Simple spark or motor control

Hi. Just a rough sketch of how I’d like to create a spark controlled by a uno board but I’m missing some stuff. I think I need a resistor For the relay to uno board link and a capacitor between probably the 12 volt supply to the automotive relay and the outgoing power wire from the relay to the coil. What resistors are required and will this even work. I’m not electronics minded so want a simple system I can understand and repair easily. It’s for a automatic start system for my turbo based home made jet engine. I usually start it manually but would like to build an automated system

You need to investigate automobile coils a bit more. The normal ignition system has a current limiting resistor in series with the coil primary. The coil operates at about 8 volts, except when starting the engine when the resistor is shorted out for the short period of cranking the engine. While cranking with the starter, the battery voltage goes down to about 8 volts. Otherwise the spark plug will have a very weak spark when the engine needs a really strong spark to begin running.

Paul

I don’t need a strong spark to get the gas to ignite. It’s not used in an automobile compression situation. Although it won’t be hard to incorporate this current limiting resistor anyway.

Shouldn't there be a cap across the big relay's contacts? This is an old-fashoined points ignition system
basically?

These days ignition systems usually have a logic-level IGBT, not a contact set, and the IGBT is rated for repetitive high voltage breakdown. Probably worth googleing "automotive ignition IGBT"

Yes it’s an old points ignition system Mark and a cap in the system is necessary but will this circuit isolate the board from any nasty voltages caused by the coil. What size cap would you recommend.

Hi,
How fast do you want these relays to switch On and Off?

Thanks.. Tom.. :slight_smile:

It doesn’t have to be quick

Ripcrow:
It doesn’t have to be quick

Sorry not enough info, relays can only operate up to certain cyclic rates, due to construction and mechanical inertia.

Thanks.. Tom.. :slight_smile:

that's fair enough and the cycle rate of the relay will be quick enough as it only has to create a spark to ignite gas in the combustion chamber. Proper placement of the spark plug and the correct amount of rate of fuel-air should get a flame very easily