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So the 16mA proposed should switch the SSR fully on.
Do you mean dissipation in the SSR itself? I've no knowledge of its efficiency. Obviously the load is dissipating 90*6 = 540W, so if the SSR efficiency were, say, 99% (that's pure supposition) then it would be dissipating 5.4W.what do you think the heat dissipation would be at 90v 6A ?
Do you mean dissipation in the SSR itself? I've no knowledge of its efficiency. Obviously the load is dissipating 90*6 = 540W, so if the SSR efficiency were, say, 99% (that's pure supposition) then it would be dissipating 5.4W.
So the FET will dissipate much less power than the SSR, even supposing the SSR is suitable for a 90VDC 11A dump load.
OK. So the dissipation, using Mr RB's figures, could be up to 1.5 x 11 = 16W. That's implies quite a hefty heatsink.
If you're not too concerned about trip-point tolerance (say 5%) the circuit could be very simple (not much more than zener and FET). Tighter tolerance would need a more sophisticated circuit.
This should do the trick. If you need a 0.1V tolerance then R1 and R2 should be 1% tolerance. The voltage reference (U1 ), opamp (U2) and transistor (Q1) are examples only, convenient for simulation; other types could be substituted. The trimpot theoretically should give a 40-48V trip-point adjustment. When the trip voltage is exceeded Q1 conducts.
View attachment 72326
This should do the trick. If you need a 0.1V tolerance then R1 and R2 should be 1% tolerance. The voltage reference (U1 ), opamp (U2) and transistor (Q1) are examples only, convenient for simulation; other types could be substituted. The trimpot theoretically should give a 40-48V trip-point adjustment. When the trip voltage is exceeded Q1 conducts.
View attachment 72326