# 18,000 rpm ac motor



## GadgetGuy (Feb 22, 2010)

I haven't done this forum thing much so I hope I am in the right place.

I've been reading and searching different threads but cant find anything on a high speed AC motor so I am asking the question.

Has anyone used a high speed spidal motor off a CNC machine for an EV?

I have a motor with the following specs (needs bearings replaced but everything else is good)
Giordano Colombo
Volt.....230
Hz.......300
RPM.....18,000 (yes 18k)
HP.......12
Kw.......8.8

I am vary new to the EV thing but it seems like if you could keep this motor fed it would handle all kinds of speed. For those who may not know the motors speed is controlled by a VFD (Variable Frequency Drive) that effectively becomes your throttle.

I don't know how to calculate how much energy a given motor will consume and that may be where the answer is but any help here would be appreciated. Has anybody tried this?


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## Tesseract (Sep 27, 2008)

Plug those numbers into the equation hp = (torque*rpm)/5252 and you get a rather dismal 3.5 ft-lbs of torque for motor that develops 12hp at 18krpm. You would be hard-pressed to use that in a motorcycle conversion because even though their gearboxes can handle much higher rpm, they can't usually handle THAT much rpm! 

As for how much power the motor will consume, that's easy: 8.8kW! At the nominal input voltage of 300Vrms, full power of 8.8kW requires 8800/300 = 29.3A of current.

Most EVs seem to work well with motors rated for somewhere between 25 and 50hp continuous output and a peak output of 3-5x that amount; this motor is about half the minimum size most feel is adequate, in other words.


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## major (Apr 4, 2008)

GadgetGuy said:


> (needs bearings replaced but everything else is good)


Hmmm, wonder why? 18,000 RPM 

The Tesla motor tops out 14,000 I think. High speed motors can be used in EVs. You just have to have the transmissions or gear reducers to handle that high speed. And typically, max power is well below max speed for these motors. 

Most of the DIYers try to keep the motor speed in line with what automotive equipment can handle. But in theory, higher motor speed can reduce the motor size for a given power output.

Regards,

major


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## GadgetGuy (Feb 22, 2010)

Thanks for the great info. I am new to this so all the info was helpful. Especially the math (thanks Tesseract.) I put those into a spreadsheet to help me understand motors better as i try to decide what to use. I am toying with the idea of getting a Mechatronics degree because I love to make things but just don't have the background for it. the degree would help me understand alot more.


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## TigerNut (Dec 18, 2009)

GadgetGuy said:


> Thanks for the great info. I am new to this so all the info was helpful. Especially the math (thanks Tesseract.) I put those into a spreadsheet to help me understand motors better as i try to decide what to use. I am toying with the idea of getting a Mechatronics degree because I love to make things but just don't have the background for it. the degree would help me understand alot more.


Make sure you do as much hands-on stuff as you have time for, so that you get a feel for the real-life applications of the material you learn in class.

On that motor, get the bearing part numbers (you can usually read them off the inner or outer race shell) and then go to your local bearing house to see what a replacement will cost. 18000 RPM capable bearings that can handle thrust and radial loads associated with 8 HP are not going to be cheap.


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