Looking at the 30A mosfet from SparkFun FQ30N06L it states that
Rdson =0.035 ohm ( ypical) at Vgs=5V and Id = 16A
Am I wrong in my calculation that the power loss in the mosfet is thus I2R = 16 x 16 x 0.035=8.96W!!!!
So if this was a 12V 16A supply (192VA) the losses are about 4.5%
Your calculations look right. You'd probably need a heatsink at 16A. It's rated up to 75W (and you would need a big heatsink for that).
RodMcM:
Looking at the 30A mosfet from SparkFun FQ30N06L it states that
Rdson =0.035 ohm ( ypical) at Vgs=5V and Id = 16AAm I wrong in my calculation that the power loss in the mosfet is thus I2R = 16 x 16 x 0.035=8.96W!!!!
So if this was a 12V 16A supply (192VA) the losses are about 4.5%
So you're thinking of having approximately 16 amp of current running through this mosfet --- constantly, right?
Possibly a current up there. I was just a little shocked with the power dissapation at what is 1/2 of the rating of the mosfet
Is there a more efficient way of switching a 16A constant current load?
If you go anywhere the continuous current rating of a MOSFET you are by definition running at near
the max dissipation of the package (assuming infinite heatsink). That rating is just another way to
say what the package max power dissipation is.
35 milliohms is a fairly low-specification MOSFET these days, many devices are available down to 5, 2 or
even 1 milliohm Rds(on) for high-current use.
And yes the I-squared dependency is easy to fall foul of in high current situations.
Thanks for that I will have a look around for lower Rdson units
Don't look around, go straight to the parametric search engine of a major electronics distributor...