JD 420 S 6v to 12v

I have a early model 420 S that I'm going to change over to 12 volt as soon as the shop frees up from the current clutch job. I have run the rabbit of rebuilt starters, generators and such but it has so much compression to it, you have limited cranking ability and charging has always been an issue. What I plan to do is install a 1 wire alternator wired straight to starter saddle switch and a 12 v internal resister coil. Do I need to unhook the old voltage regulator to prevent any parasitic drainage? I'm not concerned about any lights or Amp Guage on dash.
Any input is appreciated.

Yes,unhook the regulatpr.Run one wire from alt to amp gage,then to battery cable at starter.Or just run from alt to battery cable,bypassing the gage of you want.Better still,complete strip out the old dilapidated harness and start fresh with new wireing.

Coils designed for 12v systems are just correctly wound with slightly smaller and 2X longer than the 6v coils. No resister is inside other than the copper wire. When external resistors are used on 12v, the resistor is on the outside, and the coil is designed/wound for 6v. The resistor chops the voltage about in half. A bypass circuit is used to put cranking voltage of about 10 volts directly to the coil making a temporary hot spark. When cranking stops, the voltage goes again to the resistor. lowering the voltage for continuous running. I like to see the amps going into the battery so when I do the alternator thing, I wire it to the load side of the alternator. Delta is correct, removing the old regulator is preferred, and rebundling or replacing wires is best. 10 gauge for the Alt wire. Jim

[b:654c4848f0][i:654c4848f0]What I plan to do is install a 1 wire alternator wired straight to starter saddle switch and a 12 v internal resister coil.[/i:654c4848f0][/b:654c4848f0]

Take a look at the photos below of [b:654c4848f0]Audie[/b:654c4848f0] our Model 40S.







Hope this helps.

Thanks for the detailed pics James. I have a 40s that works good on the 6 volt system, but I have often thought about changing it to 12 volts because of the better starting offered in cold weather and the cost of 6 volt batteries.

Jim,
Check the alternator for a parasitic drain.

I installed a new alternator on Farmall and the alternator had a drain.
Many voltage regulators on lawn mowers have a drain too.

I have to run the two alternator wires through the switch to turn off the drain.

A few milliamps over the winter will drain the battery.
That's why some use a trickle charger.

I had a new battery in the lawn mower. Didn't use it since May.
Pulled battery before winter, dead battery.

George I have changed several Farmalls and an Allis to 12 volt systems. I have used keyed switches on all of them. I figured I might have to do the same on my 40s. I may not change it too. It's getting harder to find 6v batteries locally, and when I do they are almost twice as much as a 12v one.

Your question

Do I need to unhook the old voltage regulator to prevent any parasitic drainage?

ANSWER

YES there's no need for the old VR. I would wire the One Wire alternators output to the LOAD (NOT battery/starter) side of the ammeter, that's where the BAT on the old VR/Cutout wired to, you can remove that wire along with the old VR. The other INPUT side of the ammeter wires to the hot ungrounded battery post often at the big battery cable on the starter switch

IF you wired the alternators output direct to the hot battery cable at the saddle switch input THE AMMETER (if it has one) WOULD NOT READ THE ALTERNATORS OUTPUT even though sure it would still charge the battery

The new 12 Volt Coil wires to the ign switch output NO BALLAST assuming its indeed a full true 12 volt coil. I dont think I would mess with using a 6 volt coil plus a ballast and ballast by pass system as it should start fine in cold weather no problem.

I would use at least 10 Gauge (even 8) from alternator up to ammeter and upgrade the wire from ammeters INPUT to the battery/starter

If its a true One Wire Alternator you DO NOT NEED the excitation circuit but it may or may not start charging until fast enough RPM

Of course assuming the Alternator is NEG ground wire the ignition coil, battery, and ammeter accordingly

Hope this helps, any questions ??

John T

Thank you everyone for the help. I agree with Jim in NC. It's getting hard to find a 6v battery here too. If you find one, you definitely won't like the price! I put an 8v in it last time to try to keep it original and it helped a lot with cranking, but it's been a struggle to make it charge. Time for a change since battery has croaked.

The plan you described will work just fine. The ammeter will not work but you stated you are not concerned about the ammeter. There will not be any parasitic drain from the regulator so you can leave it in place. The regulator on a 420 can be hard to get to.

If you want the ammeter to work then hook the alternator to the meter or better yet just use a voltmeter. If you do use the ammeter, the connections on the meter need to be reversed since the original tractor was positive ground, at least my 420 crawler was positive ground. The 420 will turn fast enough to excite a one wire alternator but will need close to full throttle for that to happen.

The parasitic drain from a one or 3 wire alternator is small. The few milliampers or less is not going to have any real effect on battery life.

Like always, James Howell posted good photos but his photos are for a 3 wire alternator. Your one wire will be slightly different. I prefer a 3 wire but either will work.

My Jubilee and Farmall were converted to 12v before I bought them.
I had to make a new wiring harness for each.
There seems to be a lot of electrically challenged people making conversions.
Someday I'll post pics of the neighbor's 12v conversion on 8N and you will see what I'm talking about being challenged.

The pulley from your Delco generator should fit right on to most Delco 10-12SI style alternators. You might want to consider getting a smaller diameter pulley, of the right belt width, to increase the alternator rpm.