Good money after bad - Solar upgrade time

Author	Message
Solar Mike Guru Joined: 08/02/2015 Location: New Zealand Posts: 1255	Posted: 12:38am 09 Aug 2026         oreo said   Thanks for the input Mike!  Can you tell me how you arrived at me needing 150v Mosfets?  I just linearly scaled up the 80v mosfets everyone else uses in the Wiseguy 48v inverter. (see calculations below) From building numerous 1/2 bridge power circuits, some can generate quite high very short duration spikes, only picked up after looking on a scope trace, 72v base + a 40v spike is cutting it pretty fine using lower voltage mosfets. If you fire the thing up first at a lower voltage and spikes are low, then it would be safe to use a 120v device, or after measuring the ringing frequency and working out correct snubber values. I always go for at least 30% margin in device selection, thus my estimate of 150v; the common ranges are 80, 100, 150v noting that some Chinese manufactures also have 120v devices. I did use some Chinese manufactured 120v rated mosfets in one PV controller and they kept blowing up, even after measuring within spec Drain\Source voltages, Swapping out for 150v devices, never had a problem, does make me wonder at times about the validity of some manufactures published spec's. Mike