Help with JD M 6v generator.

JD51M

New User
Hello, new to the forum. I recently bought a John Deere model M. Re-did the wiring and came to the conclusion that it was not charging. I pulled the generator out and did a bench test. Tractor is an positive ground. I hooked up the positive side of the battery to the generator body as well as the field post, I then connected the negative side of the battery to the A terminal. The motor did not spin. I pulled off the connector the the A terminal and it spun. What does that mean? The Field post works and the A post doesnt work. The brushes are good, and the continuing from the post to the brushes are good.
 
You should apply hot ungrounded battery voltage to the gennys ARM post and "ground" to the gennys case/frame NOTTTTTTTT the FLD post
!!!!!!!!!!!!!!!!!!

If the gennys mounting is solid absent paint etc its case frame provides the "ground" so hot UNgrounded battery voltage to the ARM post
with belt removed should make it spin, see below. For POS ground the case/frame is to the batteries POS (even though called "ground") and
the battery NEG provides the hot UNgrounded voltage source

NOTE to be safe you should first Polarize the genny by using a jumper wire to momentarily flash jump from BAT over to GEN/ARM on a cutout
relay or a voltage regulator and you should get a small spark

NOTE on manual Low High light switch charge control system with a Cutout Relay (NOT a full fledged Voltage regulator) if theres no charge
it may be the Low High light switch has a poor ground. Theres a wire from the Gennys FLD post up to the switch where it gets its ground. if
that wires missing or the switch isnt grounded well NO CHARGE even if the genny itself is okay

NOTE BOTH the genny and cutout relay plus the Low High switch alllllll need good grounds...


FYI heres how to Motor Test a Generator:

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 case/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.

FULL FIELD TEST: TO DETERMINE IF ITS A GEN OR VR OR CUTOUT RELAY PROBLEM Your M has a Cutout Relay, see below for test

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 isn’t well grounded.

b) IF IT’S 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
isn’t 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 don’t 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 isn’t 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 don’t charge, you're left with a
bad battery or wiring or the Gen itself.

NOTE if its charging at fast RPM running a 6 volt battery voltage should rise from say 6.3 (full charged) to at least 6.5 up to near 7
volts. If battery voltage never rises nor an ammeter read + charging amps, either the Genny or Relay or Low High switch isn't working or
not well grounded

See my Troubleshooting Procedure linked below for more info

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825

John T
John Ts Troubleshooting
 
Thanks for the reply. I took a video of what I have going on. I figure it would help visualize what Im doing. Im still trying to understand how to test it. Im not too savvy when it comes to generators or how to rebuild it so bare with me. Thank you.

Well, I tried to submit a video but it wont let me. If anyone wants to look at it its on the tube as "john deere m generator help" posted by Rod G. Thanks again.
 

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