# sourcing a suitable second hand ac motor



## davidru (Apr 12, 2009)

electric_gray said:


> Where would I find a decent second hand ac motor for use in an electric vehicle, can they be found in some heavy duty household appliances like winches for example or are they only available old electric vehicles.
> 
> Cheers graham.


Nobody seems to have picked this one up, so I'll chime in. Caveats abound, but suffice it to say, there is no limit to what I don't know about motors, but I'm learning fast.

The general category of AC motors is pretty broad. A brushless, permanent magnet motor can be considered an ac machine, as is an induction motor which has no permanent magnets.

Generally, motors used in consumer goods like washing machines and winches are simply too small for ev use, except perhaps for a go-kart sized vehicle.

Second hand also encompasses a pretty wide range of possibilities. I gather from your other post you are converting a Peugeot 205, which is about equivalent to a vw golf in size and weight, I presume.

For induction motors, here are some used Solectria/Azure AC-55 systems (motor and controller) http://www.evcomponents.com/ProductDetails.asp?ProductCode=AC55 The motor may be a bit heavy for your 205 at about 100kg, but if you're using lithium batteries it would certainly be manageable, and it would definitely have enough power. At $3500US they may seem expensive, but this is about half what they are sold for new. Another source for used ev capable motors is http://www.metricmind.com/ They also sell new ac systems, but they are not very cheap. Both vendors are in the US, and I don't know of equivalent sources in Europe, unfortunately. More info on new AC systems in another thread in the motors forum http://www.diyelectriccar.com/forums/showthread.php/new-ac-motor-available-24498.html These are close to the cost of the used Azure systems, but have less power. Still useable for your 205, just at a bit slower pace.

There are large AC induction motors used in industrial applications that may be suitable for on road EVs, but the key missing element is an affordable controller. To be useful in an EV, AC induction and DC and AC brushless permanent magnet motors must use relatively sophisticated electronic control systems. Used industrial motors here in the states are dirt cheap, often sold by the pound for their copper content. Electronic drives for them are not. Many DIY AC controller projects exist on this and other forums, but the "conventional wisdom" of most is that a DC system is the most practical drive system for a homebuilt EV. Used DC motors are almost as easily obtained as AC, and the controls are much cheaper. That said, AC and brushless motors offer many advantages, high efficiency, regenerative braking and long life among them.

Hope I didn't just add to your confusion. Good luck with your build.

Dave


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## electric_gray (Jun 12, 2009)

Hi dave cheers for the reply, 

I'm very new to electric vehicles so all I have at the moment is a load of ideas and a peugeot 205 shell (which is indeed similar to a golf in size and weight).

I have a fair bit of experience with general electronics and computer programming so it might be feasible for me to make a controll system and go for an ac motor from an industrial application. 

I would also like to take advantage of the regenative breaking channeled into a capacitor bank, would this be taken care of by a production control system or would it need to be a home made system for this.


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## davidru (Apr 12, 2009)

electric_gray said:


> Hi dave cheers for the reply,
> 
> I'm very new to electric vehicles so all I have at the moment is a load of ideas and a peugeot 205 shell (which is indeed similar to a golf in size and weight).
> 
> ...


My "expertise", if I have any is mechanical, so I can only recapitulate (in distorted fashion) what others have said. I don't think any ev or industrial motor controls have specific provisions for ultracap energy storage, but in theory, you could simply hang them off the dc bus of the system. In practice, this probably would result in a lot of shredded aluminum and electrolyte splatter. I belive ultracaps need their own dedicated control system and dc-dc converter to work in an efficient way, and they typically monitor the voltage of individual caps in the string. On that subject, it takes many ultracaps in series to get in the range of an EVs DC bus voltage as the caps are typically rated for only 2.5-3V each. They also contribute loss to the system, just like any passive component because of their ESR, which isn't zero. They are claimed to be capable of many more charge-discharge cycles than any battery technology, but in a typical ev application, they might see hundreds of charge-discharge cycles just driving to work. I'm leaning towards a LiFePO4 battery like a123, which can absorb high regen current without the need for ultracaps. With either solution, you need to deal with the contingency of turning off the regen system when the storage system is at maximum capacity.

I'm pretty handy with a soldering iron as well as a cnc machine and cad box, but when I started badgering my electrical engineer buddies about igbts and space vector motor control, I took a lot of abuse, and I got a lot of responses like "...hehehe, should we tell him about Miller capacitance?...". AC motor controls are "non-trivial", for this mechanical designer anyway. Still, there are some on this forum that relish the challenge. The idea of simply modifying an industrial variable frequency drive (VFD) may be one of the most compelling routes to a low-buck controller.

It's great that we have postgrad engineering students to give us ideas , here's an interesting paper comparing batteries+regen to batteriy+ultracap+regen and other whacky storage systems like flywheels (I remember that SciAm article from 1973!)
http://www2.ing.puc.cl/power/paperspdf/dixon/35.pdf
This seems to indicate my hunch is wrong, but my limited experience with power electronics suggests simplicity trumps absolute efficiency for homebuilt systems.


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## electric_gray (Jun 12, 2009)

Cheers again dave for replying, I can't see pdf's on my phone so ill have to check that paper out in work tomorrow, you said caps generally used are 2.5 to 3V rated, is this purely because these are cheaper. I have more than a few 185uF caps rated at 3000V which I was hoping to make use of.


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## davidru (Apr 12, 2009)

electric_gray said:


> Cheers again dave for replying, I can't see pdf's on my phone so ill have to check that paper out in work tomorrow, you said caps generally used are 2.5 to 3V rated, is this purely because these are cheaper. I have more than a few 185uF caps rated at 3000V which I was hoping to make use of.


Sorry, was referring to ultracaps, which are typically a lot more C, like many tens of farads, but much lower voltage. Link with excel spreadsheets here http://www.maxwell.com/ultracapacitors/technical-support/tools-models.asp They are not really cheap by any means, but I thought they had the best energy density of all capacitor types.

The amount of electrical energy that can be stored in a cap is 1/2 CV^2, so it would appear lots more V would be the way to store more energy, but supercaps and ultracaps are almost always rated at only a few volts. I hadn't thought of using very high voltage caps, but yeah, your 3kV 185uF cap can store about 800 joules of energy (1 joule = 1 watt/sec), so that's about 1 HP/sec.

What is the capacitor type, and how much do they weigh?


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## davidru (Apr 12, 2009)

Ah, now it's making more sense as I work through the math. I guess this thread should be renamed "ultracaps again" or something. Here's my "thinking out loud" on regen.

Let's say we want our regen to be able to provide 7.5kW (~10hp) retardation for 10 seconds, a very modest amount of regen. That's 75000 joules, so in this case you would need about 94 of the 185uF 3kV caps. This is really a tiny amount of energy, just 21W/Hr. The Prius battery pack is about 2.5kW/Hr, as an example. But we're not using the caps as the primary energy source, the idea would be to use the caps to buffer the regen current as well as provide a boost to the traction battery when acceleration demand is greater than the batteries can supply without compromising their life. I think in this case, a larger capacitor bank might be needed to buffer the energy demand. Even increasing the storage capacity of the cap bank 10X to 200W/Hr, it becomes apparent you would need a lot of caps to get the job done. These are just guesses, as I imagine simulating a drive cycle to for sizing ultracaps could be quite complex.


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