# Halbach Array Motor promises higher energy-density



## crap (Dec 5, 2009)

Indeed, ironless PM motors have great potential. I myself made calculations and drawings for one of those that could deliver several hundred kilowatts with an active weight of about 10kg. (Active weight only includes copper and perm magnets, but the total weight could stay below 20kg for an air-cooled model). The efficiency would be about 97-99,9% depending on rpm and torque extracted.

However, there are a few problems. Ironless motors generally have poor torque density, so larger diameter and/or higher rpm's is prefered. Also to minimize losses a large number of poles is an advantage, it reduces the inactive copper volume. High number of poles in combination with high speeds is difficult for the controllers, for an example 24 poles and 10 000rpm requires the controller to deliver 3phase AC at 2000Hz. I doubt any of the available controllers delivering more than 100kW will do that...

And finally, the efficiency may be awesome but cooling is still a problem since the there is no iron in the stator. Both the thermal inertia and heat-conductivity is poor.
In my 500kW design the motor is oil-cooled, this should solve the problem (haven't made the calulations yet but I'm quite confident). It will compromise the efficiency slightly but it would still be more efficient than anything commercialy available that I have seen. Manufacturing cost should be quite reasonable aswell.

So the conclusion: These motors are awesome but quite tricky to design well, there are still several difficulties left to be mentioned. If anyone happen to know of a controller (other than RC controllers) that can handle around 200 000 electrical RPM please share, it would make these motors even more interesting.


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## PhantomPholly (Aug 20, 2008)

I'm not an engineer, so if I'm off base it wouldn't be surprising. However, in reading the article the advance seemed to be not in the fact that it was "ironless," but that in creating the arrays of permanent magnets in a particular way you delivered the maximum field where you needed it and NO field other places. That should (at least in my head) eliminate a good deal of the heat (from inductive processes?) associated with electric motors (and, they don't generate that much compared to ICE anyway).

Of course, 95% efficient means 5% heat any way you slice it - so they will still need to find some way of dealing with it.


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## crap (Dec 5, 2009)

The article is somewhat flawed, articles are almost never quite correct or detailed enough. But then again my post could have been better aswell. 
This is how it works:

Halbach arrays could also be used to increase the efficiency of conventional motors by increasing the torque density/decreasing the current density, thus reducing the copper losses. If designed well it would get more efficient and/or more powerful. However motors with an iron core suffer from more inductive losses, so low-load losses would increase. Which brings me to why I started talking about ironless motors: They have virtually no low-load losses and they profit more from increased magnetic field strength. Also the motor on the pictures in the article was an ironless (axial flux with overlaping windings).

The halbach array shifts almost all the magnetic flux to one side, making it stronger. A strong magnetic field is very important in an ironless motor because it increases the torque density and thus increases the output for a given rotational speed, thus increasing the efficiency. It also eliminates the need for a backing iron and thereby reduces the motors weight.

it does however deliver more magnetic flux in directions not wanted, so it actually increases the eddy losses slightly. In an ironless motor this is not a problem since the eddy losses can be made very small with litz wiring.


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## RoughRider (Aug 14, 2008)

crap said:


> The article is somewhat flawed, articles are almost never quite correct or detailed enough. But then again my post could have been better aswell.
> This is how it works:
> 
> Halbach arrays could also be used to increase the efficiency of conventional motors by increasing the torque density/decreasing the current density, thus reducing the copper losses. If designed well it would get more efficient and/or more powerful. However motors with an iron core suffer from more inductive losses, so low-load losses would increase. Which brings me to why I started talking about ironless motors: They have virtually no low-load losses and they profit more from increased magnetic field strength. Also the motor on the pictures in the article was an ironless (axial flux with overlaping windings).
> ...


 
sorry...but you are leaving in dreams...

20kg motor with 500kW of power...

yes...sure...dream on


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## crap (Dec 5, 2009)

RoughRider said:


> sorry...but you are leaving in dreams...
> 
> 20kg motor with 500kW of power...
> 
> yes...sure...dream on


Sorry about that, the 20kg is the air-cooled version and it would not be able to handle 500kW (despite having the same active component configuration). The 500kW version would weigh about 40kg since it requires oil-cooling and higher strength. That makes 12,5kW/kg, compared to the one in the article that had a bit past 8kW/kg. Cooling is almost always the limiting factor with an ironless, thus the higher power density with oil-cooling.

But let me just say, to belive it's not possible simply because it hasn't been done as far as you know, is about the stupidest thing you can do.


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## RoughRider (Aug 14, 2008)

crap said:


> Sorry about that, the 20kg is the air-cooled version and it would not be able to handle 500kW (despite having the same active component configuration). The 500kW version would weigh about 40kg since it requires oil-cooling and higher strength. That makes 12,5kW/kg, compared to the one in the article that had a bit past 8kW/kg. Cooling is almost always the limiting factor with an ironless, thus the higher power density with oil-cooling.
> 
> But let me just say, to belive it's not possible simply because it hasn't been done as far as you know, is about the stupidest thing you can do.


WELL...than DO IT...you super e-motor designer...

talk is CHEAP...

DO IT...


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## crap (Dec 5, 2009)

RoughRider said:


> WELL...than DO IT...you super e-motor designer...
> 
> talk is CHEAP...
> 
> DO IT...


Yeah like I'm really gonna waste my money on building a motor for wich I cannot afford a vehicle, controller, batteries, or anyting just because you won't believe it's possible...

I plan to build a smaller protype motor to test using RC controllers, but until then there's this other guy who built a simpler ironless motor:

http://www.youtube.com/watch?v=_TC57GCt37w&feature=related
http://www.youtube.com/watch?v=hy6jZEW9uxc&feature=related
http://www.youtube.com/watch?v=u0I0Tg8sxYw

He built his out of wood, using neither halbach arrangement of the magnets nor overlaping windings, and it's still quite impressive.


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## few2many (Jun 23, 2009)

Holy crap, I mean, hey crap, what do you think of energy from the vaccuum, zero point energy and overunity?


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## Amberwolf (May 29, 2009)

The guy in that video inspired this challenge over at Endless Sphere:
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=14484&start=0&hilit=challenge
which hopefully will spawn some light and powerful motors for ebike use, potentially even emotorcycle use.
________
VAPORIZER INFO


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