Paul3:
the mosfet should be able to do 3-5v on gate. However, if this was the case am in need of new mosfets?
That MOSFET certainly is not rated for less than 4.5V. Its threshold voltage is quoted as 1.35 to 2.35V,
which means its right on the edge at 4.5V gate drive. Normally you'd see on gate voltages about 3 times
the threshold voltage - a 3.3V safe MOSFET would have threshold of 0.5 - 1.0V or so typically.
If you look at the typical gate-charge graph in the datasheet for the IRLB8721 you'll see the
plateau voltage is about 3.6V (and remember the variability is +/-0.5V from the threshold specs.
This means the plateau could be 3.1 to 4.1V.
They really are pushing it calling it logic level at all, I'd suggest it really needs 7V gate drive for
good fast symmetric switching needed for efficient PWM.