# First EV, 3-phase



## minuti (May 15, 2008)

Hi there!

I'm planning out my first EV conversion. I haven't found the vehicle yet, but that should be the easiest part.

I'd like to use a 3-phase AC induction motor for the efficiency and regen braking, and I have some 3-phase speed controller schematics to base a design off of. Ideally, I'd like to be able to get highway speeds, and a 100mi range. I think it can be doable with a light vehicle and a good size battery bank. The high voltage on a lot of 3P motors should allow me to use thinner cables, saving a bit of copper weight. This seems like a good thing 

I found a Westinghouse like-new motor, 20hp, 230/460 VAC 3P, 3500 RPM, for $150, local. Should I jump on it this weekend? From everything I've read, 20hp should be fine, especially seeing how I'm not looking to get my tires squealing, just a general-purpose vehicle.

Also, a local surplus shop has a bunch of 12v 53AH SLA deep-cycle UPS batteries that have been taking up space for awhile now. He's asking $25 each, I should be able to get them cheaper by taking a lot of them. They're made by C&D Technologies. They seem like they'd be a fine choice to get started, am I right?


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## Twilly (Jan 22, 2008)

53 A/H seems a little small, As most are looking for 100A/H or more... Also depends on voltage too


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## xrotaryguy (Jul 26, 2007)

Are you planning a 240V system with the 53 Ah batteries? that would give you a 12.72kWh battery pack which is not too bad. How much does each of these batteries weigh?

The 20hp 3 phase motor you mentioned might be a bit large. I am building an Ev with a 15hp motor and I don't want to be outdone . Actually this motor was originally installed in a hybrid Ford Escort that was built by a university. The car must have been quite heavy. The back of the car was FULL of Optima Yellow Top batteries and it had a 3 cyl Geo motor up front too. Evidently this motor was large enough to push that car. If you're considering a light weight car, I would consider something in the 15 hp range. Perhaps even smaller. 

Actually, AC Propulsion's motor is tiny compared to my motor and some of their cars are pretty stinkin' fast. Their motor is pretty specialized though.

I agree with you about saving weight in copper with high voltage. conducting 600A under during acceleration requires much larger wire and thus much more mass than a system that only needs to conduct 250A under the same conditions.

I would be very interested in seeing the 3P controller schematics you have. I am actually in the process of designing a controller of this type myself.

You may also want to look in this thread for some more information


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## minuti (May 15, 2008)

If I had to guess, I'd say the batteries weigh 20-25 lbs each. I'm not great at estimating weight, so it might be more like 30. For a 240v system, that would be 20 batteries in series, totaling between 400-600lbs based on my weight estimates. Assuming he doesn't give me a discount, it would still only run me $500 for a 12kW bank. However, since I'm looking at AC systems, wouldn't the voltage be RMS? That would mean I would need a 336 VDC battery bank, meaning 28 batteries, which would be 560-840 lbs, costing $700. Not too much of a difference in cost or weight, and being able to get 240 rms might be worth it. I'll have to think about that one.

The motor, well, that's something else entirely. I have no idea what it weighs, but it's certainly small enough to fit in the engine compartment of just about any car I've seen. Of course, if the motor is really that powerful, adding another bank in parallel to get a 24kW total is sure tempting... Maybe I should get a light pickup truck to haul all my batteries 

As for 3-phase schematics, I've been looking at what people have done using AVR's.
Specifically, some of the design notes from Atmel look like a good starting point, although it's more software and block diagrams that actual schematics. http://www.atmel.com/products/avr/mc/ac.asp?family_id=607http://www.atmel.com/products/avr/mc/ac.asp?family_id=607 has some 3-phase AC induction controllers in software. I can't see how rigging up some mosfets or IGBT's to one of these controllers wouldn't result in what we need.


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## MrCrabs (Mar 7, 2008)

I would try and get up to 460 Vrms which would be closer to 600 Vdc.
Since the batteries are smaller in capacity, you want to minimize the amp draw as much as possible. Any idea what the motor will draw at 230 volts? I'm guessing somewhere around 40-50 amps, which would be pretty close to a 1C current draw on the batteries. If you want to keep DOD around 50%, you would get less than 30 minutes at a 1C rate.

You might also want to think about doing some cycle testing on a few batteries, before you commit to buying the whole bunch of them.
Any idea how long they were in service in the UPSs before getting pulled? If they were in a cheap UPS they could have possibly been abused (in terms of charging)

Also check out the EV Tech list http://evtech.org/ when you start getting into your controller design if you have any questions. Lots of electronic gurus on there.


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## minuti (May 15, 2008)

I have one of those batteries already, I never even thought to do cycle testing. They're all in great physical shape, so I don't think they were abused too much. Any pointers for cycle testing? If I had to guess, I'd say I could charge it up all the way, and then wait an hour or two to see if/how much the voltage drops when open. Then I would attach a known load to the battery and see how long it goes.

I would go with NiMH, but the cost is prohibitive. I don't currently have a car right now, so I'd like to have a little bit of money in case this whole electric thing doesn't work out. Ideally it would be nice to be able to get the minimum number of batteries to prove it works, and then add a number of good, hi-capacity batteries.

I registered on the EV Tech list, thank you for letting me know about it. I'm SURE it'll come in handy.


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## MrCrabs (Mar 7, 2008)

minuti said:


> I have one of those batteries already, I never even thought to do cycle testing. They're all in great physical shape, so I don't think they were abused too much. Any pointers for cycle testing? If I had to guess, I'd say I could charge it up all the way, and then wait an hour or two to see if/how much the voltage drops when open. Then I would attach a known load to the battery and see how long it goes.


It takes about 24 hours for a freshly fully charged to lose its surface charge, but at the same time, as soon as you put any load on the battery it will lose its surface charge.

I was thinking the same thing as you, charge it up fully, apply a known load and check the voltage from time to time. See if you can find any specs on the battery about what voltage corresponds to what DOD. Don't go below 10.6 volts tho, thats when you run the risk of reversing a cell (pretty much 100% DOD)
If you can try different loads, so you can try and figure out the Puekert value for these batteries


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## Mastiff (Jan 11, 2008)

> I would go with NiMH, but the cost is prohibitive. I don't currently have a car right now, so I'd like to have a little bit of money in case this whole electric thing doesn't work out. Ideally it would be nice to be able to get the minimum number of batteries to prove it works, and then add a number of good, hi-capacity batteries.


Based on this and the fact that you want a 100 mile range, I'd recommend against having a home made EV as your only/first car.

No one else here has discussed it but a 100 mile range requires a huge amount of battery power.

At highway speeds of 65MPH lets say your EV uses 350WH/Mile driven at that speed.

350WH/Mile times 100 miles = 35,000 Watt-Hours of power used.

Now you'll need at least 25% more than this(If you use a Lithium Chemistry Battery) in your battery pack meaning 43,750 watt-hours.

If you use a Lead-Acid pack, due to it's inefficiencies you'll need at least 55% more meaning 54,250 watt-hours.

This is a serious amount of batteries, at 336 volts DC you'll need 161.45 Amp hours.

Check out our Wiki if you don't trust my math:
http://www.diyelectriccar.com/forums/showthread.php/ev-information-669.html


This will not be a cheap endeavor.

Perhaps if your range requirements where less?


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## minuti (May 15, 2008)

The range requirements are one reason I'm aiming for AC. Unless I'm misunderstanding what I've been reading, a 3-phase ac induction motor is far more efficient than a DC motor. I fully understand that with a DC system, 100mi almost necessitates lithium, but I thought that with an efficient motor and regen braking, it could be doable.

Furthermore, isn't 350WH/mi a high number? According to the thread you've linked to, a lightweight car can use just over 200WH/mi at highway speeds, and a medium weight car can use around 300WH/mi. All the parts of that thread are talking about DC motors and systems, so I assume that those WH values are based on DC motors. Because my primary design goals are range and ability to reach highway speed, I plan to use as light of a vehicle as I can find, and I certainly plan to consider modifying the body for aerodynamics.

However, it's entirely possible that the increased heat losses in a controller due to switching 3 phases instead of simple PWM make the efficiency difference negligible. If that's the case, it would seem that 3-phase is more hassle than it's worth!

I'll set up a test for that battery this evening. Part of me is hoping that it performs well, so that I have a cheap source of battery, and part of me is hoping that it fails, so that I have to buy REAL batteries!


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## dataman19 (Oct 7, 2009)

Multiuti,
I agree with Mastiff, wholeheartedly.
It would be better if you used a Kit for your first AC Drive system.
In fact I have a recommendation:
...
http://www.evparts.com/prod-MT5615.htm
...
Don't like that one, try this one::
...
http://azuredynamics.com/products/force-drive/documents/AC55_DMOC445ProductSheet.pdf
..
the AzureDynamics web site is here:
...
http://azuredynamics.com/products/force-drive/TractionMotorswithDigitalMotorControllers.htm
...
I know the frustration of wanting to do your own. But most of the do your own first timers deal with DC Motors and they are more forgiving when it comes to a controller.
..
It is relatively easy to build your own controller for say a go kart - but a 100Amp AC Inverter/Controller with Current Limiting, Hysteresis monitoring and failure sensing is not for the faint of heart.
.. We are not talking about just paralleling a few Power-MOSFETs. The Device protection alone is a page of math and tons of what iffs....
..
Picture this - A plasma torch under your hood, or plasma Fireballs rolling around under the hood. Neither will be very entertaining or pleasant.
Seriously, take Mastiff's toned down suggestion and buy a kit.
..
You will be a lot happier in the end and a lot more stress free.
..
But hey, I know what you are going through, been there, done that. But take the advice of one of the masters (Mastiff) - Kit First, creative license second.
..
dataman19


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## Sunking (Aug 10, 2009)

Have not read all the responses, but based on 300 wh/mile for a DIY EV (ambitious) means a minimum 30 Kwh battery capacity for 100 mile range.


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