Quote:
Originally Posted by johnsiddle
Hi Guy's
Is a surplus industrial 3 phase motor suitable for an EV, if so what sort of rating would be considered suitable for an average size compact car, not a dragster just a potterer?
I have seen plenty advertised on ebay with ratings 3hp, 5hp and 10hp and does the number of poles feature in the equation?
regards John
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The simple answer is No. The 3 phase motors from golf carts and fork trucks are better, since they are already set up for lower voltage. But they are not often bigger than 3 HP.
A surplus motor is good for a utility vehicle. But it is likely too heavy and produces too little torque for a free-way capable car.
The industrial electric motors are designed to run 24 hours per day, for years. So they have more copper, more steel, etc in them to absorb the heat and radiate it to the local area. And most of them are air-cooled. The motors designed for use in cars are all moving to liquid cooling.
Electric vehicles are normally used for an hour or 2 before they are parked for a few hours. So you can push into the design factors .. and maybe run a 5 HP motor at 10 HP or 12 HP for that hour or 2. And push harder, to maybe 20 HP for acceleration.
One of the issues with the industrial motors is the voltage. To drive them you need quite a high voltage pack. 220V AC needs about 350V for the pack. That's OK if you are recycling a leaf pack or a bolt pack. Not so great if you have larger cells, like LiFePO4 prismatic cells.
To drive a 220V motor at 4 times the amps that it is rated for, you need more voltage. About 4 times the voltage at rated speed. Lots of these motors are 1800 rpm. That's a bit low to put into a transmission and have 60 mph out the other side. So you may also need to drive the motor at more than 60 Hz. The impedance of the motor, the inductance part, is related to frequency. So the higher the speed you want to go, the higher the voltage you need.
Alternately, you can change the wiring of the coils in the motor to drop the required voltage, but that requires a bit of luck with how the motor is wound, and some effort in tearing the motor apart, searching for and finding the coil connections, cutting the coil connections apart, soldering the coils together a different way, and putting it all back together again so that it works. There have been people that got it done, but I have not read of many.
I have access to surplus motors from work. I looked at a few larger motors as the electricians pulled them apart to replace bearings, or whatever else they were doing. The connections between coils on modern motors are not obvious to the untrained (mine) eye.