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lol that the solution to generating the inductive spike from a coil's magnetic field breaking down is to just put a relay in there and connect nothing to the load terminals if its stupid but it works 
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Dec 6, 2020 22:16
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Tomarse posted:I'm not sure why it needs 100v when its running on 12v but I am not clever enough to argue with electronics. Slack suggested a BC63916-D27Z and I found 5 x for £3.60 on ebay its not very elegant but if it works it works. the reason you need a higher voltage rating on the part is the same reason you need to implement the circuit in the first place. when you open the circuit that is feeding an inductor, the voltage spikes up and then rings. the tach is looking for that inductive spike to detect a cylinder firing event. heres an example waveform from a random website:  the reason this happens is because inductors create a magnetic field that wants to stay static. magnetic fields are created by current. as long as the current remains, the magnetic field remains; the inductor is happy and nothing happens. when the circuit is interrupted, the current flowing through the inductor is zero. but the magnetic field still exists, and it consumes itself trying to induce the current to flow again (a current creates a magnetic field, and a magnetic field creats a current). since the circuit is open, the voltage goes up and up and up trying to make a current flow, but it won't. when the magnetic field is exhausted, the voltage goes back to zero. so because you're intentionally creating a voltage spike to drive your tach, you need a part that will withstand that higher voltage. the steady state voltage is low, but a high instantaneous voltage can still damage the transistor. i hope this makes some kind of sense and also that i havent mixed up stuff i half-learned in college
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Dec 7, 2020 01:07
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