# using 400V three phase industrial AC?



## zaraf (May 11, 2017)

Dear community, I am researching on building an EV from scratch . I have a possibility to use an industrial Motor which has following specs: Voltage= 400V +-5% Power= 22KW Current=41 Amps My question is, isnt 400 V AC (565 DC from battery using rms formula) supply too much in a car? What could be the challenges in terms of design and safety? Can any Motor Guru advise me on this. Thanks.


----------



## lastcyrol (Dec 12, 2015)

Without details on the motor make and model, I'd speculate that the 400V is DC phase to phase which is around 230V AC.


----------



## Coulomb (Apr 22, 2009)

lastcyrol said:


> Without details on the motor make and model, I'd speculate that the 400V is DC phase to phase which is around 230V AC.


No, 400 V three-phase is genuine 400 VAC phase to phase, or 400/sqrt(3) = 230 V phase to neutral. [ Edit: but motors never use a neutral connection; I mention this to point out why 380/400/415 V is a common 3-phase voltage level; it corresponds to 220/230/240 V phase to neutral). ]

Yes, 400 VAC is a little high for EVs; you do need around 400 x sqrt(2) = 565 V on the DC bus, which would normally imply a pack voltage that high. I've been involved with a 720 V nominal conversion, so it can be done. We used a custom industrial motor to get 22/26 kW continuous (@ 50/60 Hz) into a 132 frame (~ 10.4" diameter).

It's occasionally possible to find an off-the-shelf motor wound for about 400 V when configured in Y, so you can re-configure it for 230 V delta (as we did), but it is rare. Generally, you want to over-voltage the motor, so you can get more than ~3000/3600 RPM from it (50/60 Hz), so that it better suits a typical EV drivetrain. That allows you to get a lot more peak power then the noninal (continuous) power of the motor, but that still requires a high DC pack voltage.

You can occasionally find motors designed for Japanese mains, which are 100 V phase to neutral, or wound for other voltages. It is also possible to rewire a motor for lower voltage, but again you have to be very lucky to find one that is suitable (see http://forums.aeva.asn.au/forums/changing-an-induction-motor-voltage_topic1237.html ). Finally, it is possible to have any motor rewound for whatever voltage you want; this involves burning out the existing wiring and starting again.

Unfortunately, most of these options take away from the main attraction of using off-the-shelf 3-phase induction motors: they are plentiful and can be found cheaply. As a result, such conversions are rare.


----------



## brian_ (Feb 7, 2017)

Some commercial EVs are converting up from battery voltage to a higher motor voltage (such as doubling about 360 V), but I can't imagine the cost of that converter making any sense, if just to use a cheap motor. It's done to support high motor speed and to limit current out of the inverter, not to enable the use of an existing motor.


----------



## Ivansgarage (Sep 3, 2011)

zaraf said:


> Dear community, I am researching on building an EV from scratch . I have a possibility to use an industrial Motor which has following specs: Voltage= 400V +-5% Power= 22KW Current=41 Amps My question is, isnt 400 V AC (565 DC from battery using rms formula) supply too much in a car? What could be the challenges in terms of design and safety? Can any Motor Guru advise me on this. Thanks.


Here is some good reading on AC electric motors for electric vehicles.


----------

