Hi, I have some noobish questions about inductance and current etc.
I captured a trace of my car's ignition coil using a scope and current clamp, and what I found was that it charges up to approx 9A in around 3.7ms or so. The alternator voltage is 13.85 and I know the coil's inductance is 5.85mH. But I don't know exactly the resistance of the whole circuit, and the ECU has some circuitry that limits current to 9A.
Is there a way that I can calculate the coil charge time mathematically? I found this calculator (
https://daycounter.com/Calculators/Inductor-Current-Power-Calculator.phtml) which uses the formula:
Ton_max= I_sat * L/Vand it gave me approx 3.8ms for the values above, which is close to the charge time I'm seeing on the scope. But I don't know if I really understand what this formula is saying. Is it "this is how long it takes to reach I_sat, given L and V" ? Is the resistance value implied, because I've specified I and V?
I thought the above formula might just be a rearrangement of:
T = L / R?
But this formula is supposed to tell me the time it takes to reach 63.2% of maximum current, right? I know that the ECU of the car limits the current to 9A. Does this mean that the current I'm seeing after approx 3.8ms is 63.2% of the maximum that would flow if it wasn't limited by the ECU?
Thanks!