AEVA Forums

Hello there; some time ago, I found an Indian company offering copper squirrel cage rotors in Ali Baba web:

http://www.alibaba.com/product-free/100 ... Rotor.html

I know Tesla motors roadster uses a copper squirrel cage; that's one of their "secret sauce" components a for killer AC motor. Less heat to move out of the motor...
Maybe somebody here would be interested. Racers could contact the company for sponsorship or some other deal.

I know I would like to have one!

Disclaimer: I don't know this company. In fact, I didn't try to contact them, my EV project is just too modest

SEW Australia sell motors with copper rotor options.
I have rewound them for people for EV's in the past.

You should note that a copper rotor motor was less torque than alloy ones.
This due to rotor resistance. High resistance rotor means more torque.

Yep, I read a pdf about copper rotors which mentioned the issue:

http://www.google.es/url?sa=t&rct=j&q=c ... Mg&cad=rja

However, it looks like a minor reduction (the example mention 85 Nm against 90 Nm), and only at the starting point.

I guess SEW sell their copper rotor products at very expensive prices, right?

You are right the full load stays around the same, Its the pull out and start up torque the is reduced with Copper rotors.

The SEW copper rotor motor is around $500 extra.

Here is a little artical on inrush currents .
http://www.danfoss.com/NR/rdonlyres/AC8 ... gTrips.pdf

Jon,

Pull out torque, start up torque and inrush currents are completely irrelevant in applications where you're running from an inverter/VFD.

For EV use, there are no downsides to a copper rotor apart from higher cost.

Hi James got the bugs out of those controllers yet?

Start up torque is a big issue for any EV,
From my real world experience with EVs an 15 years experience with Drives used with rotating Industrial machines.

An alloy rotor motor gives you more start up torque point 1.
Most Ev applications are limited by the controllers current, so you want the most torque for the smallest amount of current right.

So I think it’s very relevant no one wants a sluggish EV.

Here is another case study for you but as you know an EV is a whole new ball game.
http://www.leonardo-energy.org/webfm_send/220

Starting torque

The copper rotor motor has the advantage of a high torque at running speed. Its starting
torque is lower than in aluminum rotor motors (85 Nm instead of 90 Nm in a 5.5 kW
motor), which is bene¯cial for gear box life. In applications where lower starting torque
is a problem, a modi¯ed design of the rotor slot o®ers a solution.

3.3 Higher start-up current

The higher conductivity of copper, i.e. its lower electrical resistance, will result in a
slightly higher start-up current (7.5 times the nominal current for a 7.5 kW copper rotor
motor, instead of 6.5 times for its aluminum counterpart). The use of a soft starter can
be used to avoid that this higher current a®ects the electricity system. Also, since motors
are increasingly being driven by inverters, inrush and starting currents become less of an
issue.

3.4 Rotor inertia

The higher rotor weight increases rotor inertia. This improves the motor's e±ciency, but
can be an problem in certain applications { for example motors that frequently switch
direction at high speed.

Jon, an induction motor running from a VFD does not have a 'starting torque' or a 'start-up current'. Both of these artifacts are only seen when hard-starting with a direct (DOL) connection to the grid.

When running from an inverter/VFD, the various rotor & stator fields and currents are controlled such that the motor is running at it's optimal point at all times, there is no moving back and forward along the classic torque/current curve - that only applies when running from a fixed frequency.

Yes, copper rotors also have a higher inertia, which we couldn't care less about in an EV - you've already got 1000+kg of vehicle inertia, an extra 5-10kg of rotor mass is trivial.

Just to stir the pot some more this small company is using alloy rotors.

Catavolt wrote: Hi James got the bugs out of those controllers yet?

Loaded question?

I can confirm everything James said. The only question is whether the slight increase in efficiency is worth the slight increase in vehicle cost.

-- Happy Tritium customer

Catavolt,
is that a picture of an EV1 motor, or something more recent?
I thought GM were using PM motors now.

Its for the new VOLT from what I gather its an option .

http://youtu.be/k-34MBWNIJ4