Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[MPaulHolmes]

I'm more interested in the poor suckers that can only afford lead acid, and can only put 72v into something, and only have 3 phase AC motors available that are rated for like 480vAC. Evidently, they are everywhere in 3rd world countries. A guy I was talking to in Ethiopia was trying to do a DC conversion, and there were NO brushed DC motors anywhere that he could find. He said 3 phase AC was all over the place, but they were all industrial motors that were rated for like 1700rpm at 480V or whatever. At the time I just told him he was out of luck because AC required a ton of batteries, and his car was not going to hold that weight. Here's a pic of it:



I think he may have given up, but he could have had regen, and a reasonable top speed, etc. with boosting. I actually get a surprising amount of emails from 3rd world countries of people who really really want to drive an electric car. I remember choking on the exhaust in Nairobi. People walk around with lung lesions from that crap. The life expectancy is like 45. (Of course not all related to pollution.) The "affordable" $40,000 tesla that will soon come out isn't going to improve the lives of anybody in Nairobi. We need to get straight up ghetto. haha

[thingstodo]

Originally Posted by P-hack

since it is kinda related, I'll just leave this here. But the idea is to push the fields to their current limit, and switch to delta well into the field weakening part of wye (and careful switching back) so you can push the field current back up (though that is going to affect bemf...).

this quick and dirty needs reverse blocking on the delta switches, so it is 3x dual igbt + 3 single reversed, though it may be possible to reconfigure the inverter or something and use less switches.

I'm just guessing here, probably time to sort out a dyno (or read bajillions of speculative papers and all the hieroglyphs therein).

I have seen two motors with enough leads that this could work. The first motor has 9 leads, 6 for both ends of each delta coil and 3 for the business end of the Y coils.

The second motor has 6 leads, with the phase cables for the delta and the phase cables for Y.

Both of these motors are 400 HP continuous and weigh more than a car (5000 lbs +)

I have seen small motors (under 10 HP) with several leads, that gives you the option of 460V Y and 230V delta. This appears to be popular.

One may need to rewind a target motor to actually gain access to all of the motor leads ... and perhaps install a larger junction box on the motor to terminate the leads. Not for the faint of heart ....

[MPaulHolmes]

OK I"m done with the lookup table and binary search for going from A/D result to resistance to degrees celcius. I should have done that a long time ago. It really helps having another person test things, because then I don't just quit once variables are usable by me, but is totally weird and unusable for everyone else.

Temperature is in the range of 0 degC to 126 degC, in increments of 1 degree.

Another practical issue: What would be a more user friendly way for people to choose the variables to display? Not a lot of people know binary. In fact there are only 10 types people in the world. haha. Maybe if they can input it in binary format, it would be easier than inputting it in base 10. That way they don't need to know what they are doing. they could just do:
0001 0101 0101 1110 or something.

[Astro]

Originally Posted by MPaulHolmes

I'm more interested in the poor suckers that can only afford lead acid, and can only put 72v into something, and only have 3 phase AC motors available that are rated for like 480vAC....

With an abundance of 3-phase AC. Why not get a motor rewound to a lower voltage. My motor is just a pretty standard industrial 3-phase motor rewound for 48V. Would work reasonably well with a 72V pack. Maybe not a highway speed machine but functional.
Also most of the cost in rewinding is the labour as it is quite a labour intensive task. But if you happen to live where labour is cheap then it is probably cheaper to rewind rather than buy extra components to boost your pack voltage.
Wind the motor for a real low voltage like say 24V and your 72V pack starts to be able to get some decent RPM out of the motor.
Of course that is all based on my almost total lack of knowledge of motor rewinding and motor voltage to rpm relationships.
But i am reasonably sure nice big, high efficiency, high current handling, light weight inductors would cost him more than a days labour at the local 3rd world motor rewinding shop.

[MPaulHolmes]

That's a really good point. If it was available, that would definitely be a better option. I don't recall seeing motor rewinding people, but for $2 a day it would definitely be cheaper. They must have something. They had bike repair people on the side of the road. They only charged me 20 cents to fix my crank, and that was the mzungu (white man) getting "hustled". haha.

[Astro]

Another thought. If the controller could somehow act as a battery charger as well then that would probably be a real benefit in a third world situation. Cheap 3-phase AC motors rewound to work with low voltage packs. Cheap lead acid battery packs. And a controller that takes whatever bit of mains power that can be found and can use it to charge the batteries. Lead acid battery pack so BMS not critical and could probably be omitted. Or if the controller couldn't do the charging then half a dozen cheap automotive 12v lead acid battery chargers could do the job.

[MPaulHolmes]

You are full of awesome ideas! I know that in a 3 phase situation, you could connect to the grid and run the controller in regen mode, which would charge the batteries. I bet the software could be adapted to charge when there is only single phase too.

[P-hack]

Originally Posted by thingstodo

One may need to rewind a target motor ...

Yup, but we are already discussing winding/modding our own inductors

re paul: 72v guy (and post apocalypse), it does seem like there isn't a lot of info on hacking the motors themselves, identifying and paralleling the field groups and carefully cutting/brazing new leads, securing everything when you are done, etc. Not as interesting a puzzle as boost converters, but lighter/cheaper/simpler/more efficient, more people would be able to do it if they saw a video.

i.e. if you have a 208vrms 4 pole (say 300v dc-link) with the poles in series, you can parallel them to a 52v motor (say 75v dc-link) by modding the end turns and the leads. If it happened to be in wye then even better, now it is a 43 volt motor.

Unfortunately we don't have the same knowledge base about specific AC motors for diy EV use, like we do with dc motors, probably a matter of time. and as thingstodo says, it is intimidating at first. But the motors themselves are relatively cheap. And I'm sure it would be a useful post-apocalyptic skill ("I'll trade you half my harem for your kool-mu inventory")

[MPaulHolmes]

This was an interesting story. I think it was the only pump repair person for 600,000? I'm not sure though.
Inside a Water-Pump Repair Shop in Kenya | iFixit

[Astro]

Originally Posted by MPaulHolmes

This was an interesting story. I think it was the only pump repair person for 600,000? I'm not sure though.
Inside a Water-Pump Repair Shop in Kenya | iFixit

Now there is a shop that could probably take on rewinding motors for cars as a side line.
Do one or two and before you know it everyone wants one done. As with most things it just takes a few people to work out how to do it and then the crowd surges because now they have a proven method to copy.