AC electric motor rewinding for EV use

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AC electric motor rewinding for EV use

Post by BigMouse » Wed, 08 May 2013, 16:15

My motor was purchased from Jon, yeah. 48vac @50hz. I'm told it's rated for 200a continuous current, so 3x current overload shouldn't be outrageous. There are LOTS of parallel conductors per phase. I will have an electric fan on it, so not relying on the integral fan. I've considered putting a water jacket around it too, but I haven't come up with a reasonable method to do that yet. I don't expect that I'd be pulling full current for more than 10-20 seconds at a time.

It's a WEG 132M frame motor, 4 pole. 9.2kw original rating. I don't know what the winding configuration is, other than it being 4 pole and delta. Next time I have the end bell off, I'll take a picture. Jon may or may not release the winding details. I doubt it though.

EDIT: Checked original rating
Last edited by BigMouse on Wed, 08 May 2013, 06:51, edited 1 time in total.

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Post by Johny » Wed, 08 May 2013, 16:28

Just an observation on cooling motors. I have my external fan (172mm, 70 Watt fan mounted on the cowling) coming on when the motor windings hit 65 degrees C. Pretty much the only time this happens is the sub 40 km/h parts of my commute. It takes about 6 to 10 speed humps and the VFD decides it's hot enough.
It figures as I'm pulling high current under 20 km/h and taking off with direct drive and current is quite low when cruising.

At higher speeds the motor fan goes back off after a minute or so. My motor is kind of in the airflow under the car so it makes sense.

A normal drive home sees the motor about 30 degrees above ambient when I roll into the driveway. Using silicon temp sensor (KTY 83-110) mounted in the middle of the wiring.

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AC electric motor rewinding for EV use

Post by BigMouse » Wed, 08 May 2013, 17:01

Looking at the data for the original motor, it shows a rated full-load torque of 60.2Nm and a breakdown torque of 270% (Direct on line). So 162.5Nm peak direct on line. The best performing motor in that frame (same power, single-voltage 415v windings) says 60Nm rated, 330% breakdown, so 198Nm peak torque, also direct on line. So with a FOC inverter (capable of over fluxing and over current), maybe 250Nm isn't so unrealistic. 300Nm might be a bit up there, but a constant 250Nm should get me a 0-100kph of around 6 sec.

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AC electric motor rewinding for EV use

Post by Richo » Wed, 08 May 2013, 20:54

BigMouse wrote: It's a WEG 132M frame motor, 4 pole. 9.2kw original rating.


So a US 60Hz motor.
So the short answer is NO but the long answer is YES.
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AC electric motor rewinding for EV use

Post by mizlplix » Wed, 08 May 2013, 21:39

Mouse, your motor should look like this:
Image

It is wound for around 50 volts and has one turn in each pole and lots of parallel wires so it can handle 300 amps cont. and 650 intermittent.

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AC electric motor rewinding for EV use

Post by Stiive » Wed, 08 May 2013, 21:56

mizlplix wrote: Mouse, your motor should look like this:
Image

It is wound for around 50 volts and has one turn in each pole and lots of parallel wires so it can handle 300 amps cont. and 650 intermittent.

Miz


You've done a nice job there Miz, looks very clean.
How many "in hand" is this? Bit hard to count lol.

That'd be a great winding if only you could run it at 400V to get the RPM you want/need.

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AC electric motor rewinding for EV use

Post by BigMouse » Thu, 09 May 2013, 02:57

Miz: That sounds about right. What sort of results did you get with that motor? Seat of your pants is fine ;-)

What frame size is that? Your phase windings coming out look even bigger than mine (hence the 300a cont I suppose).
Stiive wrote:That'd be a great winding if only you could run it at 400V to get the RPM you want/need.


Like I'm doing! Getting excited now :-)

I've actually got another identical motor on the way now for another EV project, but with the same goals and same controller I'll be using on my own car. I'm hoping to connect them together to make a dyno so I can actually get some performance numbers and help with tuning. I have all the bits to connect them together (heavy duty flexible element couplings). The hard part is measuring the torque. I need to come up with a clever way to fit a load cell in there. I wonder if I could just glue a strain gauge to one side of the motor's feet and calibrate it with a known torque applied to the motor case. I was planning to support the load motor by its shaft and measuring the torque using a load cell at the end of an arm attached to the case, but there's too much fabrication and danger with that method.

Stiive, is it possible to determine rotor time constant for FOC using a locked rotor and adjusting the time constant in software until maximum torque is produced? I'm considering doing this with the motor both hot and cold to get two values, then interpolating between those points based on actual motor temperature. Not as accurate as online identification perhaps, but requires much less processing power.

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Post by coulomb » Thu, 09 May 2013, 03:31

Will you end up with two identical motors to start with?

If so, does it make sense to measure electrical power on both sides, set the currents to be the same magnitude, and assume the losses are equal on both sides?

You have easy measurement of voltage and current on both sides, and their phase, hence the real power, and of course you know the speeds quite accurately too. So then you can deduce the torque from that.

Once you have the motor mapped for efficiency verses torque and speed, you could then use one of the motors as the dyno generator, and test other motors on it.

That way, you don't need any messy mechanical measurements at all.

But I suppose you may feel that's too theoretical.
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AC electric motor rewinding for EV use

Post by Stiive » Thu, 09 May 2013, 03:32

BigMouse wrote: Stiive, is it possible to determine rotor time constant for FOC using a locked rotor and adjusting the time constant in software until maximum torque is produced?


Hmm I guess that could work trial and error is normally the best way.

The normal/industry method is to do locked rotor test. Rotor resistance can be worked out pretty accurately, but there is no easy way to differentiate between the stator and rotor reactance in this test which kinda sucks. Mostly its just estimated as half-half but can vary depending on the class on the design if its industrial standard. Unfortunately cus its a custom winding, who knows!!

I'd start with rotor reactance equal to half of the locked rotor reactance, and work from there. A good indication of how good the tune is will probably be most evident in field weakening.

Sucks even further cus the inductance changes with the current, so ideally you'd want to end up with a comprehensive mapping of stator/mag current vs inductance and rotor current / torque vs rotor inductance. Good fun because they are all interdependant as well :)
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Post by mizlplix » Thu, 09 May 2013, 03:36

That was my very first motor. If I remember right, it was 24 in hand (those motor leads were 48 strands of 18 Ga. and one turn) The motor was based on a 7.5HP core. It ran OK above 1,500 RPM but the bottom end was kinda soft.

This one was based on the 20HP core that we are now using.


Image
It is 12 strands of 18 Ga, 24 strand motor leads, and two turns.

It is a torque monster and runs like a DC motor. It easily spins the tires and has a fairly low current draw at cruise, but only has a 3,100 RPM top speed and would need a transmission to be a good EV motor.

Our fourth wind will be similar to that except it will be 8 in hand and three turns but, we will be skipping slots to change/delay saturation and pick up some RPM.

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AC electric motor rewinding for EV use

Post by BigMouse » Fri, 10 May 2013, 01:03

mizlplix wrote:It is a torque monster and runs like a DC motor. It easily spins the tires and has a fairly low current draw at cruise, but only has a 3,100 RPM top speed and would need a transmission to be a good EV motor.
Maybe a lower ratio final drive would be sufficient? It sounds like there's plenty of torque available, and if you want more top speed at low RPM, that's the way to get it. Or use a different controller ;-)

Experiences like yours with that motor do sometimes make me wish that I went for a larger frame size. I don't want to be shattering gearboxes though.

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Post by mizlplix » Fri, 10 May 2013, 03:57

You can not hurt the gearbox if you can not hook it all up. I am running skinny tires.

I tried my best to kill a powerglide and a Borg Warner T-5 both. I know that the powerglide low gear does not like cruising at 6,500RPM +, it will cause premature wear in the planet gears.

Yes, agreed. Better controller. Would you perhaps build me one?

I know less than nothing about power electronics.

Miz

PS: Yes, a 4:56 rear gear would do me fine as it has a 79 MPH top speed.

My real reason for a transmission is for a vehicle heavier than 2,000 Lbs.
and any hills with a long gradient.
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Post by BigMouse » Fri, 10 May 2013, 04:29

mizlplix wrote:Would you perhaps build me one?
Hopefully some day, but I'm not quite there yet. I already have two "beta" projects on the horizon that will use my controller, and I'm hoping to offer them pending the results of those projects.

4.56:1 final drive is up there! I wish I could find one that high for my car, the acceleration would be awesome. Highest I can find for my BMW is 4.44:1, and they're not the strongest.

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Post by mizlplix » Fri, 10 May 2013, 09:40

That's why I always use a Ford 8.8 rear axle assy. I can get from a 2.73-6.14 ratio. And they are good for up to 500 HP.

(they probably hard to get in your neighborhood though)

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Post by Canberra32 » Sat, 11 May 2013, 05:00

So dose this mean the big chunky 3phase sitting on my giant compressor can be rewound for the small ev I'm building?
I'm bout to change to a single phase to run compressor.

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Post by antiscab » Sat, 11 May 2013, 08:27

maybe, depends how big "big" is

you might find using a small cheap VFD may be cheaper than replacing the motor to run on single phase though
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Post by Canberra32 » Sat, 11 May 2013, 14:13

Already had the single phase motor :)
Ill check out the 3phase tomorrow it's about 280x400mm in size ill get the specifics :)

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Post by BigMouse » Sun, 12 May 2013, 03:07

Canberra32 wrote: Already had the single phase motor :)
Ill check out the 3phase tomorrow it's about 280x400mm in size ill get the specifics :)


280mm diameter sounds like a 132 frame motor. That's the frame size I've got. It's certainly possible. I have a spare 132 aluminium frame motor that I'd like to have a go at re-winding myself. Miz, do you have a record online of your various windings and results? I've had a look through your forum, but I didn't have any luck finding such details.

The spare motor I have is shown in this thread. Can you identify anything about it for me from the pics I've provided?

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Post by mizlplix » Sun, 12 May 2013, 03:57

On 60Hz motors, we have a rule of thumb to use to determine the pole count.

Number of poles                 RPM
        2                         3,600
        4                         1,800
        6                         1,200
        8                         900
        10                         720
        12                         600

Having said that, what really matters is that it is a 36 slot stator. That is the best one to have because it can be wound to just about anything.

(The following is my opinion from having three EV's and testing to this point, 5 custom wound motors.)

First of all, I would not consider anything but a 4 pole winding for EV usage. It is the best all around for torque and adequate RPM.

It needs to be permanently in what we think of as Delta, because there are no internal motor leads needed as it is a single voltage motor now.
(In a purpose wound, single speed motor, there really is no such thing as delta or wye anymore. It is just how the motor is wound...)

We have also determined by trial and error....that 18 Gauge wire to be optimum for an EV motor. It handles the high current, it is easy to wind with, and it is good for voltages between 30 and 90.

As far as a pattern for winding: Wait a couple of weeks for us to get the next motor wound. We feel it will be the best one yet.

It is a further modification of a basket weave style. It will have 3 turns around each pole but skips 4 slots to pick up some back iron.

We are shooting for good torque over the whole RPM range, low cruise current draw and a top RPM of about 4,500.

My motor is a 48 slot and a pattern of it would not really do you much good, but Ivan's motor is a 36 slot, so He can print the one for his motor.

Miz

PS: Ivan used to print the winding diagrams as he worked on them, but something happened to the file in the server (I think).
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Post by Canberra32 » Sun, 12 May 2013, 04:28

Ok while I can take a few bits of steel and weld them into almost anything electric motors past the on off function to me operate on what I assume is magic...

Perhaps the question I should have asked is who do I send it to to make it EV ready? :)
Mechanical engineering no probs but electrical is a fail for me :/

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Post by Stiive » Mon, 13 May 2013, 02:08

Canberra32 wrote: Perhaps the question I should have asked is who do I send it to to make it EV ready? :)


We got our SAE motor rewound at Genertech in Victoria - cost a few thousand $ tho.
There should be similar shops all around Australia.
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Post by Canberra32 » Mon, 13 May 2013, 03:44

So what would I be telling them?
Any request I should specify or just toss it at them n say "car" lol
Seriously is there anything I should say or just trust they can work it out?

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Post by BigMouse » Mon, 13 May 2013, 04:26

A motor rewind shop is only going to know industrial stuff. It'd be like going to a bakery that specializes in wedding cakes and asking them to make you a loaf of bread. They could probably do it, but they're not going to want to. If you provide the winding details (with help from Miz or others), then you might have a better chance talking them in to it. I wouldn't be surprised if they quote high for the job though.

Jon (Catavolt) has quoted me less than $1000 to have my 132 frame motor (mentioned above) rewound to 48vac delta. Not sure what shop he uses, but it'd be up in the Newcastle area. I know Arrow Electrical here in Wollongong does rewinds too, though I never got a price from them.

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Post by BigMouse » Mon, 13 May 2013, 04:31

mizlplix wrote:As far as a pattern for winding: Wait a couple of weeks for us to get the next motor wound. We feel it will be the best one yet.

It is a further modification of a basket weave style. It will have 3 turns around each pole but skips 4 slots to pick up some back iron.

We are shooting for good torque over the whole RPM range, low cruise current draw and a top RPM of about 4,500.
Why is the top RPM specified? Is that assuming your Curtis controller, or is it some limitated you expect to come from this method of winding. An effective high-torque winding pattern for an industrial 132 frame motor would be great. Even better if I could get 7500+RPM out of it on my controller.

What voltage will 3 turns give you? I really would like to stick with the same voltage (~48v) I have now.

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Post by mizlplix » Mon, 13 May 2013, 05:05

The Curtis controller throttles the motor through varying the frequency (VFD). It will do 300 Hz, which means about 9,000 RPM on a 4 pole motor.

The RPM is limited by the stator iron saturation. That is partly mitigated by driving the motor up to the point of saturation, then weakening the magnetic field (increasing the falling torque)to coax it upwards in RPM.

The current/voltage is managed by an internal algorithm (and is not user adjustable), which is set by the controller when you put it through the so called "optimization procedure".

In my case, the 4,500 RPM is determined by the gearing in my car as well as the places I drive. (Speed limits)

Roughly, on my motor: One turn is 46 feet of wire length. It puts the optimum motor voltage at about 30 (RMS).

Two turns is 72 feet and about 60 volts.

My present motor is two turns, but skipping 4 slots, giving 56 feet and around 50 volts.

The new winding: three turns and skip 4 slots should be around 68 feet and 75 volts.

As you use more wires in the bundle you wind with, you decrease the voltage necessary, but increase the current draw.

(I hope I didn't confuse the issue) Miz
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