Can someone advise how best to check/fix the charging system on my D4, please.

It used to charge OK, it wasn't blowing the needle off the ammeter, but it did retain 24 volts. These batteries are good, they came off tractors that start well.

Now after a long rest it will not charge, I put a voltmeter on the battery and it simply shows the battery voltage, not any input......for example it was sat on 24 volts, I warmed and started the machine and then it recovered to 23.4v and stayed there.

I tried earthing the field wire off the control box, no different. Also measured the voltage off the + and - poles on top the dynamo and they read 0.1v at idle and 0.5v at max revs.

Any clues where to go next?

This is a shot in the dark, but if your tractor is the model that has a red re-set button on the dash, check that switch. I had that go bad on a D6D with the same problem and that was the culprit.
As stated, it's a Strictly Wild A.. Guess!
Craig

Look up polarizing the generator. I usually think about shorting from BAT to GEN/ARM regulator terminal bypassing the cutout relay, but that may not be the recommended way to do it. I had to replace the regulator on our 944 a while back. I could manually short the contacts and make it charge but couldn’t ever get it adjusted to maintain a sufficient voltage to charge the battery properly. New old stock regulator from local shop wouldn’t charge either, but I was able to clean the contacts and got it going in the end.

Check voltage at the BAT terminal to ground on generator frame to make sure you have a good connection from battery. The circuit breaker mentioned earlier would probably kill the voltage there preventing restoring the magnetic field when you polarize it.

Hi Richard,
as above depending upon your gen/reg here are the methods from my grey OMI for 78A, 88A, 86A, 85A and 91A D4's.
Form No :- FEO-45116-02, Dated 10-68. The -02 is the change/edition/issue level of the publication --the higher this number the later the issue with later updates.

I agree first check is the Red/Blue button on the Manual Reset circuit breaker/fuse, it may have tripped open or simply rotted out if water gets in. Check it for continuity.
Hope this helps.
Cheers,
Eddie B.

Right, so I have done as per the instructions. No Joy.

I believe its the Delco setup, but not sure. Anyway I tried both methods of flashing the system

I did have 0.6v output from the dynamo, but after flashing the BAT to ARM it went to 0 volts

Is there a way to prove which component has failed?

First do you have battery voltage (24 volts) at the regulator BAT terminal?
If not, troubleshoot the reset button/circuit breaker, the amp meter and wiring to find where the 24 volts disappears as you work your way back from starter solenoid terminal where the battery positive cable connects.

Since you’re cranking it successfully I will assume the cables and disconnect switch, ground to frame etc are all good.

If you have 24 volts at the generator BAT terminal, to diagnose a generator vs regulator vs wiring problem, start by inspecting the armature, field and ground wires between regulator and generator, cleaning and tightening connections on each end.

If no problems found there, I would try to “full field” the generator with the engine running about half speed.
First you need some internal voltage in the generator. If it’s still at 0 volts on the ARM terminal, try again jumping BAT to ARM and see if you get lasting voltage output on the ARM terminal.

If so, and voltage does not build up to charging levels (24 increasing to 28 volts over time as the batteries reach full charge), then try to full field the generator by shorting ARM to FLD (momentarily)while monitoring voltage output on ARM. If you get full voltage output during this exercise then the generator is good you need another regulator.

If no change, try grounding the field terminal on the generator or regulator to ground while again monitoring voltage on the ARM TERMINAL. Again if voltage builds up during that test, replace the regulator.

If no voltage builds up, have generator serviced. You may want to open it up yourself. They’re not terribly complicated and you can clean the commutator, inspect the brushes, ohm the armature circuits and fields etc. sometimes I find something I can fix, sometimes not.

If I take the generator to a shop, I usually take the regulator along with it so they can test the combination and replace whichever or both as necessary. Many shops will recommend replacing the regulator anytime the generator is serviced or if there’s any problem with charging voltage etc, but they can be adjusted, contacts cleaned etc. if contacts are burned, filing and polishing will probably be only a short term fix.

Could the battery disconnect have been turned off while it was running? That will blow the diodes in the alternator. I have seen it happen.

Thanks for the replies, I will check that tomorrow and let you know what I found!

Simple generator test....
Disconnect fan belt, with motor grounded connect battery to Armature post. Generator should pass the motor test. Now ground the field while running and it should slow down some showing fields are good.
If all checks out the generator should charge.

right, so to update on today's findings

First I tried to get some power down the ARM cable to the dynamo. I noticed the voltmeter descend to about 10 volts, like a significant short

I opened up the dynamo to look inside, with an earth on centre shaft and multimeter + connected to 24v + I then touched the - end of the multimeter to the commutator segments, it read 24 volts.....as far as i could understand this means it has shorted to ground

Next I earthed the body of the dynamo, joined the feild and armature terminals and put the + lead to it to see if it would spin.....it barely did and the jumper wire got very hot.

Next I spun the dynamo up to see what voltage it was producing, got 0.6 volts out of it.

The conclusion i have reached is that the dynamo itself has failed



Agreed?