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Farmall & IHC Tractors Discussion Forum
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Farmall 140 Charging Circuit

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11-27-2012 10:06:00

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Installed new Delco alternator on '76 140. Charging voltage seems high, 15.4 Vdc at battery terminals. After extended use the battery got hot and began to smoke. No 'external' voltage regulator visible anywhere. Is regulator internal to alternator? See picture link below. Left wire on resistor was disconnected to prevent further charging until problem is found. Any suggestions on how to correct overcharging problem?

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Berth 29 opinions

11-27-2012 20:22:46

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 Re: Farmall 140 Charging Circuit in reply to BillyHooper, 11-27-2012 10:06:00  
I Have a late model 140 (with electrical issues)

With mine, it used to have 12v on one resistor terminal that fed the coil when cranking. When you released the key the resistor I think did supply the current to the coil thru the same wire.

On second thought - your alternator does not have the ground wire from that same bolt (resistor mounting bolt) that runs to a ground on the right side of the engine.... you can try runnning a jumper wire from the bolt to the ground bolt. If the alternator is coming ungrounded - it can cause the same effect you are having.

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11-27-2012 18:00:17

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 Re: Farmall 140 Charging Circuit in reply to BillyHooper, 11-27-2012 10:06:00  
How is the resistor connected into the circuit. Appears to be a resistor used in coil circuit and should have nothing to do with the alternator and is not normally mounted on or near the alternator.

By chance is the #2 wire on the edge plug on the alternator which is cut off on right edge of the picture the same wire that connects back to the right side of the resistor. Where does wire on other side of resistor go? If this side of resistor was connected back to battery source it could drop the voltage at pin 2 causing the sensing circuit in the regulator to see a supposed low battery voltage and increase the voltage output to make up for it.

If this is the case, eliminate the resistor and connect as Janicholson indicates and see if this solves the problem

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11-27-2012 11:03:10

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 Re: Farmall 140 Charging Circuit in reply to BillyHooper, 11-27-2012 10:06:00  
The internal regulator is probably the issue...I had a Focus that the battery died on...I thought it was the alternator had quite working..just the opposite. The regulator went haywire, and the unit was putting out 19 volts instead of 14.5 or so...have that unit redone and you'll probably be OK... I've got a '74 140 with a 12 volt generator that charges just fine...hope it continues... Bobin VA

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11-27-2012 11:02:20

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 Re: Farmall 140 Charging Circuit in reply to BillyHooper, 11-27-2012 10:06:00  
15.4 is a bit high, but i am a little concerned with the wire coming from terminal 2 on the edge of the alt. It should connect either to the larger Bat terminal (on the alt.) or to the battery side of the amp meter. This is a sensing terminal that is dedicated to assuring the proper charging voltage.
The battery should survive 15.4 volts for months of intermittant operation.
and it would take many hours of operation in warm conditions to make it smoke.
I suspect a bad cell in the battery. Have that tested first, then if it is fine, go for the VR. They are inexpensive and easy to install inside the Alt. Jim

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11-27-2012 10:08:56

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 Re: Farmall 140 Charging Circuit in reply to BillyHooper, 11-27-2012 10:06:00  
If everything is wired right, you may need to put a new regulator in the alt.

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