Gravely 816 putting out 40 volts! - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #1 of 8 Unread 10-17-2019, 02:19 PM Thread Starter
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Gravely 816 putting out 40 volts!

Hey guys. My $150 barn find has been absolutely awesome and hasnít given me any problems what so ever...until now. I installed some LEDís 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 20ís to as high as 40 volts!!! So Iím 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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post #2 of 8 Unread 10-17-2019, 09:06 PM
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Re: Gravely 816 putting out 40 volts!

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.


Dave

Last edited by tracktortag; 10-17-2019 at 09:20 PM.
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post #3 of 8 Unread 10-17-2019, 09:23 PM
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Re: Gravely 816 putting out 40 volts!

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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post #4 of 8 Unread 10-18-2019, 02:02 AM Thread Starter
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Re: Gravely 816 putting out 40 volts!

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Originally Posted by tracktortag View Post
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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post #5 of 8 Unread 10-18-2019, 02:07 AM Thread Starter
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Re: Gravely 816 putting out 40 volts!

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Originally Posted by franklin2 View Post
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.
Whatís odd is I havenít noticed a problem until I blew up my LEDís. The tractor always fires right up even after sitting for weeks. I would think that if the battery was seeing 40 volts it wouldnít last very long. But just yesterday I ran the tractor for about 45 minutes while Aerating the lawn. Thatís when the LEDís failed. So obviously the tractor was over charging.
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post #6 of 8 Unread 10-18-2019, 03:47 PM
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Re: Gravely 816 putting out 40 volts!

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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post #7 of 8 Unread 10-18-2019, 04:06 PM Thread Starter
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Re: Gravely 816 putting out 40 volts!

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Originally Posted by franklin2 View Post
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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post #8 of 8 Unread 10-18-2019, 08:35 PM
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Re: Gravely 816 putting out 40 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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