A topic of motors
 

As my signature shows, I am an ASE certified day-dream engineer. :thumbup:

I'm always dreaming of making things better. Anywhere fat can be trimmed I process it in my mind. And this time, the issue of controller efficiency is on my mind. And the idea rests upon the restructuring of the motor. Although this is sprung from the hub motor topic in EC, I felt it went a different enough route to warrant a separate topic.

Imagine for me if you will, the permanent magnet motor. As I recall, it has several sets of windings, and only one or perhaps 2 windings are activated at any given point by the brushes. (I use a brushed motor for this example as I've only just as I'm writing this topic looked up how a brush-less motor works, and the concept has not yet sunk in).

My idea is, in the case of a hub motor, wherein there would not be a driveshaft, rather, the whole front face and outer circumferential face, (think of it like a brake drum), would rotate, while the coils would fixed. Now lets say that while the case materials are rated for the motor to put out 10hp, each coil only provides 1hp.

Now, in this case, each coil would consume ~770w. Which I believe is switchable at reasonably high voltages without significant arcing. So now the controller, instead of firing mosfets to control motor current draw, fires relays, to activate or deactivate windings based upon load demand.

Obviously this would require a motor re-designed from the ground up, but sometimes that's not a bad thing. Now anyone with some real credentials want to poke holes into my daydreaming? :p

</3am half-awake ramblings>

DISCLAIMER: I have no credentials.

You would have 10 pairs of wires into the motor, or can you use a common ground return? Also, how many times can a relay switch 770w before burning up, and can it switch quickly enough? I imagine you'd want to use mosfets anyway, since they're solid state.

If you'd like, I can post your idea to the EVDL and see what the credentialed folks say. (Too bad we can't get Jim Husted to be a regular contributor here; he's a master motor modder.)

Common ground would be preferable, I would think.

As for mosfets, perhaps. I honestly haven't worked with them enough to know whether or not they develop significant heat if they are running below their rated load capacity.

And please do. I'd like to see the response.

Edit: Also, it didn't occur to me when I read your post the first time, but I'm not using switching speed as a controller, rather a motor with 10 separate windings would have 10 separate output levels, which would simply be switched on or off as demand required, not as a duty cycle setup.

Ok! No real credentials here neither,but in my opinion after your edit that clarifies the idea,I think what would happen is during "low demand" when a single coil is switched on,it would try to do all the work all by it self and quickly go up in smokes unless there is some type of current limiting.
Plus I would design the motor so one coil is actually two coils,in a sense to utilize both ends of the magnetic field that it creates. Example: the south end of the coil would have a north pole of a magnet approaching and the other end that is now a north field would have a south pole of a magnet in the same position.(wich is exactly how the brushless outrunners are set up) Ofcourse the whole thing would have to be designed with all the possibilities in mind and that's quite the challange but for some (me included) that's the fun part. :)

My idea is to size the coil such that it draws a known amperage at a known voltage under full load. Self-current limiting, if you will.

Making it 2 mating coils instead of one is a good idea as well. :thumbup: