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Farmall C charging system will not work

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Greg 2010

06-12-2008 20:02:06

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I have a !951 Farmall C that I can't get the charging system to work on. I have had the generator rebuilt and put it back on. I worked for a week trying to get the system to work. I finally gave up tooke the generator and the regulator to a shop that could check both. I did have a problem with the generator and the voltage regulator was bad so I bought a new one. I came back put on the generator and new regulator and polarized the system (Positive ground) started the tractor and expected to see the anmeter charging which is also new and allit shows it is discharging when I turn on the lights it discharges more. I called the shop where I had the generator reworked to ask if there was any possiblity that they didn't get something fixed and the gentleman assured me everything worked.
Does anyone have any ideas I am really frustrated right now. I got my wiring diagram from Melvilles wiring diagrams. I know I probably have something not wired right. When I turn on the switch the anmeter shows discharge but it will not show its charging. Any help would be appreciated.

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El Toro

06-13-2008 09:24:56

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
Take a volt meter and check the charging voltage at the battery with the engine at 3/4 throttle. Should get around 7.2 volts on a 6 volt system. Hal

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06-13-2008 07:55:10

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
I ran into the same problem with my Super A. Had the gen rebuilt and still no charging. Checked all the wiring per the procedure above...still not charging.

My thought was when the gen repair shop tests the gen they probably spin it faster than the 1500 max RPM the engine turns. So I took off the inspection cover and moved the third brush about 3/4 inch in the CCW direction (when viewing from rear). Started up and it charges! On my unit, there is a single screw on the back of the gen that when loosened, you can slide the third brush to a new position on the commutator.

Feel free to send me an email if you want more detail.

Good luck.

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John T

06-13-2008 04:26:39

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
This may be wayyyyyyy more then you want or need but heres my Troubleshooting Procedure so you can go throught the process systematically to see where the problem is. Para 5 tells how to determine if non charging is a Genny or a Voltage Regulator problem (like Jims post) and the Para 8 Motor Test can help deterine if the Genny itself is okay.

Since all is so new and rebuilt Id suspect a grounding or a wiring problem which the first few paragraphs address especially ammeter and VR wiring cuz even if the genny and VR are fine (what the shop says) it cant charge the battery via the ammeter if miswired.

You might place a voltmeter on the battery and measure its voltage setting (6.3 volts on 6 volt 12.6 on a 12) and then when running at fast RPM it should rise (6.5 to 7 or 13 to 14) and if so its indeed chargign but the wiring or ammter wiring isnt correct


ARE YOU SURE THE AMMETER IS WIRED CORRECT AND WORKS????? If you turn the lights or ignition on (if coil ignition not a mag) when sheís not running, the ammeter should swing over to the - discharge direction, does yours??? Are BOTH the ammeter terminals reading hot battery voltage?? They MUST !!!!!!! Thereís but one wire on the ammeters Supply (from battery/starter) terminal while its other Load terminal wires to the BAT terminal on a Cutout relay or VR PLUS wires to feed loads like lights or ignition, unless where a 4 terminal VR is used where lights n ignition are fed from the LOAD terminal on the VR.

To Polarize the Generator, first temporarily dead ground the Gens Field post to case/frame, then momentarily flash jump a wire from the Cutout Relay or VR's "BAT" terminal over to its GEN (or ARM) terminal and you ought to get a small spark. Same things accomplished by momentarily flash jumping a hot wire (BAT terminal on Cutout Relay or VR or starter post etc) direct to the Gens ARM post to get the spark.


1) For a good working Gen to get to and charge the battery, it has to have a path usually from the Gens ARM post,,,,,,,,,,to and through the Cutout Relay (between its GEN and BAT terminals, regardless if on a VR or Relay),,,,,,,,,up to the Load (NOT to battery) side of the Ammeter,,,,,,,,,to and through the Ammeter,,,,,,,,,,from BAT side of Ammeter to ungrounded battery terminal, often via the starter lug post. Is yours wired that way or equivalent ??? The ammeter should read hot battery voltage on BOTH terminals, does yours??? Even if an ammeter were stuck (but still continuous) as RPM increases the battery voltage should rise from 12.6 to near 14 volts and/or the lights glow brighter (half that on 6 volt systems). Have you tried that in case the ammeter isnít working right?????

2) If the above is so, the BAT terminal on the VR or Cutout Relay MUST ALWAYS READ HOT BATTERY VOLTAGE. Does yours??? If not, the Gen cant get to and charge the battery.

3) The Gen to VR (if it has one) wiring is as follows:

BAT on VR to ammeters load (NOT battery) side

ARM (or GEN) on VR to Gens Armature post.

FLD on VR to Gens Field post.

(L) Load (if you have a 4 wire VR) up to BAT supply input terminal on switch to feed loads like lights and ignition.

WIRING ON CUTOUT RELAYS: They wire BAT side to ammeters Load terminal,,,,,,GEN side to gens Armature post. On cutout relay systems, the Gens Field post is wired to the light switch where it gets a dead ground for high charge or a resistive ground for low charge. Therefore, there must be a good connection from the Gens Field post up to the switch PLUS the switch is good and itís well grounded !!!!!!!!

4. THE GEN AND VR OR CUTOUT RELAY MUST BE WELL GROUNDED AND THE BELT GOOD N TIGHT. If any doubt, run a ground wire from the grounded battery post or clean solid frame member direct to the Gen and see what happens????????????????????????????

NOW, if the Gen and VR are grounded,,,,,all is wired correct,,,,,,,,BAT terminal on VR or Cutout Relay is HOT,,,,,,,,Belt is tight,,,,,,,,,Ammeter is good n continuous n works but she wont charge, have you had the batteries tested lately????? Is there electrolyte above all the plates and no cells have a gray or milky appearance?????? A bad battery may not accept a charge you know!!!!!!!! If the battery checks okay, proceed below to see if its a Gen or VR problem (AFTER you have insured the wiring per the above)


5. a) VOLTAGE REGULATOR SYSTEM: With the tractor running, temporarily ground the Gens Field post to case. If she charges then but NOT otherwise, the VR may be bad, or a wires missing from VR's Field post to the Field terminal on the VR, or the VR isnít well grounded.

b) IF ITíS A CUTOUT RELAY SYSTEM and she charges only if you dead ground the Field but NOT otherwise, its either a bad switch or the switch isnít well grounded or else the wires bad or open from the Gens Field post up to the switch. INSURE THAT GOOD SWITCH GROUND AND WIRING

6. If she still donít charge, leave the Field grounded and jump a wire across from the VR or Cutout Relays BAT terminal over to its GEN terminal (jump by passes the cutout relay) and see if she charges. If then but not otherwise, a VR's cutout relay isnít working correct (maybe points burned/carboned) or a Cutout Relays NOT working or not wired correct.

7. With the 2 steps above, you have basically by passed the VR or Cutout relays functions, so if she still donít charge, you're left with a bad battery or wiring or the Gen itself.

8. MOTOR TEST. You can Motor test the Gen. If its grounded and you remove the belt and apply hot battery voltage direct to its ARM Post and have the Field Post dead grounded to frame, it should motor n run well (Armature n Brushes and Commutator likely okay). Then, if you next remove the Fields ground and it speeds up some, the Fields probably good. If it passes both those tests, it should charge, and if not, it may be a wiring or battery or grounding problem. The hot battery voltage may be taken off the VR's BAT terminal or the starter post or the battery itself for this test.

9. Typical Gen problems may be the brushes are worn down or the hold down spring assemblies are stuck/corroded/dirty and arent pushing the brushes tight down against the commutator. Check those things out. Worse may be bad fields or armature etc. Air and WD 40 etc can clean and free them, the hold downs must be free n snap and hold the brushes DOWN TIGHT and they cant be worn down too low.

SUMMARY: Check the wiring,,,,,the grounds,,,,,,insure BAT on VR or Relay is hot,,,,,,,check battery (maybe load tested and Specific Gravity checked),,,,,,,,,good tight belt,,,,,,,insure ammeter is continuous (BOTH sides HOT),,,,,,see if battery voltage rises above 12.6 (half that for 6 volt system) and/or light glow brighter,,,,,,,,,do the Field and cutout relay VR by pass checks,,,,,,,,insure the Gens brushes arent worn down and the hold down springs are free n clean and push the brushes down tight,,,,,,,,,,,check the connections,,,,,,,,,try the Gen Motor Test to see if its good.

You may just have a bad battery or bad ground or connection if the Gen and VR or relay are okay. Good Luck n God Bless, let us all know.

John T Nordhoff in Indiana, retired electrical engineer who usually lurks over on the Mother Deere pages instead of over here on the "dark side" lol

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06-12-2008 22:15:09

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
Step 1
With it running at about 1/2 throttle, Use a jumper and ground the field terminal on the generator. Don,t disconnect abything, just do that. If it charges then, try grounding the regulator frame to the tractor frame. the ground must be good.
If still no go, (with tractor off), Jump (for one second) between the Bat terminal on the VR, and the Gen term on the VR. This polarizes the gen field poles. There should be a substantial spark when doing this.
Now try it.
If no spark, the generator may be improperly grounded to the engine. This ground is also very important.
If still no spark, the wire from the Amp meter may not be connected to the amp meter.
Keep us informed, JimN

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06-12-2008 21:06:05

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
Clean, shiny, and bright is the rule for ALL your connections. If you've replaced the regulator, I'd expect you cleaned up everything on the front end. And it's a pain in the neck to get into the back of the box to clean up the studs and connectors on your ammeter, but you need to get in there, too. And don't forget the connections on your starter (from the ammeter and the hot side of your battery).

ALL important is your ground. Your symptoms are very much like what I had going on my SuperC (also a '51). I don't know where the battery box is on the C, but if it's right in front of the steering post like it is on the SuperC, you will find that your ground cable is VERY short, so there's a lot of tension on it. It doesn't take well to a lot of removing and putting back over time. In my case, the female threads for the ground had wallowed out, and I had to drill and tap the hole out for a larger thread, and get a new bolt. Not sure without dragging out the books, but I think I took it up from 3/8" to 7/16"NF, and it's been fine since.

But that may be extreme. I'd recommend you clean up all your connections, including the ground, as a first step. If that doesn't fix the problem and, if the thread on your ground is set up like mine and at all squirrely (like the thread rolls over when you tighten it down), only then would I look at the thread on your ground.


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i love tractor

06-12-2008 20:36:45

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 Re: Farmall C charging system will not work in reply to Greg 2010, 06-12-2008 20:02:06  
if you have any choroded wires it can change everyhting around maybe check that

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