any thoughts on things to check or rule out I appreciate any advice.


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## Bill Kapaun (May 8, 2007)

Posting the Sears 917.xxxxx number can't hurt. It might identify which ONAN you have.

IF this has a battery/points ignition, then the ignition requires power to operate. I "think" this is what you have.

Measure the AC voltage across the 2 wires from the alternator (VR disconnected).
ONAN's require different amounts, depending which engine/charging system it has, BUT.. I can assure you it has to be at least 28VAC MINIMUM. (I think some ONAN's may be as high as 40 VAC??)
IF the alternator passes, then the VR is suspect.

Also make sure the ground to the VR is good.


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## mdroll7780 (Apr 26, 2017)

Thanks Bill. And good point on model, I should have posted that. I will test the voltage you mention tomorrow. I'll see if I can find what it "should" be, but haven't been able to find this type of specs yet for this engine. Maybe looking in wrong spot. 

Here is sears model and Onan numbers:

Sears model is 917.25884
Sears Serial 8155

Onan model: BF-MS/2833D 
Onan serial : D753110349


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## Bill Kapaun (May 8, 2007)

Looks like 28 VAC is the number-


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## mdroll7780 (Apr 26, 2017)

Thanks for the advice. It seems to be working correctly. Amp meter is showing positive when running. Wierd part is that I didnt find anything wrong. The only thing I can think of is that even though I checked all the grounds and seemed fine, I took them off and cleaned connections all real well. Maybe it was just "barely" a ground problem?? 

FWIW, I did check the VAC across the stator and it reads about 30VDC, so that seems good. And now shows about 13.5 volts across the battery circuit when running at WOT. I guess its good to go through the exercise because now I know what to look for if it becomes problem in the future.

What a great forum. Thanks for the help! Happy INDEPENDENCE DAY to all!

MGD


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