Rewinding an Induction Motor for Lower Voltage

Thread Starter

TechWise

Joined Aug 24, 2018
80
I would like to run an induction motor from 12V batteries for a small electric vehicle application. I would like to use a three phase induction motor as they are cheap, readily available, robust and low maintenance.
My question is whether it is possible to rewind an off-the-shelf 400V three phase induction machine to run at lower voltage but higher current. I have a 2.2kW motor here which suffered a winding failure and I feel like I would have nothing to lose by experimenting on it. Ideally, I would like to run from say a 96V battery pack.

Does anyone have any thoughts on why this would or would not work?
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
I would not even consider it, especially having to make a custom 3h invertor for it.
Max.
I should have also mentioned that I am doing a PhD in Power Electronics at the moment and I will be making a three phase grid tie converter around the 2kW power level. I was hoping that the power electronics side of this would be a brilliant learning opportunity. It's the practicality of rewinding the machine that worries me!
 

mvas

Joined Jun 19, 2017
537
I would like to run an induction motor from 12V batteries for a small electric vehicle application. I would like to use a three phase induction motor as they are cheap, readily available, robust and low maintenance.
My question is whether it is possible to rewind an off-the-shelf 400V three phase induction machine to run at lower voltage but higher current. I have a 2.2kW motor here which suffered a winding failure and I feel like I would have nothing to lose by experimenting on it. Ideally, I would like to run from say a 96V battery pack.

Does anyone have any thoughts on why this would or would not work?
If the Magnetic Flux in the new Stator Coil is similar to the Magnetic Flux in the old Stator Coil then
does the Induction Motor really care if the Voltage and Amperage are different?

What about I^2xR heat loss ?
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
If the Magnetic Flux in the new Stator Coil is similar to the Magnetic Flux in the old Stator Coil then
does the Induction Motor really care if the Voltage and Amperage are different?

What about I^2xR heat loss ?
That was my thinking. The flux in the machine is going to be proportional to the number of turns in each coil times the current in each turn. So if I reduce the number of turns and increase the current I should get the same flux, shouldn't I?

My thinking is that if I reduce the machine from 400V to around 100V then I need to quadruple the current which means the losses will be 16 times higher. I'm thinking I can get round this through a combination of improved cooling and starting with an oversized machine for the job. Also, the EV application won't require the motor to run at full load for long periods of time. Most of the time it will be performing a few seconds of acceleration then a lot of coasting along.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
Have you considered a automotive starter motor, these are very high torque due to being series wound field, this is why they are/were used in locomotive type applications, the down side is they must always be connected to a load.
Max.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
Have you considered a automotive starter motor, these are very high torque due to being series wound field, this is why they are/were used in locomotive type applications, the down side is they must always be connected to a load.
Max.
I initially discounted using a starter motor as I had assumed that they would not be designed for continuous duty. I was also thinking back to my undergraduate machines class where we were warned against this type of machine in applications with a chain drive as a sudden loss of load due to a chain break or suchlike can cause the machine to "run away" and destroy itself.

I like the induction machine idea as we have a number of them powering machines around the yard at they really are bomb-proof zero-maintenance fit-and-forget motors. What really got me thinking about the induction machine was that there is a company selling low voltage induction machines for electric vehicles and it says on their website that they are made at the time of ordering. It looks to me that they are off-the-shelf 400V machines that they are rewinding as they are in standard IEC footprints and it looks as if stickers have been put on instead of the original data plates.

I stripped down the 2.2kW machine I had laying around today but it was too far gone to consider rewinding. I've ordered a new 750W machine to strip down and have a good look at instead.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
A starter motor would most likely not be taxed at all in that application, and in an electric vehicle could be connected at all times to the transmission.

For re-winding the AC motor, you will need to make up or obtain use of a coil winder, preferably with turn counter on it, also the necessary slot insulation material and coil wedges.
Usually the old coils are sheared off at one end of the lamination's with a cold chisel and driven out with hammer and flat bar.
Max.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
A starter motor would most likely not be taxed at all in that application, and in an electric vehicle could be connected at all times to the transmission.

For re-winding the AC motor, you will need to make up or obtain use of a coil winder, preferably with turn counter on it, also the necessary slot insulation material and coil wedges.
Usually the old coils are sheared off at one end of the lamination's with a cold chisel and driven out with hammer and flat bar.
Max.
Thanks for that Max. That's exactly the sort of wisdom I'm looking for. The top hit on youtube for "coil winder" shows quite a nice DIY machine and it's winding quite heavy gauge enamel wire which is what I would be after. I'm fairly well equipped in terms of metalworking tools so building one might be the way to go. There's no harm in asking at my University if they have one I could use though as they're usually really supportive of student projects.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
Are you connecting it up internally in Delta or bringing all connections out for both options?
Max.
I think if I'm starting with an off-the-shelf machine with the six binding posts I may as well bring the six winding ends out of the machine to leave that option open. On the other hand, if the windings are much thicker it might be difficult to do that.
 

dendad

Joined Feb 20, 2016
3,566
In stead of thicker wire, you can use multiple smaller wires in parallel. Just make sure the same numbers of turns are added.
Get thinner wire, and wind the turns together so for example, each winding turn has 8 wires in it.
Two wires are "Bifilar", three "Trifilar".
It is a common practice.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
In stead of thicker wire, you can use multiple smaller wires in parallel. Just make sure the same numbers of turns are added.
Get thinner wire, and wind the turns together so for example, each winding turn has 8 wires in it.
Two wires are "Bifilar", three "Trifilar".
It is a common practice.
We have often done that in the past, sometimes with as many as 50 small strands so that we could wind relatively large conductors around small core formers when making custom inductors.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
Also ensure you observe the 'polarity' of each coil, start and finish.
Are you looking at a 2 or a 4 pole?
Max.
Hi Max,
Part of my reason for buying a small test machine was so that I could get a good look at the winding configuration and take some notes and pictures of how it should be done. Essentially I'm trying to keep the winding layout exactly the same but with fewer turns. The one I've bought is a 4 pole machine. My thinking here was to go with the lower synchronous speed and hopefully eliminate the gearbox from the vehicle.
 

MaxHeadRoom

Joined Jul 18, 2013
20,911
If you need a winding sequence at all I have the motor winding 'Bible' by Robert Rosenburg that shows the various pole count coil sequences.
Max.
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
If you need a winding sequence at all I have the motor winding 'Bible' by Robert Rosenburg that shows the various pole count coil sequences.
Max.
Thanks for that Max, I might take you up on that if I run into difficulty. I've noticed quite a nice pile of old motor repair books waiting by the recycling bins in the office so I might have a sift through those on Monday :)
 

Thread Starter

TechWise

Joined Aug 24, 2018
80
Thanks for all the info. It's pretty horrifying the stuff that universities throw out. Anything that looks old and doesn't fit with the modern look gets chucked. Still I shouldn't complain - I was offered as many analogue scopes as I could carry. Sadly I couldn't take any due to all the transformers and the two signal generators in my bag :) At least the technicians prefer to see stuff going to students that will use them rather than in the bin.
 
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