RC-Monster Forums - Turnigy Trackstar 150A GenII ESC

Quote:

Originally Posted by Lizard (Post 428900)

Not sure if it's really necessary to use lowest-resistance FETs, atleast Uber on rcgroups says it's not needed when ESCs are properly designed. It's just a few watts, if you have the cooling to remove the heat that doesn't matter I guess (?)

For the FETs, there are many other considerations besides the on-resistance, but in general, lower is better, and more expensive.

One of the big reasons not to use higher resistance FETs is the energy that the die can absorb. The lower the resistance of the FET, the larger the die (the piece of silicon that is actually the semiconductor) and therefore the cooler the die runs.

"just a few watts" is enough energy to destroy a FET, and can make a HUGE difference in survivability of a controller.

Heat sinks can only do so much, because the package (the plastic and metal surrounding the die) has significant thermal resistance. So during high energy events (fast acceleration, hard braking) the die temperature rises much faster than the heat sink temperature.
Th larger the die, the more survivable the MOSFET.

Today, there's no reason to use a 3 milliohm MOSFET, other than maximizing profit. It's easy and fairly inexpensive to use better FETs with much larger die.

Thanks!

Patrick