# Using an "off the shelf" VFD as a Drive?



## lazzer408 (May 18, 2008)

http://www.diyelectriccar.com/forums/showthread.php/igbt-firing-circuit-building-my-own-17319.html


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## Johny (Jul 21, 2008)

Hi Jim Check out http://www.evalbum.com/1149 There are at least 3 others in Australia that have already purchased drives and motors and I'm hunting down suitable drives at the moment. The main contender appears to be Danfoss and generally they use a drive that is about 3 times the rating of the motor. I.e. an 11kW motor with a 30 or 37kW drive. Other drives that apparently have been used are Allen Bradley and TECO. look for Torque Control rather than HVAC or fan/pump drives. You want the 150% for 60 seconds extra rating. Motors of choice appear to be in the 11 to 18kW range - all 3 phase. Generally 48 to 50 times 12 volts giving 587 or 600V. John


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## xrotaryguy (Jul 26, 2007)

Haha, you guys beat me to it.  I will mention one more thing though. I have been tentatively looking for a VFD as well, but every time I find one that can control a 15hp motor, it is say too expensive - generally more than $1,500, sometimes more than $2,500. I still have my eyes out for a used one, but I have not had luck finding one that will readily do what I want for a reasonable price.

I am actually working on a 460V AC system... slowly. That's about 650 V peak. I am using 52 12V 17Ah AGM batteries. The total pack weight will be close to 600 lbs which is not outrageous and the pack size will be about 11KWh which is certainly on the small size, but it's a start


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## lazzer408 (May 18, 2008)

Maybe one of you motor guys can answer this. Why can't a 3-phase motor be wound as shown? Padron my crappy schematic. My other schematic software quit working for some reason.


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## xrotaryguy (Jul 26, 2007)

Is that drawing indicating that (using the water flow theory) electricity enters the motor through the armature and exits via one of 3 armature windings? For starters, an AC induction motor doesn't have any windings on the rotor. The rotor only has an aluminum squirrel cage. All of the windings are in the armature. The current that exists in the rotor and squirrel cage are induced by the changing current in the armature windings in the same way that a transformer uses induction to induce a current in a secondary set of windings. Here's a vid of a guy spinning a steel can around with a rotating magnetic field. Same concept. I was trying to find a video of a person spinning a bar magnet beneath metal lid that was hanging from a string, but I couldn't find it.

http://www.youtube.com/watch?v=RIGp1k0Nt2I


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## lazzer408 (May 18, 2008)

xrotaryguy said:


> Is that drawing indicating that (using the water flow theory) electricity enters the motor through the armature and exits via one of 3 armature windings? For starters, an AC induction motor doesn't have any windings on the rotor. The rotor only has an aluminum squirrel cage. All of the windings are in the armature. The current that exists in the rotor and squirrel cage are induced by the changing current in the armature windings in the same way that a transformer uses induction to induce a current in a secondary set of windings. Here's a vid of a guy spinning a steel can around with a rotating magnetic field. Same concept. I was trying to find a video of a person spinning a bar magnet beneath metal lid that was hanging from a string, but I couldn't find it.
> 
> http://www.youtube.com/watch?v=RIGp1k0Nt2I


No it's wye-wound but with a common connection in the center. No commutator. Each leg of the Y is a coil. The center of the Y is B+. Sorry the connection points arn't drawn. I'm not saying to drive exhisting AC wye-wound motors this way but to rewind the motor so this configuration would work. This way the windings can be low side switched instead of the 3-phase H-bridge.

"All of the windings are in the armature"
I think you mean all of the windings are in the stator. No windings in the armature/rotor.


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## Jim (Jun 1, 2008)

Thanks guys. So then a VFD can actually be used. 

Can anybody tell me off hand if the Leeson brand of VFD's might work? I'll do a bit of digging when I get back to the office tommorew and see what I can come up with for both specs and pricing. We have an OEM account with them (Leeson) as we use a lot of their products so I've been able to get some pretty creative prices for some of my "projects". If it's something that will work, I'd be happy to bring in a few extra for you guys if you want to try them and "learn" with me.

My personal preference would be to get a unit with a 208v input (300 DC) just too keep my overall voltage down. The thought of sitting on a 600 volt "capacitor" / "ejection seat" so to speak sounds a bit on the risky side, but maybe I'm just a bit cautious.

Again any suggestions are much appreciated.


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## lazzer408 (May 18, 2008)

[email protected] seat


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## Madmac (Mar 14, 2008)

> Maybe one of you motor guys can answer this. Why can't a 3-phase motor be wound as shown? Padron my crappy schematic. My other schematic software quit working for some reason.


No reason at all. Some AC motors are started by connecting in WYE and then switch to DELTA for running. 

Using a single switch per phase depending on motor type in theory would be more efficient but in reality the lower switching voltage of the DELTA drive and using bridge drive mean the result is about the same.

With PWM drive you will need diodes to circulate the current.

For the maths behind the two 
http://en.wikipedia.org/wiki/Y-%CE%94_transform


Madmac


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## major (Apr 4, 2008)

lazzer408 said:


> Maybe one of you motor guys can answer this. Why can't a 3-phase motor be wound as shown? Padron my crappy schematic. My other schematic software quit working for some reason.


Hey lazzer,

With that circuit you would only get half wave AC. You need the full 6 switch bridge to get positive and negative swing on the synthesized AC waveform. What you show might work, but most likely very poorly.

Regards,

major


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## lazzer408 (May 18, 2008)

major said:


> Hey lazzer,
> 
> With that circuit you would only get half wave AC. You need the full 6 switch bridge to get positive and negative swing on the synthesized AC waveform. What you show might work, but most likely very poorly.
> 
> ...


The negitive side of the wav would be from flyback. I'll be speaking with a motor rebuilder later today. He claims he can wire a motor for any spec I want. He was talking about voltage and current I'm sure but I'm going to throw him this curve ball and see what he thinks. If there is a reason it won't work I want to know why.

Here's a little better schematic.


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## major (Apr 4, 2008)

lazzer408 said:


> The negitive side of the wav would be from flyback.


Hey lazzer,

I don't see how that can happen.

The short and long of your approach is that for equal performance to the standard winding and 6 switch bridge, you will have to increase the copper in the motor (and size of the motor) to the extent that it will outweigh the cost of the extra three transistors. Not to mention the fact that you'll have to do all the programming from scratch.

But what the heck? Go for it. Get a small induction motor and try it. 

BTW, the stator is the armature in the induction motor.

Regards,

major


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## lazzer408 (May 18, 2008)

major said:


> But what the heck? Go for it. Get a small induction motor and try it.
> 
> BTW, the stator is the armature in the induction motor.
> 
> ...


I was told the stator stays and the rotor rotates. I didn't know the armature could be either. That makes sense by definition I guess.

I'm going to try it soon. Follow me through the phases if you can. The 3 windings from top left going clockwise are 1 2 and 3. The mosfets from right to left are 1 2 and 3 and control the forward current through their respective windings. The diodes from top to bottom are 1 2 and 3 and handle reverse emf from their respective windings. Lets start with mosfet 1 in a conducting state and a forward voltage is flowing through coil 1, then switch to mosfet 2 conducting (1 is off). When the switch occurs we have forward through coil 2 and reverse through coil 1. Switch. Forward through coil 3, rev through coil 2. Switch. Forward through coil 1, reverse through coil 3. Switch. Forward through coil 2, reverse through coil 1. Switch...
See how both the high and low sides of the phase are chasing around in circles? It's also flowing the same direction in 2 adjacent coils. Isn't this what 3-phase AC does for the most part?

I'm going to run with it and see where it leads me. If a motor could be re-wound to make this work, it significantly lowers the cost and complexity of a controller. Maybe it's for production reasons, and compatibility with real 3-phase AC power, that motors are grandfathered in the way they are. It could be this reason that invertors are built how they are rather then redesign the whole industry.

I'll keep you posted. I might try it on an alternator first if I can find one that isn't delta wound.


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## major (Apr 4, 2008)

lazzer408 said:


> See how both the high and low sides of the phase are chasing around in circles? It's also flowing the same direction in 2 adjacent coils. Isn't this what 3-phase AC does for the most part?
> .


Hi Lazzer,

Looks like we hijacked this thread.

The way I see it is you are basically are using 3 DC buck converters (like DC motor controllers). One on each of your coils. This will not give you reverse current flow thru the coils. Not near what a 3-phase bridge does.

Regards,

major


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## lazzer408 (May 18, 2008)

major said:


> Hi Lazzer,
> 
> Looks like we hijacked this thread.


I sent you a pm.

Sorry about that Jim! I'll get out of your thread.


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## frodus (Apr 12, 2008)

doesn't an induction motor need the current flow through the armature/rotor to be sinusoidal? I'm not 100% sure, but I thought the repel and attraction of the field windings and the induction core need a sinusoidal input by design.

Just something to think about, but other than that, I don't see why you couldn't.

You kinda want to operate it as a brushless DC? Most of those use a permanent magnet, so its not an induction motor, but then again, not sure what you're using.


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## Jim (Jun 1, 2008)

From what I can tell, the VFD's are a usable alternative that seem to work quite well, but it appears that there are only a small handful of guys using them. I gather the biggest part of this is due to the cost.

Since this is my first conversion, would you suggest in the interest of simplicity that I abandon the VFD route and rather pursue the DC?


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## kittydog42 (Sep 18, 2007)

I think that you should try it. I would suggest using the Danfoss VLT6000 (HVAC) or ABB ACH400/ACH550 (HVAC) drives, since they are very common, and could probably be purchased used. It is definitely possible. Both of these VFD's have Modbus, which you could use for easy instrumentation to an inexpensive touch screen interface. The VFD could possibly be used as a charger if done properly as well. Regen would be easy to implement as well. You could make do with as low as 312VDC if you use a 208V VFD and motor. I am guessing that a 15HP motor might do the trick.

I have a lot of experience with VFD's (Danfoss, ABB, and Square D certified start-up technician), so I would be able to offer you some more specific help if you need it. I also could help you with the programming of the interface; PM me if you need any help.


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## OHM (Jun 30, 2008)

Hello Jim,
Ive been searching for months on the lightest most powerful AC motor I could find and surprisingly the Leeson 801057 is 25hp and 166lbs.
Do you have prices on the Leeson VFD by any chance? Im looking at buying a new one to be safe.
There is one for sale in England for about 600US but its condition unknown and does anyone know if there is a reason to use the HVAC over what was stated earlier by johny?



Johny said:


> Other drives that apparently have been used are Allen Bradley and TECO. look for Torque Control rather than HVAC or fan/pump drives. You want the 150% for 60 seconds extra rating. Motors of choice appear to be in the 11 to 18kW range - all 3 phase. Generally 48 to 50 times 12 volts giving 587 or 600V. John


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## Jim (Jun 1, 2008)

Thanks Kittydog an OHM,

I may very well take you up on your offer, give me a bit of time to see what I can come up with. I just got a heads up on two high end 60 HP Toshiba (460v) units being taken out of service at a local manufacturing facility. I may be able to get those for a song.

As for the Leeson motor / Drives, I'll call our rep tommorw and see what I can pull for numbers. Do you have a part# for the VFD? What size and voltage would you prefer? I can send you a PM once I know more / you can do the same.


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## kittydog42 (Sep 18, 2007)

My logic for using HVAC drives is simply based on the fact that they are very readily available. They should work just as well as any other drive.

Be aware that you will need a high DC voltage to operate a 460V VFD. You should consider using a 208V unit for that reason.


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## OHM (Jun 30, 2008)

Thanks Kit, I want to stay away from such high voltage, it just increases the complexity of my battery setup.


Jim, I have no idea which drive to use Im quite open minded to anything above 40kws.

I havent looked at the Leeson drives but will do that now online.

The motor is a pump motor and dont know if its suitable but they are built for industrial applications and this baby is so light for its power rating.


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## aeroscott (Jan 5, 2008)

OHM said:


> Thanks Kit, I want to stay away from such high voltage, it just increases the complexity of my battery setup.
> 
> 
> Jim, I have no idea which drive to use Im quite open minded to anything above 40kws.
> ...


that's a 2 pole motor (3500) stay with a 4 pole (1800 ) it will weigh the same but be rated at less power . you want more torque . numbers are for 60 cycle with vfd will go to 400 cycles . get a high efficiency motor with thin lamination's for less heat at the higher cycles.


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## lazzer408 (May 18, 2008)

aeroscott said:


> that's a 2 pole motor (3500) stay with a 4 pole (1800 ) it will weigh the same but be rated at less power . you want more torque . numbers are for 60 cycle with vfd will go to 400 cycles . get a high efficiency motor with thin lamination's for less heat at the higher cycles.


I think you want a lower rpm motor don't you? A motor rated 3hp 60hz 1720rpm will have twice the torque of a motor rated 3hp 60hz 3450rpm. The vfd will still be able to crank it up to 10k-rpm. Just a thought.


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## aeroscott (Jan 5, 2008)

lazzer408 said:


> I think you want a lower rpm motor don't you? A motor rated 3hp 60hz 1720rpm will have twice the torque of a motor rated 3hp 60hz 3450rpm. The *vfd* will still be able to crank it up to 10k-rpm. Just a thought.


 *tesla* and others run 4 pole but at very high rpm . I think a 6 pole rated at 1200 with 8 hp can be spun at 6000 rpm @300 *hz* . the hp will go up too. the motor I was working on is about 200 lbs and is a inverter/ high eff. aluminium motor frame , frame size 254, US Motors model s628a ,new $1200-1400


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## OHM (Jun 30, 2008)

aeroscott said:


> *tesla* and others run 4 pole but at very high rpm . I think a 6 pole rated at 1200 with 8 hp can be spun at 6000 rpm @300 *hz* . the hp will go up too. the motor I was working on is about 200 lbs and is a inverter/ high eff. aluminium motor frame , frame size 254, US Motors model s628a ,new $1200-1400


Thank you for the clear-up now I finally have a direction besides 2 poles 

I found this lil Leeson too is this a 4 pole if so pretty cheap no?

*801051* *15hp 1760RPM 254JP Frame * *43.0* * 155 lb.* *$645.32*


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## lazzer408 (May 18, 2008)

OHM said:


> *801051* *15hp 1760RPM 254JP Frame **43.0* *155 lb.* *$645.32*


Ah good you went with lower RPM. Maintain the torque curve and you'll get more HP at higher RPM.


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## Jim (Jun 1, 2008)

Wouldn't you want to go with a TEFC with a "C" type frame? This way you could adapt it right to your mounting plate of the trans. 

I was looking through the Leeson catalogue today and found that they have some really low rpm (780-1080) units in the larger HP sizes. List prices seem reasonable as well. (I'm still waiting for motor and VFD costs to come back)

I was also going to mention. I saw they reciently came out with Vector drives. They're supposed to do the same job as the regular VFD's without all the frills at a much lower cost. Unfortunitly they only go up to 20 HP with a 208v input, but I figured it might still be worth trying, any thoughts on them?


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## OHM (Jun 30, 2008)

a heavy tefc frame motor with a 20hp max from a drive defeats the purpose of a powerful motor with more potential.


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## morvolts (Jun 19, 2008)

Jim said:


> Thanks Kittydog an OHM,
> 
> I may very well take you up on your offer, give me a bit of time to see what I can come up with. I just got a heads up on two high end 60 HP Toshiba (460v) units being taken out of service at a local manufacturing facility. I may be able to get those for a song.
> 
> As for the Leeson motor / Drives, I'll call our rep tommorw and see what I can pull for numbers. Do you have a part# for the VFD? What size and voltage would you prefer? I can send you a PM once I know more / you can do the same.


I can pretty much guess that those 60HP Toshibas are quite heavy..
Good thread tho


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## Jim (Jun 1, 2008)

kittydog42 said:


> I think that you should try it. I would suggest using the Danfoss VLT6000 (HVAC) or ABB ACH400/ACH550 (HVAC) drives, since they are very common, and could probably be purchased used. It is definitely possible. Both of these VFD's have Modbus, which you could use for easy instrumentation to an inexpensive touch screen interface. The VFD could possibly be used as a charger if done properly as well. Regen would be easy to implement as well. You could make do with as low as 312VDC if you use a 208V VFD and motor. I am guessing that a 15HP motor might do the trick.
> 
> I have a lot of experience with VFD's (Danfoss, ABB, and Square D certified start-up technician), so I would be able to offer you some more specific help if you need it. I also could help you with the programming of the interface; PM me if you need any help.


Kit, In the above quote you mention that if done properly the VFD could be used as a charger as well as regen. Can you please elaborate. The other link for the Suzuki (http://www.evalbum.com/1149) also mentions the same and I'm currious how that can be done as naturally this could take care of some 28 chargers...

Based on all the good advice and with all the apparent pros on this sort of system, I'm leaning towards a 208V VFD running 28 - 12 volt gels. 

In doing some preliminary calculations, I figure if I was to run a 6 pole motor up to 400 Hz into a 4 or 5 to 1 planetary reducer, I may even be able to loose the trans and go direct drive. (Now we're back to the dual motor thread which I won't go into, but I think that should be overcome with the VFD as well)


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## rankhornjp (Nov 26, 2007)

Jim said:


> Kit, In the above quote you mention that if done properly the VFD could be used as a charger as well as regen. Can you please elaborate.


Anyone have an update on this??


Also, how would you wire the batteries to the VFD? Most of the EVs Ive seen use 2/0 -4/0 cabling on the batteries and the VFDs that I know about use 10ga-12ga wire. Would you be able to step it down that far and still have it (the wire) hold up to the power requirements without melting??


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## Johny (Jul 21, 2008)

HVAC drives are the only type that are NOT entirely suitable for EV use. HVACs generally do not have torque control - only speed control. They also usually only allow 110% overload and have limited or no resistor braking system. It's a shame because they are the most common inexpensive drives.

General use VFDs WITH torque control are best.
As long as the drive does not need 110VAC to drive fans etc it is usually suitable.
Look for mention of linking up the DC bus on multiple drives and you have found a suitable drive.


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