How does an ignition coil work?
- Thread starter Shel_B
- Start date
Induction... because the wire is coiled up the magnetic energy is staged. Kinda like when you turn a blender on and all the water spins around even after you turn it off. The coil is also a transformer with primary and secondary windings-- the secondary side is the high voltage that jumps the spark gap.
When the 12 volt power going into the coil is spontaneously stopped, the coil fires. This used to be done with breaker points which wore out, and would shift timing as they wore, but has been solid state controlled since the mid 1970s.
Coil over plug was chosen because it takes coils a while to recharge, and because the high voltage wires are hard to maintain. If you cross section an ignition wire there's about 1mm of conductor and 8mm of insulation trying to hold it all in. So if you have a coil for each cylinder you get a hotter spark due to the longer recharge time. We used to do it with a distributor, rotor, wires, and one coil for the whole engine... that whole getup was limited by available technology.
Current ignition technology is capable of a way hotter spark than needed under most circumstances... there have been pictures of neglected spark plugs with no ground electrodes at all that were still sparking and running with a 0.250" gap vs the stock 0.060". This was motivated by emissions laws requiring a car to not need a tune up for an ungodly long amount of time, and this is where platinum/ iridium/ ruthenium slow-wearing spark plugs came from too.
When the 12 volt power going into the coil is spontaneously stopped, the coil fires. This used to be done with breaker points which wore out, and would shift timing as they wore, but has been solid state controlled since the mid 1970s.
Coil over plug was chosen because it takes coils a while to recharge, and because the high voltage wires are hard to maintain. If you cross section an ignition wire there's about 1mm of conductor and 8mm of insulation trying to hold it all in. So if you have a coil for each cylinder you get a hotter spark due to the longer recharge time. We used to do it with a distributor, rotor, wires, and one coil for the whole engine... that whole getup was limited by available technology.
Current ignition technology is capable of a way hotter spark than needed under most circumstances... there have been pictures of neglected spark plugs with no ground electrodes at all that were still sparking and running with a 0.250" gap vs the stock 0.060". This was motivated by emissions laws requiring a car to not need a tune up for an ungodly long amount of time, and this is where platinum/ iridium/ ruthenium slow-wearing spark plugs came from too.
Pretty good explanation. "Longer" is a relative term these days too. Some engines, such as the one in my Mercedes, will fire the spark plug up to 5 times per stroke! I doubt that could be accomplished using plug wires, and definitely not with a point type ignition.
