Quote:
Originally Posted by jyanof
The pictures provided show massive voltage spikes at a low current of 12A. The voltage spikes will get larger with increasing current (they're proportional). Even still, the smallest spike shown is 80V.
With Paul's design, we measured a voltage spike of 20V or so... at hundreds of amps!
You're correct that a flyback diode alone can be ineffective at clamping these voltage spikes. It must be implemented correctly with a proper layout that minimizes parasitic inductance.
Also, note that a coil resistor load will have significantly higher resistance and lower inductance than a real motor. So much less inductance that those spikes may be caused by the lack of input caps moreso than the inductance in the load. An air core inductor would be easy to make and put in series with the load, if you have some extra wire. The larger resistance will dampen the ringing more. Maybe use an old starter motor or something?
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I have tried my circuit both with and without capacitors across the battery terminals in different locations but I cannot find that they do anything to reduce inductive feedback or oscillations on the drain of the mosfets. As far as my testing goes, these capacitors do absolutely nothing to reduce inductive feedback on the drain. Is there somewhere on the internet that I can find before and after oscilloscope readings on the drain for a controller with and without these capacitors in place? At this point, I have to rely on my own testing and will call this myth busted.