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Farmall & IHC Tractors Discussion Forum
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coil w/ internal resistor PLUS external resistor?

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e-manhunt

07-29-2006 08:04:26




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I've been chasing down an electrical problem on my 1940 M converted to 12v, and got it fixed thanks to the people in this forum -- a shout out to you guys.

Aside from replacing the coil, the condensor and points, I found that the coil that was already on there had an internal resistor, plus there was a resistor wired into the line running from the ammeter. This doesn't seem correct from everything I've read in this forum.

Except for various other problems, the tractor had been running fine. I'm not so sure where my current problem originated, but what problems would the external ballast resistor plus the internal resistor in the coil have caused?

Thanks, everyone.

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John T

07-29-2006 08:57:16




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 Re: coil w/ internal resistor PLUS external resist in reply to e-manhunt, 07-29-2006 08:04:26  
Manhunt, I agree with Jim, if its a true full 12 volt rated (some call internally ballasted) coil then there should NOT be another external Ballast Resistor, and if ones in place, the spark energy is less, although if so and the spark intensity is still sufficient for good starts n running, heck the points n coil should last a longgggg gg time as the current draw n resulting heat is far less then their rating. If the engines in good shape and the carb n ignition are top shape there would be less problems but if shes low compression or an oil burner etc it may be harder to start in winter plus less power from using a 12 volt coil PLUS an external ballast.

I sort of question how you know or if it has an "Internal Resistor" Most all coils that are true full 12 volt rated (some call internally ballasted) coils are rated 12 volts cuz their primary winding resistance as measured between their lil + and - terminals, is somewhere around 2.5 to 3.5 ohms VERSUS a 6 volt coil which is more like 1.25 to under 2 ohms. The way the added resistance is usually achieved in a 12 volt coil IS USUALLY NOT via any discrete internal resistor BUT from either more turns of wire or wire of a higher resistance. The purpose n theory of how many ohms of ignition circuit primary total (coil + any ballast) resistance is to limit the amount of current the points are required to switch is around 4 amps maximum cuz otherwise they would burn up prematurely.

Sooooo take an ohmmeter on the Rx1 scale and measure the coils primary resistance between its lil + and - terminals, and if its around 3 ohms (means its a true 12 volt coil) YOU DONT NEED THE EXTERNAL BALLAST.

NOTE: True full 12 volt rated coils may be labeled something like "12 Volts" or "12 Volts NO Ballast required etc" HOWEVER if labeled "12 volts for use with external ballast" etc then its in reality a 6 volt coil AND THE EXTERNAL BALLST SHOULD BE USED or it will run too hot (you could barely hold your hand on it after running) plus the points burn up prematurely.

Read the coil label and/or use an ohmmeter to see if its a 6 or 12 volt coil, and if its a 12 REMOVE THE BALLAST BUT IF A 6 LEAVE IT IN PLACE

Hope this helps, best wishes n God Bless

PS I have reason to believe Delco may have made some coils that had a ring n groove at the top with a seperate compartment in which a discrete internal ballast resistor "may"?? have been housed HOWEVER most alllll ll 12 full true 12 votl coils Im familair with acgheve the 3 ohms of primary resistance (making them a 12 volt coil) from higher resistance wire or else more wire period.

Post back any questions

John T

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e-manhunt

07-30-2006 07:13:54




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 Re: coil w/ internal resistor PLUS external resist in reply to John T, 07-29-2006 08:57:16  
John, I figured that the old coil had an internal resistor not because of any mechanical genius, but it was printed on the side of the coil. The M is running good right now, but it seems louder and runs a little hotter. Is this the type of thing when I put in a new coil, condensor and points?

thanks.
Eric



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Janicholson

07-30-2006 10:00:45




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 Re: coil w/ internal resistor PLUS external resist in reply to e-manhunt, 07-30-2006 07:13:54  
The ignition provides only the initiation of the combustion process. If it works it works. It will have no affect on the loud or hot. Timing however will. Adjusting the points to .020" (correct) might change the timing enough to warrant a check. Look in the archives, there must be fifty entries on timing an M. JimN



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Janicholson

07-29-2006 08:07:49




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 Re: coil w/ internal resistor PLUS external resist in reply to e-manhunt, 07-29-2006 08:04:26  
Just reduced spark intensity. Possible poor starting. Change the coil, or remove the resistor. If the coil gets so hot that you cant touch it after 30min. it may need the resistor!, or be a bad coil.
JimN



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