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Tractor Talk Discussion Forum

JD 3020 24volt light/short question

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Author  [Modern View]
bstover7@hotmail.com

01-13-2018 19:46:38




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I completed installation of a new 12 volt battery, hooked the 2 12volts in series (right battery negative to left battery positive) and established a positive ground off the left battery. Vola, the lights worked..until I started the tractor. I did some reading and polarized the generator by momentarily connecting the batt to arm/gen contacts on the regulator. No dice. Volt meter show -24volts at the regulator and starter. Is this reverse polarity normal? The gen light also has come on, with the key off, when the positive ground is attached. It goes out when I disconnect the positive ground, so I think there must be a short in the system?
Any advice, other than 12volt conversion?

Thanks again!

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bstover7@hotmail.com

01-16-2018 20:47:28




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Hey everyone. Just wanted to give a big thanks to everyone for their knowledge and wisdom, and your willingness to share it. I ended up putting a ground wire in with a 20amp fuse on the series cable. I achieved the correct voltages and got the lights working; however, I discovered that the lighting harness/switch was where the short causing the generator light to come on was located. So, successful, kind of. A new lighting harness and switch should get things working until the restoration.
The correct wiring diagram is below.
I'm sure I will have many more questions.
Thanks again!

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erskine2017

01-14-2018 14:51:28




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Dear bstover, see my lengthy post above on how to trouble shoot a drain in the positive side of the 24 Volt System.



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John T

01-14-2018 10:42:41




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Your post "Volt meter show -24volts at the regulator and starter. Is this reverse polarity normal? "

It depends on which way and where your meter was attached. The Generator and Starter are two wire 24 volt floating devices NOT subject to frame/ground, they operate strictly off 24 volts obtained by two 12 volt batteries (or four sixes) in series. If your meter leads match the series batter(ies) + and - it will show correct polarity if not it shows reversed.

So called "idiot lights" are "in effect" a lamp across a voltage regulators cutout relay so if not charging the discharging current lights the lamp, but if she's charging sufficient closing the relay the voltage is near the same on both sides so she goes off.

JOhn T

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Tx Jim

01-14-2018 10:15:58




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Bob

Thanks for correcting my mistake & now I remember the resister you referred to. I haven't had "hands on experience" with a 24 volt elect system since '87 when I left JD dealership.

Jim



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Bob

01-14-2018 09:19:16




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Quoting Removed, click Modern View to see

Jim, generator "idiot light" operates on 24 Volts, and doesn't depend upon the chassis ground at the midpoint of the series-connected 12 Volt batteries to operate.

The older ones had a resistor built into the switch to allow the use of a 12 Volt indicator lamp, the newer design had a resistor connected to one of the pigtails of the "idiot lamp".

I just dealt with this a few months ago when I installed an isolated ground 2 Volt alternator on a 24 Volt 4020.

IIRC, the resistor connected to the pigtail Ohmed out at about 53 Ohms.

If you look closely at the two diagrams posted by the O.P., you can see the resistor in both diagrams.

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JDEM

01-14-2018 06:24:39




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
One common problem on these awful systems designed by AC Delco is the starter-motor loses its isolation and provides a path to chassis-ground. Sometimes all it takes to fix is to take the starter apart and blow all the brush-dust out of it. I never understood why Deere did not use the 24 volt system like used in the 1010s instead.



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Tx Jim

01-14-2018 03:44:21




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
bstover

If small ground wire isn't completing connection from rear LH battery post to frame then gen light shouldn't be "on" as it should have no 12 volt ground without small wire making connections. If generator light is on when ign switch is off something is back feeding gen light which is probably the volt regulator at fault.

What do you imply when you state "you have no fire insurance"?? Does this 24 volt system have the circuit breaker kit(AR47675) installed(see photo below)? If CB kit isn't installed then 24 volt system is more subject to catch fire from bad wiring insulation.
third party image

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Olliejunkie

01-13-2018 21:39:24




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
I think I mis spoke. I believe I ran a cable straight from one battery to they other and then attached the fusible link to it. Now you have me second guessing wether it's right or not.



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Olliejunkie

01-13-2018 21:16:22




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Quoting Removed, click Modern View to see

I would hook the batteries up with the updated diagram. That is what I did with my 3010 to keep it from burning up. And do what Bob said.



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bstover7@hotmail.com

01-13-2018 21:30:52




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 Re: JD 3020 24volt light/short question in reply to Olliejunkie, 01-13-2018 21:16:22  
Great. Just to be sure, the updated diagram is the black/white one I posted a picture of?

Thanks!


Bruce



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Bob

01-13-2018 20:51:37




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Quoting Removed, click Modern View to see

Sounds like you MAY have blown the small jumper wire to chassis ground at the midpoint of the series-connected 12 Volt batteries.

This (oddball) to most system really isn't that tough to troubleshoot or repair if you read up on it and DON'T listen to statements like "The starter was the only thing that saw 24 volt power. ", or "If you have your batteries hooked in series they are not wired correctly." or " My understanding of the fuse is that it will protect the lights from blowing from the 24volt load in case of a short?" you'll get it fixed!

The main difference between the early and late diagrams is that the early system used the cast iron chassis as the common/crossover connection between the series-connected 12 Volt batteries, and the later system used an actual battery cable to join the two series-connected 12 Volt batteries, with a jumper wire or fused jumper wire joining the midpoint of the series-connected batteries to chassis "ground".

From the point of view of the starter, generator, and voltage regulator it's a 24 Volt system created by connection two 12 Volt batteries in series.

From the point of view of the fuel gauge and lights, half of the load is fed from what's effectively a (+) grounded 12 Volt system, and half from a (-) grounded 12 Volt system.

Pay attention here...

The large stud (highest up) on the stater solenoid should read (-) 12 Volts (nominal) with respect to the chassis.

Stud on the engine block side of the starter belly" should read (+) 12 Volts (nominal).

The "BATT" terminal on the voltage regulator (blue wire) (-) 12 Volts to chassis, and the A2 terminal (brown wire) at the generator (+) Volts.

If you want help, check the voltages at those points and post back.

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bstover7@hotmail.com

01-14-2018 09:17:52




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 Re: JD 3020 24volt light/short question in reply to Bob, 01-13-2018 20:51:37  
Bob,

I've rewired the batteries as per the black and white diagram posted. I've obtained all the correct voltages in the proper locations. The generator light is on, even with the ignition off, and the lights are not working. The generator light goes out when I disconnect the 12volt negative terminal to the starter body. I'm thinking the short is in this circuit?
I'm going to clean the starter post, just trying to figure out how to get the 3rd bolt out of the starter.

Bruce

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Bob

01-14-2018 11:21:33




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-14-2018 09:17:52  
"Bob,

I've rewired the batteries as per the black and white diagram posted. I've obtained all the correct voltages in the proper locations. The generator light is on, even with the ignition off, and the lights are not working. The generator light goes out when I disconnect the 12volt negative terminal to the starter body. I'm thinking the short is in this circuit?
I'm going to clean the starter post, just trying to figure out how to get the 3rd bolt out of the starter."

I did NOT suggest that!

BOTH circuits are electrically equivalent, and the newer diagram adds the safety of small wire, fuse, or fusible link in the connection from the midpoint of the batteries to the chassis. I would NOT have changed it back to the older, individual battery cables to chassis setup.

What I DID suggest was taking some voltage readings and posting back.

Also, please measure and post the voltages with respect to the chassis at the two circuit breakers on the removable dash panel. Measure at both sides of each breaker with the key switch and light switch "ON". (These are for the lighting circuit.) One should have (-) 12 Volts on both terminals, the other should have (+) 12 Volts on both terminals. These feed battery voltage to the B1 and B2 terminals on the light switch. (Older ones MAY be marked "Bat A" and "Bat B"?)

Also, remove and isolate the (white?) wire from the A1 terminal AT THE GENERATOR and see what effect that has on the lighting of the generator "idiot light". (I'm suspecting the generator may be internally shorted and/or the points in the "cutout" section of the VR MAY be stuck closed.

Also, FWIW, a COMMON source of problems with these tractors is poor, dirty, or burned connections in the wiring harness connectors toward the back of the hood, over the RH rear of the engine.

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JD Seller

01-13-2018 21:52:15




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 Re: JD 3020 24volt light/short question in reply to Bob, 01-13-2018 20:51:37  
Bob I am wondering if he has the two cables on the wrong terminals on the starter??? You have told him the correct way to check it.


To clarify my statement about the system not really being a true 24 volt one and that the starter is the only thing that sees the 24 volts. This system is not a common 24 volt one like you find one the majority of military vehicles. I will stand corrected in that the Alternator sees the 24 volts as well as the starter. The rest of the system just sees 12 volts. Either positive or negative ground.

Long story short. The system works fine when it is working. When it does not then if one of the two major components, starter or alternator, are bad then I would recommend switching it over to a 12 volt system.

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bstover7@hotmail.com

01-13-2018 21:29:27




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 Re: JD 3020 24volt light/short question in reply to Bob, 01-13-2018 20:51:37  
Bob,

Thank you. I will put all your suggestions to use tomorrow and let you know how it goes.

Bruce



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Olliejunkie

01-13-2018 20:06:03




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
Did you put a fusible link to the chassis on the cable that goes between the batteries?



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bstover7@hotmail.com

01-13-2018 20:24:00




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 Re: JD 3020 24volt light/short question in reply to Olliejunkie, 01-13-2018 20:06:03  
No I did not. My understanding of the fuse is that it will protect the lights from blowing from the 24volt load in case of a short? I have disconnected the 12volt system because I don't have fire insurance...although maybe I should get some and hook it back up:)



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JD Seller

01-13-2018 19:53:31




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 19:46:38  
The JD system is not a true 24 volt one. If you have your batteries hooked in series they are not wired correctly. The original wiring would have the none grounded cables going to the TWO different terminals on the starter. The starter was the only thing that saw 24 volt power.



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bstover7@hotmail.com

01-13-2018 20:21:17




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 Re: JD 3020 24volt light/short question in reply to JD Seller, 01-13-2018 19:53:31  

third party image

third party image
I have attached two possible wiring diagrams for the 24volt 3020. I had understood, although I'm quite possibly wrong, that the colored diagram was for later models and the other (which I believe is the way you are referring), was the original system?

I'm open to advice,

Thanks!!

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JD Seller

01-13-2018 20:27:09




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 Re: JD 3020 24volt light/short question in reply to bstover7@hotmail.com, 01-13-2018 20:21:17  
Yes there are early and late model wiring differences. You have it wired to the early diagram I am assuming??? So it is kind of a 24 volt system as they are just hooking the 12 volt side at the starter rather than the fusible link at the one battery.



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