# AC Motor Selection



## etischer (Jun 16, 2008)

The requirement to match a motor to a controller is a sales gimmick. 

There are plenty of VFD's that can learn the properties of a motor allowing you to hook up any AC motor to that VFD. Manufacturers of controllers want to sell you a motor and drive combo. Instead of allowing the user to auto tune a motor, type in all the motor parameters and select proper feedback devices, they insist on you just selecting your motor from a list box. 

Assuming the controller (VFD) is sized appropriately; allows the user to input motor data or auto tune the motor, and is populated with the correct feedback card (encoder, tachometer...), it should run an AC motor from any manufacturer.


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## xrotaryguy (Jul 26, 2007)

I have seen a couple of chips that are actually designed to learn a motor curve. That's pretty impressive stuff. I guess I could have gone into more detail, but I didn't want to confuse the issue. Generally speaking, the AC motor controllers that most DIYers would be able to use come "pre-matched" so to speak. Most DIY EV builders lack the level technical knowledge required to install a non-EV VFD into an automobile let alone install a set of velocity sensing hall sensors and a reluctor and adapt it all to a random industrial AC motor.

Perhaps we could mention in this article that controllers do not necessarily need to be matched to the motor, but that most EV-specific AC controllers are part of a motor/controller combo to keep installation simple for the DIY EV converter.


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## JRP3 (Mar 7, 2008)

Someone might want to add the MES and Brusa motors, or just put a link to the table here: http://www.metricmind.com/motor.htm
Also the lower power HPG motors should be mentioned: http://www.thunderstruck-ev.com/AC_drive_performance.htm


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## JCR (Nov 26, 2009)

How can I determine Battey Pack voltage for a 15 KW AC motor. Is it as simple as what is stated ie such as 230/460 volts, etc. Can I get an inverter to take me from 96 VDC to 230 VAC and run the motor with decent performance? 

Is it all in the windings of the AC motor? The HPGC AC-50 motors run on 96 volts so is it the design of the motor?

JCR


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## major (Apr 4, 2008)

JCR said:


> How can I determine Battey Pack voltage for a 15 KW AC motor.


Hi JCR,



> Is it as simple as what is stated ie such as 230/460 volts, etc.


Not quite. 230 would be the AC voltage for the 3 phase needed at the motor leads. The battery voltage needed to get 230 VAC when inverted would be about 320 VDC. IIRC, VDC = 1.4 times VAC, because you need the VDC to equal the peaks of the AC sine wave.



> Can I get an inverter to take me from 96 VDC to 230 VAC and run the motor with decent performance?


No. Unless you add a boost converter in front of the DC to AC inverter. And that is something you're unlikely to find.



> Is it all in the windings of the AC motor?


Pretty much so.



> The HPGC AC-50 motors run on 96 volts so is it the design of the motor?


Yeah, I guess they have them wound for that.

Regards,

major


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## JRP3 (Mar 7, 2008)

The HPG motors can run higher than that, not sure how much higher in stock winding, but the Curtis controller they use cuts off at 130 volts.


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## JCR (Nov 26, 2009)

JRP3 said:


> The HPG motors can run higher than that, not sure how much higher in stock winding, but the Curtis controller they use cuts off at 130 volts.


I see that with the HPGC AC50 motor running on 96 volts you run at 500 amps from out of the gate. Have you seen the motor curves .... I don't get the 500 amp straight line can someone help me out here? 

JCR


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## JRP3 (Mar 7, 2008)

Are you referring to this chart?


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## major (Apr 4, 2008)

JCR said:


> I don't get the 500 amp straight line can someone help me out here?


Hi JCR,

Thanks to JRP3 for posting the curve. It shows the maximum output for the motor and inverter. The "amp" trace is AC motor current. It is proportional to motor torque. So at low speeds, at maximum torque, current is about 550 Amps, AC. But at the low speeds, motor voltage is low. And as the RPM increase up thru 3000, the motor torque and current stay pretty constant. The motor voltage has been increasing as the RPM increase. At around 3000 RPM, the maximum available motor voltage is applied. Beyond 3000 RPM (base speed), the torque decreases as does the motor current because the motor voltage can no longer be proportionally increased.

Realize that this plot shows motor current and battery voltage. Battery current curve shape would resemble the shape of the Horsepower curve.

Hope that helps ya 

major


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## JCR (Nov 26, 2009)

major said:


> Hi JCR,
> 
> Thanks to JRP3 for posting the curve. It shows the maximum output for the motor and inverter. The "amp" trace is AC motor current. It is proportional to motor torque. So at low speeds, at maximum torque, current is about 550 Amps, AC. But at the low speeds, motor voltage is low. And as the RPM increase up thru 3000, the motor torque and current stay pretty constant. The motor voltage has been increasing as the RPM increase. At around 3000 RPM, the maximum available motor voltage is applied. Beyond 3000 RPM (base speed), the torque decreases as does the motor current because the motor voltage can no longer be proportionally increased.
> 
> ...


 
Major, 

Thank you. 

So the yellow line is battery pack voltage at 96 volts and stays about the same. The red line is motor and inverter alternating current and shows that the motor will put out 550 Amps at full torque up to about 3,000 rpms. 

Does this mean that if the motor is at 20% max torque the battery current draw will be about 110 amps? And if the motor is at 50% max torque the battery amp draw will be 275 amps and if the motor is at full torque the battery amp draw will be 550 amps. Realizing that the motor alternating current and power both drop after 3,000 rpms. Am I getting this correctly? 

Also, from 0-3,000 rpms the battery current draw depends upon torque the motor has to produce for the given load. 

JCR


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## major (Apr 4, 2008)

JCR said:


> Does this mean that if the motor is at 20% max torque the battery current draw will be about 110 amps? And if the motor is at 50% max torque the battery amp draw will be 275 amps and if the motor is at full torque the battery amp draw will be 550 amps. Realizing that the motor alternating current and power both drop after 3,000 rpms. Am I getting this correctly?


It has been my experience that at base speed and max torque, AC and DC amps are about equal. But at higher and lower RPM, I don't know a simple relationship for you to use. You probably should revert back to power to figure the DC battery current. Use the motor output power and divide by 0.8 or 0.85 for efficiency to get battery power and then divide by battery volts to get battery current.


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## Twaksak (Nov 27, 2010)

major said:


> Hi JCR,
> 
> 
> 
> ...


Quite different when using H Bridge configuration as drive electronics the way I understood. Actually a lot depends on the voltage control, switching frequency and PWM scheme. I think it best to contact the VSD manufacturer for DC link specifications.


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## mizlplix (May 1, 2011)

If it is any help,(on my AC50 system) I too only get a few hundred amps out the gate if I slam the throttle open from dead stop. It then builds up to as much as 586 AMPs (for my set up and pack). 

A similar DC set up, If I would slam the throttle open from zero, I would get 400-500 amps momentarily, then begin to fade down to about 280 or so, there I would have to shift up.


Miz


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## JRP3 (Mar 7, 2008)

Were you measuring battery amps or motor amps with the DC system?


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## GrfxImage79 (Jul 4, 2012)

This maybe a dumb question. I found a website that has low priced ac motors. My question is how do I know if these are good for an ev conversion or build? The website is automationdirect.com any help that you guys could give me would be great.


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## mizlplix (May 1, 2011)

There are several threads about this subject and a LOT of different opinions.

There is no readily available way to immediately use one of these industrial motors without a ton of mods or a very special inverter and a very expensive battery pack.

If you are very electrically inclined, you can "bodge" up something and eventually get it running in an acceptable manner. It will take time and money.

1-Rewind motor and use a Curtis controller and a normal battery pack.

2-Use motor as-is and convert a stationary inverter to do vehicle duty and then build a high voltage pack to support it. (shorter range unless you double the pack size)

3-Buy an existing AC vehicle system. Use a normal pack.

I'm sure others will point out my flaws, but this is what I see.

Miz


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## PStechPaul (May 1, 2012)

GrfxImage79 said:


> This maybe a dumb question. I found a website that has low priced ac motors. My question is how do I know if these are good for an ev conversion or build? The website is automationdirect.com any help that you guys could give me would be great.


I have dealt with www.automationdirect.com and I have found them trustworthy, and their products have been of good quality. I have looked at their motors on their website and they seem to be pretty good, and reasonably priced, especially for new motors. They are most likely Chinese and often it seems that their products have a few flaws which may range from minor to major. If you do buy from them, ask about their warranty to see if it applies to EVs.

I have found lots of good deals on motors on eBay, andI even found a 5HP three phase motor on Craigs List. IMHO you should get a premium efficiency motor, even though it may be bigger and heavier, and try to get a frame type that is easy to mount in your conversion, and which is protected from water and dirt and has a good means of cooling.

Best thing is probably to pick out a few motors that you think will work, and post a thread to ask the experts what they think.


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## mizlplix (May 1, 2011)

Note to all:

There are two camps in the AC motor subject, High voltage and Low voltage.
Each has it's own talking points. It's own positives and negatives.
I am in the Low Voltage camp. 

The single largest cost in the construction of an EV is the battery pack. 
In both systems, you use the same cell capacity in the pack (which is set by your daily driving needs.) BUT, in the high voltage system, you need additional cells in series to gain that higher system rating, adding significantly to your build cost and car room to put them.

Another big value component is the controller. 

In the Low Voltage system, you have several choices and they are an engineered, tested, finished product.

In the high voltage system, you are limited to two choices, modify an industrial controller or build your own........Both are challenges.(there might be a ready-made unit out there, but I was not able to find one.)

Where I have a decent grasp of electronics, I am not an engineering level Tech, nor do I want to spend money doing R&D perfecting a controller and even then "settling" for a unit that gets me 90% of the control I expect and need. 

If and when someone finally "proves" a decent, dependable, high voltage AC controller that even comes close to a Curtis system in quality of operation, I will revisit my position. (even then there's still the Pack cost and room to mount it, to deal with.)

There are few easy to adapt AC industrial motors and the best of the breed, "the inverter duty" ones with an encoder,are expensive.($1500-$3500)

But, to convert almost any AC industrial motor to low voltage is pretty straight forward. 

Low motor cost: Use a salvage motor.
Rewind cost: $500-$800.
Encoder= $150

You can get into that custom built motor for the same price or even cheaper than an industrial "Inverter Duty" and an off-the-rack motor.
(I have also found several persons actively rewinding Industrial motors to EV use. Both on the internet and here locally. It is not as easy or mainstream as one would think, but it is being done.)

So, Choices are:

1-More expensive pack-cheaper motor-Amateur made controller of dubious service reliability.
2-Normal cost pack-dependable controller-medium priced (but cheaper than a ready built motor) motor.

In performance and range, the high voltage system wins. But at this writing, that type system is still unreliable.

Miz

(The internet, being what it is today, will yield some nay-sayers to my above opinions, but I still find them valid. It is for each to find what they will settle for or need in vehicle propulsion )


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## PStechPaul (May 1, 2012)

A few things to consider:

Many standard AC induction motors can be reconnected internally for 138V instead of 240V three phase. These can be overclocked to 100 Hz for 70% greater speed and HP, so a 4 pole 1750 RPM will be about 3000 RPM which is just about right for EVs. And you can usually get 2x to 3x torque for short bursts as needed. And this can be done using a standard motor. For about $800 you can get a nice 30 HP motor and get 52 HP continuous and 150 HP peak. 

A standard industrial VF drive rated 30 HP can be had for about $500. Many of these are surplus and still come with warranties. If there is a failure, it will usually be the IGBTs and you can get replacements, perhaps with higher capacity, for about $200/set. 

It is possible to boost the voltage of a battery pack to a higher voltage as needed by a VFD. So you can use a 144V pack and get 288V with a voltage doubler. For 30 HP at 288V you need 22 kW or 78 amps. You can make an isolated 144-144VDC converter rated 11 kW and add it in series with the battery pack. An 11 kW switching supply could be made for under $500. 

For lower power systems you can get discount laptop batteries for about $0.60/W-Hr. 30 pieces of these will cost about $1000 and will give you 330 VDC and 1.8 kW-Hr, and nominally 5 amps (2.5 HP) or pushing them to 8x you can get 20 HP. If you can achieve 150 W-Hr/mile as I've seen posted, you have about 10 miles range for each $1000 of batteries. 

That's enough to get started on a project with a total cost of under $2500, and you can always add more batteries to get the power or range you want. Using standard components makes service and replacement simple and inexpensive, and the industrial components are exhaustively tested and backed up by major brand companies.


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## Coulomb (Apr 22, 2009)

mizlplix said:


> The single largest cost in the construction of an EV is the battery pack.
> In both systems, you use the same cell capacity in the pack (which is set by your daily driving needs.) BUT, in the high voltage system, you need additional cells in series to gain that higher system rating, adding significantly to your build cost and car room to put them.


Not true. For the same power, a higher voltage system (AC or DC) uses less current, so you use lower capacity cells, but more of them. Lithium Iron Phosphate cells are basically sold per Ah of one cell, so the cost of the actual cells is the same for low or high voltage.

There are plenty of other costs when you go higher voltage, but cell cost is not one of them.

The other costs include cell interconnects and the labor to install them, BMS cost (if used), fuses are more expensive, you may want to use many more contactors to break up the pack into ELV segments (120 V or less), and above 600 VDC it starts getting hard to find components that withstand the higher voltage for long periods of time. Chargers and DC/DC converters above about 417 V (Elcon / TC Charger and MeanWell) are difficult to find, so you may need two chargers and/or DC/DCs.

There are benefits to the higher voltage of course; thinner cables, smaller cells are easier to fit into awkward spaces, and so on.


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## mizlplix (May 1, 2011)

Have you driven a vehicle with an industrial controller? Have you ever driven a vehicle without torque control? I have, they will make the vehicle move, but they lack the smooth, nice feeling a vehicle duty controller does.

Just be aware that not all AC controllers are suited for vehicles.

Miz


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## PStechPaul (May 1, 2012)

Most modern VFDs seem to have control settings and "hooks" that should allow whatever "feel" you want. Here is the manual for a controller very similar to mine:
http://igor.chudov.com/manuals/GE-Fuji-AF-300-VFD-Manual.pdf
and the exact model I have (which is a 2HP 240V version):
http://www.geindustrial.com/publibrary/checkout/GEH-6643?TNR=Installation%20and%20Instruction|GEH-6643|generic

The main control input is essentially a speed control, but there are ways to tune the actual performance using torque boost, torque limiting, and acceleration and deceleration time. You can also program an analog output to read the torque, and you can implement a PID loop which can essentially control the torque from throttle position by setting the frequency (speed) appropriately.


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## E30_Dave (Apr 19, 2012)

This tine in the right place !

It would be great to see a section on Permanent Magnet Synchronous, BLDC, Axial Flux, and most of all, Hybrid Permanent Magnet motors.


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## High Tension (Apr 29, 2009)

Hello, I see that this thread seems to have stopped some 3 years ago. I have a few Hyundai Smith Edison motors with their large Enova inverters and wondered if anyone might have stumbled across a reasonably priced modern motor controller EV suitable that could be used with them since then?


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## Pradox (Oct 28, 2021)

I have a vintage Ansaldo 11Kw 220/380 3 phase electric motor. Can I use it for my VW bug 1969 conversion?. How much do I need to invest in controller and other components?. This is my first EV conversion:


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## remy_martian (Feb 4, 2019)

How much does that motor weigh?


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## Pradox (Oct 28, 2021)

remy_martian said:


> How much does that motor weigh?


Around 140 pounds. Please see attached photos of the motor.

Thank you for your help Remy.


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## remy_martian (Feb 4, 2019)

You can get the same power of motor for around $300 used and maybe 35 pounds (I'm thinking something like Motenergy ME1114 Brushless Motor 24-72V, 5000RPM, 10 kW cont, 24 kW pk ). 

100 extra pounds is a lot of weight to be hanging out the butt end of a Bug and is about 60km more range in battery weight you could replace that weight with.


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