CrossRoads:
The IRF520 does not turn on very much with such a low gate voltage. It is expecting 10V to turn on full.
Interesting, thank you! If I may ask a question, where is that information? I see that the device has this spec:
Rds(on) = 0.27Ω @ 10v
Does your 10v figure come from the voltage at which the resistance is defined? As in, that's specifically the voltage for which the resistance is defined because at that voltage the device is considered to be fully on?
The IRL520 would do much better.
http://www.vishay.com/docs/91298/sihl520.pdf
Thank you. If I cannot get an IRL520, would an STP55NF06L or P55NF06L be a fitting replacement? This is the STP55NF06L datasheet:
https://www.mouser.co.il/datasheet/2/389/cd00002690-1795961.pdf
The STP55NF06L has this spec:
Vgs(th) = 1.7v (typical)
I'm trying to make sense of it. What is the "th" in parenthesis? What does it mean when a part number starts with "ST"?
From the graphs, I see that the STP55NF06L passes over 100 A at the Drain when Vgs=4v.