Changing an induction motor voltage

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Changing an induction motor voltage

Post by Stiive »

cts_casemod wrote:
Johny wrote:
cts_casemod wrote:I need a 192Cell array and the BMS itself costs almost as much as the batteries themselves.
Have you looked into BMSs that handle 16 cells per board?


I have. The most simple ones are about 80$ each = 1300$ + Shipping + 20% VAT + Import taxes.

What I need is something "simple" with an output to an external contactor and without balancing, but I would like to have a reading of the individual cell voltages


If its something simple like that, your better off designing your own.
What exactly will the BMS be doing?
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Changing an induction motor voltage

Post by Johny »

What would be ideal for higher voltage pouch or Headway packs is a variation of Neville's BMS re-layed out for 16 cells per board.
If no shunting was really required then just leave the shunt resistors off the board.
viewtopic.php?title=low-cost-bms&t=2753
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Changing an induction motor voltage

Post by cts_casemod »

Johny wrote: What would be ideal for higher voltage pouch or Headway packs is a variation of Neville's BMS re-layed out for 16 cells per board.
If no shunting was really required then just leave the shunt resistors off the board.
viewtopic.php?title=low-cost-bms&t=2753


I have asked him how to get those boards, actually is the best solution I have seen.

He said on an older post that depending on the memory present on the master it could hold a couple hundred cells ok, maybe I could use the same master and conect my 4 packs (I may not have the same pack on the car all the time) which would be just great!

I was wondering, Will I be able to modify the VFD to work with only 320V? Just in case I had a problem with the packs and wanted to limp back home using the remaining good/charged ones.

Last edited by cts_casemod on Wed, 14 Nov 2012, 07:13, edited 1 time in total.
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Changing an induction motor voltage

Post by cts_casemod »

Stiive wrote:
cts_casemod wrote:
Johny wrote: Have you looked into BMSs that handle 16 cells per board?


I have. The most simple ones are about 80$ each = 1300$ + Shipping + 20% VAT + Import taxes.

What I need is something "simple" with an output to an external contactor and without balancing, but I would like to have a reading of the individual cell voltages


If its something simple like that, your better off designing your own.
What exactly will the BMS be doing?


I would like to have something like an analog multiplexer reading each cell using an optocoupler. The micro then would give me a reading that I could use to trigger the HVC and LVC and an alarm to indicate the battery was almost empty (Soc =<20%)

Using this method I could know if a cell was bad and where it was located on the pack.

Neville's BMS does all this with the option to disable the balancing which is very atractive.

My packs are removable (4x15Kg) so I will bring one home each time I use the car, so the Soc of the modules may not be the same.
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Changing an induction motor voltage

Post by ChrisRider »

I have a similar project coming up also, i wasnt sure if it was actually possible to physically change the induction motor voltage. Seems as though it may cost a bit in spare parts and materials, but i think it could be worth it as long as i dont break anything in the process, hehe
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Changing an induction motor voltage

Post by ale0502 »

Hello everyone, this is my first time I write in this forum.
First of all sorry for my English, I'm from Argentina.

I'm working on an electric conversion of a car from a three-phase induction motor and a bank of lead acid batteries. I'm developing the controller and all the staff.
I read the forum and understand some things and not others, plus the use of the language that makes I have to ask.

My motor is 4Kw , 2870rpm , 380V / 220V , 14.4A / 8.3A , 18 slots.
My battery bank is 120V, so I would like to modify my motor to have the best possible power with the voltage available.
What dou you recommend?

Because is a 2-pole, I can only lower the operating voltage to half, being of 380/2 = 190V, is that true??.

thank you very much in advance for sharing all this with the community
Last edited by ale0502 on Fri, 01 Apr 2016, 05:22, edited 1 time in total.
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Changing an induction motor voltage

Post by antiscab »

ale0502 wrote:
My motor is 4Kw , 2870rpm , 380V / 220V , 14.4A / 8.3A , 18 slots.
My battery bank is 120V, so I would like to modify my motor to have the best possible power with the voltage available.
What dou you recommend?

Because is a 2-pole, I can only lower the operating voltage to half, being of 380/2 = 190V, is that true??.


If you are very lucky, all 3 x 2 pole groups will be presently wired in series.
If that is the case, then you could rewire to parallel giving 190V star and 110V delta
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Changing an induction motor voltage

Post by coulomb »

antiscab wrote: If that is the case, then you could rewire to parallel giving 190V star and 110V delta

I'm quite rusty on this stuff, but I think with 120 VDC you will only get about 80 VAC (line to line). So that would only be 73% of full voltage for the motor. So you'll only get to about 72% of rated speed. You'll need a lot of current to get any power from this motor.

It will be a challenge.
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Changing an induction motor voltage

Post by Richo »

Mmm 2-pole isn't a great place to start.
The rewind would need to be ~50Vac to run on your 120V pack.
Peak ~5000RPM.
If your lucky you might get 20kW out of it.

Under 50kW the BLDC motors are probably a better option.

So the short answer is NO but the long answer is YES.
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Re: Changing an induction motor voltage

Post by ale0502 »

hello,

I know it's been a long time since this post.
But just now I have my motor with the coils reconnected and running.
It is a three-phase induction motor from:

2,2Kw/3CV
50Hz
4 poles
1430rpm
220V/380V

I already reconnected the 4 coils of each phase in parallel instead of in series and it works well. How do I know it works well? because I spin it with a controller in openloop mode and it works very smoothly in the whole speed range.
The problem starts when I want to make it run with the feedback control, where I need the motor parameters. In particular I find problems with the parameters of SLIP, is it possible that they have changed the minimum and maximum SLIP and therefore the straight V / Hz just by changing the connection of the coils? I guess not, because it is applying the same voltage as before to each coil and therefore the same current flows, but it does not work and I do not know what to try.

Thanks!
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Re: Changing an induction motor voltage

Post by weber »

I don't know about the slip, but the V/Hz should be 1/4 of what it was.
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Re: Changing an induction motor voltage

Post by francisco.shi »

The slip will be the same as before assuming you did not change the winding pattern only the turns.
When you enter the parameters you enter the scaled voltage and current.
Say you put 1/4 the number of turns. Then your current rating will be the times and your voltage rating will be 1/4.
Most inverters will just need this.
The only other problem you may have is that your inductance has been reduced by the square of the turns ratio. So say if you have 1/4 of the turns then the inductance will be 1/16 of before. What this means is that the ripple current at full voltage will be 16 times. This is probably not that much compared to the motor current. But effectively you have a motor with the times the power so you will need an inverter 4 times the size.
Say your motor was 415v and 10A and you put 1/4 of the turns so now your motor is 103.75v 40A. So now you need a 40A inverter. Your 10A inverter will not be able to drive it. At 103v your current ripple (that is the ripple produced by the switching frequency of the inverter) will only be 4 times but at 415 it will be 16 times.
If you are using a sensorless vector drive the inverter looks at the current and voltage being applied to the windings and using some fancy maths it can work out the position of the rotor's magnetic field. If your ripple has gone up then the inverter will have trouble getting a clean reading.
The slip value is used for the torque settings.
For an induction motor (very) roughly the torque is proportional to the slip. That means if you double the slip you will get double the torque. But there comes a point when it goes the other way. More slip = less torque. So the inverter has to know what that value is so the control loop does not go unstable. What that peak slip is will depend on the construction of the rotor.
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Re: Changing an induction motor voltage

Post by Bukes »

Francisco, thank you for explaining. I think I am starting to understand the what this change does.
Say your motor was 415v and 10A, and you put 1/4 of the turns so now your motor is 103.75v 40A. So now you need a 40A inverter...
So this change is taking a 415v and 10A motor, rewiring from series to parallel (so it's profile is now 1/4 volts = 103.75v), and then over volting it at 415v (which is now 4 x nominal power) so it consumes 40A instead of 10A.

Can you achieve a similar outcome by wiring an AC motor in delta but delivering star voltage? Perhaps using step up transformers? So if I have a 415v delta / 690v star motor, could I wire it in delta, but deliver 690v to it and increase the current about 1.65 times? (I imagine this would require a VFD similarly rated for the additional 1.65 current)
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Re: Changing an induction motor voltage

Post by coulomb »

Bukes wrote: Mon, 08 Nov 2021, 08:01Can you achieve a similar outcome by wiring an AC motor in delta but delivering star voltage?
Yes. But instead of 2:1 or 4:1 you get 1.73:1.
Perhaps using step up transformers?
A transformer is totally impractical in a vehicle. It would have to be a relatively low frequency type, which means it would likely weigh more than the car. It would also have to handle a wide frequency range, which is not practical either.
So if I have a 415v delta / 690v star motor, could I wire it in delta, but deliver 690v to it and increase the current about 1.65 times?
Yes, but generating 690 VAC phase to phase requires something over 1000 VDC (from poor memory and a quick search). So really you're better off finding a motor that is designed for a low voltage in star, then rewiring it for delta. For example, Weber and Coulomb's MX-5 motor is wound for 400 V star and 230 V delta (both phase to phase; quoting middle of the range values). Those figures rise to 460 V and 265 V at 60 Hz. But that usually means a custom motor, or at least buying one off a catalogue. You are unlikely to find a surplus motor wound like that. I think it's because of the fear of circulating currents in delta connection; these currents don't happen in star connection.
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Re: Changing an induction motor voltage

Post by francisco.shi »

If you change the voltage of the motor you need to apply lower voltage or spin the motor faster.
In the example of reducing the turns to 1/4 you will need to apply 103.75v. If you want to run it at 415 you will need to run at 4 times the frequency (4 times the original RPM)
You need a VFD for that.
But if the motor was 10A before now it will need 40A to produce the same torque and still at 103.75v. If you put 415 on the rewound motor without increasing the frequency you will get a lot more current. More than 4 times. It will be almost a short circuit.
In the case of an EV the VFD will apply the correct voltage as the speed increases.
The idea of rewinding the motor is so you get more power.
Within limits the motor size gives the torque. So say you have a motor rated at 50Nm at 3000rpm with 415v.
If the motor is running at 1500rpm (using a VFD) you still only get 50Nm but now the speed is half so the power is half.
As you increase the speed it gets to 415v and the VFD runs out of volts so the torque starts to decrease.
Now say we rewind it to 103.75v then you will be able to spin up to 12000 rpm before the VFD runs out of volts.
So now you can get 50Nm at 12000rpm which is 4 times the power. So say your tail shaft spins at 3000rpm at 100kph.
With the standard wound motor you get 50Nm at 100kph
With the rewound motor you put a 4:1 reducer that will change the 12000rpm 50Nm into 3000rpm 200Nm.
So the rewound motor will give you 4 times more acceleration.
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Re: Changing an induction motor voltage

Post by antiscab »

To add on, using the 415 delta motor up running it at 690v at 86.5Hz with a 1000v dc bus will give you sqrt(3) times more power (same torque to 73% higher rpm), but that will also increase the current ripple by 3 times.

it's not the rewinding that causes the increase in current ripple, but the ratio of dc bus voltage to motor inductance. if you increase the dc bus voltage, or decrease the motor inductance, your ripple will go up.
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Re: Changing an induction motor voltage

Post by Bukes »

coulomb wrote: Mon, 08 Nov 2021, 09:49
Bukes wrote: Mon, 08 Nov 2021, 08:01Can you achieve a similar outcome by wiring an AC motor in delta but delivering star voltage?
Yes. But instead of 2:1 or 4:1 you get 1.73:1.
Perhaps using step up transformers?
A transformer is totally impractical in a vehicle. It would have to be a relatively low frequency type, which means it would likely weigh more than the car. It would also have to handle a wide frequency range, which is not practical either.
So if I have a 415v delta / 690v star motor, could I wire it in delta, but deliver 690v to it and increase the current about 1.65 times?
Yes, but generating 690 VAC phase to phase requires something over 1000 VDC (from poor memory and a quick search). So really you're better off finding a motor that is designed for a low voltage in star, then rewiring it for delta. For example, Weber and Coulomb's MX-5 motor is wound for 400 V star and 230 V delta (both phase to phase; quoting middle of the range values). Those figures rise to 460 V and 265 V at 60 Hz. But that usually means a custom motor, or at least buying one off a catalogue. You are unlikely to find a surplus motor wound like that. I think it's because of the fear of circulating currents in delta connection; these currents don't happen in star connection.

Thanks coulomb. What about putting the transformer on the battery side? I think VFDs start with a single phase rectifier? So could take a lower battery DC, convert to AC, step up to 690v and feed it into the VFD (rather than step up afterwards). This 25kVA one isn’t exactly cheap at $1,100, and that doesn’t include the initial inverter which probably wouldn’t be cheap either. Maybe a ridiculous idea, probably lots of losses, just exploring options.

https://m.alibaba.com/product/16003657 ... b7eaQQ80Ej

Probably better just spending the money on more batteries :p
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Re: Changing an induction motor voltage

Post by Bukes »

francisco.shi wrote: Mon, 08 Nov 2021, 12:28 If you change the voltage of the motor you need to apply lower voltage or spin the motor faster.
In the example of reducing the turns to 1/4 you will need to apply 103.75v. If you want to run it at 415 you will need to run at 4 times the frequency (4 times the original RPM)
You need a VFD for that.
But if the motor was 10A before now it will need 40A to produce the same torque and still at 103.75v. If you put 415 on the rewound motor without increasing the frequency you will get a lot more current. More than 4 times. It will be almost a short circuit.
In the case of an EV the VFD will apply the correct voltage as the speed increases.
The idea of rewinding the motor is so you get more power.
Within limits the motor size gives the torque. So say you have a motor rated at 50Nm at 3000rpm with 415v.
If the motor is running at 1500rpm (using a VFD) you still only get 50Nm but now the speed is half so the power is half.
As you increase the speed it gets to 415v and the VFD runs out of volts so the torque starts to decrease.
Now say we rewind it to 103.75v then you will be able to spin up to 12000 rpm before the VFD runs out of volts.
So now you can get 50Nm at 12000rpm which is 4 times the power. So say your tail shaft spins at 3000rpm at 100kph.
With the standard wound motor you get 50Nm at 100kph
With the rewound motor you put a 4:1 reducer that will change the 12000rpm 50Nm into 3000rpm 200Nm.
So the rewound motor will give you 4 times more acceleration.
Ah, ok! Spinning the motor 4 times as fast and using gearing to produce normal shaft speed (so 4 times torque) makes perfect sense. Which explains the need for a VFD running up to 200hz.
I imagine you rely on the motor bearing being able to handle the 12000 rpm, too. Not sure if this is a problem?

This explanation makes sense to me because it doesn’t seem to create power from nowhere :p i also appreciate your explanation of the limiting factor of the VFD (ie the power consumption increases with speed, until the VFD power limit is reached).
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Re: Changing an induction motor voltage

Post by Bukes »

Antiscab, I don’t understand voltage ripple very well, and most of my circuit knowledge is at low voltage . But my questions probably give that away :) so, while I’m asking dumb questions… can you reduce the voltage ripple with inductors?
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Re: Changing an induction motor voltage

Post by Bukes »

Hmm the 2020 Toyota Mirai does something like this (boosts voltage to over 650v… with 4 phases??) ref page 9
https://www.toyota-europe.com/download/ ... 64265.pdf
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Re: Changing an induction motor voltage

Post by francisco.shi »

The cheapest way is to rewind the motor to a lower voltage so you can spin it faster and get more power.
That is why most EVs have about a 10:1 ratio between the wheels and the motor.
Most run at about 6krpm at 100kph.
Any other method will cost more weigh more and be less effecient.
The cheapest and most effecient is battery->VFD->motor.
You can use an industrial VFD but they are very bulky because they are air cooled and need to have mains filters.
In the end you still need a VFD. For say a 50kw industrial VFD it will be 3ph which means 560 bus voltage.
I have rewound a permanent magnet motor successful to get more power by dropping the voltage and increasing the current.
It is in my conversion thread here:
https://forums.aeva.asn.au/viewtopic.php?f=33&t=5721
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Re: Changing an induction motor voltage

Post by coulomb »

Bukes wrote: Mon, 08 Nov 2021, 19:35 What about putting the transformer on the battery side?

This is actually done in the Toyota Prius. [ Edit: and apparently in the Mirai as well, per a previous post. ] A 230V (from memory) battery is boosted to 500 or 650 VDC (depending on the model), but the power level is some 10kW, and it's done at a high frequency. The 25kVA transformer you linked to is a 50-60Hz one, which would weigh something like 175kg, and it's at least 4x too small for a car. Transformers need AC, they can't operate on DC. With a suitable high frequency DC-AC converter, it could be done, though the VFD's rectifier probably can't handle high frequency, so you'd have to high speed rectify the output to DC before the VFD. So you end up with a DC-DC converter. It would be too expensive, bulky, lossy, and heavy (even though much lighter than a low frequency transformer).
Maybe a ridiculous idea, probably lots of losses, just exploring options.
It's worth thinking these things through, even if just to get a feel for what is and isn't practical.
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Re: Changing an induction motor voltage

Post by Bukes »

Holly crap Francisco, your inverter is tiny. I am reading your build, really admire all you’ve put into it!

I was thinking about modifying the second hand 32kVA ups I got to make a temporary VFD until I could afford a bigger one.
Here are a few pics of the inside. Yours… is tiny… you literally have IGBTs going straight to the motor?

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I’m still investigating the engineering diagrams on this to work out what all this stuff does. I figure (1) locate IGBTs, (2) replace their drive circuit with my own, (3) the rest works magically…. I’ve since learnt it’s only a 208V 3 phase system though. So that won’t work :p
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Re: Changing an induction motor voltage

Post by antiscab »

those inductors, needed in a stand alone inverter, aren't needed for a VFD or a motor controller, as the motor itself is an inductor (or rather used as an inductor)

looking at the unit, it may be a multi-level inverter - such units are much larger and require more power electronics, inductors and caps than a standard 2-level inverter. However, they're much more efficient with way better power quality, which if limited in heat dissipation means higher continuous power output.
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Re: Changing an induction motor voltage

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