# AC motors in NZ



## Richard Wood (Jun 27, 2008)

I've been planning a DC conversion but feel I must research AC before I go further. There are aspects I do like such as regen and the suggested safety angle.
Is anyone using AC motors in their current builds in NZ? Does anyone supply suitable AC motors in NZ? 
I prefer to support New Zealand business and benefit from their support, but failing that, where have people sourced from?


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## rwt33 (Dec 4, 2008)

Yeah there's a fair few good quality builds around using AC motors.
Look up "greenstage" and carrott.org
They're using induction machines. I'm using a perm-mag sync too.
There's huge advantages to AC motors. You actually get _accurate_ torque control. On top of that they're much more efficient and they don't wear out (no brushes).


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## Jens Rekker (Oct 26, 2007)

It all just depends how technologically elegant you want your conversion to be?

Efficiency? Yep, AC induction and synchronous motor have slightly more efficiency. DC series motors have brushes that wear out (eventually). The brushes also make regenerative braking a bridge too far in EVs.

Durability? Yep, AC has got a bit more durability, unless you've converted with a dicey inverter system.

Regen? Yep, apart from separately excited DC conversions, AC offer regen that DC can't.

Safety? Apparently AC conversions have greater failsafe against runaway acceleration. I'm not convinced myself, but I'd be prepared to concede the point.

At the end of the day, the crux of an EV is the battery system. That's where most of the maintenance and durability questions rest. If you saved the money that you might spend on an elegant MetricMind or Azure AC drive and spent it on the best energy dense, highest performance and durable battery system going, then I think it would out-trump the advantages of AC. Lack peak efficiency and regen? Put in another battery and shave some more weight out of the vehicle.

EV conversion is still a very expensive personal luxury. It's also very individual. Some folks are greatly attracted by the elegance of AC, and I can understand why. But, EV conversions on a beer budget will tend to conform to a DC drive system and not be greatly disadvantaged in doing so.

The main game changer is the use of second hand industrial induction motors and variable speed drives (VSD). There have been a few of these AC conversions done by industrial electricians and engineers which have been inspiring efforts for very little money. 

But, at the end of the day it comes doen to batteries, batteries, batteries. You might be able to guess that I am a bit down on my own lead acid batteries and I have absolutely no problems from the DC drive system. In another life I will go with LIFePO4 batteries. Although there is probably zero justification in not going with LiFePo4 bats, I just can't afford them at current prices.


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## Nick Smith (Oct 26, 2007)

I am dreaming nightly of the AC50 motor and Curtis 1238 contoller available from a number of EV suppliers. Unfortunately for us NZ'ers this stuff all has to come in from overseas.

I did look into doing it on the cheap recently as I see no reason why industrial AC motors and frequency controllers could not be used for EV conversions. I realised pretty soon that there is an issue to be aware of if you want to use an industrial AC motor and that is that they are wired for 415v 3-phase power and hence use relatively "light" wire in the windings. You can get 240v 3-phase (US spec NEMA) motors but again the windings are still "light".

If you are intending to go for a low voltage AC system (ie 144v) then the current draw in the motor (for the same power) will be higher and the windings will burn out sooner or later.

You can always get a motor rewound to suit whatever voltage you desire but at the end of the day you will end up spending the same or even more than buying a proven EV motor.

If you are looking to go much higher voltage then the industrial motors can be had second hand pretty cheap but they are usually quite BIG. That said - if you can afford a 300v + pack then you can afford the motor and controller to go with it .


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## JRoque (Mar 9, 2010)

Hey Nick, got any info on what's a typical wire diameter for a 230V (US) industrial motor? I plan to use one of those motors in my conversion. It is inverter rated with over 2500V insulation. The motor specs are 230/460V @ 60/30A. The motor will be wired for 230V and the bus voltage will be around 320VDC.

From what I heard, industrial motors are very conservatively rated because they are expected to run 24/7 at full power. A typical EV application will drive them hard but only intermittently. 

JR


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## Nick Smith (Oct 26, 2007)

Richard, sorry - can't answer that one. I am a mechanical engineer  so my info on motor windings is generic rather than specific.

By the wording of your response it would appear that you will be feeding it the correct voltage so I wouldn't expect any issues. You could however (as a precaution) wire the motor thermistor (assuming it has one) to chop back the controller power if it goes over temp.

Your project sounds interesting - keep us posted.


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## rwt33 (Dec 4, 2008)

The reason for the light wiring in industrial motors is that they're used for a completely different application. Industrial motors are designed to do their rated power (nominal voltage and current) for 24 hours a day, for 20 years. Designers try to design every part of the motor to go at about the same time, and as a result the motors also tend to run at lower RPMs to get the best life out of the bearings. Even then, at 50Hz (or 60) the max speed is still only 3000rpm (just under really).
Traction AC motors have quite different operating conditions. They have huge short term torque requirements, aren't constrained to a fixed frequency and don't run for 24 hours a day. Most traction AC motors operate at high frequencies, up around 150Hz isn't uncommon at top speed. Commercial aircraft commonly have an onboard AC bus that runs at 400Hz (rather than 50/60Hz) for the sole reason of keeping motors/generators small.
As an example, DesignLine buses in NZ have a series-hybrid range of commuter buses. The custom motors reach full torque (nominal voltage/nominal current) at only one third of their rated speed. Above one third speed field weakening is used.


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## Hemon Dey (Jul 31, 2008)

I'll just chime in here. I had spent a fair bit of time investigating using industrial AC induction, and though it is viable (see some of the folks over at AEVA for inspiration) it doesn't come easy, nor are you guranteed to get it cheap. 

Industrial AC induction are typically 4 pole motors which are rated to run at about 1500rpm. 2 pole motors run at 3000rpm. This is not to say they can't run higher, the bearings in them are rated to about 4500rpm. As the rotor is a squirrel cage, it doesn't have a huge momentum to overcome and can spin up relatively quickly. They tend to have a flat torque curve up to their rated RPM, which then diminishes in an exponential way as the RPM goes higher. As torque x RPM is power, you go from constant torque system to a constant power system beyond the rated RPM. This is the reason that Red Suzi (in its original form) was speed limited to ~80km/hr as it was a 4 pole motor directly tied to the diff. The torque output of the motor was similar to the original engine + gearbox.

I had been thinking along the lines of a 2 pole however. You get half the torque in the same motor package, which means you need a gearbox to obtain the different speeds. I had bought a 15kw AC 2 pole motor with a matching 15kw controller (with 60 second over rating to 20kw) ... total cost was about NZD$1500 second hand off trademe. So yes, cheap - but here is the thing:

1/
The motor was a cast iron one, with a flange mount it weighs 150kgs, which is about what a typical 2L 4 cylinder engine weighs?? When accounting for battery weight as well, now you are loading the vehicle up fairly seriously with little room for extra weight. Even two people lifting off the back of the trailer was a decent amount of effort. You can get an aluminium one, but hard to find second hand and typically more expensive to buy new. The controller is another 30kg.

2/
The controller needs a 1500-2000 parts per revolution tacho in order to do pure torque control in closed loop. This will add to the cost. Some controllers can do sensorless feedback which don't require a tacho, however the torque control isn't as good especially at low RPMs.

3/
You need about a 600V DC bus (420Vrms) which is a HUGE battery stack. I considered using 2x10aHr Headway lithiums for this as it had the continuous C rating and was smaller than the other large format LiPeFO4 cells. Why smaller? because I needed about 220 of these cells to create the HVDC bus. Packing these (and associated weight) into a car is an exercise in itself.

4/
The BMS you'd need for the battery stack would be massive. Even designing my own, the costs were going to be high. 

5/
You would need HVDC contactors that were able to break the pack at short circuit current. I was going to use a few of the Tyco EV200s to do this as these are fairly amazing devices and can handle amazing ratings. Note that even at a modest 100A, you are breaking 60-80kw. The headway cells I've tested to grunt out at 8C for 20 seconds until they exceed their temperature rating. 10C is not unexpected, so that is 160kw. The EV200s can do 300V at 2000A ... so plenty of safety margin. Not sure about what the NZ law states about pack voltages these high as having a manual cut out is plain dangerous! these contactors are electrically enabled.

6/
At the voltages concerned, safety is paramount - so leakage detectors are essential IMHO (actually even 144V DC systems are extremely dangerous). 

Also like any conversion, you have to really take the battery more as a consumable (that last anywhere from 5-10 years for Lithiums), hence you aren't really driving a carbon zero setup. Although pretty difficult to work out the embodied carbon in the batteries, I estimated it to be equivalent to driving (conservatively) at 30% of the carbon that my current car emits per km. This was done very unscientifically based on a paper I read on embodied carbon on Lithium cobalts ... so I might be miles off, and is so dependent on how long the battery lasts, which nobody really knows yet in a real world setup. However I did figure that driving a Prius with an extra battery pack would be a vastly simpler project which could achieve better results in both short and long terms - both on carbon and back pocket analysis. 

Sorry for the essay ... hope some of this information helps. Keep us updated on your progress. I have paused on this project to rethink options. I also became a father for the 2nd time, so my life is just a bit busy at the moment. 

Regards,
Hemon


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## JRoque (Mar 9, 2010)

Hello Hemon, congrats on the new cell addition to your family pack 

I bought off eBay an industrial 25HP (18KW) AC motor designed for inverter duty (ie: 2500V insulated, higher rated copper windings). It's a 2 pole that spins ~3540 RPM at 60Hz and can do 5400 RPM safely. The motor weighs 170 pounds (78kg) in a 256 frame size with both c-face and base mounts. It's dual voltage 230V/460 that I plan to run at 230VAC (~320VDC). I paid $476 USD shipped to me.

The controller, a 5 HP Hitachi VFD also off eBay for $317 USD will have it's IGBTs and current sensors replaced with externals - or - I'll fallback on a Semikron module, quoted at $1K USD. Other than possibly the adapter and motor mounting work, I stand to lose little if the experiment with an industrial motor fails. 

Part of my motivation is that vendors tie up their motors to their own controllers as if this were a hard requirement to make them work when everyone knows that's not the case. If I had the opportunity to buy an AC motor designed for EV use and not have to overpay for their controller also, I'd go for that. If my experiment fails, I'll fall back on an AC50 with a Curtis controller at 96V bus or so that will let me move and be a lot cheaper on the bat pack too.

JR


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## rwt33 (Dec 4, 2008)

Good writing Hemon, I agree completely.
Like I said in my previous post, industrial SCIMs really aren't suitable for EV conversions. At the end of the day you'd end up with a horrifically over weight conversion.
My PMSM is a 220V machine so my pack is at present 120 LFP cells in series (400V nominal, 505V fully charged) and I'm looking at going higher.
And you're _exactly_ right about earth leakage, and not just at those high voltages. I think there's a lot of people out there who have no idea about the dangers of DC. I don't think it's strictly necessary to have current-breaking contactors as the fuses should be entirely adequate for this job. I have 63A fuses although expect to be drawing well in excess of this. If people study the fuse Time vs Current spec chart for the fuses you'll quickly realise that a '63A' fuse only blows at that current after a year or two continuous! A DC-breaking contactor is still a good idea though for kill switch functions.
Earth leakage circuits are relatively easy to design and build and should definitely be considered by anyone who's constructing their own circuits etc.


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## enp13 (Mar 26, 2009)

I'm planning to use an EVE AC motor. However, this is not an approach for the faint hearted as their info is limited and sometimes poorly translated from Italian. There's nothing like a bit of adventure to keep life interesting!

They have some info here on the M2 series:

http://www.electro-vehicles.eu/shop/browse.asp?cat=60&path=47,60&tipoprod=AC_Induction_Motors

but they also have an M3 series of larger ones (40, 60, and 90kW continuous for 2880, 2980, and 3820 euros respectively) which I am currently in discussion with them about. Note that these motors don't have as much short term overdrive capacity (around 80% for 2 minutes) as some other manufacturers claim so you need to factor that in. For that reason I'm currently leaning towards the 90kW although the 120kg weight might be a show-stopper.

My planned controller is the TIM 600:

http://www.electro-vehicles.eu/shop/details.asp?prodid=MES04&cat=0&path=49,63

but again, you'll need to email them and ask for the manual to get a better idea of it's performance.

I plan to decide and purchase in about a month's time if you're interested in a combined order. I would allow at least 2 months for delivery since they manufacture to order.

Edward


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## carrott (Aug 19, 2008)

JRoque said:


> The controller, a 5 HP Hitachi VFD also off eBay for $317 USD will have it's IGBTs and current sensors replaced with externals - or - I'll fallback on a Semikron module, quoted at $1K USD. Other than possibly the adapter and motor mounting work, I stand to lose little if the experiment with an industrial motor fails.


Check out the open source Tumanako Inverter. The website is really poorly organised, but we have a mailing list and we have motors spinning. Most of the development is currently in Auckland and we'd be happy to give a demonstration to anyone that is interested.

Check out http://www.youtube.com/watch?v=nNbhbYjD5Rk (in the car) and http://www.youtube.com/watch?v=Zhjh-dAjgqk (on the bench)


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## JRoque (Mar 9, 2010)

> Check out the open source Tumanako Inverter.


Hi, already belong. Great project that hopefully stays open source.

Hey so which Semikron module are you specifically using in the project? There are so many on that company's website - and talk about disorganized website! I've seen references to SKiiP and SKiiM (?) but would like to know which module you're actually using. I'd be looking for a 600V/400A model if I go that route.

JR


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## carrott (Aug 19, 2008)

JRoque said:


> Hi, already belong. Great project that hopefully stays open source.


We are very committed to open source. There are some hurdles to overcome, but it will happen.




JRoque said:


> Hey so which Semikron module are you specifically using in the project? There are so many on that company's website - and talk about disorganized website! I've seen references to SKiiP and SKiiM (?) but would like to know which module you're actually using. I'd be looking for a 600V/400A model if I go that route.


Phil's SkiiP is a special custom one made for Evisol, see http://carrott.org/cgi-bin/twiki/view/ElectricSaker/EVI200Controller

Ask on the tumanako mailing list, Ed will be able to give you some advice on what power stage to choose. I believe the difference between a SKiiP and a SKiiM is that the SKiiM does not have gate drivers, but I'm not entirely sure.


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