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Ed Blackmond wrote:
> Agreed, but these MOSFTEs don't have to switch the full pack voltage.
> Such MOSFETs with single digit mOhm Rdson are pretty inexpensive and when
> paralleled to get to the required current, reduce Rdson even more. This
> doesn't make any one MOSFET cooler, but the combination is cooler than a
> single MOSFET with a larger Rdson. The copper connection between them can
> also double as a heat sink.
>
1milliOhm is 40W of heat at 200A, 250W at 500A. The size you would need
is probably 10"x4"x1" just for the power electronics themselves, unless
you want to undersize them. Then add on cooling apparatus, which would
probably be another couple inches of thickness.

> Once I had a module that could ether be zero volts or V volts, the
> idea of
> a multilevel converter made sense. The BMS can be used to generate a darn
> good sine wave. Make three strings and operate them 120 degrees out of
> phase and the BMS becomes a variable frequency 3-phase drive. The
> multilevel converter makes a good charger too either from regen or the
> utility.
>
This is bad because it pulses high current into the batteries instead of
DC. My previous investigation into this showed the losses in this system
were unacceptable (I don't quite remember, I'm guessing 70-80% efficient
versus a controller at 96-98%).

Cory
 
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