- Sat Jul 30, 2016 9:26 am
#60605
That is so not how the coil works.
The coil is a transformer, it is an AC device and it does not work like the simple light bulb in series experiment. Transformers, and the coil, are rather counter-intuitive. For a start it is a current device not a voltage device. If you place a low resistance load on a transformer it will pull-down the voltage. If we place a resistance in the circuit it forces the coil to maintain a higher voltage during the spark discharge. They will only produce just enough volts needed to push their current through the given load (which then satisfies Ohm's Law); more load, more volts output. The spark gap may also be considered as a resistance. Electricity sparks jump at 10kV per centimetre in dry air at STP. The spark gap of 0.7mm is not in dry air and it is not at STP but some 8.5atm. Back of envelope 1kV per centimetre then. So a spark might jump 0.7mm at only 70V but we want a much higher voltage spark there to provide heat of ignition.
The equations are well known. We could use SPICE (software) or paper and pencil to work it out.
Read "Valve Amplifiers" by Morgan Jones ISBN 0-7506-5694-8, I worked with him, nice chap but he rides a Ducati.
This is the primary reason for using a suppressor in the circuit, to make a better spark. The secondary reason is reduction of radio frequency interference and electromagnetic pulses. An unsuppressed spark spits emf all over the place and can damage nearby (inverse square law) electronic equipment, the ecu, the sensors (incl EI) and your mobile phone or satnav.
