70 ign problem update

got a chance to work on the 70 this weekend. picked up a "tune up kit" from A&I had points, rotor, condensor. so, put in the new condensor, made no difference. put in the points, still same thing. took carb apart, had some water and rust in it, so thought that was it. NOPE ran the same. still putt putt bang smoke. idle was fine. thought i"d try a new coil, even though the one on there has about 3 hours of run time on it. ran like it always did. so, thats the 3rd coil in a total of about 8-10 hours of run time. what would keep taking coils out like that? first one i put on was internally ballasted. second one was not and i had not gotten around to adding the external resistor yet. this third coil is an A&I 6 & 12 volt it says and does not require resistor. i"m 12 volt positive ground and coil hooked up correctly. wondering if there is a bad ground between dist. and tractor case?
 
"an A&I 6 & 12 volt it says and does not require resistor"

NO such thing.

You have a 6 Volt coil, which CAN be used on 12 Volts by the addition of an external resistor, no matter what the "documentation" may erroneously say, or what you care to believe.
 
the resistor i have that i was gonna put on is 2.5 ohms. is that gonna be enough? stated right on the coil is "no external resistor required".
 
(quoted from post at 12:48:35 11/18/13) "an A&I 6 & 12 volt it says and does not require resistor"

NO such thing.

You have a 6 Volt coil, which CAN be used on 12 Volts by the addition of an external resistor, no matter what the "documentation" may erroneously say, or what you care to believe.
onder if this is the coil in question?
A-21A552 Ignition Coil - 6 Volt W/O External Resistor or 12 Volt W/ External Resistor print this page

Price each
 
The 1.5 ohm 6V coil is used on 6V systems.
The 1.5 ohm 6V coil is used on 12V systems with a balast resistor.
The 3.0 ohm 12V coil is used on 12V systems without a ballast resistor.
 
"i thought the resistor was to keep the points from burning up. will it also cause the coil to go bad?"

The ballast resistor is there to drop coil voltage (from 12 down to 6) and reduce coil current (from say 8 without down to acceptable 4 amps with resistor). If its a 12 volt tractor with a 6 volt coil and theres no resistor, the coil will overheat PLUS the points will burn up prematurely........

John T
 
"the resistor i have that i was gonna put on is 2.5 ohms. is that gonna be enough?"


For an ideal 50/50, 6volt/12volt voltage divider, the ballast resistance is the same as the coils LV Primary resistance. Typical of ballast resistors is say 1.25 to near 2 ohms. 2.5 sounds a bit high, but can work depending on the coils LV primary resistance. If the ballast ohms is too high the spark may be a tad weak, if to low the coil might run just a bit hot



"stated right on the coil is "no external resistor required"."

If its a 6 volt coil used on a 6 volt tractor THATS TRUE. If its a 6 volt tractor used on a 12 volt tractor THATS NOT TRUE. If its a 12 volt coil used on a 12 volt tractor THATS TRUE.

John T
 
thanks for the input. gonna put the resistor in and see what happens. hopefully i wont have to change the coil again in a couple of months.
 
For a 12 volt tractor the coil can be EITHER:

a) A full true 12 volt coil NO BALLAST REQUIRED

b) A 6 volt coil if you add a series in line voltage dropping (12 to 6) current reducing ballast resistor.

c) A coil labeled "12 volts" or "12 volts NOT for use with ballast or no ballast required" is intended for a 12 volt tractor and requires no ballast.

d) A coil labeled "6 volts" or "12 volts for use with or requires ballast resistor" IS A 6 VOLT COIL

John T
 
My understanding of a 'Ballast Resistor' is: they are used to vary the resistance by the influx of heat. To make more sense, when the resistor is cool, almost all of the 6v goes through to power the points system with as much juice available. As the electron keep flowing through the wire coil of the resistor, the coil heats up, reducing the energy to the points system, primarily to lower the power input to the coil, thus reducing heat to the coil. (mostly for longevity I suspect)
 
While that has some truth for all resistors since resistance increases upon warm up, what you describe reminds me more of a THERMISTOR. A typical old tractor ballast is more like 1.25 to under 2 ohms fixed, although sure it would be somewhat less when its cold. Its primary purpose is to drop 12 tractor volts down to 6 when using a 6 volt coil while the limited thermal characteristics can indeed improve cold weather starting

Fun chat

John T
 
Beg to differ. A 'reducing' resistor does just that with in a second or less, a 'Ballast Resistor' slows down the process with the use of a longer (lengthwise) wire coil, hence a slower response to the loss of energy that goes to the starting system = more juice to the coil/points system during starting. Seems to me the # series had that system hard wired into the "Ignition
switch".
 
Many moons ago when I got my '60'(1971), it didn't have a coil. I went to the local parts store and bought an inexpensive 12v 'Generic' coil. Sucker is till on there ! Thing was already -grnd.
 
Yep I think the 720 etc had the stand alone discrete white ceramic bathtub style of ballast resistors while the new generation had more like a wire link or fusible link looking thermistor on the ignition switch that acted more like the resistor/thermistors you described. My answer covers the old style two cylinder tractors with more of a fixed resistance voltage dropping current reducing ballast which isn't the same as what you're describing. I think youre more right for new generation and Im more right for the old two cylinder tractors.

Very fun chattin with ya, thanks for the info

John T
 
Those are good approximate figures for typical two cylinder ballast resistors. Ive seen a lot of ballast resistors from 1.25 to 1.85 ohms range.

John T
 
Right back at ya. My limited knowledge of the subject is based on the 2 'N' Ford's I had. My '60' has a resistor as part of the 'ignition' sw., but I think it has to do with the lights.
 
As previously posted and from the substance of this post you can see why I went to electronic ignition kits and never visited these issues again.
 
Youre right, many brands of tractors with that wire coil resistor on the ign/light switch THATS A LIGHT DIMMING RESISTOR.

Many other tractor light/ign switches have TWO RESISTORS on the switch. One (flat wound) is the generators field current limiting resistor for Low or High charge on tractors that used a cutout relay NOT a Voltage Regulator and the other coil of wire/resistor is for light dimming.

The older two cylinder Deeres (720 etc) used a stand alone discrete fixed bathtub style ballast ignition resistor and and a start by pass system so the coil got battery voltage while cranking but reduced (6 volt) when running.

Some of the 12 volt New Generation Deeres (that used a 6 volt coil) had a thermistor/resistor type device on the switch or wired to it (looks like a wire fuse link etc) AND THERE WAS NOOOOOOOOOO START BY PASS NEEDED because the resistance was low for starting but when it warmed up its resistance increased so the coil only saw 6 instead of the closer to 12 volts at starting. I THINK THATS THE TYPE OF DEVICE YOU ARE THINKING OF

Whewwwwwwwwww got all that lol post back an questions

John T
 
This has got me thinking about my 70 gas. I don't recall seeing any type of resistor on the ignition. I always assumed it was straight 12 volt just like a car, only Pos ground. Am I mistaken? Is it 12V start and 6V run?
 
(quoted from post at 20:40:10 11/19/13) This has got me thinking about my 70 gas. I don't recall seeing any type of resistor on the ignition. I always assumed it was straight 12 volt just like a car, only Pos ground. Am I mistaken? Is it 12V start and 6V run?
70, used ign resistor between coil & ign sw and during start, resistor is bypassed.
 

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