Help with starter-JD 70 diesel with 24 volt start -PICTURES

[andy r]

Just began work on a John Deere 70 diesel that has been converted to 24 volt electric start. The tractor's big engine runs great, but has recently been started with a belt. Electric start wise everything is there and the conversion was done properly. I do not necessarily care for the electric start and will eventually look into making it pony start again in the future, but want to make sure the tractor is worthy of restoration first. Picture #1 is the manufactures tag on the starter. Picture #2 is from the flywheel side. Picture #3 is from the pulley side. Here are some questions I have:

1) I see there are two heavy insulated battery cables running from the starter to the battery box. One battery cable goes to the solenoid and one goes to the end of the starter. Does the positive go to the solenoid and the negative go to the end of the starter? Is that correct? How was it intended for the conversion to be hooked up? Two 12 volt batteries must be connected in series in the battery box - negative on the first battery to the positive on the second battery or vice versa? There were no batteries remaining in the battery box and no "jumper cable" for between the batteries when I bought it. So, just trying to wire it up correctly.

2) The battery box must not do any grounding? There are still a couple of short ground cables bolted to the box, but these may have been for the 6 volt starter when it was still pony start and were just not removed? Why didn't JD use the tractor body for the ground? Is the starter sort of isolated?

3) Is this starter used in other known applications?

4) Any other advice on the 24 volt conversion will be helpful. I know it isn't as powerful as the gas pony engine. I know batteries will have a hard time starting a 70 diesel when it is cold.

Thanks for the help.

 

[Bob]

DEERE 24 Volt systems of that era left the factory with the (-) 12 Volt battery cable going to the starter solenoid and the (+) 12 Volt battery cable going to the brush end of the starter.

The midpoint of the 4 (or now 2) batteries is connected to the chassis, giving a (+) ground 12 Volt source and a (-) ground 12 Volt system for light and accessories.

For the system to work properly, any lighting or other loads need to be split as evenly as possible between the two sources.

I would GUESS the reason DEERE went with this system is that it allowed a standard 12 Volt fuel gauge and common 12 Volt lamps to be used.

Also, if you accidentally short between any connections in the system to the chassis you just get a 12 Volt spark, a LOT less nasty than a spark from a system grounded at one end of the series-connected batteries, which makes a MUCH more nasty 24 Volt arc.

Although this is common practice on lots of newer 24 Volt industrial stuff.

Will it have a charging system? Generator or alternator?

Post back with any questions about making that work, if you'd like.

 

[55 50 Ron]

Never seen a 70 converted to 24 volts, but I have converted one to 12 volts. What exists for lights? 12 V or 24 V? Can you post pictures of battery box and light switch and lights? Also post the generator and VR pictures for additional help.

 

[karl f]

I think the lighting switch also
is special for this to work. It
is two switches with one knob to
allow left and right 12v systems
to coexist--one is called B+ and
the other B-, opposite polarity
but not the way we think of it
conventionally. Lots of potential
for smoke if you are careless or
arrogant when working near the
wiring. Also think the charging
system was 12v, not sure. I had a
link saved years ago on a
computer when I fulfilled my
curiosity about these systems...

Be careful and check the
schematics twice!

Karl f

 

[andy r]

Thanks for the reply. So, those two grounding straps in the battery box were used to complete the circuit - one goes to each battery. I thought they just were left over
from the pony 6 volt battery when one strap went bad and they put another new grounding strap in without taking the old one out. So, if I read your reply correctly, the
negative terminal from one battery goes to the starter solenoid and the battery's positive terminal gets grounded to the frame. On the other 12 volt battery the positive
terminal goes to the brush end terminal on the starter and this battery's negative terminal gets grounded to the frame. I am assuming later electric start tractors like
the JD 730 were not necessarily wired this exact way. I have a 730 and the batteries are hooked together in series in the battery box. Is this better? I assume I would
have to do some major rewiring on my new purchased 70 if I were to put the batteries in series. With the two grounding straps attached to the battery box you would
assume that each battery has a terminal grounded to the frame??? Thanks.

 

[Bob]

(quoted from post at 21:03:14 02/23/20) I think the lighting switch also
is special for this to work. It
is two switches with one knob to
allow left and right 12v systems
to coexist--one is called B+ and
the other B-, opposite polarity
but not the way we think of it
conventionally. Lots of potential
for smoke if you are careless or
arrogant when working near the
wiring. Also think the charging
system was 12v, not sure. I had a
link saved years ago on a
computer when I fulfilled my
curiosity about these systems...

Be careful and check the
schematics twice!

Karl f

Karl F, the factory charging systems on the @4 Volt DEEREs of that era were 24 Volt.

 

[Bob]

Andy, I would connect the two batteries with a cable made for the purpose, and eliminate the two cables to the battery box.

If you are going to have lights and/or a working fuel gauge, you then run a 16 GA fusible link wire from that cable between the batteries to the chassis, or a wire with a fushholder with a 20 Amp slo-blo fuse.

This provides protection from certain short circuits starting a fire.

 

[andy r]

Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?

 

[Bob]

(quoted from post at 21:37:56 02/23/20) Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?

They did just that with the 730ES.

The two cables yours has are just the P.O.'s idea of how things should be done.

Note the "ground wire" from the cable between the two rear batteries to the battery box/chassis ground.

 

[andy r]

Thank you Bob. I think I will drop a couple batteries in the tractor, connect the two batteries, and add the wire to ground and see what happens.

 

[TR3driver]

I know folks don't like it, because it's different than what they're used to; but the "split" 24 volt system does make some sense. The big advantage is that the lights, ignition and so on can be 12 volts, rather than 24, and without having a complicated solenoid to switch battery configurations.

It's actually a lot like 120v house wiring, where there are two legs and either leg to ground (neutral) gives 120 volts. But going between the two legs gives 240 volts, for high power items like cooking stoves and water heaters.

It's my understanding that Deere continued using that system for some time, even on "New Generation" diesels. Eg,

 

[TR3driver]

Here's a bigger copy of that diagram.

 

[Tx Jim]

(quoted from post at 21:03:14 02/23/20) I think the lighting switch also
is special for this to work. It
is two switches with one knob to
allow left and right 12v systems
to coexist--one is called B+ and
the other B-, opposite polarity
but not the way we think of it
conventionally. Lots of potential
for smoke if you are careless or
arrogant when working near the
wiring.
Karl f

I think a more correct definition of a JD 24 volt light switch would be one switch with 2 circuits(+ & -) not 2 switches. Yes I agree the 24 volt system is prone to ""creating smoke""

 

[Blksmok]

Andy...."other advise", you must make sure all electrical connections are clean and very tight. 24 volts will melt the battery posts in a few seconds if the cables are not tight. Wires must be of the proper gauge, etc. I have a couple of 70 diesels that were converted to 24 volt systems and frankly they scare me. Can make a lot of sparks and smoke quickly if something is not right. Big difference between the original 6 volt system and a 24 volt set up.

 

[Bob]

.

"I have a couple of 70 diesels that were converted to 24 volt systems and frankly they scare me."

NOT a bad thing to be a bit scared of them or at least RESPECT them!

 

[Blksmok]

Bob....one of the reasons they scare me is that I have a pacemaker/defibrilator and the doctor told me to be careful around DC power sources. Welders, generators, alternators, batteries, etc. can cause the devise to malfunction.

 

[rrlund]

"Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?"

I don't know that the little ground wire had anything to do with the starter,but I do know from experience that the lights won't work without it hooked up.

 

[Tx Jim]

(quoted from post at 10:49:40 02/24/20) "Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?"

I don't know that the little ground wire had anything to do with the starter,but I do know from experience that the lights won't work without it hooked up.

JD did install from factory a battery cable between both 12 volt batteries on 4020's starting at SN 091,000 & on 3020's at SN 068,000. 24 volt starter & it's elect circuit was designed to be insulated/isolated from tractor frame IE small ground wire should have no relation to correct starter operation.

 

[Bob]

(quoted from post at 11:03:23 02/24/20)

(quoted from post at 10:49:40 02/24/20) "Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?"

I don't know that the little ground wire had anything to do with the starter,but I do know from experience that the lights won't work without it hooked up.

JD did install from factory a battery cable between both 12 volt batteries on 4020's starting at SN 091,000 & on 3020's at SN 068,000. 24 volt starter & it's elect circuit was designed to be insulated/isolated from tractor frame IE small ground wire should have no relation to correct starter operation.

Isn't it strange that DEERE used heavy jumpers between the batteries in the 2-cylinder era, with a small wire to chassis ground, then went to the two individual ground cables on the 4010, etc, and then a ways into the 20 series went back to the heavy jumper with the small chassis ground wire?

 

[Bob]

(quoted from post at 10:49:40 02/24/20) "Why didn't Deere just connect the two batteries together with a good big jumper cable since that is what the two ground straps do anyway - plus add a small wire to the frame from the cable between the two batteries?"

I don't know that the little ground wire had anything to do with the starter,but I do know from experience that the lights won't work without it hooked up.

I was not aware that it was suggested in this thread that the small ground wire was needed for the operation of the starter.

May I ask where you saw that?

 

[Tx Jim]

(quoted from post at 11:12:08 02/24/20)

Isn't it strange that DEERE used heavy jumpers between the batteries in the 2-cylinder era, with a small wire to chassis ground, then went to the two individual ground cables on the 4010, etc, and then a ways into the 20 series went back to the heavy jumper with the small chassis ground wire?

I forgot 2 cyl 24 volt electrical systems had battery cables between battery posts. I think the reason for the change to short cables to frame on 10 & early 20 series battery rear posts was to save JD $$$$$

 

[Tx Jim]

I'll bet going to cable between rear battery posts vs cables to frame help slow down electrical fires until the kit for the 2 circuit breakers at starter was introduced/installed.

 

[Tx Jim]

I'll be very glad when the edit function is reinstated!!

As we all know also cable between rear battery posts offers 2 less opportunities for corroded electrical connections