# BLDC controllers suitable for very low inductance motors



## Tesseract (Sep 27, 2008)

circuit said:


> ...
> So, since there ARE such motors, what controllers do they run with? Anyone know of such controller available to buy or any kind of info at least?


The rule of thumb here is the lower the winding inductance the higher the switching frequency needed to maintain control over the winding current, all else being equal.

However, both "iron" and winding losses go up with frequency, and in the specific case of the iron losses they typically increase at the 1.6 power of frequency. Also, switching losses in the inverter go up with frequency, so you will have reduced efficiency there, too.

Whether or not what you want is practical will depend on the max battery voltage and phase current desired. A high switching frequency generally means using MOSFETs as the active devices in the inverter, but above 250V and 300A per phase they give way to IGBTs, which typically max out at about 20kHz in hard-switched applications (as compared to resonant or soft-switched modes of operation).

Finally, the need to meet EMI emissions regulations - especially in the EU - also limits the PWM frequency. Most such regulations begin measuring emissions at 150kHz and since PWM waveforms contain significant amounts of odd harmonics (proportional to 1/n, where n = harmonic number) this is often the biggest limiting factor on the switching frequency, regardless of the capabilities of the hardware.


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## circuit (Jan 16, 2012)

Well, thanks for the theory. Nothing new there.

But my question is still open. I want to find any production controller and how it (if any exist) solves the problem:
1. Used only with coreless motor and feed enormous frequency PWM
2. Work in enormous frequency and filter it out with onboard LC filters
3. Any other, maybe smarter way to achieve the goal.


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## Arlo (Dec 27, 2009)

Circuit. Here is what I can find off the top of my head. 
These guys had a claim they could get some really tough to drive 3phase AC permanent magnet motors ripping. http://www.rinehartmotion.com/products.html
And the Tritium wave sculpture but the pages can not be found???
There is one or 2 more companies I have seen talked about over on ES but I have to find them.
There is a reason I have learn't how to build and design 3 phase motor controllers and I have had 2 colossus paperweights for over 2 years!
If I could get someone to do my 60+ hours of work I have a week right now my motor controller would be done in no time!


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## Tesseract (Sep 27, 2008)

circuit said:


> Well, thanks for the theory. Nothing new there.


Yeah, well, you asking the question in the first place kind of implied you didn't realize this. Also, you didn't specify an operating voltage and desired power level so how could anyone suggest a specific inverter?


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## circuit (Jan 16, 2012)

Arlo said:


> If I could get someone to do my 60+ hours of work I have a week right now my motor controller would be done in no time!


Same here. Started the project back in 2009.
Will drop them an email.




Tesseract said:


> Yeah, well, you asking the question in the first place kind of implied you didn't realize this. Also, you didn't specify an operating voltage and desired power level so how could anyone suggest a specific inverter?


Sorry I did not make it clear from the start. To me this problem looks so huge, that I was asking for a link to ANY KIND of controller that is able to turn low inductance motors without pushing enormous amps at no load.


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## Arlo (Dec 27, 2009)

circuit said:


> Same here. Started the project back in 2009.
> Will drop them an email.
> 
> 
> ...


I ran colossus with a 18fet controller with no load at ~6500-7000 rpm (100v) and it was sensored running ~7 amps so thats not huge. Are you sure you dont have another problem???


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## circuit (Jan 16, 2012)

Arlo said:


> I ran colossus with a 18fet controller with no load at ~6500-7000 rpm (100v) and it was sensored running ~7 amps so thats not huge. Are you sure you dont have another problem???


Are you still running it? Somehow I did not see anyone actually running it.
I ran similar motors with 18fet LYEN "just fine". And current draw was "not that high". Only few amps at battery, but a hundred amps on phase...
7 amps at 100V is 700W of loss, while doing nothing. Colossus is a bit too small to get rid of 700W heat by its own.
And what is the inductivity of colosssus? From its dimensions I'd guess its around 15-20uH.


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## Arlo (Dec 27, 2009)

Collossus is 8uh its liquid cooled and been rated at 20-30 hp continous. Splinter has a working bike with colossus in it using a kelly. No running hi power but it does drive like a normal bike. I have posted a few videos of colossus running on the bench and using external inductors to ride it around. But now im using lebowskis chip for my controller all i need is a free afternoon to be running it!


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## frodus (Apr 12, 2008)

> 7 amps at 100V is 700W of loss, while doing nothing. Colossus is a bit too small to get rid of 700W heat by its own.


That's not 700W of loss, that's 700W going to the controller. Just because it's not loaded doesn't mean it's not doing work. The motor is still moving and using energy.


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## Arlo (Dec 27, 2009)

Yeh at those rpms there is a fair bit of eddy current losses and then you have hysterious losses and bearing losses and colossus has a 80x100x10 mm skirt bearing (the new version is smaller). So 700watts at those rpm with all the air moving is no big deal!


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## circuit (Jan 16, 2012)

frodus said:


> That's not 700W of loss, that's 700W going to the controller. Just because it's not loaded doesn't mean it's not doing work. The motor is still moving and using energy.


A 5W fan is doing more work than spinning colossus. Think about it.


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## Coulomb (Apr 22, 2009)

Arlo said:


> And the Tritium wave sculpture but the pages can not be found???


I don't know what pages you mean; if the AEVA pages, yes the server is rather unreliable.

In the Honda Civic Conversion, they added 3 400 A 50 uH inductors in series with the ironless motor.


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## Arlo (Dec 27, 2009)

circuit said:


> A 5W fan is doing more work than spinning colossus. Think about it.


 I would put money on colossus unloaded lol. Its moving a lot of air and more then a 5w fan would be. But at ~7000 rpm is has big eddy current losses. If I lowered it to ~ 4000 rpm then the unloaded current draw is less. 
OH and one big thing we forgot colossus is NOT using the whole 700watts the controller has its losses too!


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## Arlo (Dec 27, 2009)

Coulomb said:


> I don't know what pages you mean; if the AEVA pages, yes the server is rather unreliable.
> 
> In the Honda Civic Conversion, they added 3 400 A 50 uH inductors in series with the ironless motor.


 Yes its working now. http://www.tritium.com.au/products/TRI50/index.html


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