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John Deere Tractors Discussion Forum
Show Parts for Model:

Re: whats burning my points?

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John T

12-27-2012 14:53:55
216.249.82.117



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A couple things (among others I can post if needed) that can cause premature points burning up are:

1) Weak or Open or not connected or way wrong sized Condensor

2) Excess (too much over 4 amps) coil current caused by:

a) Wrong coil (like a 6 volt coil on a 12 volt system with no external series voltage dropping (12 to 6) ballast resistor)

b) If its a 12 volt tractor and you have a 6 volt coil buttttttttttttt theres too low ohms of ballast. Ballast ohms is near what the coil LV primary ohms is i.e. maybe in the range of 1.25 to 2 ohms.

On a 12 volt tractor you need EITHER

A) A 12 volt coil which may be labeled "12 volts" or "12 volts NO ballast required"

ORRRRRRRRRR

B) A 6 volt coil PLUS an external series voltage dropping (12 to 6) Ballast Resistor

NOTE if the points are having to switch too much over 4 amps of coil current they WILL BURN UP TOO FAST. In order to limit points current to 4 amps on a 12 volt tractor the TOTAL (coil PLUS any Ballast) primary ignition resistance needs to be around 3 ohms as 12/3 = 4 amps

SOOOOOOOOOO insure coil is a "12 volt" or "12 volts NOT for use with ballast" (around 2.5 to 3+ ohms) or if its a 6 volt coil (around 1.25 to 2 ohms) theres sufficient ballast resistance.

NOTE Im talking typical old tractor stock coils here NOT high voltage or high energy or after market or super coils or Accell or Mallory types etc OLD STOCK FARM TRACTOR COILS FOR POINTS IGNITIONS

NOTE if coil is labeled "12 volts for use with or requires ballast" its in reality more like a 6 volt coil and it means what it says BALLAST REQUIRED or esle it will overheat and points burn up fast

Got it??? If I missed anything the other fine gents can add to this

PS Contrary to what most lay persons believe you likely will NOT find a typical old 40's 60's vintage tractor coil that has a stand alone discrete "RESISTOR" tucked away somewhere inside the can.....X Ray or disect one if you like, I bet theres no compartment or seperate area with a "Resistor" hidden inside. NOTE for those in Rio Linda or no electrical expertise whatsoever or are unfamilair with electronics terms and components, A ResisTOR has ResistANCE and wire has some slight ResistANCE butttttttttt a wire is wire and resistORS are resisTORS, if you go to Radio Shack and ask for resistors they wont show you wire and if you ask for wire they wont show you resistors lol

John T

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