I need help =(

[Tom F]

Well power devices can usually withstand higher temperatures then say, a big chip like a CPU or something (usually a max junction temp of 120ºC+)

I would have expected the controller to thermal before it got to a FET killing point anyway?

But i agree, it would explain the excessive heat and possibly the erratic performance (especially if just one phase of FETs had partially or completely failed)

Still haven't measured any loaded voltages...going to do that in a bit

[BrianG]

Originally Posted by Tom F

Well power devices can usually withstand higher temperatures then say, a big chip like a CPU or something (usually a max junction temp of 120ºC+)

Yeah, but the current spikes from a BL setup are very quick and any internal protection circuitry may not respond fast enough. Besides, I would NEVER want any electronic device I owned to get that hot! 120ºC is 248ºF!! Yikes.

If several FETs are bad, all that current load is being forced through what is left. The FETs have a low resistance, but this is reduced when you have several in parallel. With fewer available, there is more total resistance which creates a voltage drop and power loss, hence the heat.