# convert an AC stator to form a BLDC inrunner



## silentknight (Aug 19, 2014)

Hi guys, 

1st off, im a newbie in to this field. ive dabbled a bit in using an RC BLDC motor & controler to power a a custom milling machine head. but ive no experiance in EV's.

Ive been thinking of ways to add-on a Regen capable EV assist system to reduce the fuel consumption when accelerating. to that end, Im leaning towards powering the propshaft via a converted AC motor stator to run as a BLDC & sleeve on the propshaft to hold the inrunner Magnets. 

Its a Independant rear suspension vehicle so the Propshaft movement isnt an issue. 

my question to you guys is, Assuming all the fabrication issues are overcome, for a vehicle weighing 1.5T, is such a setup powerful enough to move the vehicle? especially being a BLDC with the only torque multiplication at the rear diff??


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## dougingraham (Jul 26, 2011)

I think you will find that the ends of the prop shaft moves around too much to use as the rotor in a motor. You will need to support it with bearings. You will probably find that cutting out a section of propshaft and connecting each end to a motor in the middle is the most effective approach to do what you are considering.

Your motor is going to need considerable torque to move the vehicle with just the final drive gear reduction. There are several ways to increase the torque of a motor when you are designing it. You can make it longer. You can make it larger in diameter. You can increase the number of poles. You can increase the number of turns of wire. Each of these has downsides. Even the large series DC motors can only do this with huge amounts of current (thousands of amps). Smaller high revving motors with additional reduction could be used but not directly inline.

What you are wanting to do is admirable but actually making a hybrid perform better than the original vehicle is difficult which is why so many hybrid vehicles barely perform better than the ICE only version and at great additional cost. And this is with hundreds of millions of dollars of R&D money spent. You add in the electric stuff which increases the weight so much that the benefit is barely realized. Hybrids have the worst of both worlds to deal with.

It is easy to rip out the ICE stuff and make it all electric and work better than it did as an ICE with only the limited range and long charging as downsides. And for the vast majority of people the range is far enough and the long charging takes place when they are asleep anyway so it is not a problem.


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## major (Apr 4, 2008)

silentknight said:


> Ive been thinking of ways to add-on a Regen capable EV assist system to reduce the fuel consumption when accelerating. to that end, Im leaning towards powering the propshaft via a converted AC motor stator to run as a BLDC & sleeve on the propshaft to hold the inrunner Magnets.


Doug makes some valid points. I'll add that you'd be better off using the induction rotor. You would not be able to turn off the excitation (magnetic field) on the PM rotor and so would suffer Fe losses whenever there was rotation even when the hybrid (electric) wasn't in use. It would be like an eddy current brake. Whereas the induction motor would rotate freely when unexcited.


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## silentknight (Aug 19, 2014)

major said:


> Doug makes some valid points. I'll add that you'd be better off using the induction rotor. You would not be able to turn off the excitation (magnetic field) on the PM rotor and so would suffer Fe losses whenever there was rotation even when the hybrid (electric) wasn't in use. It would be like an eddy current brake. Whereas the induction motor would rotate freely when unexcited.


Thanks for the info Major. i supose the only way around that would be to implement a Non-coast capable setup... i think the Tesla'a work that way.


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## silentknight (Aug 19, 2014)

dougingraham said:


> I think you will find that the ends of the prop shaft moves around too much to use as the rotor in a motor. You will need to support it with bearings. You will probably find that cutting out a section of propshaft and connecting each end to a motor in the middle is the most effective approach to do what you are considering.
> 
> Your motor is going to need considerable torque to move the vehicle with just the final drive gear reduction. There are several ways to increase the torque of a motor when you are designing it. You can make it longer. You can make it larger in diameter. You can increase the number of poles. You can increase the number of turns of wire. Each of these has downsides. Even the large series DC motors can only do this with huge amounts of current (thousands of amps). Smaller high revving motors with additional reduction could be used but not directly inline.
> 
> ...


Thanks for the wisdom shared Doug, this idea was purely a thought excercise in what would be possible in this field. i agree there are plenty of problems with this concept.. but im still pretty keen on it so i guess ill be researching some more.


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