4020 24 voltage regulator question

Ray

Well-known Member
I just had a 24 volt generator rebuilt with new fields and bought a new voltage regulator for a JD 4020. It didn't work when I installed it.I called the shop and was told that it was polarized to a negative ground system.He said I told him it was negative ground,but I didn't.
It's a positive ground system. He told me to disconnect the field wire at the regulator and ground it with the tractor running.Is that the right way to polarize it? That didn't work either.
 
A generator is normally polarized with the wires connected, and not running. Then polarized with a jumper wire. That way the gen knows which way to send the little juicies when it IS running!
 
With the engine off, use a short piece of wire and hold one end on the VR Batt terminal. Touch the other end momentarily to the VR ARM terminal. You should see a small spark and the generator will be polarized for your positive ground set up.
 
Thanks, I wasn't sure if the 24 volt was different than a 12 volt to polarize.
 

The 24V system is neither positive or negative ground. All the 24V power travels through electrical cables and not through the engine castings.
Half of the lights and accessories are +12V to chassis. The other half of the lights and accessories are 12V- to chassis.
The regulator is supposed to float electrically free from the chassis on rubber insulating donuts.
Polarizing is simplest and safest by using an insulated stick to momentary close the cut out relay contacts.
 
"Touch the other end momentarily to the VR ARM terminal."

Only trouble is, those 24 Volt regs don't have an "ARM" terminal, but rather am "A1" and an "A2" terminal.

I can never remember which to jumper to the "BATT" terminal, can you?
 
Ray, my answer is based on John Deere service literature (SB 268, see below, yes for earlier 24 volt Deeres, but true for later also as far as 24 volts is floating, NOT Pos or Neg grounded) and how John Deere 24 Volt Tractors came originally from the tractor, its NOT my opinion, blame or give credit to John Deere, not me lol.

As shown below based on John Deere Service Bulletin 268 of August 1958, the 24 volt system IS NOT POSITIVE OR NEGATIVE GROUNDED, its floating off frame ground and the two wire 24 volt Generator and Starter are electrically insulated and isolated from the frame ground I.E. NOT POS GROUND NOT NEGATIVE GROUND. In all my years as a used tractor dealer and all the reads of any official John Deere publications and having given electrical JD Seminars and Workshops and written electrical articles for certain JD magazines and how all were actually factory wired, I've only heard one individual claim it was Positive ground. However, I choose to believe John Deere engineers and designers and how they were actually built, NOT Pos Ground NOT Neg ground.

SO TAKE OR LEAVE WHAT JOHN DEERE (Not me) SAYS BELOW AND FORM YOUR OWN BELIEFS


JOHN DEERE SERVICE BULLETIN (SB) 268 August 1958

THE electrical system used on John Deere Diesel (E l e c t r i c Cranking) Tractors is a 24-volt split-load system using 24 volts for the cranking and charging circuits and 12-volt circuits for
the lighting and accessory load. Figure 41A is a schematic drawing of the system. A 24-volt generator, controlled by a 24-volt regulator, supplies current to carry the electrical load and charge the four 6-volt batteries connected in series which supply current at 24 volts for cranking the engine.

The cranking circuit and the charging circuit are two-wire circuits-the entire circuit is carried
through wires and no part of it is grounded to the tractor frame.

NOTE: The generator should be polarized, whenever the generator or voltage regulator, or the batteries are disconnected…….. This is accomplished, by momentarily connecting a jumper wire between the "BAT" terminal and "GEN" terminal on the regulator.

John T (What John Deere says, NOT me, so take up any disagreements with them lol)
 
I am not here to argue with you , but I would not recommend closing the cut-out points. As you know magnets always attract unless it is 2 magnets with like poles. So If you close the points they will tend to stay closed as the current flows through the windings to the generator. Be prepared to pry them open again if you do.
 
John Deere Service Bulletin SB 268 says to Polarize you should.....

"NOTE: The generator should be polarized, whenever the generator or voltage regulator, or the batteries are disconnected…….. This is accomplished, by momentarily connecting a jumper wire between the "BAT" terminal and "GEN" terminal on the regulator."

That's what Deere says, NOT ME lol Im ONLY the Messenger

John T
 
The regulator has three terminals on the bottom,
battery,arm and field.Also has one on top marked gen.I'll try jumping tomorrow.Thanks.
 

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