early jd 4020 24v charging system question

steve-in-ga · Nov 18, 2018

How is the best way to tell how much charge the generator is generating. I've connected my volt meter to the starter to the lugs where the two large battery cables connect and I can see the voltage increasing ever so slightly as the tractor runs. Is there a better place to check and how much voltage should I be reading?

thanks for the help

John T · Nov 18, 2018

The voltage on the batteries themselves is actually a decent way to determine how the charging system is performing. Those old 24 volt charging systems were never known to set the world on fire and charge at very high amps. The batteries connected together in series if full charged stabilized and at rest should read around 25.2 volts and at high RPM under a charge subject to the batteries Id expect voltage to rise to at least 26 volts after some time and perhaps 28+ at the most. Maybe if it aint broke don't fix it lol

John T

steve-in-ga · Nov 18, 2018

What is the proper way to polarize the generator? Ive read several ways and am not sure which is proper.

Bob · Nov 19, 2018

Correct way to polarize these DEERE 24 Volts systems is to momentarily jumper "A1" (labeled "GEN") at the voltage regulator and the regulator terminal labeled "BATT".

steve-in-ga · Nov 19, 2018

ok, I did that by using a small wire to touch those two terminals together and I got a spark. I'd like to check the voltage at the generator if possible. I found a link that said to connect the field terminal on the generator to A2 on the gen and then connect the positive lead of the volt meter to A2 and the negative lead to A1. When I do this I get 200mv of output at 1100 RPM. Is this the correct procedure? The voltage seems very low to me. What should the voltage be when connected this way?

Again, thanks for the help

Bob · Nov 19, 2018

When you jumper "A2" and "F" you are "full fielding" the generator and it should be outputting over 30 Volts measured across "A1" and "A2".

(Normal regulated battery charging voltage is 27.5 to 29.5 Volts.)

John T · Nov 19, 2018

The output of the genny is across the Armature and that's indeed A1 & A2 so a measly 200mv when you should get 26 to 28+ when coupled to a load/battery tells me the genny isn't working...?.

John T

steve-in-ga · Nov 19, 2018

Could this small output indicate that i didnt polorize the generator properly?

Sorry for all the questions. I have some time now to work on this so im trying to make the most of it.

Thanks again

John T · Nov 20, 2018

If a Genny is reverse polarized then the engine is started there could be VR damage, but if the VR is still okay and you then correctly polarize the genny it should charge. However when you full field (like Bob described) the VR is essentially out of the equation so if it still dont charge I suspect a bad genny.

John T

early jd 4020 24v charging system question

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