How can I change 6 v pony motor to run on 12v

chas036

Member
I have a 720D with a pony motor. I want to convert it to run on 12v. I seem to have read somewhere that you can replace the 6 v coils with 12 volt car coils. Does anyone have any plans or can give me some ideas how I would do this and how I would wire it up and what type of coils I would use? Also will the 6v starter on the pony motor work with 12v without burning out?
 
Years back I had some older 6 volt restorations. At times they failed to turn over fast enough to start in adverse conditions. The cheap and easy way is replace the 6 volt battery with an 8 volt battery. No starter, generator, coil to replace, regulator needs to be set up a bit to charge the 8 volt, but starter cranks it like it was a 12 volt system.
 
Car coils would be difficult to get to work properly beside the fact you would have a Cobb job with car coils. The easiest way to convert to 12 volts would be to run two six volt batteries. Use power from one battery for the ignition only and use the original pony ignition. If you desire a 12 volt ignition use two split fire coils from a battery ignition two cylinder opposed Kohler, Briggs or Onan engines.
 
Chase, I have done several. All you need is good 6 Volt coils and install a ballast resistor between the ignition switch and the "distributor".

It can be hidden up under the hood and not even be seen.

IIRC, I wound up using two in series on one of the tractors.

The trick is to use as much resistance as possible, within the limits of still having enough primary current high enough to make a spark that will start and run the engine with as little coil heating as possible.

Also, check the archives for "coil protection circuit", which will show you how to wire up an oil pressure switch that will cut off coil current when the pony is not running or cranking. Leaving the switch on ONCE with the pony stalled can kill a good set of coil.
 
I have rigged them using car coils but it was a pain and hard on the points.

I suggest you do as Bob did, use external series ballast voltage dropping (12 to 6) resistors so the Wico distributor only sees the 6 volts as intended.

12 volts on the 6 volt starter makes her spin very fast and it can be a bit tough on the drives. If I converted Id use a thinner wimpy battery cable on starter and ground like a No 4 max or even 6 to soften up the blow on the starter. The dash lights and run light etc need changed. Also, of course, the charging system.

John T
 
Here is the set up I put on mine. Been using it this way for the last 10 years and has worked just fine. Last set of new original style coils I had in it lasted about a month so I switched to this set up. Could easily make it work for 12 volts but 6 works just fine. It's a work tractor so didn't feel it had to be "correct looking".
a191507.jpg

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Bob,,,,your solution sounds perfect. Can you give the name of the exact type of resisters you used and where I might be able to buy them. Also can you send me a basic wiring diagram on how I would install them in the circuit. Also, what kind of 6v coils do you recommend to use. Can I still run the starter motor from the 12 volt battery, or do I have to reduce the voltage there also?
 
Bob,,,,your solution sounds perfect. Can you give the name of the exact type of resisters you used and where I might be able to buy them. Also can you send me a basic wiring diagram on how I would install the resisters in the circuit. Also, what kind of 6v coils do you recommend to use. Can I still run the starter motor from the 12 volt battery, or do I have to reduce the voltage there also?
 
Until Bob gets back to you on the ballast resistors he uses, the newer stock JD Pony Motor Wico Distributor Coils hold up far better then the originals. If you reduce the input voltage to the Wico Distributor to 6 to 7 volts (by using external series ballast resistance per Bob) it acts and works like all is original with a 6 volt battery input.

NOTE I believe the original pony motor ignition also had its own ballast resistor which reduced the Wico distributor input (and therefore coil voltages) down to around 4.5 volts while running but the full 6 (or whatever battery voltage was) ONLY while cranking. BUT I THINK WITH THE NEWER COILS MANY NO LONGER USE THE ON BOARD BALLAST WHICH DROPPED 6 DOWN TO 4.5 WHILE RUNNING.

If you had read my post below, I state Id use smaller gauge wimpy battery cables and grounds like 4 or even 6 gauge if running the 6 volt pony starting motor at 12 volts to reduce the shock on the drive mechanism. Of course as I also stated earlier, you have to change bulbs to 12 volts and change the charging system to 12 volts.

John T
 
Yep and actually even 8 gauge might do the trick??? 4 Gauge is likely too big to help much??

John T
 

You want to convert the tractor to 12V why? To use an alternator, 12V power to a towed implement or to use 12v coils?
A matching set of 6V coils with the matching wires work just fine. Use the wrong coil and wires together and spark will be weak or non existent.
 

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