Re:How a Norco case killed 13TB of our data
by ChuckMcM on Sunday November 04, 2012 @01:50AM
(#4739160)
Came here to say essentially the same thing. In designing a 400A speed controller for my Battlebot I got to learn all about MOSFETs and their current ratings.
In this case the MOSFET is rated with a max current of 5A @ 25 degrees C if the gate is driven with a 5v signal. It has an 80 mOhm resistance when fully enhanced. So at 5A that is 2Watts of power dissipation (p = i^2r) and since the case has a thermal constant of 62 degrees C/W that means the case will be at 149 degrees C (25 + 62 2W) which causes Rds(on) to double and that 'explodes' the MOSFET. If the device was successfully carrying .5A loads then then the case is only good for about 20mW of power dissipation (which looks reasonable given the package size). So gluing a copper heak sink to the FETs with at least 2 sq inches of surface area would probably keep them alive with a .75A load. If you combined that with about 150 CFM of air flow at sea level (225 CFM at 8,000 ft) you'd stay pretty solidly inside the 'not to be exploding' parts of the parameter graphs.
In this case the MOSFET is rated with a max current of 5A @ 25 degrees C if the gate is driven with a 5v signal. It has an 80 mOhm resistance when fully enhanced. So at 5A that is 2Watts of power dissipation (p = i^2r) and since the case has a thermal constant of 62 degrees C/W that means the case will be at 149 degrees C (25 + 62 2W) which causes Rds(on) to double and that 'explodes' the MOSFET. If the device was successfully carrying .5A loads then then the case is only good for about 20mW of power dissipation (which looks reasonable given the package size). So gluing a copper heak sink to the FETs with at least 2 sq inches of surface area would probably keep them alive with a .75A load. If you combined that with about 150 CFM of air flow at sea level (225 CFM at 8,000 ft) you'd stay pretty solidly inside the 'not to be exploding' parts of the parameter graphs.