380~ AC motor + DC/DC boost powerconverter

2663 Views 7 Replies 5 Participants Last post by etischer, Oct 22, 2010

Alexander_B

Discussion Starter · Oct 19, 2010

soooo.. I have a problem.

I can get a VFD and AC (induction) motor for very cheap(tm), but.. 380-400v 3phase AC = 600v DC. so, I would need a 600V battery bank, wich is just not gonna happen.

I'm looking for a cheap conversion, best power/price battery atm is ofcourse the "standard" 50AH 12v deep cycle battery, but a 600v bank would weigh around 2000 pounds, maybe if I were to convert a bus or something, but not for a zippy sportscar.

Now I have 3 options:
- go LiXX and get 25-30 AH cells, weighing a lot less, but costing more than my student beer budget allows.
- get my 60$ motor rewound for lower volts for 500$. seems silly to me.
- build a xx kW DC/DC boost converter. (probably a couple 100$ too, hoping that it works the first time around)

boost converter would have some advantages, it would be easy to implement regen, (cheapo vfd probably doesn't support it standard so modifying power electronics is gonna happen anyway) and it seems like the most geeky solution, I can always take it out if i convert to LiXX later, rewinding a motor is hard to undo. on the other hand, a multi KW converter quickly becomes the bottleneck again.

so.. now what?

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frodus

· #2 · Oct 19, 2010

why would it weigh 2000lbs? just because you go up in voltage doesn't mean your current stays the same for the same power. It decreases. use smaller SLA batteries, and lots of them.

I'd either ditch the motor/controller and use a different motor/controller, or go more small batteries. If you rewind for lower volts, you may not be able to use the inverter.

a DC-DC boost converter is going to overcome the cost of the entire project for the amount of power you'll need for a "zippy" sportscar. And you'd be convertering power again, and decreasing efficiency. I guarantee its going to cost more than a couple $100. You're talking 10's of kilowatts (I'd estimate over 40kw), not hundreds of watts.

How much power continuous is this AC motor? how many amps continuous?

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major

· #3 · Oct 19, 2010

Alexander_B said:
so.. now what?

Lithium!

You probably should do this regardless.

Ditch AC, get different motor.

What most DIYers do.

DC/DC boost converter.

Try to find a suitable product on the market. Then search and find those who have done this, like when using ultracapacitors. You will see that ballpark cost is about $1/watt. And if you choose to design and make it yourself, you will spend your time and money making a converter and not making an EV. But on the other hand, it works for Toyota in the Prius.

AC motor rewind for 1/4 volts, 4x paralell strands wire.

Sounds simple, but try it and find out it will cost more than you think. And after that, you will need a VFD with 4 times the rating. But likely a better approach than the DC/DC.

Don't know/don't care.

Yep, it is up to you.

major

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Alexander_B

Discussion Starter · #4 · Oct 19, 2010 (Edited)

frodus said:
why would it weigh 2000lbs? just because you go up in voltage doesn't mean your current stays the same for the same power. It decreases. use smaller SLA batteries, and lots of them.

I'd either ditch the motor/controller and use a different motor/controller, or go more small batteries. If you rewind for lower volts, you may not be able to use the inverter.

a DC-DC boost converter is going to overcome the cost of the entire project for the amount of power you'll need for a "zippy" sportscar. And you'd be convertering power again, and decreasing efficiency. I guarantee its going to cost more than a couple $100. You're talking 10's of kilowatts (I'd estimate over 40kw), not hundreds of watts.

How much power continuous is this AC motor? how many amps continuous?

you're probably right, but the smaller (sla) batteries are (per ah) much more expensive compared to the 'normal' sized ones here, I'd end up with a lead acid pack of 3k+, in that case I'd rather get lithium for 5k that lasts twice the cycles and twice the distance per cycle, but I'm trying to keep the costs low for my first conversion.

motor.. something like 7.5kw continuous 24/7 rating, that would be something like 12.5 amps dc @ 600v. ofcourse I'd like to uprate it a bit, say 4x peak, and 1.5-2x cont. for not too long, ofcourse. should work?

and with zippy, I mean not slower than stock at the lights.

hm, the more I think about it, the less goodlooking this motor becomes.. time to call the forklift company, lol.

[edit:] aaaaaaaand nevermind. I called off the deal on the motor and vfd I had, now to look for a better suited motor.. call the forklift company during office hours, they're not awnsering their e-mail.

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frodus

· #5 · Oct 19, 2010

you're probably right, but the smaller (sla) batteries are (per ah) much more expensive compared to the 'normal' sized ones here, I'd end up with a lead acid pack of 3k+, in that case I'd rather get lithium for 5k that lasts twice the cycles and twice the distance per cycle, but I'm trying to keep the costs low for my first conversion

not if you buy them in bulk from a battery vendor. They're about the same cost per Ah for most SLA batteries.

motor.. something like 7.5kw continuous 24/7 rating, that would be something like 12.5 amps dc @ 600v. ofcourse I'd like to uprate it a bit, say 4x peak, and 1.5-2x cont. for not too long, ofcourse. should work?

that all depends on your VFD and what it can put out and if you can keep it cool. Thats not a ton of continuous power though. How heavy is the motor?

and with zippy, I mean not slower than stock at the lights.

good luck on a low budget with SLA's.

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Alexander_B

Discussion Starter · #6 · Oct 19, 2010

frodus said:
not if you buy them in bulk from a battery vendor. They're about the same cost per Ah for most SLA batteries.

thanks, I'll look into that.

that all depends on your VFD and what it can put out and if you can keep it cool. Thats not a ton of continuous power though. How heavy is the motor?

no its not that powerfull no, and I have no idea on the weight, so nyah.. nevermind that motor..

good luck on a low budget with SLA's.

thanks, I'll try. besides, I'd rather use LiXX over FLA over SLA, but I'm limited in funding, and if I have my EV rolling and legal, I can always upgrade, and if it doesn't work out, its better to get rid of a 1.5k pack of FLA's compared to buying a 5-10k pack of LiXX (not that I have 5k at this moment anyway.)

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DawidvC

· #7 · Oct 21, 2010

If you 1/4 Volt the motor as per AEVA, you can stay with your current gearbox, and get usable torque up to how much volts you are prepared to pay for. Remember that not all rewinders will do it, so check around to find someone willing to help you.

BTW, with the new HE ACIM ratings, a lot of manufacturers rerated their motors so as to get the best eff. figures. If you get a hi-eff motor, you should be able to get a higher nominal rating than the nameplate rating out of the motor, which means you get a better 60min rating as well.

For your invertor, you want to see what the maximum amps that the motor will allow you to draw, or the maximum the pack will allow, whichever is the lowest. Do not size it according to the motor nameplate.

Good luck with the conversion

Dawid

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