# Identify winding scheme, induction motor



## peggus (Feb 18, 2008)

Bottomfeeder and I picked up this cheap inverter rated induction motor on a bit of gamble that we'd be able to reconfigure it for lower voltage and use it in EV application. 

The motor is almost perfect: design A rotor, aluminum frame, high efficiency, not too heavily varnished.

Unfortunately I can't quite make sense of the winding scheme so I thought I'd post some pictures here to see if anyone recognizes it or know of some good motor winding resources.

The stator is a 36 slot design, 4 poles so 3 slots per pole per phase.

What I can make out is 2 concentric coils spanning 9 & 7 slots respectively. I could open up the lacing to see what the other coils are doing but I was hoping to find a winding diagram that matches what I can see so I don't have to compromise the motor, we may have to resell it.

The 2 concentric coils is not good news since they are of different size and so cannot be paralleled. Unless there are 2 more concentric winding of the same size; the lowest voltage we can get the motor down to is 138Vrms, which is not great since we have 150V packs.


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## major (Apr 4, 2008)

Through your day job, can you contact an EASA shop? They would have the WD on file, I think.


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## peggus (Feb 18, 2008)

Thanks Major, I had forgotten they exist.

Writing up the post above got some new neurons triggering and I realized what I'm looking at. There are quite clearly 4 sets of concentric coils (per phase) spanning 90 degrees each. For 460V they are all in series, for 230 they are configured 2 in series & 2 in parallel. 

Which means I just have to find the crossover wires and the star point, then I can open them up and rewire for 4 coils in parallel/delta giving me a 67VAC motor.

I can easily see two of the crossover connections, one of them appears in the pictures, it's a group of 4 wires going of to the right from the slot at about 4:20 o'clock. Now I just have to dig out the other 4.


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## alvin (Jul 26, 2008)

After you parallel your coils , how many amps will you be able to use?

Just asking. 

I saw this some time ago. You may have seen it already.

http://forums.aeva.asn.au/forums/forum_posts.asp?TID=1237


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## peggus (Feb 18, 2008)

The nominal rating will be 75A per phase.

Yes, I've seen the AEVA forum thread on the same topic. Some interesting data there!


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## peggus (Feb 18, 2008)

So I found the star point and the crossover points for all the coils. Turns out the crossovers are all on the "back" side of the motor, all the regular connection are on the front. 


What I originally thought to be a couple of crossover points on the front turns out to probably be just part of the coils.

I've opened up the crossover points in the second picture. Guess we're fully committed now


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## alvin (Jul 26, 2008)

Yes that is committed. Were the crossovers obvious once you pulled back the coils?
Alvin


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## peggus (Feb 18, 2008)

The coils are in three layers, one per phase. The outer coils were real obvious after just shining a flashlight in there. The inner coils were somewhat obvious and the coils in the middle layer required me to dig around quite a bit before I could even see them . The crossover wires are all at 60 degree intervals so once you've found the obvious ones it is easy to guess where the hidden ones should be.


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## alvin (Jul 26, 2008)

I found the three on the inside I think. They come out every 12th slot. One goes back in 9 slots away the other two diappear in the coils.
I see a hammer and a wooden wedge on your bench. It looks like it does take some persuading to move those coils.
Alvin


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## toyolla2 (Jun 21, 2010)

peggus said:


> The nominal rating will be 75A per phase.
> 
> Yes, I've seen the AEVA forum thread on the same topic. Some interesting data there!


 
Peggus, well you saw the post but clearly you missed something, it's the important but sadly neglected issue of Volts/Hz.


I am sure you are aware that when ACMOTOR started with a 415v 50 Hz motor and rewired it to 104v, he thereby altered the V/Hz from approx 8 to 2. You are also probably aware that his industrial inverter had a bus voltage of around 660Vdc behind it in order to pump out that final 415Vac.


With your rewire I expect you intend to reap similar advantages in gaining a 400% power boost on your 7.5Hp motor. 

But based on your declared 150Vdc supply bus frankly, I am not sure you are going to achieve that. Not even close.


Let's look at a real world design like the EV1 prototype which ran a similar 4 pole machine to a base speed of 6600rpm at a frequency of 220Hz. At this point their inverter, running from a Pb-Acid battery supply of 320Vdc, would deliver 150Vac meaning that their motor needed to have a V/Hz of (150/220) = 0.68.


You , on the other hand, are attempting a V/Hz of only 2 which is at least 3 times too large if you were to use it with the EV1's 320Vdc supply.

Since you are contemplating using a battery supply voltage of only half that, your motor will need a V/Hz of 0.34. That makes your intended rewire at 2.0 about six times too large.


V/Hz is a double edge sword in that a high value gives lots of torque per amp whereas a low value prevents the motor from running out of voltage as it gathers speed. If you decide to stay with 2.0 then you are going to experience a good launch followed by a rapid tail off in torque. You will find that by changing up and therefore spinning the motor down will bring the motor back to life only to have the motor fade again as you continue to accelerate. I don't think that is the EV experience that you really want.


Although more than twenty years have passed I still consider the EV1 the gold standard in EV design. 

Their motor reached base speed at 42mph (6600rpm) and continued until 75mph(11,900rpm). They used a 10.5 :1 ratio. That ratio sits between first and second gear in a conventional manual transmission of course.


I see that Marathon rate their Black Max series at 4250 rpm. I wouldn't read too much into that if I was you. That is probably just the speed they check them out at the factory. The aluminum conductor bars on the rotor sometimes contain occlusions during the casting process which can cause unbalance.


You can always get your rotor balanced for a higher rpm as ACMOTOR did seeing that you've now got the motor apart. 


My limited experience with a 12 kw motor, allegedly good to 11,000rpm, was that the gearbox began to "complain" first, at around 6800rpm. 

If things don't work out 400hertz.com may have a more suitable machine for under $1000.


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## peggus (Feb 18, 2008)

No, you missed that I'm also rewiring it for delta, so 1/7th the V/Hz.

My pack at the moment is 150V, I have more modules sitting around unused so that will increase. My inverter power-stage is a 425V 125kVA liquid cooled unit so I have plenty of space to grow.


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## toyolla2 (Jun 21, 2010)

No, you missed that I'm also rewiring it for delta, so 1/7th the V/Hz.


Yep, I may have missed that. To be honest I was not interested in how you were wrestling with this motor to make it suitable for 150Vdc, I was just looking to see if you were cognizant of the real goal which is to get to the desired V/Hz.


Clearly if you add info that changes the rules - like the flexibility to go to 425Vdc - then you alter the dynamics. Perhaps you could help us appreciate your project more by outlining what rpms you are seeking to cover.


Another thing, if you could stand back a moment it seems to me that this motor is pushing you around. 


First you're going delta, which means that you may have circulating current problems unless the magnetic circuits for all four coils per phase are identical.


Consider the parallel Y connection that Marathon supports. It has effectively 6 legs. Each leg of the first Y has two coils probably selected from opposite sides of the machine. The corresponding leg of the second Y will do likewise. Hence any disparity between the induced voltages from the two magnetic circuits will be cancelled out. I am convinced that's why they were ok with putting it on the nameplate.


Whether it is Y or delta is immaterial, your idea to parallel all FOUR coils of one phase will now make your motor susceptible to circulating currents within the phase itself NOT just those that circulate around the delta. 


The second thing is that you seem to be very casual about your ability to jump from 150Vdc to 425Vdc just now. You have unused modules lying about, so you say, but have you factored in the extra cost of the battery management system that that decision might entail not to mention the battery charger itself ? Long strings of batteries are bad news, there is bound to be an infant mortality in there. Now it's got you fishing about in a 400+Vdc matrix. Not fun. 


The majority of Prius have the 201Vdc battery not the original 273Vdc which they dumped eight years ago btw.


That doesn't change my argument that your intended V/Hz which I just calculated is standing at 1.11 and is still too high. 


For 150Vdc you need 0.34. It's not that critical of course you can be off 20% either way but you seem to be heading for 300% and that is going to land you in lame-ass territory unless you're building a NEV or golfcart.


best of luck anyway.


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## peggus (Feb 18, 2008)

I design inverters and battery management systems for a living, you're not telling me anything I don't know. 

This is strangely enough also my hobby, I do this for fun. The journey is more interesting than the destination. (Or I would have bought a leaf by now)

I never said I would go all the way to 400VDC, I'm just looking for performance similar to my current curtis, + regen. According to my mathcad calculations this should get me there.

Yes, the motor is not ideal, circulating currents is a possibility. I wish that it had integral pitch windings, that would have helped.


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## peggus (Feb 18, 2008)

Winding diagram


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## peggus (Feb 18, 2008)

Connection scheme for low voltage delta.


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## mizlplix (May 1, 2011)

I like this one....










MIZ


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