JD 4020 24v Questions

I have a 4020 with the 24v battery system and I have several questions.. just trying to understand a little better, and the do's and don'ts (charging specifically).

The left (drivers side) battery is + --> right -, and - to the starter. Right battery has its positive going to the starter.

1) It's my understanding that if I have a 12v charger, I can just hook it up to the battery, as I would any battery. + to +, - to -. No need to disconnect the cables at all. Is that correct?

2) The tractor started fine after sitting in the cold shed all winter, but I put a trickle charger on the left battery the night before last and let it charge all night, and when I went to start it yesterday, it wouldn't turn over at all.

3) Jumping.. When the tractor was dead, I hooked a charger up to the right battery (figuring the left battery was full from the trickle charger all night) and it didn't help. As soon as I hooked it up to the left battery, it started right up.

4) The tractor ran it for probably 3-4 hours yesterday, and cranking over today was still very weak.. is that normal?

Plus on a battery is always plus and
negative is always negative. You can charge
one at a time as long as you keep the
polarity right.

I have a 4020 and fought the 24 volt problem for years. I had the old generator replaced with an alternator when I had the tractor in the shop for some other
issues, but still had some intermittent starting problems. Turns out that when I had an alternator installed, it was not wired up properly, but I didn't know
that until I switched it over to 12 volt. But in 24 volt configuration, the batteries must be in balance according to what I've read on this forum over the
years (you will find a lot of old posts about the 24 volt problem). I have no idea how you balance electricity, but I got tired of having a tractor that would
not start reliably. My problem was that the tractor would only start about half the time. Batteries would act like they were dead. When it didn't start, I
would put the battery charger on one side and wait a few minutes. And I never disconnected the cables when I did that. At that point, if it did not start, I
would switch the charger to the other side, give it a few minutes, and then it would start. It was always random as to which side would work. And even though
it acted like the batteries were dead, a few minutes charge and it would fire right up as though the batteries were fully charged. I usually only had to use the
charger for a few minutes. And once I got it started, I didn't shut it down, because the problem was the same whether the tractor was shut off for a minute or a
week. And the batteries would only last about a year or so before they were shot.
I got a complete new wiring harness from Agri-Services (you will see many good reviews on here about them), new 12v starter and alternator. They made a custom
harness, all wires were marked, and the instructions were clear. Now it fires up on the first crank, and I've not had to replace the batteries since doing the
conversion.

i must been lucky ,my 4010 on 24 volts never gave me trouble.
neighbor had trouble all the ti,e with his 4020 on 24 volts. but id
look and 1 terminal on 1 battery not real clean or 1 battery go bad
replace 1. never had luck putting 1 battery new in a set . guess i
was lucky

My 4020 had been switched to 12 volts before I purchased it. The two 12 volt batteries were connected in parallel. A connection would get bad and the charging system would not completely charge to the correct voltage. After a while one battery failed.

My repair was to make a battery box to hold one group 31 with stud post connections. End of problems.

One idiosyncrasy of JD 24 volt system is if one battery voltage is lower than other battery then generator can only charge both batteries up to highest voltage level of lowest voltage battery.

I think I stated this correctly but if not some member please correct me.

If jumping off 24 volt system with 2 12 volt vehicles never let vehicle body(frame) parts touch the tractor.

I never saw a 24 volt deere that didn't get turned back to 12 volt to solve the problem. I worked for a guy had 2 4020's both 24 volt. I would get the M out if it would do the job to save fooling around with the 4020 nightmare of starting.

JD 24 volt electrical systems served their purpose 55-60+ yrs ago. But with the advent of more powerful 12 volt starters I'd change a JD 24 volt system to 12 volts the very 1st time the 24 volt system even had a ""hiccup""!!!!!

And I'd venture to guess I understand JD 24 volt electrical system much better than the average tractor owner.

I've seen where a build up of copper dust particles in the starter can discharge only one of the batteries.
YES you can charge each 12 volt battery one at a time with a 12 volt charger JUST BE SURE POLARITY FROM
CHARGER TO BATTERY IS CORECT + TO + AND - TO -.....

John T

Thanks for the info guys.

The batteries are not real old, I think 2-3 years.

I'd love to convert it to 12v, but its actually not my tractor and only gets used for food plots and some random brush mowing, but probably 20 or so hours a year, so hardly worth the expense unless actually needing to replace something.

Can anyone answer question #2? Why when I put a trickle charger on it, does it basically kill it? Do I need to trickle charge both batteries at the same time?

You should be able to trickle or regular charge each battery individually IF you attach charger cables polarity correctly + to + & - to -

(quoted from post at 06:04:54 04/10/23) Thanks for the info guys.

The batteries are not real old, I think 2-3 years.

I'd love to convert it to 12v, but its actually not my tractor and only gets used for food plots and some random brush mowing, but probably 20 or so hours a year, so hardly worth the expense unless actually needing to replace something.

Can anyone answer question #2? Why when I put a trickle charger on it, does it basically kill it? Do I need to trickle charge both batteries at the same time?

Click to expand...

Firs0t thing to do is to install a battery disconnect. This will solve your issue andbe safer. Batteries will last longer if disconnected.

You need to cut the power cable between both batteries,plus thesmall grounding wire. You can get a battery disconnect wity an alternator shutfown for that purpose.

Tx Jim, I think (emphasis on think!) the charge goes up to the level of the highest voltage battery. The 730 diesel I maintain for a friend still has four 6 volt batteries and works correctly. The generator puts out about 27 volts across the four batteries. All batteries were new about 3 years ago and all from the same store and same brand which probably helps to keep things healthy. This is just a parade and show tractor so it sits in the shed most of the time.

(quoted from post at 06:04:54 04/10/23) Can anyone answer question #2? Why when I put a trickle charger on it, does it basically kill it? Do I need to trickle charge both batteries at the same time?

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You are drawing a cause and effect conclusion where there isn't necessarily one. The simple act of starting the engine may have done a battery in.

Have you done any troubleshooting to see if either, both, or neither of the batteries are dead? If neither battery is dead, then you've got a simple connection problem somewhere. That MAY be indirectly related to the trickle charge in that you disturbed connections when you connected the trickle charger.

Firs0t thing to do is to install a battery disconnect. This will solve your issue andbe safer. Batteries will last longer if disconnected.

You need to cut the power cable between both batteries,plus thesmall grounding wire. You can get a battery disconnect wity an alternator shutfown for that purpose.

Click to expand...

I've done this on a number of the 24 Volt systems with great success.

May be a stupid question, but where is the small ground wire? I don't remember seeing one anywhere. Is it on the starter, or somewhere on one of the batteries?

(quoted from post at 09:36:10 04/10/23) May be a stupid question, but where is the small ground wire? I don't remember seeing one anywhere. Is it on the starter, or somewhere on one of the batteries?

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Should be from the (+) battery terminal on the LH battery to the chassis.

Either a length of fusible link wire or a fuseholder with a 20 Amp slo-blo fuse.



Don't confuse it with the accessory power lead from the (-) post.

Near me is a Navistar OTR truck dealership. I
have been using their 31 size, 3/8 stud batteries
for, many years in all my tractors with a battery
box large enough to accommodate their size.

The icing on the cake is their price.....still
around a hundred bucks in today's market.

Should be from the (+) battery terminal on the LH battery to the chassis.

Either a length of fusible link wire or a fuseholder with a 20 Amp slo-blo fuse.

Click to expand...

Just looked when I was home and didn't see anything connected to the + terminal except a wire I have attached there for my planter marker control box. I'll look again this evening now that I know for sure what to look for.. and I'll take the floor plate and see if there is anything under there?