AC electric motor rewinding for EV use

[mizlplix]

Greetings:

For the past year, there has been a group of people studying AC propulsion systems. They all eventually noticed the huge gap in the AC motor offerings.

The present AC50 and soon to be AC75 are the top of the "lower" cost systems out there for DIY people.

Among this study group, are engineers, scientist types and some talented machinist /fabricators, as well as people like me (I'm more like a swiss army knife).

They have decided to work out the methodology and materials required to do a DIY motor customization. Their findings, so far, are really simple and cheap. We include controller optimization programming also.



We have started a new forum dedicated to sharing this information to the DIY crowd.            www.ivanbennett.com/forum/




So, anyone really interested in making their own AC propulsion motor is encouraged to view, ask questions and contribute to the discussion.

The forum is only 2 days old at this date, so please be patient, contribute and help us grow.

TYVM,   Miz

[mizlplix]

__________________________________________________________________________
            "The newest motor in our test Mule"
__________________________________________________________________________


It is a 12" aluminum cased monster. On the test bench it pulls 65 amps @ 60 volts at 60Hz.(mains current)

Miz

[mizlplix]

The first of three sections of the Curtis optimization routine has been performed and the motor is being permanently mounted in the car.

It did three pulls 30 seconds long reaching 647 Amps at times.

This was to estimate and set the field weakening amount in the controller.
It gets it about 80% of the way there.

The other two tests are 0- 60 MPH runs with varying settings to get the final optimization settings.

Pics and information when it is done later this week hopefully.

Miz

[elmex]

Hello Everybody.

I am New Here From Terminal Blocks Company. We Provide Custom Word Wide Terminal Blocks service as per client requirement. So if you have any question about that are welcome.

Thanks.

[mizlplix]

Welcome to the forums Elmex.


I have been kind of remiss in my posting lately. But, I have been busy.

I have driven my car with the new motor. It had great bottom end torque, a decent current draw under cruise, but was limited to 3,100RPMs. This winding used 1/6th the slot worth of 18 Ga. wires and wound two times around each pole, times the three phases filled the slot. A second winding type was needed.

The second winding was a full 1/3rd of the slot worth of 18 Ga. wire , but only once around each pole. Times all 3 phases. It moved the torque up some and softened the initial take off some, but extended the RPMs up to 4,100, but it was at the cost of increased current draw under a cruise.

We currently have the third generation winding in the motor. It is back to 1/6th of the slot worth of 18 Ga. wires, but we are skipping 2 slots on each pole. It too softened the bottom end torque some, but extended the top RPM to 3,800 and lowered the current under cruise to an acceptable rate between the other two tries.

We have figured out another winding pattern for a fourth try. It will use 1/9th the slots worth of 18 Ga. wires and go three times around each pole, but skip 2 slots per pole. We are expecting it to strengthen the bottom end torque, keep a decent cruising current draw and still raise the top RPMs to maybe 4,500 or so.

It will be a couple three weeks or so before we can get it done.

Miz

[Stiive]

What voltage are you running?

[mizlplix]

I am running 36cells for a pack voltage of 122.

I have wound several motors and have tried 30 volts RMS, 60 RMS and 70RMS volts.
I have the best overall at winding the motor for 70RMS, but the Curtis controller will not give much above that.
On the 1238R Curtis, the RMS is determined by how the controller sees the motor,s needs, not by pack voltage.
Pack voltage only means increased mileage, not Increased RMS voltage.

Miz

[Stiive]

I am running 36cells for a pack voltage of 122.

I have wound several motors and have tried 30 volts RMS, 60 RMS and 70RMS volts.
I have the best overall at winding the motor for 70RMS, but the Curtis controller will not give much above that.
On the 1238R Curtis, the RMS is determined by how the controller sees the motor,s needs, not by pack voltage.
Pack voltage only means increased mileage, not Increased RMS voltage.

Miz

The Curtis automatically tunes/senses the maximum winding voltage? I cant believe that, surely its an input parameter - or based on the sensed flux and inputted nominal RPM/freq. [EDIT - if not, i'd be looking for a new controller ]

I'd try go with a lower voltage windings + over voltage to get your higher RPM.

[Stiive]

I have driven my car with the new motor. It had great bottom end torque, a decent current draw under cruise, but was limited to 3,100RPMs. This winding used 1/6th the slot worth of 18 Ga. wires and wound two times around each pole, times the three phases filled the slot. A second winding type was needed.

i.e. From your description this winding sounded like it was best. Then you can overvoltage if/when you need higher RPMs

At what RPM did torque start to fall off? With higher voltage you will be able to keep constant torque going for longer.

Is winding star or delta?

[mizlplix]

: )     The Curtis controller has no voltage parameter settings that can be changed. The voltage/current relationship is fixed by whatever the controller "sees" during the Auto-run portion of the initial optimization routing performed when a new motor is installed to the controller.

Motor RPM is determined by the frequency only. But, is limited by the saturation of the stator. More windings=better bottom end torque but earlier saturation and lower top RPM.

Top end torque is increased by weakening the field in the stator. It is a changeable parameter as is the RPM point where the weakening starts and the curve as to how aggressively it happens.

The first motor winding had a base weakening speed of 770 RPM (as recommended by the controller).   The second winding had a 2,400 RPM base weakening speed. The third motor has a 1,400 RPM base speed.

Yes, this can be played with giving different driving characteristics, but at the end of the day, it is the overall driving experience that counts.

The very first motor winding with 2 turns per pole was the best "street" motor, but required a transmission due to the 3,100 RPM top speed (My car weighs 1,900 Lbs . and is direct drive- so I need all three- Good starting torque, good top end torque AND sufficient top RPM for street driving.)   

An AC motor used as a traction drive and using our Curtis controllers need to be always wound in Delta, because Wye would be too soft on torque at the voltages this controller maxes out at...about 90 or so.

Miz

[Stiive]

: )     The Curtis controller has no voltage parameter settings that can be changed. The voltage/current relationship is fixed by whatever the controller "sees" during the Auto-run portion of the initial optimization routing performed when a new motor is installed to the controller.

Motor RPM is determined by the frequency only. But, is limited by the saturation of the stator.

The flux (saturation) should remain fairly constant until field weakening. Most controllers run the motor near saturation where possible while under load. I'd try increasing the nominal RPM/freq and see if that helps.

Top end torque is increased by weakening the field in the stator.

No, just the speed is increased, the torque can only decrease in field weakening.

It is a changeable parameter as is the RPM point where the weakening starts and the curve as to how aggressively it happens.

Who knows how this controller works, but perhaps setting a high value here will ultimately open the motor up to more volts - keeping it from going into weakening until a higher RPM is reached

An AC motor used as a traction drive and using our Curtis controllers need to be always wound in Delta, because Wye would be too soft on torque at the voltages this controller maxes out at...about 90 or so.

Yeh, 9 times out of 10 I would recommend Delta - but it depends on the application of course.

Sounds like you need a new controller. Perhaps a Tritium? Probably more worthwhile than randomly trying new windings to suit this curtis auto-tune

[mizlplix]

"Sounds like you need a new controller. Perhaps a Tritium? Probably more worthwhile than randomly trying new windings to suit this curtis auto-tune."

No argument there. It just becomes a question of cost. The Curtis controller is about $2,000USD which is hard to beat for cheap.

Our other purpose in doing all of the rewinds is to have first hand experience with AC motors, reading and studying only goes so far.


"Top end torque is increased by weakening the field in the stator."

My reason for that statement is that is exactly how it seems to work (with this controller). My present motor will free-run to 4,900 RPMs, but when any size load is placed on it, it only runs 3,100 RPMs, until I start to work with the field weakening parameters and I can carefully work it up (under load)to around 4,000 RPMs.

Miz

[Richo]

That's an interesting car you have there - what is it?

[mizlplix]

It is a 1930 Model A Ford, Speedster. Basically 1930 frame, suspension with a Marine plywood floor and firewall. The body is built from 22 Ga sheet metal with spruce ribs. It weighs 1,900 Lbs.



I originally had an AC50 motor with a Powerglide-2 speed transmission with the torque converter removed and a direct drive coupler.

Then I got involved with this group of persons doing a project of rewinding AC industrial motors to use in EV's, so I volunteered to test the motors.

It is my third electric car.

Miz

[woody]

Nice!

[T2]

Hi Miz , nice work.

On your site I noticed that you had chosen a 2-pole as a candidate for a rewind. AEVA is probably a more neutral site for advising against the re-use of 2- pole machines. This exact idea has been discussed here just recently.

I wrote the following on 2nd OCT 2012 on the "14000rpm machines" thread regarding 2-pole and 4-pole stators.
"My experience is that I noticed 2 pole (machines) are smaller perhaps because hi-speed fan cooling (at 3000rpm) allowed designers to downsize slightly"

To which WEBER replied

"Yes. There would be a small effect from that. But Woody and others have compared Tmax or breakdown torque, which has nothing to do with cooling and they still show that 4-poles have nearly twice the peak torque of same-frame-size similar-mass 2-poles."

In an attempt to reason why this is so Weber went on to note that the rotor of an equivalent horsepower 2-pole machine is of smaller diameter - about 70% - from examination of quoted rotor inertia values as found in manufacturers catalogs.

This kind of makes sense since the machine needs only to develop half the torque since it is rotating at twice the speed. Meanwhile the outside diameter of the stator remains at the same size as the equivalent horsepower 4-pole stator, the reason is unclear however the longer magnetic paths of the 2-pole probably do benefit from the larger back iron of the stator available with its rotor core being that much smaller.

Recent examination of the SEW Eurodrive online catalog suggests that demand for two pole machines may in fact be disappearing from the industrial landscape above 3 Hp.

With an adequately balanced rotor it is of course possible to duplicate a 3600rpm motor for 460Vac by taking a 4-pole dual voltage 230/460Vac machine and hooking it up for 230Vac. In other words rewiring from a large Y to a smaller double Y parallel configuration. It would then be run up to 3600 rpm by feeding it with 120Hz current from a 460Vac inverter. Doing that has the advantage of enabling, say, a 5Hp machine to do the work of a 10Hp machine. The current draw from 460Vac will be the same that it would have pulled from 230Vac while developing 5Hp.

Bearing in mind that a 5Hp motor at 1800rpm provides the same torque as a 10Hp machine at 3600rpm. We are asking nothing more than that same torque at double the speed by doubling the voltage without increasing the current. The same current but at twice voltage infers that the 5hp is not going to be running at an appreciably higher case temperature than before.

The purpose of "14000rpm machines" is about the ramifications of taking this idea forwards beyond the 60Hz culture.

[mizlplix]

While I can see your point of view, It makes very little difference due to the way we build motors.

We do not deal with the factory wiring, We clean it out and rewind with heavier gauge wire and there are no pole connections in the motor. (Our motors are all single speed,4 pole and permanently Delta when we get done.)

The difference in an identical 2 pole and a 4 pole motor's back iron is so close that it is not worth worrying about when you are rewinding them to 4 pole. (in my experience) In fact, my motor actually measures to have more back iron than the identical 4 pole motor Ivan has under his bench. My rotor is 3/4" larger in diameter also.

For the reason of there not being a better EV controller that we can afford, We are stuck with the big Curtis for now. So we do not advocate the use of the small/multi turn factory wires. They will not handle the Curtis' low voltage/ high current scheme without severe damage.

At this point, we are using the Curtis 1238-7601 controller. Once the controller performs the optimization procedure, It sets a fixed algorithm that controls the RMS current and RMS voltage together. (the ratio). There are no user set able parameters for those.

The Curtis controller uses a Variable Frequency strategy to throttle the motor. It covers 0-300 cycles. (Which for a 4 pole motor is almost 9,000 RPM in theory)

We figured out early that a 2 pole motor was not useful in an EV and a 6 pole would need special gearing to overcome the small RPM band it would have, to get your low current and decent top speed.

We are on our 12th winding if I remember correctly. Every one was instructional, both good and bad.

We have a 3,000 RPM torque monster motor, a 4,900 RPM lazy motor and all in between. We are very close to our motor goal, a 4,500 RpM range- good low and mid range torque and an acceptable current draw at cruise speed (for under $1,000).



Miz

      

[Stiive]

For the reason of there not being a better EV controller that we can afford, We are stuck with the big Curtis for now. So we do not advocate the use of the small/multi turn factory wires. They will not handle the Curtis' low voltage/ high current scheme without severe damage.

Have you look at just paralleling some of the windings to increase the current / decrease voltage? Much cheaper than buying fresh copper but obviously your winding choice become limited.

At this point, we are using the Curtis 1238-7601 controller. Once the controller performs the optimization procedure, It sets a fixed algorithm that controls the RMS current and RMS voltage together. (the ratio). There are no user set able parameters for those.

The Curtis controller uses a Variable Frequency strategy to throttle the motor. It covers 0-300 cycles. (Which for a 4 pole motor is almost 9,000 RPM in theory)

Wow, so no vector control?
Surely you've spent more money blindly trying to match the controller (12 rewinds!), rather than just buying a decent controller.
Ahwel, atleast your doing research for the community of Curtis owners Props to you.

Hopefully this next rewind is right on the money.

[mizlplix]

The first winding was almost perfect in my car,
but it is our goal to amass some usable data
for everyone.

It costs about $300 per winding. Sometimes we
can reuse the old stuff in a different pattern.

At this point, we have been up and down the
wiring road...from the whole slot fill and
one turn, to 8 strands and three turns,
(our next one). to which we start by skipping
some slots. Skipping changes the whole
saturation curve. It is hard to predict,
but we are looking for 500 more RPMs over
our first motor, but keeping the current
and torque the same.

The 70 volt range seems to be the sweet spot
in the Curtis controller.

Ivan almost has his dyno done, we found it
necessary to be able to give out reliable
answers and feel that they are good ones.
(Other than my seat-of-the-pants method I
am currently using)

Miz

[BigMouse]

I'm loving this thread. Great stuff. When you find a suitable combination, do you intend to release the winding details?

I have a 4 pole 132 frame motor wound for 48vac delta. My controller will provide it up to 600amps peak current, so I'm hoping for some very exciting performance with ~constant torque (up to 300Nm?) to ~7500rpm on my ~400v battery. Maybe a bit extreme, but it should work in theory.

[mizlplix]

Mouse: That sounds like a really good deal you have there. I wish I could run a 400 Volt pack.

What kind of controller do you have?

A 132 frame would put you in the same class as an AC50 from HPEVs.
But that motor is a little soft on torque up to 2,000RPMs or so, then it takes off. The top RPM is 8,000 but the torque starts dropping off at 6,500RPM or so.

How heavy is your car?

Thanks, Miz

[BigMouse]

Controller is custom (my own design). Waiting for some new batteries to show up so that I can continue development, but having good results so far. Running FOC.

Some (outdated) details here: viewtopic.php?title=my-homebuilt-vfd-progress&t=2660

Post conversion weight will be around 1600kg (26kwhr pack). May go for a smaller pack to save some weight (and money) though. With the discussion recently about the contribution of regen, a 26khwr pack should get me somewhere around 200km to a charge @70kph average speed if seeing a 15% gain from regen. Enough to get me to Sydney and back comfortably.

Do you have a torque curve for the AC50 handy?

EDIT: Found the HPEV torque curves for the AC50 and AC75. They're showing peak torques around 160Nm (AC50) and 240Nm (AC75), both of which are quite a bit less than what I was hoping for. This is disappointing if these tests are done using FOC (vector) control. According to the 1236/1238 datasheet the curtis controllers do have vector control. Whether it's enabled for the dyno runs is another question, though it would make sense for it to be.

Maybe 300Nm is a tad optimistic?

[Stiive]

I have a 4 pole 132 frame motor wound for 48vac delta.

with ~constant torque (up to 300Nm?) to ~7500rpm on my ~400v battery.

Is this 48vac @ utility line freq RPM? e.g ~1500rpm for 4pole.
Or 48vac @ nominal speed (sounds like 7,500RPM)?

Sounds like line freq and then over speeded/voltaged to 7500RPM. This is something Mizplix doesnt seem to be able to do, but is almost required in an EV motor - KILL THE CURTIS

This motor was wound by Jon @ catavolt, yeh?

[Stiive]

Maybe 300Nm is a tad optimistic?

TBH, I'd say so. The Siemens 1PV5135 is [EDIT; 200Nm. 300Nm for 30secs] and that's designed for high torque EV application + its water cooled. It doesn't say what the nominal speed/voltage is, so cant really comment on the comparison of the winding, however its rated for 280A for 3min with water cooling @ 16 l/min.
[EDIT; AZD list the motor as nominal 3,500RPM, 50kW, 136Nm@220A 300VDC. So basically winding would be v/f ~ 1.8 whereas yours seems to be about 1]

I'm also intrigued at the square shape and assume it has extra back iron behind each of the 4 poles for MOAR fluxingz - i've never taken the front plate off to confirm this though.

300Nm for 4 pole is pretty high, and your winding seems pretty high current low voltage so its possible - but i think if it is wound for 300Nm, you wont be getting it for long before things start to heat up dangerously - but thats the beauty of actual trial and error I guess we'll know soon enough!

Do you know the winding config + motor structure? I could simulate it and give you an estimate.

[mizlplix]

The Curtis controller was originally made for airport tugs, mining cars and other industrial equipment like pumps.

It was not made for any one motor or application. That makes it like a Swiss army knife.....it can do about anything, just not really as well as it could.

Miz