# AC Motors and drives



## madderscience (Jun 28, 2008)

About all I can contribute here is that you need to locate an 'inverter rated' AC motor and a matching VFD (variable frequency drive) unit to power it. Like with DC, continuous Horsepower rating should be about 10HP per 1000lbs for your car (minimum) and peak horsepower should be several times that.

After that, all the other issues you usually consider will come into play: efficiency, cost, reliability, weight, etc.

Since you are thinking AC, a unit that supports regen would be a good idea too.

Good Luck.


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## Kirk_Wallace (Nov 20, 2008)

Here is what I have been thinking about. I have converted a few CNC machines. One of the common features I add is a VFD for spindle motor control. These have worked well and are getting pretty cheap, especially used ones from eBay. I am thinking that using a 5HP motor
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270295756304
http://surpluscenter.com/item.asp?UID=2009010314562625&item=10-2396&catname=electric
and vfd
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=140292368807
to convert a golf cart might yield some success.

An inverter rated motor might be better, but I believe these only allow for for a higher maximum RPM. Improving rotor balance, cooling and maybe bearings, of a standard grade motor may help.

I think regen for a DIY system is over rated, and should be considered after everything else is working in an acceptable manner.

One of the problems with these VFD's on my CNC machines, is low speed torque is pretty low, so a two speed transmission may be needed.

A braking resistor feature is included on most VFD's, but I think using a mechanical braking system as the primary braking would be prefered.

My guess is that the major problem will be in providing acceptable input power. 220 Volt three phase AC is the norm, but this is rectified to DC in the VFD, so 220 VDC might work. This will also require a large number of battery cells to get 220 Volts.

I have a 200 Watt VFD available to do some preliminary testing. I hope I don't blow it up.
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Kirk
http://www.wallacecompany.com/machine_shop/


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