View Single Post
Old 03-05-2010, 01:31 AM   #3069 (permalink)
jyanof
Joe
 
Join Date: Feb 2009
Location: phx
Posts: 260
Thanks: 0
Thanked 41 Times in 34 Posts
Quote:
Originally Posted by CamLight View Post
Hi Joe,
Thanks for the links, I'll check them out.

Sounds like you have a good cooling system already in place...no need for heat pipes.

I'm a bit sleep-deprived right now but isn't the heat generated by the static resistance of a MOSFET proportional to the square of the current? That is, going from 200A to 400A would increase the power (heat) that needs to be dissipated by four times (Power = Current-squared times Resistance)?
Yah, the fan/heatsink seems to work well. I had thought about using heat pipes for an IGBT based power section. But, this is a whole other discussion

As for mosfet heat generation, it depends (mathematically at least) which term - resistive or switching - dominates the heat generation. The formula for switching losses is linear with respect to current, whereas the resistive losses are proportional to current squared as you mentioned. In our case, with the 20 ohm gate resistors in the controller and the really low Rds_on characteristic of the mosfet, the switching term greatly dominates the heat generation of the mosfet. Thus, the heat generation appears to be roughly linear with current (as calculated).
__________________
ReVolt AZ testing thread:

http://ecomodder.com/forum/showthrea...ting-9325.html
  Reply With Quote