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Farmall & IHC Tractors Discussion Forum
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H Overcharging

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MarkOhio

09-20-2007 23:53:01




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My '49 H still has the 4 position light switch and 3 brush generator with the cut out relay. It charges just fine, actually too good. With the switch in the H (High charge position) it puts out about 10-11 amps which is just fine. However with the switch in the L (Low charge position) it still charges at the same rate. The switch is good as is the field resistor. With the switch in the H position I measure 0 ohms from the field wire to ground. With the switch in the L position I measure about 4 ohms to ground which I think is about correct, The field wire from the light switch to the generator field isn't shorted anywhere. Also with the lights on either in the dim or bright position the generator is putting out full charge as it should. Also, all grounds are good, light switch to box, box to steering post, steering post to frame, etc. so I feel that all wiring, resistor, and the light switch are in good condition. Could the field windings inside the generator be at fault and grounded to the generator frame? Would the generator still work as it does if that were the case? What I'm doing now is simply turning the lights on to reduce the amperage going into the battery when I feel that the battery is sufficently charged. So far no problems running it this way, the battery is going on 7 years now and still in good shape. I realise that this is a minor problem but would like to get it working as intended. If necessary I'll have the generator rebuilt. I'd rather keep the tractor original with just the cut out relay rather than convert it to a voltage regulator just to let my nephew and granddaughters know how it was done in the "old days". Oh yeah, even though it's a '49 model it still has the origional magneto and I'll keep it that way. The tractor was purchased new by my grandfather 3 months before I was born. Thanks in advance for your help.

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gene bender

09-21-2007 10:55:59




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
Check to see if your generator has the third brush that adjusts the out-put. Simple way is just loosen the belt that way the gen dont run so fast. No need to buy a reg as the cut-outs worked just fine if the rest of the system is in shape.



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Bob M

09-21-2007 09:24:42




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 Re: H Overcharging in reply to Fromjb2, 09-20-2007 23:53:01  

John T said: (quoted from post at 10:38:06 09/21/07) Come to think of it if she always charges at max rate and theres NOT an external wiring short to the light switch, a short where the Field post passes through the gennys case IS A PRIME SUSPECT..... .
John T


A prime suspect indeed John T!
All it takes is a bit too much torque on the generator's field terminal nut to fracture the brittle, 60+ year old post insulator underneath and cause the terminal stud to short to the case. (Don't ask how I know this...!)

Bob M

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Pat-CT

09-21-2007 07:39:02




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
i completly got rid of my field resistor i let it charge all the way and the voltage regulator should kick it off when its full but then i also have my lights hooked up wrong where D is the headlights and B is the headlights and rear lights but i like it that whay i say leave it as it is if it works good for you. if it aint broke dont fix it just keep the lights on



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John T

09-21-2007 07:38:06




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
Whether or not it can still charge with an internal Field ground short depends on where the short is located. One suspect (unless its a winding to pole piece short) is where the 2 field windings splice and another chance where the last winding goes to the Fld post. Based on what you say UNLESS theres a short in the wire from the gennys Field to the Light switch (Bobs suggested unhook the wire test will quickly show that) it must be shorted somewhere electrically near the connection to the gennys Fld post.

If its a three brush genny one can relocate the third brush for a lesser rate charge also.

If you remove all the gennys external wiring connections an ohm meter might tell something. With one lead to case/frame and probe the other, Id expect very low ohms on the Arm post (if brushes n arm all okay) and maybe around 1.5 to 3 ohms on the Field post. If the Field shows around 0 Id look for an internal short close to where the field winding wires to the Field post and/or suspect a short in the pass thru stud insulator right at the Fld post. Come to think of it if she always charges at max rate and theres NOT an external wiring short to the light switch, a short where the Field post passes through the gennys case IS A PRIME SUSPECT..... .

John T

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teddy52food

09-21-2007 06:15:26




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
If your battery is 7 years old, I would continue using the tractor with the generator as is. It takes a lot to get them charged back up after starting.



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Owen Aaland

09-21-2007 00:17:45




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
A field winding shorted to ground at the F terminal of the generator will act the same as if the light switch is in the high charge position.

Remove the band covering the brushes. Two of the brushed are 180 degrees apart from each other. These are the brushes that carry the charging current. The third brush (may be adjustable but later ones were not) is attached to one end of the field coils. The F teminal is the other end. With the third brush held away from the armature there should be no continuity to ground at the F terminal.

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MarkOhio

09-21-2007 00:02:05




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 Re: H Overcharging in reply to MarkOhio, 09-20-2007 23:53:01  
I should have added that the tractor is still 6 volt positive ground and I intend to keep it that way since it's never failed to start even at below 0 temps.



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Bob M

09-21-2007 04:21:18




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 Re: H Overcharging in reply to MarkOhio, 09-21-2007 00:02:05  
Mark - As Owen mentions an internal short in the generator field winding will cause overcharging. So also will a short to ground in the wire running from the generator F terminal to the light switch, or a short in the light switch.

Suggest disconnecting the wire from the genny F terminal then running the engine. If it still charges hard the problem's internal to the generator. However if the ammeter shows no charge with the field wire disconnected it means there's a problem with the wiring or the light switch.

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