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Farmall Super M 12 volt conversion


 
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B. Cole
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PostPosted: Sat May 04, 2013 4:15 pm    Post subject: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

I"ve been trying to get my Super M running ever since I did a 12 volt alternator conversion but I get a really weak spark. I"ve replaced the plugs, wires, condensor, rotor, points and am using a new battery. The coil I"m using says "For use with external resistor" so i used a generic Chrysler resistor. The thing spins over fine but will not fire. So I replaced the resistor with a new one and weak spark still. So on a whim I bypassed the resistor and it fired right off. Am I looking at burning up the points doing this? Any other ideas? I"ve been beating myself up on this evenings for a couple of weeks now. I think I"ve read most of the threads here on these conversions and I wired it with new wiring following Bob Melville"s schematic. (Nice job on the info to Bob) Thanks for any info as I really need to get the old girl running to put out some hay!!
 
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Charlie M
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PostPosted: Sat May 04, 2013 4:19 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

If the coil is 12 volts then you don't need a resistor. Adding one would create a weak spark. if you're coil is 6 volts then you need the resistor.
 
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B. Cole
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PostPosted: Sat May 04, 2013 4:26 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Okay, thanks. I guess I have it right then but somehow it seems backwards in my head Smile
 
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buzzinduzzin
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PostPosted: Sat May 04, 2013 4:26 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

what you need is a ballast resistor. I know nothing about a chrysler resistor but it may only function properly in conjunction with its other components. If there is a terminal on your starter solenoid that is 12v ONLY when the starter is engaged connect it to the coil side of the ballast for a hotter cranking spark.
 
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Janicholson
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PostPosted: Sat May 04, 2013 4:31 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

If the coil has a resistance of 4 to 6 ohms it can be used WithOut the resistor. If in the area of 2.5 to 3 ohms it needs a resistor. It could be mislabeled, or just wrong. If the coil draws less than 4 amps when turned on and grounded through the points, it can be run without the resistor. Jim
 
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CNKS
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PostPosted: Sat May 04, 2013 5:07 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Put a 12 volt coil on that does not use a external resistor.
 
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John T
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PostPosted: Sat May 04, 2013 5:55 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

About all the coils Ive seen that are labeled "for use with external resistor" MEAN JUST WHAT THEY SAY and can overheat if you do NOT do as they say......They are typically 6 volt rated coils, thus on a 12 volt tractor they indeed need the external series voltage dropping (12 to 6) ballast AS THEY SAY.

HOWEVER the size of the ballast needs to be matched to the coil used, so if the ballAst is the wrong size (like maybe that Chrysler) YOU MAY GET A WEAK SPARK

If I were sizing a ballast on a 12 volt tractor in order to use a coil labeled requires a ballast, I would use one that has around the same ohms as the coils LV primary (+ to -) that way the ballast drops 6 volts leaving 6 for a 6 volt (one that requires ballast) coil. Another way to size it is use a voltmeter and with ign on and points closed, you wanna see around 6/7 volts on a coil thats labeled "requires ballast'

Check coil and ballast resistance, they need to be near the same ohms or spark may be weak (or coils too hot if ballast is too small ohms)

A typical old farm tractor 6 volt coil has a LV primary resistance around 1.25 to 2+ ohms,,,,A typical 12 volt is more like 2.5 to under 4 ohms.

The points shouldnt switch much more then 4 amps thus on a 12 volt system 3 ohms is typical ign primary resistance (12/3 = 4 amps) and on a 6 volt 1.5 ohms (6 /1.5 =4)

Got it???

John T
 
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B. Cole
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PostPosted: Sat May 04, 2013 6:33 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Maybe. I'm digesting it. Thank you.
It seems to me that the simplest way to correct it would be to get a 12 volt coil that does not require a ballast resistor and be done with it.
 
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Farmall005
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PostPosted: Sat May 04, 2013 9:21 pm    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

I used the petronix 12 volt electronic ignition system on my Super M 1954...starts in all weather...did away with the points, condenser and ressitor....
 
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John T
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PostPosted: Sun May 05, 2013 3:38 am    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

If its a 12 volt tractor it would indeed be very easy to just use a 12 volt coil no ballast needed

John T
 
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mattwillson
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PostPosted: Sun May 05, 2013 6:40 am    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Just a thought, when you changed system to 12v from 6v. Did you leave the coil hooked the the same as before ie. reverse polarity..that can cause weak spark.
 
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teddy52food
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PostPosted: Sun May 05, 2013 6:50 am    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Why not wire it up to by-pass the resistor while using the starter? That is the best way.
 
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T in NE
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PostPosted: Sun May 05, 2013 9:35 am    Post subject: Re: Farmall Super M 12 volt conversion Reply to specific post Reply with quote

Chrysler points ignitions used a ballast resistor with a 6v coil, with a by-pass built into the starting circuit for hotter spark while cranking.

I used one on my SM with the coil that was on there. Which, externally, is the same size that Chrysler used.
 
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