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Old 06-17-2017, 12:24 PM   #3131 (permalink)
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Originally Posted by MPaulHolmes View Post
If it's a permanent maget motor, and you have an encoder, you shouldn't need different firmware. You might just have to set the number of pole pairs, motor type (permanent magnet with encoder) etc
Thanks Paul,

Some time ago there was a question about lowering the cost of the AC Controllers for a production run by using parts that were rated for lower voltage, less capacitance, etc.

Did you ever look into the cost savings? I remember thinking (and I think I posted) that the cost savings would not be significant compared to the PITA of tracking all of the extra components.

The SEVCON controller is *TINY*. 1.5 inches thick, about the length and width of a sheet of paper, air cooled, and not much for fins. I have trouble believing that it will do 650A for more than a few seconds before it overheats. The back of the controller is maybe 3/16 inch aluminum and is just bolted to the frame. No thermal grease even! ... or none that is left after the guys at the mine did their service, anyway.

The caps inside that SEVCON must be very small and have incredibly low ESR.

After I get one of these things running I expect that I will be adding a *LOT* of instrumentation to see the temperature the controller is at, the battery amps and motor amps, the motor temps, etc. I'm also looking at monitoring the ESTOP circuit. The interlocks include a safety lockout switch, the key switch, the parking brake, the 'gear' selector (F, N, R), the speed selector (L, M, H), charger plugged in, feedback that the contactors closed ... and perhaps other stuff? Troubleshooting the thing when it stops is not going to be fun without some monitoring and some sort of display ... maybe even a single LED that flashes morse code? How Geeky would THAT be?

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Old 06-17-2017, 04:47 PM   #3132 (permalink)
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I know they have low power 6 pack chips that can be very affordable, with a maximum current of maybe 10 amps or something. But they are not isolated. I"ve never messed around with those, but I would like to eventually. Those are rated for 600v though, so the sevcon probably uses some low voltage mosfets and boot-strapping (however the heck that works). The 6 isolated supply way of doing it is the sledge hammer approach.

I love the idea of the LED morse code!!
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Old 06-17-2017, 06:43 PM   #3133 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
I know they have low power 6 pack chips that can be very affordable, with a maximum current of maybe 10 amps or something. But they are not isolated. I"ve never messed around with those, but I would like to eventually. Those are rated for 600v though, so the sevcon probably uses some low voltage mosfets and boot-strapping (however the heck that works). The 6 isolated supply way of doing it is the sledge hammer approach.

I love the idea of the LED morse code!!
If the controller is very close to the motor, and it pretty much HAS to be on a vehicle ... then the reflected wave stuff is minimized (since the impedance of the cable is quite different from the impedance of the motor, any waves or pulses will 'reflect' from the motor and you can see a bit over 2X buss voltage at the motor terminals and the controller terminals). A 48V (57V) buss with full reflection is only 96V (115V). Add some safety factor ... 200V (230V) or so? That's still well within the MOSFET range. But driving MOSFETs to switch both the high side and low side takes a bit more circuitry and effort .. so I read. The EVTV episode where they take apart a blown-up TESLA controller showed a *BUNCH* of what looked like TO22 MOSFETs clamped to water-cooled tubes ... not sure if they mixed P channel for switching the positive side with N channel for the negative side?

Mouser lists 300V 400A IGBTs at $35 each, you'd need 6, plus the low esr caps .. anything else that would change based on the lower voltage? I know that you have 6 isolated supplies - would that change with the lower voltage? Somehow I doubt it.

400A does not match the 650A SEVCON I have but SEVCON have a 450A model available for the Ranger EV as well. I'm not actually sure what they would do continuous either. If you are pulling 650A for more than a few seconds, you would melt the cables, the motor, or the batteries even if the controller COULD put out that sort of power.

It's interesting to think about, anyway

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