Quote:
Originally Posted by jbrewer
I've seen this comment many times in various places in this and other forums. The thing that puzzles me is that transformers/inductors are very efficient at what they do and aren't lossy (at least compared to other electrical components).
So... I googled to find an answer, and what I found doesn't make a lot of sense:
Like any other electronic component, excessive current flowing through the ignition coil may cause it to overheat. This occurrence is due to the spark plugs and wires having more resistance than anticipated, resulting in a voltage-current overload on the ignition coil.
I get the Ohms law heating especially since the wire gauge is likely very tiny in order to get the higher voltage on the secondary by lots of turns of wire. But "spark plugs and wires having more resistance" doesn't make sense to me in coil heating. And "voltage current overload" sounds like something AI would write. When voltage is high, current is low, and vice versa.
Higher voltage doesn't cause heating, and higher resistance doesn't cause "current overload" , but in fact does the opposite.
The position of the coil in a cub is pretty ideal... it's down low away from the cylinder temperature. In a typical V8 old car, it's on top of the engine near water jackets (hot) and, well...heat rises.
I'm not saying coils don't get hot but just curious as to why they seem to cause (or be blamed for) so many problems in our garden tractors. Is it just the DC current in the primary causing the heating? And if so, why is there no resistor block as in older engines to limit the primary current and in turn keeping the heavy IR drop outside of the coil? Resistors are much cheaper than transformers :-)
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I think the way to look at is this.....
Coils are devices which are low voltage, high current on the primary side and low current, high voltage on the secondary side. They are designed to use a happy medium of current on both sides to produce the desired spark on the secondary side.
If you consider the energy required to make a spark jump an air gap such as the electrodes on a spark plug and put in perspective that air is the ultimate resistor, if you widen the air gap you have essentially increased the resistance of the secondary. If you were to continuously keep widening the air gap (i.e. increasing resistance) you would require a continuously higher voltage out of the secondary to maintain spark. This would require continuously more current thru the primary to keep the secondary supplied. All resulting in heat and eventual breakdown.
The analogy of air gap is to represent the resistance of plugs, plug wires, etc. but it is also part of the secondary resistance.
Sorry if I made no sense but you won't be the first person I've confused.
