/diy/ - Do It Yourself

>>1249510
the flyback diode will theoretically conduct 210A for a fraction of a microsecond. it only needs to be pulse rated for that, but most diodes have pulse ratings listed for a half mains cycle (~8ms) so you'll inevitably end up with a much bigger diode than you need.

assuming you're switching this coil with a fet and not a relay (please don't try to break 210A with a shitty relay) then the relevant parasitic elements are in pic related. the diode's inductance will try to prevent the inductor current from flowing through the diode as the fet is turned off, which will result in a voltage spike as the coil tries to force the current through the diode anyway. a capacitance (or RC snubber) directly across the fet can counteract this if it's sufficient. in less extreme cases the fet's inherent capacitance can manage sufficiently but not for you. the implications of this are that your diode won't ever actually see 210A, and your switch will see a voltage spike that could kill it if you don't add a snubber.