# Industrial VFD and AC motor



## brian_ (Feb 7, 2017)

jbman said:


> I have a friend that has offered me a 100HP VFD and the matching AC motor to use with it. I'm not remotely familiar with these, and I was wondering if it would be feasible to run it off of a battery pack for an EV conversion?


Probably not. The Variable Frequency Drive puts out what the motor needs, but it is almost certainly designed for AC power input... probably 3-phase. That would mean one of two solutions would be required:

a fixed-frequency inverter between the battery and the VFD (you might as well just toss the VFD and get a suitable DC-input 3-phase-output inverter), or
modification of the VFD (which is probably not practical).


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## jbman (Oct 26, 2017)

brian_ said:


> Probably not. The Variable Frequency Drive puts out what the motor needs, but it is almost certainly designed for AC power input... probably 3-phase. That would mean one of two solutions would be required:
> 
> a fixed-frequency inverter between the battery and the VFD (you might as well just toss the VFD and get a suitable DC-input 3-phase-output inverter), or
> modification of the VFD (which is probably not practical).


My friend said that the VFD takes a single phase input. I'll have it in hand on Sunday so I can look more closely, but that's what he tells me.


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## brian_ (Feb 7, 2017)

jbman said:


> My friend said that the VFD takes a single phase input.


While single-phase is simpler than 3-phase, this also confirms an AC input. Same required solutions apply.


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## jbman (Oct 26, 2017)

brian_ said:


> While single-phase is simpler than 3-phase, this also confirms an AC input. Same required solutions apply.


Gotcha. I had read that there is a DC bus input that is easily accessible on some VFDs. I guess I'll have to take a look and see on Sunday.


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## Duncan (Dec 8, 2008)

Hi Jbman

The way I understand it these VFD's all work by converting to DC - then back to AC for the motor so you should be fine

BUT you will need a battery voltage that is high enough
230 v AC = 360 v DC
And it may be a bit heavy


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## major (Apr 4, 2008)

Duncan said:


> Hi Jbman
> 
> The way I understand it these VFD's all work by converting to DC - then back to AC for the motor so you should be fine
> 
> ...


That's right Dunc. Those variable frequency drives go AC to DC and then DC to variable frequency AC. In most cases you can connect DC power to the DC bus. In fact most have such connection points normally used for braking resistor banks. Often the contactors and fans are driven from AC mains power. 

It'd be strange to have a 100 hp drive powered from single phase, and uncommon to see at 230 V. More likely 460-480 V 3ph. And the 100 hp motor likely is a half ton monster.

Regards,

major


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## brian_ (Feb 7, 2017)

jbman said:


> Gotcha. I had read that there is a DC bus input that is easily accessible on some VFDs. I guess I'll have to take a look and see on Sunday.


If it's easily accessible, that would be a substantial head-start on the VFD modification. 



Duncan said:


> The way I understand it these VFD's all work by converting to DC - then back to AC for the motor so you should be fine
> 
> BUT you will need a battery voltage that is high enough
> 230 v AC = 360 v DC
> And it may be a bit heavy


True, there must a be DC stage, but that doesn't mean it's accessible or usable. And I agree that the voltage is important.



major said:


> In most cases you can connect DC power to the DC bus. In fact most have such connection points normally used for braking resistor banks.


So there's reason to be optimistic about making the DC connection? Excellent , but...



major said:


> Often the contactors and fans are driven from AC mains power.


There's a good example of a potential issue.



major said:


> It'd be strange to have a 100 hp drive powered from single phase, and uncommon to see at 230 V. More likely 460-480 V 3ph. And the 100 hp motor likely is a half ton monster.


That's what I thought, and why I was expecting 3-phase. 100 hp or 75 kW at 240 V RMS is 313 A; in what installation would anyone run a single-phase circuit to support that current, instead of using 3-phase higher-voltage power?


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## MattsAwesomeStuff (Aug 10, 2017)

The reason an inverter is called an "Inverter" is because the challenging part is taking flat, positive DC, and creating negative (inverted) pulses from it. It inverts the positive voltage for the negative part of the sine wave (and keeps it positive for the positive part). If it didn't invert it, it would just be controlling the on/off pulsing of positive DC, which is what a DC controller is "Pulse, Width, Modulation", PWM.

A "VFD" is a "Variable Frequency Drive" which means that it can control, or vary, the frequency (how many times per second) of the switching between positive and inverted pulses. It could switch it many times, or few, or anything in between. A VFD is an inverter that isn't set to a fixed rate.

An inverter is needed from a battery pack because there is only positive voltage that way, and to create AC you need negative parts. If you already had negative parts, you wouldn't need an inverter, because you'd already have a cycling source of voltage that is positive/negative/positive/negative/etc. There's nothing for the inverter to "invert", it's already back and forth being inverted. In this case you may want to use a Transformer to Transform the voltage (which can only be done on AC), but no inverter. A transformer can make the AC voltage higher or lower, but it can't change how fast it's pulsing, the frequency.

So, a VFD presumes you have an AC source, but which needs to have its frequency changed which a transformer can't do. The way it accomplishes this is to take your AC source, then put it through a rectifier to flip the negative parts of the sine wave positive, then puts some capacitors on that to help fill in the gaps to more closely approximate the steady flat positive DC of a battery. Once it has that, it chops it up however fast it wants to and inverts every other pulse to negative so it resembles AC again, but AC at a different frequency.

...

So... a VFD has a couple extra components to first convert AC into DC before it uses it. It has to, that's how it works. The electronics won't work on AC, it'll mess them all up and confuse them.

So yes, it will have a DC bus. A bus is just a power rail of Positive and Ground. It will not be hard to find, follow the traces, it will be between the giant capacitors right by the input, after the big black rectifiers. The wires will be gigantic, probably the heaviest traces or wires on the board. It might not be "accessible" in terms of having output terminals, but, it's not going to be some sneaky hidden microscopic wire inside a 16 layer board, it'll be big huge traces, or, likely giant bus bars or cables. It'll be about as hard as finding the front seat on a car "Open the door, in front of the steering wheel, there you've found it."

Ignore the first part of the input, strap your batteries to the DC bus directly, and roll out.



> And the 100 hp motor likely is a half ton monster.


Bah, no it won't be.


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## brian_ (Feb 7, 2017)

I think it's likely that everyone involved in the conversation understands what an inverter is, what a Variable Frequency Drive is, and that an AC-powered VFD has a rectifier as a first stage.

The fact that the DC internal bus should be prominent is clear. Ability to safely and reasonably connect to it without any consequences is not so obvious. But I hope it does work out.


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## brian_ (Feb 7, 2017)

major said:


> And the 100 hp motor likely is a half ton monster.





MattsAwesomeStuff said:


> Bah, no it won't be.


I suspect that major was exaggerating a bit for emphasis, but an industrial motor rated for 100 horsepower (continuous, and likely with only air cooling) will likely be quite heavy and bulky by automotive standards.

jbman, please let us know how big this motor turns out to be.


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> ... the steady flat positive DC of a battery. Once it has that, it chops it up however fast it wants to and inverts every other pulse to negative so it resembles AC again, but AC at a different frequency..


That would be a roughly square-wave output; for an AC motor, you want a sinusoidal output (and actually three outputs each 120° in phase from each other), but the details of that are not important to this discussion (since the VFD does this already).


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## MattsAwesomeStuff (Aug 10, 2017)

> I think it's likely that everyone involved in the conversation understands what an inverter is, what a Variable Frequency Drive is, and that an AC-powered VFD has a rectifier as a first stage.


I think it's quite obvious from several of the replies, that that is not true. There seem to be a number of people who do not understand the first thing about some of these., but worst of all, mistakenly think they do.

Also, it's nice to give soft introductions to other people who are reading and curious, not necessarily able to contribute on a technical level. Everyone starts somewhere.



> That would be a roughly square-wave output;


If it wasn't obvious, I was explaining things from a beginner's standpoint. Yes of course, you're correct, there's more to it.


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## brian_ (Feb 7, 2017)

brian_ said:


> I think it's likely that everyone involved in the conversation understands what an inverter is, what a Variable Frequency Drive is, and that an AC-powered VFD has a rectifier as a first stage.





MattsAwesomeStuff said:


> I think it's quite obvious from several of the replies, that that is not true.


Sorry, I meant to say (but was not clear) that _*by now*_ (and by several posts before this comment of mine) people in this conversation understand these terms... after several posts giving the meaning of "VFD" and then going through the components.


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## major (Apr 4, 2008)

brian_ said:


> I suspect that major was exaggerating a bit for emphasis, but an industrial motor rated for 100 horsepower (continuous, and likely with only air cooling) will likely be quite heavy and bulky by automotive standards.
> 
> jbman, please let us know how big this motor turns out to be.


Example, 1173 pounds. 

https://www.weg.net/catalog/weg/US/...-60-Hz-IC411---TEFC---Foot-mounted/p/11355340 

major

Edit: 2nd example 1335 lbs. See attached.


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## brian_ (Feb 7, 2017)

major said:


> Example, 1173 pounds.
> 
> https://www.weg.net/catalog/weg/US/...-60-Hz-IC411---TEFC---Foot-mounted/p/11355340
> 
> ...


Wow - so no exaggeration at all!

And the are running at what seems to me like bizarrely low voltage for the power level.

I suppose my expectations are biased by past exposure to large industrial motors which put out 3500 to 5000 HP, and probably not so heavy per horsepower... perhaps because they ran at much higher voltage.


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## MattsAwesomeStuff (Aug 10, 2017)

major said:


> Example, 1173 pounds.


I was gonna say, "Yeah, you can cherrypick ones made of cast iron" but then I did some searching and, yeah, 1000 lbs is probably fair for an average.

I came across some that were 1500 lbs, and some that were only 500lbs.

Basically the motor is 500lbs (or less), and then add in the frame. Normally these are used in stationary places, bolted down to the floor, so they're purposefully built with a frame that outweighs the motor just for mass's sake. It's quieter and more stable with all that extra mass. If you're unlucky the frame and motor will be the same, but I think in most cases it's detachable.

I mean, 500lbs is what a V8 would weigh. It's not that stupidly large. A Tesla drive unit is 300lbs.


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> Basically the motor is 500lbs (or less), and then add in the frame. Normally these are used in stationary places, bolted down to the floor, so they're purposefully built with a frame that outweighs the motor just for mass's sake. It's quieter and more stable with all that extra mass.


I agree that's a reason for the mass, but it's also a heat sink.



MattsAwesomeStuff said:


> I mean, 500lbs is what a V8 would weigh. It's not that stupidly large. A Tesla drive unit is 300lbs.


Since the engine doesn't need a huge battery, and has a far higher power output, it's not a straightforward comparison. And the 300 pounds for a Tesla drive unit includes the entire transaxle.


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## major (Apr 4, 2008)

MattsAwesomeStuff said:


> I was gonna say, "Yeah, you can cherrypick ones made of cast iron" but then I did some searching and, yeah, 1000 lbs is probably fair for an average.
> 
> I came across some that were 1500 lbs, and some that were only 500lbs.
> 
> ...


I showed two of the first three off a Google search where the weight was readily noted on the specs. The third was 960 lbs IIRC. Please give the links or references to a few of those 500 lb motors that you mention. Thanks.

Also please elaborate on your detachable frame. Perhaps an example or two. I'm not aware of such so may be misunderstanding you.

But in a nutshell, when the OP says he's getting an industrial 100 hp motor, chances are it's a NEMA standard like the WEG or Baldor which I showed. Let's hope he posts the info.

Regards,

major


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## MattsAwesomeStuff (Aug 10, 2017)

major said:


> Please give the links or references to a few of those 500 lb motors that you mention. Thanks.


Sorry, didn't make notes while searching specifically to give references. Didn't think anyone would care. One had a square cross section (not round), no fins, and was red. No base or anything. Form-factor-wise looked like a Nema23 with a disproportionately long midsection, but, obviously massively bigger, they didn't have anything else in the photo for scale. New off some industrial supply site.



> Also please elaborate on your detachable frame. Perhaps an example or two. I'm not aware of such so may be misunderstanding you.


I might be mistaken I suppose. I think almost all of them mentioned a cast iron mounting frame and showed feet, etc. I presume the motor body itself isn't cast iron. Wrong permeability/etc. The few industrial 3phase motors I've been around had the round-ish finned motor attached to a massive cup-shaped slab of a base. Bolted together and then usually a weld along the seam for good measure, but, not much of a weld, easily cut.



> Let's hope he posts the info.


I'm curious too. Like, I'm presuming the guy offering it has seen the motor and has pictured it in a vehicle. It's not for example:










That, or if it is he's being joked with


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> I'm curious too. Like, I'm presuming the guy offering it has seen the motor and has pictured it in a vehicle. It's not for example:
> <large image shown above>
> 
> That, or if it is he's being joked with


The person who offered it may be thinking of the motor as directly replacing an engine, and might have considered a motor of that size suitable. We just don't know yet.


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> I think almost all of them mentioned a cast iron mounting frame and showed feet, etc. I presume the motor body itself isn't cast iron. Wrong permeability/etc. The few industrial 3phase motors I've been around had the round-ish finned motor attached to a massive cup-shaped slab of a base. Bolted together and then usually a weld along the seam for good measure, but, not much of a weld, easily cut.


I assume that the "frame", which is really a structural housing, serves as mechanical support, enclosure, and heat sink... but is not part of the magnetic circuit. It is commonly cast iron or aluminum. There are industrial motors with big bases like that, but there are also motors with just feet; I don't think the feet are a significant part of the motor mass.


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## brian_ (Feb 7, 2017)

major said:


> Example, 1173 pounds.
> 
> https://www.weg.net/catalog/weg/US/...-60-Hz-IC411---TEFC---Foot-mounted/p/11355340





MattsAwesomeStuff said:


> ... Like, I'm presuming the guy offering it has seen the motor and has pictured it in a vehicle. It's not for example...


The motor which major linked is a 404/5T frame (which I assume means 404T or 405T frame size) which has a body a couple of feet long and 16" in diameter (plus feet, etc)... so yes, a 100 hp industrial motor certainly could be the size of the one shown on the pallet carried by the forklift.

Do 100 hp motors come in smaller frame sizes? I don't know, but I hope so...


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## MattsAwesomeStuff (Aug 10, 2017)

brian_ said:


> so yes, a 100 hp industrial motor certainly could be the size of the one shown on the pallet carried by the forklift.


The one I linked was 150 hp. So, yeah, roughly that ballpark.

I'm saying, the guy offering it, if he's seen it, surely can't be thinking of one pallet-sized, right?


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## weber (Apr 22, 2009)

An ordinary industrial aluminium frame 4-pole induction motor with a nameplate rating of 11 kW can easily be made to produce 12 times that power, i.e. 132 kW, for long enough to get you pulled over for speeding. 

You just have to provide it with about 4 times the voltage it was designed for. And let it pull about 3 times the current. Which usually means you have to get it rewound to a nominal voltage that's about a quarter of the maximum voltage your VFD can feed it. Or order a new motor with a custom voltage (typically in the range 75 to 100 V).

It will then produce about 3 times its rated torque all the way out to about 4 times its rated r/min (i.e. about 7200 r/min for an originally 60 Hz 4-pole motor).

Here are the guys who've done it:

ABB motor and VFD selection
http://www.aeva.asn.au/forums/viewtopic.php?f=41&t=1227

AC motors, multipoles, torque
http://www.aeva.asn.au/forums/viewtopic.php?f=41&t=585


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## aeroscott (Jan 5, 2008)

Weber your right, I learned about this on the endless sphere . They used 1/3 hp 3 phase motor ,cut the winding or rewound to lower voltage .
This cuts the back emf (voltage) as the motor spins faster it generates voltage fighting battery voltage, so at high rpm say you have 400 v pack and 
200 v bemf ,now you only have a effective battery of 200 volts . 200v will flow less amps then 400 v. so torque falls off as speed is increased,
I said 1/3 hp ,I don't know if that's right .They did say fractional hp and they ran it at 12 times rating (5000 or so rpm) and said it was putting out less heat then at rated speed and power. with higher Hz.


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## weber (Apr 22, 2009)

aeroscott, can you point us to the thread on Endless Sphere. I wonder if you may be misremembering where it was. You may be thinking of this brilliant experiment by Tuarn Brown of Perth Australia, also posted on the Aussie forum (with many digressions). Thanks for reminding me about that one.
http://forums.aeva.asn.au/viewtopic.php?t=1237

If you want to skip to the punchline: 
http://forums.aeva.asn.au/viewtopic.php?p=14962#p14962

It doesn't put out less heat. Not sure where you got that from. It's possible that the _percentage _losses decrease slightly, but the kilowatt losses certainly increase, nearly proportional to the output power increase. And it's possible the temperature rise was less, but that would only be because the shaft fan was running faster.


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## brian_ (Feb 7, 2017)

weber said:


> An ordinary industrial aluminium frame 4-pole induction motor with a nameplate rating of 11 kW can easily be made to produce 12 times that power, i.e. 132 kW, for long enough to get you pulled over for speeding.
> ...


Interesting, and seems perfectly plausible to me, but the motor discussed in this thread is reportedly a 100 hp industrial motor with drive. That would be the nameplate rating, not what a smaller motor could be driven to with modification. So we're expecting an enormous motor, because a 100 hp industrial motor is enormous; there's no question that a smaller motor could put out 100 hp. This just isn't that smaller motor, and that's why its suitability for an EV is in question.


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## aeroscott (Jan 5, 2008)

weber said:


> aeroscott, can you point us to the thread on Endless Sphere. I wonder if you may be misremembering where it was. You may be thinking of this brilliant experiment by Tuarn Brown of Perth Australia, also posted on the Aussie forum (with many digressions). Thanks for reminding me about that one.
> http://forums.aeva.asn.au/viewtopic.php?t=1237
> 
> If you want to skip to the punchline:
> ...


That must have been it , I remember it was the Aussies . I think I was linked to endless sphere then to this site. It was greater efficiency not less total heat except at 4 or 5 X.I thought he was saying say 87% eff. motor, 50hz, @ 100 w would put
out 13 w. of heat if running at 200 hz ,97% ,400w it put out 12w of heat.
Thinking about it he was not using 12x power for this part of the experiment but more like 4 or 5x


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## weber (Apr 22, 2009)

brian_ said:


> Interesting, and seems perfectly plausible to me, but the motor discussed in this thread is reportedly a 100 hp industrial motor with drive. That would be the nameplate rating, not what a smaller motor could be driven to with modification. So we're expecting an enormous motor, because a 100 hp industrial motor is enormous; there's no question that a smaller motor could put out 100 hp. This just isn't that smaller motor, and that's why its suitability for an EV is in question.


I totally agree. An industrial induction motor with a nameplate rating of 100 hp is completely unsuitable for an EV, due to its size and weight. Unless of course it's some kind of monster EV (and then you want the motor rewound for 1/4 voltage and you'd need a way bigger VFD to power it). 

I was just adding that it's also _unnecessary_, since full power is only needed in an EV for at most 10 second bursts, and this can be achieved by overvoltaging, overspeeding and overcurrenting a much smaller motor.

The Industrial VFD might be suitable, used with a smaller motor rewound for lower voltage. But as mentioned by others, the VFD will also be heavier and bulkier than a purpose-built EV VFD, and it will need a 680 volt battery.


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