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Hey guys. My $150 barn find has been absolutely awesome and hasn’t given me any problems what so ever...until now. I installed some LED’s and the other day I was trying them out when all 3 flickered then died. Bad connection, right? Well today I found they were all bad. So I checked voltage at the battery and found 12.7v. When I started the tractor it was jumping around from the 20’s to as high as 40 volts!!! So I’m assuming there is a voltage regulator somewhere. Anyone know where it is and how to replace? A part number would be great if at all possible. Thanks!

This is the 816 with the Onan engine.
 

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It's tucked in the lower left rear of the engine behind the flywheel (which I believe has to be removed in order to get at it). The Onan part number is 191-0886. New Onan replacements are supposed to be pretty expensive (~$200-300). Some have replaced them with 20 amp Kohler rectifiers, and installed, and rewired them behind the dashboards.
 

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I suspect you have a bad connection between the battery and the rest of the electrical system. No alternator can raise the voltage on the battery to 40v. The alternator can raise the voltage if the battery is not there. If the charging system is overcharging the battery, you might see 18v on the battery.

Most alternators when they are thrown into wide open charge, can generate close to 100v depending on the rpm. It's the battery that brings the voltage down in check. The battery will boil and possibly blow up before it lets the voltage get very high.
 

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Discussion Starter #4
It's tucked in the lower left rear of the engine behind the flywheel (which I believe has to be removed in order to get at it). The Onan part number is 191-0886. New Onan replacements are supposed to be pretty expensive (~$200-300). Some have replaced them with 20 amp Kohler rectifiers, and installed, and rewired them behind the dashboards.
Ah man I was afraid of that.
 

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I suspect you have a bad connection between the battery and the rest of the electrical system. No alternator can raise the voltage on the battery to 40v. The alternator can raise the voltage if the battery is not there. If the charging system is overcharging the battery, you might see 18v on the battery.

Most alternators when they are thrown into wide open charge, can generate close to 100v depending on the rpm. It's the battery that brings the voltage down in check. The battery will boil and possibly blow up before it lets the voltage get very high.
What’s odd is I haven’t noticed a problem until I blew up my LED’s. The tractor always fires right up even after sitting for weeks. I would think that if the battery was seeing 40 volts it wouldn’t last very long. But just yesterday I ran the tractor for about 45 minutes while Aerating the lawn. That’s when the LED’s failed. So obviously the tractor was over charging.
 

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You can think of the battery changing the 40v output to current. When the output of the alternator goes up, the current flowing to the battery or whatever load it has goes up, but the battery will always keep the voltage in check, unless the battery is not in the circuit like it's supposed to be.
 

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Discussion Starter #7
You can think of the battery changing the 40v output to current. When the output of the alternator goes up, the current flowing to the battery or whatever load it has goes up, but the battery will always keep the voltage in check, unless the battery is not in the circuit like it's supposed to be.
Ok to be clear this is not normal for these tractors, correct? Should charge at about 14 volts?
 

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Ok to be clear this is not normal for these tractors, correct? Should charge at about 14 volts?
Something in the neighborhood yes. Probably more in the 13v area but 14 is in the ballpark. I don't have a wiring diagram for your tractor, but something is definitely amiss somewhere.
 

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Discussion Starter #10
Found 3 wires coming from what I think is the stator. Two are part of a plug. Where does this 3rd wire go?
 

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Thanks for that. Looks about right. I’m really having a hard time understanding how I’m getting unregulated voltage. It’s as if I don’t have a regulator. And that diagram doesn’t show one.
Anyone know how many wires come off the stator and where they go?
 

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On the later Briggs motors they had two wires, one was a straight A/C that they ran directly to power headlights, and then other was the charge wire. It usually had a diode inline and then went directly to the battery with no regulator. The diode rectified the voltage a little bit and kept the battery from discharging back into the stator windings. I don't see a diode in the diagram link I posted. And in that Briggs style charging system, the only thing that kept the voltage down to a reasonable level was the battery itself.
 

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Check out me fixing my 817 over the summer. The ignition feed back can do weird things! Also show an onan regulator at about 6:10 I get into that. 90% of the time the regulator is bad and its behind the flywheel mounted to the oil pan. Very common fix is to take it out and add a kohler regulator with longer wires to reach else where.

At 16:14 im looking at the factory regulator and its 4 wires
 

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The stator puts out a/c voltage, and around 40 volts a/c isn't out of the question. The regulator knocks it down to 12-16 volts dc current.
 
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