730 diesel 24volt electrical help needed

J Hamilton

Well-known Member
I'm working on a 730 diesel for a friend,
the charging system isn't working and
hasn't for a long time. First off I DO have
a JD service book and have been studying
the wiring schematic and understand this is
a 12/24 split load system, the problem is
the generator light on the dash will not
come on, the bulb and socket is good as
well as the switch, I have tested those. I
also had the generator tested and checked
at a reputable shop. I have also cleaned
the contacts in the regulator but need
advise on how to test that and what voltage
readings I should get at which terminals. I
have also found if I unhook the wire from
the gen light (the one that goes to the two
white wires) and leave the other hooked to
the gen terminal at the switch and run a
jumper wire to the one I unhooked to the
positive battery terminal that goes to the
starter I can get the gen light to come on
and off using the ignition switch. Any help
and advice would be greatly appreciated.
 
First off, have you polarized the generator by momentarily jumpering the "BATT" and "GEN" terminals an the regulator (engine NOT running)?

Don't worry about the charge indicator light 'til you get the generator working, that in itself MAY "fix" your light.

What is voltage between A1 and A2 terminals on generator with engine running, should be over 28 Volts if the generator is working, with A2 being the (+) side of the voltage.

If not charging, take the regulator out of the picture for a moment by "full-fielding" the generator by temporarily jumpering "F" and "A2" and note the voltage reading between "A1" and "A2".

Post back and tell us how all that went!
 
If its already correctly polarized and in very broad general terms (NOT exact too many other factors) you full field it as Wore Out described but it still doesn't charge, I (in very general) suspect the genny as the VR function is effectively by passed.

Heres a link which has some Troubleshooting Tips that may help. Those systems are hard to troubleshot over the net

http://www.petcaretips.net/john-deere-24volt.html

John T
John Deere 24 Volt System Explained
 
I did the test at A1 and A2 but my meter showed a negative reading, I did verify the leads on the meter are correct by testing it on a battery. I had the tractor running about 1/2 throttle during this test. So this tells me there must be a wire or wires switched somewhere to get a reverse polarity reading, right? FYI This tractor is using 2-12 volt batteries and I did verify they are correctly hooked to the starter.
 
This is the reading I got
cvphoto55637.jpg
 
The series combination of your two 12 volt batteries still has a definite POS and a NEG which the Generators A1 & A2 must correspond IE they also must have a matching POS and NEG. You indicated you did Polarize correct ??? If you reverse the meter leads I assume it just reads the opposite polarity.

To charge the 24 volt batteries you need at least 26 to 28+ charging volts and its the voltage THE BATTERIES RISE TO that matters NOT any open circuit unloaded generator output alone. If the batteries are sitting there NEVER with rising voltage at fast RPM with the genny full fielded they obviously ARE NOT BEING CHARGED regardless what the gennys A1 to A2 might read. Its ONLY AFTER the gennys output is sufficient that the Cutout Relay closes in which case the A1 and A2 are then tied to the battery and if working battery voltage should rise above 25.

John T
John Deere 24 Volt Troubleshooting
 
You say the batteries are connected correctly, yet the polarity is reversed at the generator.

If you figure what's going on there, likely your generator light issue will be resolved at the same time.

Also, check the polarities of each battery.

It HAS happened where a dead battery gets recharged with polarity reversed.
 
Wore out,

I'm impressed with your electrical knowledge. I'm an electrical engineer and would like to know more about you. I don't think you have been posting on YT for very long. But I may not have been paying attention. My email is attached if you prefer to reply. I'm in Southern Minnesota. Thanks
 
Ok, I will double check all battery and starter connections, this time I will check by disconnecting each cable where neither end is attached so there is no chance of backfeed for false reading and check continuity with my meter. I will post back on this later this evening. Thanks again for the help and advice
 
That 36.4 volts is what one might get for open circuit unloaded voltage HOWEVER if the cutout relay is closed then I would expect more like 26 to 28+ volts

John T
 
That A1 to A2 polarity needs to match the two batteries tied in series 24 volt polarity. I question proper polarization and the battery connections, let us know your findings

John T
 
Its actually the Generator instead of the regulator that requires polarization. Once the batteries are connected and you polarize that should set the gennys A1 & A2 polarity to match and charge the batteries.

John T
 
PS Hey Ron, the more of us Electrical Engineers here the better (I hope) lol

Take care

John T
 
That reading of 28.5 volts indicates your generator is working OK. That is about the reading I get on my JD 830 when I check it to verify if it is charging OK when I start it up in the spring.

Al
 
Ok, so I need to polarize at the generator or regulator? Or both? And which terminals do I use? When I polarized the regulator I used the BAT and ARM terminals, was this correct?
 
Yes, the batteries are correctly wired for 24 volts with the positive battery cable attached to the starter terminal that my finger is on, and the negative is on the other terminal.
cvphoto55690.jpg
 
(quoted from post at 13:21:52 09/12/20) Ok, I will double check all battery and starter connections, this time I will check by disconnecting each cable where neither end is attached so there is no chance of backfeed for false reading and check continuity with my meter. I will post back on this later this evening. Thanks again for the help and advice

Your starter is NOT original and is a much newer version.

I question if it is made for this unique split 24 Volt system. If it IS correct the stud in the CE endbell should NOT show continuity to the starter "frame". (You'd have to disconnect the batteries and the wires at the starter to check this for sure.

At the starter the BLUE wire should read -12 Volts with respect to the chassis, the BROWN wire should read +12 Volts with respect to the chassis. Can you check this?

Also, is the ground wire from the chassis to the midpoint of the batteries intact?
 
Its the GENERATOR that gets polarized although you do it at the VR terminals, same as posted above:

To polarize, momentarily jumper "A1" and "F".

To "full field", jumper "A2" and "F".

John T
 
In case it got lost down below one more time:

To polarize, momentarily jumper "A1" and "F".

To "full field", jumper "A2" and "F".

John T
 
I had all the battery connections off and re cleaned everything, I also tried to polarize as you described but I did NOT get an arc when I touched the terminals, something doesn't seem right. Could the problem be in the VR?
 
Right on John. I'm certain we need each other. I certainly don't think I know all the answers. I've learned a lot here on ignition stuff. Ignition wasn't what they taught where I went to EE college. I studied the radio and electronics side. But of course DC theory is the same every where. At the "top" end of the EE curriculum, I studied Maxwells equations and I don't remember anything about them and NEVER had to use them in my employment.
 

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