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Coil question

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Mike C.

10-13-2001 23:12:04




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I have a model 50, positive ground. I am replacing
the coil with a standard ballast type automotive coil. Since this coil is intended for negative ground systems, should I connect the Positive or negative to the points? What is the effect of hooking the negative to the points on a positive
ground system? Also it seems to me coils used to
be labeled "ign" and "dist" instead of "+" and "-". This would make more sense as it seems to me
that you would want the "bottom" of the coil winding to go to ground (the points)regardless of
polarity. It also seems to me that if you have a coil that is intended for a negative ground system
and you hook the "+" to the points you are connecting the "tap" to ground instead of the "bottom" of the winding.

Mike C.

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John T

10-14-2001 18:47:19




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 Re: coil question in reply to Mike C., 10-13-2001 23:12:04  
Mike, the short answer like clooney told ya there is hook it positive ground if the battery is positive ground system. In addition to other factors besides your and clooneys thoughts, the mutual magnetic inductive coupling efficiency of two closely wound coils (what a coil/step up transformer is) is related to the direcion of current flow and the physical lay out (direction coils are looped) of the wires themselves (somethign we called the right hand screw rule at Purdue in the sixties regarding direction of magnetic field lines versus current ) because the magnetic polarity (like N and S poles) is dependant on the currents direction. An ignition system is designed to be most efficient and may produce less waste heat (in the coil) for a particular orientation. You will still get a spark if you reverse the coils polarity, but the physics and efficiency and wasted heat may be less desirable. Also, many modern high energy igntions operate a little diferent than the old type coils and points, which allowed curent flow to store magnetic energy in the coil and then when the current ceased (points opened) the collapse produced the high voltage in the coils secondary. On some electronic units, the coil is more like pulsed with a sharp sudden on/off voltage spike instead of a slower saturating curent flow then opening the points. Therefore, such a coil intended to be fired/pulsed may not operate as efficient (more waste heat) than one intended for points type ignitions. Ol John T

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Clooney

10-14-2001 06:31:43




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 Re: coil question in reply to Mike C., 10-13-2001 23:12:04  
Mike, you have a good question there & you are correct the performance of an ignition coil falls slightly (probably 10% or less) if the polarity is reversed from coil design. The offsetting factor is..... .The coil polarity must be connected into the primary circuit so the coil polarity (+ or -) marks correspond to those of the battery. If the battery negative post is grounded, the negative terminal on the coil must be connected to the distributor points. This will ground it through the contact points. By connecting the coil in this fashion, the center electrode of the spark plug will assume negative polarity. The center electrode of the plug is always hotter than the side electrode. Since it takes less voltage to cause electrons to move from a hot to a cold surface, current flow must be from the hot center to the cooler side electrode. If the coil is connected so the plug center electrode is positive, up to 40% more voltage will be required to fire the plug. Now I know the new automobile ignition systems using the lost spark system fire every other plug with reverse polarity but they are also using extremely high output coils, multiple firings & platinum plugs with big plug gaps.

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Mike C.

10-14-2001 14:41:06




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 Re: Re: coil question in reply to Clooney, 10-14-2001 06:31:43  
Thanks for the response Clooney. I had not thought
about it from the perspective of the spark plug
and the fact that a hot electrode will much more
easily emit electrons, an effect similar to a vacuum tube rectifier

Mike C.



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Mike C.

10-14-2001 14:38:57




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 Re: Re: coil question in reply to Clooney, 10-14-2001 06:31:43  
Thanks for the response Clooney. I had not thought
about it from the perspective of the spark plug
and the fact that a hot electrode will much more
easily emit electrons, similar to a vacuum tube.

Mike C.



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Mike C.

10-14-2001 14:38:32




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 Re: Re: coil question in reply to Clooney, 10-14-2001 06:31:43  
Thanks for the response Clooney. I had not thought
about it from the perspective of the spark plug
and the fact that a hot electrode will much more
easily emit electrons, similar to a vacuum tube.

Mike C.



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