The Ford Barn - View Single Post

steve s · 05-30-2018, 09:38 AM

The science of what's going on is pretty simple. The executive summary is that it's easier for electrons to jump from the hotter spark plug tip than from the cooler spark plug rim.

More details:

The coil is basically an electrical transformer. It responds to a changing amount of current flowing thru its low voltage winding (due to points opening and closing) by creating a MUCH higher voltage, or energy, difference between the two ends of its secondary winding. In order for Conservation of Energy to be obeyed, the higher, secondary voltage can generate only a much smaller amount of current (albeit with a powerful "poke"!). If there's no viable, conductive path connecting the two ends of the secondary winding to each other, the electrons will be jamming up at the negative end and wanting in the worst way to get to the positive end--possibly even to the point of jumping through air to do it.

A sparkplug's spark consists of electrons jumping from one side of the gap to the other as they endeavor to get from the negative to the positive end of the coil's secondary winding. Depending on how the battery is connected to the coil, one or the other end of the coil's secondary winding will be negative and thus the potential source for jumping electrons.

The hotter any metal is, the easier it is for electrons to jump off of it, AND since the tip of the spark plug is out there surrounded by either combustion or that white insulator stuff, whereas the edge of the spark plug has a better thermal connection to the "cooled" cylinder head, the tip will be hotter and provide a stronger spark if it's at the negative end of the coil's secondary winding.

So, you want to set things up so that electrons are coming down the wire from the coil to the distributor, then out of the sparkplug tip, across the gap, and back thru various ground connections to the other end of the coil's secondary winding (which is unseen and always grounded).

As others have indicated, once that coil pumps electrons' energy up to a few thousand volts, they will jump the gap in either direction, but they'll do it better in one direction than the other.

05-30-2018, 09:38 AM	#8
steve s Senior Member Join Date: May 2010 Location: Kalamazoo Posts: 1,656	Re: Are Model A coils polarity sensitive ?? The science of what's going on is pretty simple. The executive summary is that it's easier for electrons to jump from the hotter spark plug tip than from the cooler spark plug rim. More details: The coil is basically an electrical transformer. It responds to a changing amount of current flowing thru its low voltage winding (due to points opening and closing) by creating a MUCH higher voltage, or energy, difference between the two ends of its secondary winding. In order for Conservation of Energy to be obeyed, the higher, secondary voltage can generate only a much smaller amount of current (albeit with a powerful "poke"!). If there's no viable, conductive path connecting the two ends of the secondary winding to each other, the electrons will be jamming up at the negative end and wanting in the worst way to get to the positive end--possibly even to the point of jumping through air to do it. A sparkplug's spark consists of electrons jumping from one side of the gap to the other as they endeavor to get from the negative to the positive end of the coil's secondary winding. Depending on how the battery is connected to the coil, one or the other end of the coil's secondary winding will be negative and thus the potential source for jumping electrons. The hotter any metal is, the easier it is for electrons to jump off of it, AND since the tip of the spark plug is out there surrounded by either combustion or that white insulator stuff, whereas the edge of the spark plug has a better thermal connection to the "cooled" cylinder head, the tip will be hotter and provide a stronger spark if it's at the negative end of the coil's secondary winding. So, you want to set things up so that electrons are coming down the wire from the coil to the distributor, then out of the sparkplug tip, across the gap, and back thru various ground connections to the other end of the coil's secondary winding (which is unseen and always grounded). As others have indicated, once that coil pumps electrons' energy up to a few thousand volts, they will jump the gap in either direction, but they'll do it better in one direction than the other.