Esp32 ignition coil

Hey i am trying to build ecu for my bandit250 its only control sparks its four cylinder bike with waste spark system.
My problem is how long i should supply curent to the coil to make spark.

The coil makes a spark when the current is interrupted, not when it is held steady.

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Can you observe it working and record the timing?

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I built an electric fence controller to keep chipmunks out of my tomato patch. It worked; there were no dead chipmunks and no half-eaten tomatoes.

Here is the schematic. I used a 10ms pulse every 800ms. I sold my oscilloscope so I couldn't measure the HV, but I could draw a 1mm spark.

You probably need to get an oscilloscope and look at the timing of the primary on the actual engine.

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If you do then don't connect anything directly to the oscilloscope. Take a small length of wire and wrap it twice around the spark plug leads and wire the scope input and ground to each end of the wire. You still get about 200V from this so keep your fingers clear and connect it up before you turn on the engine.

In fact you can get a wire ended neon light to flash by wiring it up to a pickup coil like this.

Have a look at other ignition projects from Arduino or auto labs ( Megajolt) . Most are open source and you’ll find coil control circuits .

Google is your friend

The term for how long you send current to the coil is called dwell. Need to see if you can find a data sheet for the coil.
If you can't find one, go to the MicroSquirt forum and someone might have the answer.

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The primary of the spark coil is at battery voltage.

Thanks thats what i have been looking for.
I have another question that why bjt use as ignition coild drivers. Not mosfets

Just a guess- speed. A BJT switch is faster than a MOSFET as a switch.

The timing of the current to the coil is interesting.
When the supply is connected the current rises at di/dt = V / L amps / sec
where V = 12V and L = inductance of coil primary.

The stored energy is the time integral of L i di/dt (sorry I cant do symbols.)

So the time that the "charging current" flows is important.

IF it has time to reach its maximum value (limited by a ballast and the coil resistance) then you get maximum spark energy.

You also need to allow enough time for the energy to be dissipated as a spark.

Now the "bandit250" revs up to 14,000 rpm which does not allow much time for all that.
This is one reason why modern petrol engines use a coil pack with a seperate coil for each cylinder.

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