Convert AC Induction Motor To BLDC(or PMDC///PMSM)

Thread Starter

AmirZia

Joined May 13, 2019
11
Hello! I'm gonna make a bldc motor out of an old induction motor stator.
I'm rewinding this stator like a bldc motor and making a rotor using neodymium magnets
it will be an inrunner rotor/
my point is increasing its efficiency and Power(Torque and Speed)
/ can I use a variable Frequency and voltage source to drive a 3 Phase induction motor and have the same efficiency in induction motor as a BLDC motor?
 

shortbus

Joined Sep 30, 2009
7,349
can I use a variable Frequency and voltage source to drive a 3 Phase induction motor and have the same efficiency in induction motor as a BLDC motor?
Not without very extensive modification to both the rotor and stator. There is a large difference between the two types of motors in just the stator. Induction motors are wound in a distributed pattern, and a BLDC is a salient pole motor. The induction rotor has no magnets and is basically a shorted turn, and the BLDC has individual permanent magnet poles.

But if you have access to a full machine shop and plenty of time to devote to both research and doing it you could probably end up with something that might turn but not have much power.
 

Thread Starter

AmirZia

Joined May 13, 2019
11
،
Sounds like you are making a banana out of a pineapple.

The magnetic structures of an induction motor are ill-suited for BLDC motors.
Tnx for reply/
U mean its stator's (lamination Layer) materials are different? (it's not the same silicon steel or electrical steel?)
I observed inrunner BLDCs stator and it's like them/ I'm emulating the BLDCs winding. so its magnetic fields will be different? it has 48 teeth.
so if I get silicon steel sheet and laser cut it(design stator laminates) to make an inrunner bldc its magnetic structures will be different due to different material?
 

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Thread Starter

AmirZia

Joined May 13, 2019
11
Not without very extensive modification to both the rotor and stator. There is a large difference between the two types of motors in just the stator. Induction motors are wound in a distributed pattern, and a BLDC is a salient pole motor. The induction rotor has no magnets and is basically a shorted turn, and the BLDC has individual permanent magnet poles.

But if you have access to a full machine shop and plenty of time to devote to both research and doing it you could probably end up with something that might turn but not have much power.
Tnx for reply/
I Know the structural differences between induction and PM motor/ my question is: is it better to change induction motor to PMSM(permanent magnet synchronous motor) or BLDC to raise the efficiency or not touching them and work on a good driver to run them in different speeds?
and THE IMPORTANT question is which one is more efficient? induction motor?(knowing that we can change its voltage and frequency) or a BLDC? actually I'm making an electric car.
 

cmartinez

Joined Jan 17, 2007
6,670
Tnx for reply/
I Know the structural differences between induction and PM motor/ my question is: is it better to change induction motor to PMSM(permanent magnet synchronous motor) or BLDC to raise the efficiency or not touching them and work on a good driver to run them in different speeds?
and THE IMPORTANT question is which one is more efficient? induction motor?(knowing that we can change its voltage and frequency) or a BLDC? actually I'm making an electric car.
I'd say a bldc is more efficient than an induction motor for what you want. Among other things, they have a higher power density, and can be controlled through proper coil switching and pwm. While an induction motor would require converting your DC source into a sine three-phase one, and would also end up being larger and possibly heavier.
 

Thread Starter

AmirZia

Joined May 13, 2019
11
I'd say a bldc is more efficient than an induction motor for what you want. Among other things, they have a higher power density and can be controlled through proper coil switching and PWM. While an induction motor would require converting your DC source into a sine three-phase one, and would also end up being larger and possibly heavier.
Tnx/ So why can't we use the square wave to run induction motor? (it hurts ballbearings? what happens if we don't have a good Sinosoidal Harmonics?(Except a little lower efficiency )
 

cmartinez

Joined Jan 17, 2007
6,670
Tnx/ So why can't we use the square wave to run induction motor? (it hurts ballbearings? what happens if we don't have a good Sinosoidal Harmonics?(Except a little lower efficiency )
You could use a square wave for an induction motor, but (as you've just said) with horrible efficiency. Plus the motor would warm up quite quickly. An easier technique than running them with a sinewave is to run them with trapezoidal waves instead. That is, to very roughly approximate a sine using 3 or 4 discrete voltage steps that end up resembling a short staircase.

Of course, the more steps you add to said staircase, the more it will resemble a true sine wave, and thus the more efficiency will be attained.
 

Thread Starter

AmirZia

Joined May 13, 2019
11
You could use a square wave for an induction motor, but (as you've just said) with horrible efficiency. Plus the motor would warm up quite quickly. An easier technique than running them with a sinewave is to run them with trapezoidal waves instead. That is, to very roughly approximate a sine using 3 or 4 discrete voltage steps that end up resembling a short staircase.

Of course, the more steps you add to said staircase, the more it will resemble a true sine wave, and thus the more efficiency will be attained.
yep! I couldn't understand why I cannot convert an induction stator to a bldc stator yet. somebody explain it, please
 

cmartinez

Joined Jan 17, 2007
6,670
yep! I couldn't understand why I cannot convert an induction stator to a bldc stator yet. somebody explain it, please
Are you saying that you want to replace an induction motor's wound rotor, with a rotor fitted with permanent magnets, and then modify the stator's windings' connections so as to be able to drive the whole thing as a BLDC?

I guess it could be done, but keep in mind that large bldc motors have quite a few poles in them, and that induction motors normally have fewer. Plus, perhaps the work and resources invested in building/modifying the rotor and adding large permanent magnets in it will prove to be so expensive that it will most probably not be worth it un the end ... and you'd have to design a special driver for that specific project, which would multiply exponentially the amount of work you'd put into it.
 

Thread Starter

AmirZia

Joined May 13, 2019
11
Are you saying that you want to replace an induction motor's wound rotor, with a rotor fitted with permanent magnets, and then modify the stator's windings' connections so as to be able to drive the whole thing as a BLDC?

I guess it could be done, but keep in mind that large bldc motors have quite a few poles in them, and that induction motors normally have fewer. Plus, perhaps the work and resources invested in building/modifying the rotor and adding large permanent magnets in it will prove to be so expensive that it will most probably not be worth it un the end ... and you'd have to design a special driver for that specific project, which would multiply exponentially the amount of work you'd put into it.
I am winding its stator like an inrunner BLDC's stator(number of poles depends on how I wind it)
and buying a bunch of neodymium magnets to make the rotor(gluing magnets to the rotor using epoxy resin and kevlar)
I guess it will be cheaper than buying a new bldc motor.
magnets are expensive but not more expensive than a 5KW bldc!
it will need a little machining( I'm gonna machine the squirrel cage rotor so I can glue magnets to it, although I can machine a shaft instead. I don't need the squirrel cage rotor anyway)
machining the rotor+epoxy+kevlar fiber+ magnets will be cheaper than a 5kw bldc I guess.
about the driver: any sensored driver for bldc can run it! cause the stator will have hall sensors/ and I designed my own sensored bldc driver
THAT'S the whole Concept! any comments will be appreciated!
again thanx for replies.
 

cmartinez

Joined Jan 17, 2007
6,670
I am winding its stator like an inrunner BLDC's stator(number of poles depends on how I wind it)
and buying a bunch of neodymium magnets to make the rotor(gluing magnets to the rotor using epoxy resin and kevlar)
I guess it will be cheaper than buying a new bldc motor.
magnets are expensive but not more expensive than a 5KW bldc!
it will need a little machining( I'm gonna machine the squirrel cage rotor so I can glue magnets to it, although I can machine a shaft instead. I don't need the squirrel cage rotor anyway)
machining the rotor+epoxy+kevlar fiber+ magnets will be cheaper than a 5kw bldc I guess.
about the driver: any sensored driver for bldc can run it! cause the stator will have hall sensors/ and I designed my own sensored bldc driver
THAT'S the whole Concept! any comments will be appreciated!
again thanx for replies.
It sounds like a very interesting project. It would be real nice if you were to come back here every once in a while and reported your progress. There's lots to learn from what you're doing. At least for me.
 

MaxHeadRoom

Joined Jul 18, 2013
19,733
I am winding its stator like an inrunner BLDC's stator(number of poles depends on how I wind it)
and buying a bunch of neodymium magnets to make the rotor(gluing magnets to the rotor using epoxy resin and kevlar)
I guess it will be cheaper than buying a new bldc motor.
magnets are expensive but not more expensive than a 5KW bldc!
.
Also you will have to take great care to balance the rotor, as PMAC or BLDC generally run at double the rpm's of a typical induction motor.
Generally these two types vary from 2 to 8 pole.
The construction of each is largely identical, just the way they are commutated, the PMAC is 3phase sine wave, and the BLDC only has any two winding's powered at any given time.
Max.
 

shortbus

Joined Sep 30, 2009
7,349
magnets are expensive but not more expensive
If your set on making something for your self, look into something called a SRM Switched Reluctance Motor. It has some of the attributes of a BLDC but without using any magnets on the rotor, just iron poles. There is a lot of information on the web about them. It's one of the first electric motors ever developed, back in the 1830's and was used in a vehicle. But until recently it wasn't used much, not until the invention of mosfets and IGBTs to do the switching. The type, SRM motor is used in a lot of mining equipment today. And is being developed into cars now.

Do you know about this forum - https://www.diyelectriccar.com/forums/ There is a lot of information there about what people are doing and you may even get some ideas and how to avoid some problems others have found and solved.
 

Thread Starter

AmirZia

Joined May 13, 2019
11
If your set on making something for your self, look into something called a SRM Switched Reluctance Motor. It has some of the attributes of a BLDC but without using any magnets on the rotor, just iron poles. There is a lot of information on the web about them. It's one of the first electric motors ever developed, back in the 1830's and was used in a vehicle. But until recently it wasn't used much, not until the invention of mosfets and IGBTs to do the switching. The type, SRM motor is used in a lot of mining equipment today. And is being developed into cars now.

Do you know about this forum - https://www.diyelectriccar.com/forums/ There is a lot of information there about what people are doing and you may even get some ideas and how to avoid some problems others have found and solved.
what are the differences between Permanent Magnet Switch Reluctance Motor and Brushless DC Motor? the waveform for both are Square(switching-PWM)
 

shortbus

Joined Sep 30, 2009
7,349
what are the differences between Permanent Magnet Switch Reluctance Motor and Brushless DC Motor? the waveform for both are Square(switching-PWM)
I never heard of a motor you are calling, " Permanent Magnet Switch Reluctance Motor". A switched reluctance motor(SRM) is similar to a BLDC, BUT uses NO magnets. The rotor is just made of steel. So it makes them less expensive to build.

Also they both use a 'trapezoidal' wave form not a square wave.

https://en.wikipedia.org/wiki/Switched_reluctance_motor
 

Thread Starter

AmirZia

Joined May 13, 2019
11
I never heard of a motor you are calling, " Permanent Magnet Switch Reluctance Motor". A switched reluctance motor(SRM) is similar to a BLDC, BUT uses NO magnets. The rotor is just made of steel. So it makes them less expensive to build.

Also they both use a 'trapezoidal' wave form not a square wave.

https://en.wikipedia.org/wiki/Switched_reluctance_motor
what's Tesla's model 3 Electromotor? and Thanks. Yep their waves have to be Trapezoidal/ permanent magnet or magnetically assisted
 
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