# Emerson Commander SK 40hp VFD



## alexcrouse (Mar 16, 2009)

Got my hands on a commercial VFD, finally. Sadly, it seems this model has a non-removable DC Bus low voltage limit. This would require me to assemble a >400 volt battery pack! Does anyone have any experience with these drives?

As a side note: Where does one find an ACIM for a reasonable price? They seem pretty expensive for the "simple" motor design!

Thanks in advance!


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## subcooledheatpump (Mar 5, 2012)

I have used these drives before. I had a commander SK 30 HP VFD. They do work well for an EV in torque control mode, but in speed mode I'd be cautious about using it. If you have one with the built in brake chopper, attach a brake resistor. Otherwise it will just keep tripping on overvoltage fault. 

Several surplus stores sell induction motors pretty cheap. Use google and search for industrial surplus stores in your area


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## alexcrouse (Mar 16, 2009)

Nearest surplus shop has a 30hp motor for 2000$. Ouch.


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## alexcrouse (Mar 16, 2009)

Thanks for the brake resistor idea. What size motor would you recommend for a mid size car? Is a 40hp drive large enough?


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## subcooledheatpump (Mar 5, 2012)

ouch indeed, thats way too much. 

I can't really say for sure if 40 HP is really suitable or not. It would work, although it might not be ideal. Don't know if this will help but, I have a 75 HP drive and a 30 HP motor in an extended van. It works but it's not exactly a road rocket. I'm pretty confident it can go 60 MPH, only had it up to 50 though. So if you're talking half the vehicle with about half the motor and controller it should be able to achieve something like that I would think


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## Siwastaja (Aug 1, 2012)

alexcrouse said:


> As a side note: Where does one find an ACIM for a reasonable price?


Try junkyards. These motors come in from dismantled industrial machines and if they turn freely they are 99% surely perfectly fine. I have paid 2€/kg for these motors at a local junkyard and every motor so far has been fully functional, even the bearings. This is also the most efficient way of recycling. Try to find a 4-pole motor with as low voltage windings as possible.

There is also a possibility of simple rewiring to halve the nominal voltage of a 4-pole motor which would allow you to double the power with the nominal battery voltage.

Try to find a motor which is 230V in delta instead of 400V. Then reconnect the windings for 115V. 115Vac = 160Vdc, which would allow you to overclock/overpower by factor 2.5 with a 400V battery pack. For a 1800 rpm motor, this would be 4500 rpm with nominal torque. This would allow you to go to highway speeds.


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## Siwastaja (Aug 1, 2012)

You can also try to modify the VFD low voltage limit. It very likely has a resistor divider for voltage measurement somewhere, so just change the resistor values. Of course there will be some limit to this if it uses the DC bus to power itself.


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## alexcrouse (Mar 16, 2009)

Siwastaja said:


> You can also try to modify the VFD low voltage limit. It very likely has a resistor divider for voltage measurement somewhere, so just change the resistor values. Of course there will be some limit to this if it uses the DC bus to power itself.


 This is what i was thinking. The drive will power up from 220vac, but says Er UU (cheap screen, it means UV). Drive will do nothing but run the fans in this state.


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## alexcrouse (Mar 16, 2009)

Would LOVE to get my hands on one of these, but alas, 400$ shipping kills the deal. http://www.ebay.com/itm/60KW-GE-ELE...99155982?pt=BI_Generators&hash=item3f24bab70e


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