Another charging system post

Dennis K (WA) · May 23, 2013

I can't believe this system is whipping me but it is.
Farmall H, 6V positive ground, cutout relay and four position light switch.
Problem is no charge at low setting and cutout points do not close in low setting.
Normal output in hi, 10-15amps warm and as high as 18amp when cold. The third brush is moved up as far as it will go, 3 bar spacing on the commutator and against a stop on the end plate.
Checked grounds with ohm meter;
batt gr to dash screw or switch .1 -.2
batt gr to gen/cutout .4 -.6
F post on gen to switch .1 -.2
This has been this way since restored a few years ago and finally decided to deal with it.
Thanks for any advise
Dennis

Bob M · May 23, 2013

Sounds like the field resistor (the resistor at the bottom of the light switch) has failed.

With the light switch in the "L" position take a resistance reading across the resistor. If the meter shows infinity, the resistor is bad. (I don't recall the precise resistance value but a good resistor should read several ohms).

You might also check the cutout ground. Your reading of .4 to .6 is high (it should be essentially 0 ohms).

Jim Becker · May 23, 2013

(quoted from post at 16:18:40 05/23/13) With the light switch in the "L" position take a resistance reading across the resistor. If the meter shows infinity, the resistor is bad. (I don't recall the precise resistance value but a good resistor should read several ohms).

If the switch is wired in and the resistor is bad, I believe this test will measure the resistance back through the generator field coil (giving a false appearance of GOOD). If you disconnect the wire from the generator F to the switch and set the switch on L, you will get a good reading from the resistor. It should be 2.8 ohms.

By the way, you should back the third brush off a little to keep the charge under about 13 amps. As I racall, IH said to go no closer than 3.2 bars from the other brush.

Janicholson · May 23, 2013

I think a 2.5 to 3 ohm wire wound with 80 watt dissapation would do as a replacement. A ballast resistor might work well. The owner could see if it will work by hooking an ignition ballast resistor to the f terminal and to ground Jim

Jim Becker · May 23, 2013

The cut-outs with a "F" terminal have a rarely used field resistor on the bottom side. All you need to do is add a jumper wire from the generator "F" to the cut-out "F". Leave all the other wiring as original.

Dennis K (WA) · May 23, 2013

Thank you guys for the quick responses. I'll check out the suggestions in the morning.
Later
Dennis

John T · May 23, 2013

I"m with the guys as far as its a failed/open Low charge Field Resistor on that LHDB switch. I think thats the flat wound one and the coiled wire one is the light dimmer resistor???

The switch itself must have a good ground if she charges so well on high charge which essentially places the Field at dead (no resistor) ground.

If you unhooked the wire on the light switch that feeds down to FLD on the genny and place an ohm meter there to frame ground, it should read near 0 ohms in High Charge and around 3 or so in Low charge. If in Low charge its an open circuit (not the 3 ohms) she cant charge in that Low position.

John T

Dennis K (WA) · May 24, 2013

Well guys I am reporting back with todays findings.
I first went with John T's suggestion checking ohms through the F wire to the switch with it disconnected. In Hi charge, as suspected '0', in Lo the meter was all over the place so then disassemble the dash and check the resistor as Bob suggested. I had a resistor connection issue and while trying to repair it I damaged the resistor. I had another switch that checked good and installed it. Readings are now 0-hi, 2.5-lo. Bob, I also rechecked readings of the gen/cutout and they are at '0'.
Jim B, I took your advise and backed off the third brush, now reading 12amps @ hi idle.
Still no obvious charge in Lo so I checked amps with my meter between the gen A and cutout gen and had 1.8-2.0 amps at hi idle. Seems low to me, thought 4-5 would be the norm.
Maybe I am chasing a ghost.
On another note,
I would like to thank you guys, Bob, Jim and Jim, and John for all your expertise and input into this forum. I and I'm sure others have learned much from you.
Keep up the good work
Dennis
sorry for the long post

Janicholson · May 24, 2013

Tractors that are idles or operated slowly at low part throttle are often set with a higher charge rate to compensate and allow some charging when operating in daylight. Resetting the brushes closer, or dropping the resistance to about 2 would do it. We get used to the sophistication of modern solid state charging systems and realize just how difficult the old days were. Jim

Dennis K (WA) · May 25, 2013

Thanks Jim for all your input.
This is just a hobby tractor that sees a few parades and an occasional plow day, so I think what it is, is what it is.
I'll just remember to give it a little extra charge from time to time.
My background is IH and Case construction eq. so the YT forums and those like yourself have been a great information source on ag equipment.
This all became a hobby after retirement. This H was the first and I now have eight tractors. It is a great hobby and keeps me busy.
Thanks to all
Dennis

Another charging system post

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