T-Pain Is On A Boat: Re: [Electric Boats] Progress with DC brushless motor controller

Friday, August 1, 2014

Re: [Electric Boats] Progress with DC brushless motor controller

Remember that you must keep leads as short as you can. You will get induction problems if you don't. Another thing you must consider is that the leads are the same length to keep timing the same for all transistors, and yes it makes a difference. You have taken care of back emf at the motor and this should be fine. You may want to make sure that no sag on the output voltage. If the voltage is not up to snuff add the caps, as this is what they are for.

If you add caps after the output it will serve to smooth the output and reduce interferance with your electronics. Added caps will increase losses in heat but then nothing is perfect.

Last but not least, your mods are not fcc approved. You will want to make sure that interferance is at a level that will not receive complaints.

Kevin

On Tue, Jul 29, 2014 at 1:28 PM, jortlif@msn.com [electricboats] <electricboats@yahoogroups.com> wrote:

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