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AC conversions

Posted: Mon, 24 Sep 2007, 18:05
by roddilkes
Does anyone know of a motor manufacturer that can produce a motor with the following specs?

250VAC three phase, air or water cooled
10-15kW continuous input
50kW+ pulse input
0-8000 rpm
< 60kg

I am convinced that the future of EVs lies with AC technology. Natural regen, high efficiency, light weight etc. The motor in the Tesla roadster weighs 30kg!
The cheapest commercial AC conversion is about US$20K but I think we can do better than that.

Control is not the problem as far as I can see, it is the lack of an affordable motor that is the sticky issue here.

AC conversions

Posted: Tue, 25 Sep 2007, 04:34
by Thalass
I haven't seen an AC motor for a decent price, yet. I agree, though. AC is the future, it just needs a kick start for mass production to lower the prices - though the same could be said for DC, it has a head start. :P

AC conversions

Posted: Tue, 25 Sep 2007, 07:37
by acmotor
The motor you seek is an off the shelf industrial item in USA and Japan in the 240V AC 3 phase version. (240 in delta and 415 in star)
In Oz it will be 415V (connected in delta or 690 V in star).
Don't be afraid of the voltage though. It means you have less current.

You would have to make a special order for one of the OS models or you could rewind a SH unit in Oz.

Suitable motor is Western Electric 1AL132M-2 induction motor. Around 90% efficient.
2 pole 11kW @ 3000RPM cont (36Nm). will rev to 6000RPM at reduced torque (50Nm peak) @415V or full torque all the way if supply is 830V.
Peak torque at 0-3000RPM will be approx 100Nm (415V supply) That's around 36kW @ 3000RPM and up to 72kW @ 6000RPM if you have the voltage.

If you get one re-wound you can select suitable voltages.

The controller you use needs to be able to supply at least 4 times the name plate motor current to handle the peaks.

Air cooled ! Image

Weight 67kg
Check ABB they have a 57kg version from memory, HO range.

Beware of a 30kg motor with water cooling. The cooling system may add another 30kg and added complexity !

Beware also the high output high revving motor that requires a 35kg gearbox to get the revs down to something useable !

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Do consider though using a 4 pole motor (1500RPM nominal at 50Hz) as it's torque is twice that of a 2 pole motor.
True it can be up to twice the weight. I plotted up kW/kg and Nm/kg from data sheets and found that an 11kW 4 pole motor is the best option in induction motors by as much as 3:1 over other kW and pole options in the 1.1 to 22kW range of motor.
The 1500RPM speed is most suitable to couple direct to a differential... no gearbox.

AC conversions

Posted: Sat, 29 Sep 2007, 05:36
by Thalass
Well... this is very interesting! Which motor was this, that you found to be the best from the data you gathered?

More importantly... how much! :P

AC conversions

Posted: Sat, 29 Sep 2007, 06:20
by acmotor
I ran the specs for 1.1 to 22kW 2,4,6 and 8 pole motor (Nm,kg,Nm/kg and kW/kg) through excel and graphed them.
Very interesting. For the Western Electric motors (fairly typical of most manuf.), the 11kW 4 pole induction motor was by far the best combination of size, weight and power. By a factor of up to 3 over other sizes.
This was the start point for my AC electric conversion....Plus the fact that a one tonne vehicle seems to need around 11kW of power to cruise at 60-80kmph.
In an AC conversion, much of the complexity is in the controller. However the constant torque over much of the rev range and full power regenerative braking is the plus.
I bought an 11kW 4 pole for $250 S/H (an older heavier 80kg unit) But also priced a new WE motor at $535 + GST from New Era in Welshpool. Image

AC conversions

Posted: Sun, 30 Sep 2007, 04:23
by Thalass
...Wow. That's alot cheaper than I thought it'd be. And the place is in Perth? Awesome.

Perhaps we should compile a list of suppliers in WA for other newbies (like me :P). I've found it hard to locate info, especially for AC systems. Maybe my google-fu isn't up to scratch.

AC conversions

Posted: Fri, 26 Oct 2007, 07:40
by rbennett
Have you run into any problems with noise? I am assuming that you have no chokes or filters on the regen line. Do you knock out every radio station around you?

AC conversions

Posted: Sat, 27 Oct 2007, 04:14
by acmotor
Good point.
However I can wave the flag for Danfoss here as I have used their controllers in some quite electrically sensitive situations.
They use a 3 phase H bridge of IGBT's and return diodes in full quadrature returning to a massive 4700uF 800V capacitor bank and then via DC coils and RFI filters to the battery bank. The motor is connected with shielded cable and the whole system is rated to comply with EC and Australian EMI standards (in the R3 format).
Remember, this is all part of the Danfoss VLT5042 that I run. The designers expect the DC bus to be used !
Note. Danfoss do supply some controllers in R0 format (no additional RFI filtering) in the US as their EMI standards are not as high as EC or Oz. Look for the 'R'value in the full part number.
I would suggest that most commercial DC controllers and quite likely the homemade AC/brushless DC types do not meet the fairly stringent industrial EMI standards.
If you are interested you can visit and get their low down on EMI. Image