Just to clear the air. The mosfet/clock failed without ever being in the car. It was test running on the service bench, safely connected to a well filtered 13.6 volt power supply. (unfortunately one that does NOT have current limiting..) So I think we can eliminate externally generated events.
Kerry On Tuesday, January 14, 2020 at 9:43:11 AM UTC-5, GastonP wrote: > > As we are talking of an event that took days to happen, on a solenoid coil > that can take up to 5 amps and in an automotive environment I wouldn't > discount that repetitive effects of seemingly negligible effects and > perhaps marginal components and unexpected power surges could fry a MOSFET > that drives a relay that uses an 1N4007 as freewheeling diode. > > We also know nothing about the car itself and we cannot assume that we > have the old watch in a new car. Actually I think it is reasonable to > assume that the situation is quite the opposite: an old car with extreme > power transients all over it at crank up time. One of this cranks, or a > failing alternator or dynamo regulator plus a weak (high internal > resistance) battery can send even hundreds of volts transients through the > power line, zap the MOSFET and then burn the coil. > > On Monday, January 13, 2020 at 4:33:33 PM UTC-3, gregebert wrote: > >> >> If the MOSFET turns off very fast, it's possible the free-wheeling diode >> will not turn-on sufficiently fast to clamp the spike to a safe level; >> given the currents involved in this circuit, I doubt this would happen. But >> if this was an electric vehicle, engineers will be spending a lot of time >> optimizing the design tradeoffs and probing around with a scope. >> >> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/579032c2-1cc1-47f7-b0b5-51157b25e294%40googlegroups.com.
