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Colin Furze Wheelchair replication , 800 Volt Drive

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patrick1:
Hi Guys !!.  i have been working on this one for 6 months. really cool build, almost as exciting as aviation.

Here is the inspiration for my project,              https://www.google.com/search?ie=ISO-8859-1&hl=en-AU&source=hp&biw=&bih=&q=colin+furze+wheelchair&gbv=2&oq=colin+furze+wheel&gs_l=heirloom-hp.3.0.0j0i22i30.1776.4795.0.6188.17.17.0.0.0.0.296.2109.7j6j4.17.0....0...1ac.1.34.heirloom-hp..5.12.977.fSaWeAO1Xms

I Have designed and built my own motors for the projects, several prototypes so far, and im slowly working my way up through the voltage problems, - so far my motor is up too 720volts - 730 volts without exploding, but i have made some silly compromises that render it inviable. - the electronics that is, - the motor is great ;-)



patrick1:
please be gentle ;-D

patrick1:
really my issue is the VB0e etc ratings on these transistors, - etc etc,

When i connected the Base, From the Collector.   it is leaking through and activating the transistors, - ,  EG it may work fine @ 200v, but problems @ 600v.

Also Back feeding and charging the gate, via the emmiter,

The best i could get the motor running, is using a completely separate power supply for each transistor, - in this case, small transformers with high resistance secondaries.

but this is wasteful of money and input power.,   it will run reliably at 700volts but with less torque than should be avaliable. (which is ok),  - but at 2watts per external transformer, = 8watts total. ... it is almost doubling my unloaded input power.

Circlotron:
Those four 10A10 diodes are a disaster waiting to happen. If any of the mosfets turn off while they are still passing current, there is absolutely nothing to stop the interrupted motor current putting a very high voltage across that mosfet. I think the diodes should be replaced by wire links. Of course, you may then run into issues with reverse recovery time of the parasitic body diode in the mosfets, and current crowding during that recovery leading to device failure. Power electronics is not as easy as some YouTube videos would have you believe.

patrick1:
I just recorded a video update of the motor, as it is, today.

hehe indeed, the backemf's were a problem from the start of this project,  i found that after about 280volts, the transistors would simply blow, even though they are NTP rated. - but they are still a concern because of how old they are technologically. ...  but i solved the offtime emf problems with a paralell capacitor across the motor,  (see the MOT cap, in the video)

but after i achieved about 400volts, i noticed the rotation of the magnets were generating a voltage, that exceeded the input voltage, - which reduces the input current, but it also backfed the drain pin, and wouldnt allow the transistor too switch off properly.,  but some diodes fixed that (albeit slow ones)

and after i hit 500v,  the collectors started too leak on the bottom end of the H Bridge.,  which is still a problem, - i had too remove darlington pairs at that point, and drive the FETS with seperate power supplies, - thats my biggest problem right now, - but running up too the max of my power supply right now, 740 volts, - .   im about too replace the base drive transformers with some tiny SOC package dedicated dc-dc converters.  - but i give that 50/50 change ... at best.

anyway when the big motor gets built next, i might consider just making my own base drivers with IR leds and solar cells.   -  either that or just bite the bullet and use a commutator

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