# Relatively cheap ~45kW BLDC for EV



## khojka (Dec 8, 2019)

Hey everyone, I'm on a budget and looking for a BLDC motor for an EV project. I have about $1000 to work with for the motor. I was considering using a Leaf motor but because it's AC I'd need a pretty expensive inverter with it and 
compensation with more batteries in parallel since AFAIK an inverter/AC motor
combo like this would draw more current than just a standalone DC motor with the same power rating. I'm also thinking about buying an AC induction motor stator and just building a custom BLDC type rotor for it. Does anyone have any cost-effective sources for BLDCs that would work well in an EV? Thanks.


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## kennybobby (Aug 10, 2012)

Wouldn't the inverter for a BLDC motor be nearly identical or slightly more complicated (hall sensors or resolver/encoder for commutation) to that for an AC motor?

Inland Motors made some large BLDC motors with external copper tubing for a liquid cooling jacket. High quality motors made in Radford VA.


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## brian_ (Feb 7, 2017)

khojka said:


> I was considering using a Leaf motor but because it's AC I'd need a pretty expensive inverter with it and
> compensation with more batteries in parallel since AFAIK an inverter/AC motor
> combo like this would draw more current than just a standalone DC motor with the same power rating.


A three-phase inverter is the most expensive type of motor controller (whether the motor is synchronous or induction).

Why would you think that an AC motor would draw more current? Are you expecting a synchronous permanent magnet three-phase AC motor to be *less* efficient than a brushed DC motor, or an electronically commutated (square drive waveform) motor?



khojka said:


> I'm also thinking about buying an AC induction motor stator and just building a custom BLDC type rotor for it. Does anyone have any cost-effective sources for BLDCs that would work well in an EV? Thanks.


I don't understand what your think a brushless DC stator would be, or how it would be different from the rotor for a permanent magnet AC motor... or even a permanent magnet brushed DC motor. 

BorgWarner makes the HVH motor series with the buyer's choice of induction or PM rotors - the stator is the same either way. That's three-phase synchronous AC with a permanent magnet rotor... not square-wave "BLDC".

I think at the core of this confusion is the usual lack of clarity on what is meant by "BLDC".


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## khojka (Dec 8, 2019)

brian_ said:


> A three-phase inverter is the most expensive type of motor controller (whether the motor is synchronous or induction).
> 
> Why would you think that an AC motor would draw more current? Are you expecting a synchronous permanent magnet three-phase AC motor to be *less* efficient than a brushed DC motor, or an electronically commutated (square drive waveform) motor?


Isn't the Leaf motor an AC asynchronous induction one, hence the inverter used for driving it? If it was a PMAC, couldn't it have been plugged straight into DC power without the need for an inverter?



brian_ said:


> I don't understand what your think a brushless DC stator would be, or how it would be different from the rotor for a permanent magnet AC motor... or even a permanent magnet brushed DC motor.


What I meant was to buy a commercial asynchronous AC motor, and switch out the squirrel-cage rotor with a permanent magnet one, effectively making a PMAC/BLDC motor.


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## brian_ (Feb 7, 2017)

kennybobby said:


> Wouldn't the inverter for a BLDC motor be nearly identical or slightly more complicated (hall sensors or resolver/encoder for commutation) to that for an AC motor?


Yes, except that it doesn't need to produce a sinusoidal waveform.


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## brian_ (Feb 7, 2017)

khojka said:


> Isn't the Leaf motor an AC asynchronous induction one, hence the inverter used for driving it?


No, induction motors are the EV technology of the 1990's through to about 15 years ago. Essentially every EV since then has used a permanent magnet AC motor... including the Leaf.



khojka said:


> If it was a PMAC, couldn't it have been plugged straight into DC power without the need for an inverter?


No. Any motor has an unchanging magnetic field and a changing one: in a brushed DC motor the unchanging one is the stator and the commutator changes the rotor; in everything else the rotor is unchanging and the stator field is rotated around by feeding it AC power... sinusoidal, or just square-wave in an "electronically commutated" or "brushless DC" motor.

So any motor needs a commutator or inverter to run on a DC power source.



khojka said:


> What I meant was to buy a commercial asynchronous AC motor, and switch out the squirrel-cage rotor with a permanent magnet one, effectively making a PMAC/BLDC motor.


That's what I meant about the HVH motors: they actually build them all with the same design of stator, but squirrel cage (for induction) or permanent magnet (for PMAC) rotors... and of course it makes sense to buy the right thing, rather than buy the wrong one and convert it.

If the idea is to get affordable stator by getting a common induction motor, then make it PM by building a new rotor, then I understand the logic... but constructing that rotor will not be easy or cheap. It would make more sense to me to just use it as an induction motor: while not the popular current technology, it certainly works (as it does in the Tesla Model S and Model X).

Most importantly, changing the rotor to change from induction to PM makes no difference to the cost or complexity of the controller/inverter, unless you want to use a slightly cheaper square-wave "BLDC" inverter rather than the sine wave inverter used with both asynchronous (induction) and synchronous (PM) AC motors.


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## khojka (Dec 8, 2019)

Alright, I think I get it now. I thought "inverter" was referring to a DC-AC inverter which converted the DC battery voltage to a three phase AC sinewave which the motor accepted. Turns out it just meant a three phase sensored ESC that switched a square wave signal, just like a BLDC.


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## brian_ (Feb 7, 2017)

khojka said:


> Alright, I think I get it now. I thought "inverter" was referring to a DC-AC inverter which converted the DC battery voltage to a three phase AC sinewave which the motor accepted. Turns out it just meant a three phase sensored ESC that switched a square wave signal, just like a BLDC.


Yes, either way it's an inverter. Since the complexity and cost are similar, EVs all use sinusoidal AC power, once you get past about the size of an electrified bicycle.


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