Yikes! People spend a lot of time and usually a few tubes of mosfets
figuring out those sorts of parameters. I still don't have complete
reliability at high powers in my BLDC controllers (eg, 40+ battery
amps, 36+ volts). I think if I make all the gate wires twisted pairs
straight from the IC pins I may have dealt with the transients. But I
haven't had time to try it yet... in fact I haven't made a controller
in a couple of years owing to other projects (like the Electric Caik
motor and now the Electric Weel).
My controller is on http://www.TurquoiseEnergy.com somewhere under 'manuals'.
Craig
=====
>My test setup using an inexpensive low power (10-30 Volt 10 amp) PWM
>motor controller to drive a bank of high power STP75NF75 MOSFETs
>looks very promising. These MOSFETs are rated 75 Volts and 80 AMPS
>so I plan to parallel at least 6 of them for 480 AMPS. The Battery
>Bank will be only 48 volts, which is sufficient for the ME0709 motor
>in my sailboat installation.
>
>In my test set-up I used a 400V 70 Amp blocking diode to across the
>motor leads to block the reverse EMF and a 1000 ohm resistor to
>maintain the MOSFET gate at ground when not energized by the
>controller. The unloaded motor responded very well over full range
>of controller. Questions for electronic experts:
>
>1. 1. Can I just simply parallel the MOSFETs on a single heat
>sink or do I need some resistive isolation between them on the gates?
>
>2. 2. What else should I use to protect the MOSFETs from
>transients? More diodes? Zener diodes? Capacitors? Have seen various
>written advice
>
>3. 3. If I assume all motor starts will be ramped up from low
>levels, and there will be no starting surge it does not seem that I
>need pre-charge capacitors found with many commercial controllers.
>Is this correct or am I missing something?
>
>Thanks in advance for any suggestions.
>
>Art
>
>
>
Posted by: Craig Carmichael <craig@saers.com>
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