Ballast resistors

This is about an old Ditch Witch J20:
There is something wrong, here, and I am hoping someone will see what it is as I can't explain why it behaves the way that it is:



I was continually burning out coils, so I got a automotive ballast resister and placed it before the coil. I have now been through three resisters. Each one got exceedingly hot and neither one of them continue to provide their rated ohms. With each resister, the motor will start, but when the starter switch is closed, the motor stops. If I move the coil '+' wire to bypass the resister, the motor runs without problems ? except I will soon burn out the coil. I tried a ballast resistor with a 1.2 ohm rating and two with 1.6 ohm ratings. With all resistors, I am only getting about ? volt to the coil when I stop the starter. The battery is a new 12volt automotive battery, and it is putting out about 12.7 volts
I'm hoping another pair of eyes will see something obvious that I am not.

You show a wire connecting the positive post of the relay to the S terminal. That is wrong the S should go thru the start switch first or the engine will keep cranking until the batt runs down.

That wiring looks right, the ballast resistor should knock the 12 volts down to 6 when the start circuit is removed. Try one from a Farmall, I don't remember the value but right now you are placing too much of voltage in the resistor which why it is getting too hot. It will get warm but not take it down that far in voltage, looking for 6 volts. Others with the value of the resistor will likely chime in.

Oops I see the relay is wired after the Floor switch. So ignore the previous. I don't under stand why it's that way though

If the solenoid is stuck, then the I terminal would be always connected to the starter which would cause the symptoms you describe. The starter would be drawing current through the resistor like an almost short which would be about 8 Amps heating the resistor as that is at least twice the current it is rated for. This would also steal power from the coil which would kill the engine. Since you have the floor switch in series with the contacts in the solenoid you may not notice the solenoid is not doing anything.

1) Anytime and all the time voltage is present on the solenoids S terminal the solenoid is closed.....

2) Anytime and all the time voltage is present on the S terminal, the I terminal is hot

3) While the I terminal is hot its supplying full unballasted voltage to the coil (ballast is by passed) and if you use 12 volts unballasted on a 6 volt coil it runs hot, can eventually fry, plus the points burn prematurely.

The way its supposed to work is the solenoid is closed ONLY while cranking and therefore the coil receives unballasted battery voltage ONLY while cranking for improved cold weather starting. The big battery cables go trough the solenoid and its closed by applying low current via a start switch to the S terminal

John T

I have seen degective start solinoids as several have said. You will keep getting 12 through that terminal. Check the terminal from the solinoid with the wire unhooked, engine running, and with a good meter. Should be around ten volts while cranking. The resistor should drop it down to between 6 and 8 volts while running. Something is a little Squirrel type problem here. Check and see if the solinoid is getting hot. You might be backfeeding everything through that jump wire where you have on the solinoid. I need to look into this a little further.

Wiring looks right. I would try a different coil as it appears the coil is pulling to much current.

I would do some simplification.

Take the battery cable straight to the solenoid.

Run a small wire from the floor switch to the S terminal of the solenoid.

Buy a 3 ohm 12v coil, wire it straight from the ignition switch, eliminate the resistor and resistor bypass circuit. With a good battery, healthy starter, and proper sized cables, it won't need the resistor bypass. That is only needed for large high compression engines.

Everyone here is 'assuming' that they know which type of solenoid that he has. Not good assumption. Mr. Poster, what is solenoid part number? ....and , is your floor switch capable of handling starter motor current? If yes, then why is the solenoid even in the circuit?

I agree. Simple is better. Your plan provides a good solution. I would add a single test before going that way. I would take the wire off of the coil S terminal and see if it still cranks when the floor switch is pushed. If it does, the solenoid is stuck on. and thus causing the ballast resistor to try to power the starter motor. If it doesn't crank, I would hold down the floor switch and touch the solenoid S wire to the terminal where it was connected. If it now cranks, I would eliminate the floor switch by hooking the cable to the starter to the battery side of that switch and use the now empty terminal to power the S terminal on the solenoid. Leave all other parts as is. Jim

Well here is where i would make some chqanges , (1) run the main HOT batter cable to the solenoid and by pass the starter switch , next run a 10 gauge wire from the hot post on the solenoid to the starter switch then run a 10 ga wire back to the S post on the solenoid . Next if your usen a resistor then the coil needs to be a 6 volt coil . The I post and wire running to the + post on the coil is fine as when you hit the starter it sends a shot of 12 volts to the coil for a HOT start . NO IF you have a 12 volt coil with a built in resistor and and external resistor then ya's got's a problem . Of all the 6to 12 conversions i have done i have always used a 6 volt coil with a resistor or the OLD STOCK coil .

Problem solved - Thanks, Folks for your responses. The system is currently a 12 volt system. Because when the floor switch is released, current stops going to the solenoid which causes the starter to stop turning. No further charge should be coming from the solenoid's 'I' terminal, but it turns out that the wire to the 'I' terminal was the guilty culprit. (Thanks, Deanostoybox for pointing me in that direction.) I took the wire off the 'I' terminal and just held it there while cranking the starter. Once it started, I took the wire away and the motor continued to run and the resistor did not overheat. Touching the wire back on the 'I' terminal caused the engine to stop. I tried starting the engine without the 'I' terminal connection and the engine started without any hesitation, so I'll just leave out that part of the circuit. Your right, Jeffcat & Jmor, the solenoid is the basic problem as all I did was grab a four post solenoid without any further deliberation. I added it to the circuit because I thought I needed that temporary bridge to compensate for the extra current while starting. I am not sure what will happen during the cold winter months ? I'll wait and see.
I wanted the floor switch because I, or anyone else borrowing this machine, then must be up sitting in the seat to start it ? safety. The ignition switch is simply a keyed, off/on switch.
Thanks again to everyone for taking the time to respond to this dilemma of mine. It's great to know there is a place to go if things just don't seem to make sense.

Bypass circuits entered the automotive world with the advent of large V-8s requiring serious starter motors and a lot of voltage drop while cranking. If only 8 or 9 volts (while cranking) was available to the ballast resistor then the voltage would be even lower thru the primary of the coil, making for difficult starting in January winter climates...... My 2 bits

If the starter relay ("solenoid") was wired up the right way you would have known about this problem immediately, that is if the relay is stuck closed. The way your circuit is wired totally defeats the purpose of a relay too, I would hook it up correctly or bare minimum remove it. That floor switch must be strong to carry all the current to the starter huh.

If you want to correct the circuit and use the relay then run the batt+ cable to the big lug on the relay the floor switch is currently hooked to, take the floor switch off the big lug and run to the "S" terminal only.