BLDC motor questions

DC motor questionsAll, I am making, or at least attempting to make, an electric high speed spindle that fits in a confined space. I do not want to use air as the motive force. So I have been experimenting with BLDC motors made for model airplanes and the like. I would like to cool the stator, I think I may need to in fact if I want the motor to run continuously. Liquid cooling would be best. To do this most efficiently the stator should be submerged in the cooling liquid. There is not enough space between the windings for even very small diameter tubes carrying fluid to fit through. So if the stator gets submerged the liquid must be constrained to the stator only. I thought about making plastic end caps for the stator and sealing the perimeter of the stator with a sheet of plastic or maybe plastic and some sort of metal sheet. The motor is built with the outer rotating, inside out compared to most motors we see, but common in floppy drives. There is about .008" air gap between the outer diameter of the stator and the magnets. I'm afraid that if I use brass sheet, for example, to wrap around the stator it will short out the laminations and increase eddy current losses in the motor. If the brass sheet could be insulated from the laminations would eddy currents in the brass sheet start to heat it significantly? This is a 1000 watt motor and the stator is about 1.18 diameter x 1.18 long (30mm x 30mm). If the stator can be wrapped with something to seal it what kind of fluids would not tend to soften varnish on the windings? Anybody here know? Thanks, Eric

Reply to
etpm
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It sure sounds to me like you're approaching the point where air will be less work!

What power will you be using to drive the motor? If you're driving a

1000W motor with 1000W or less, then I would expect that air cooling would be sufficient -- just make sure that it mostly goes over the stator. You can get centrifugal fans for those things, which should do the job well (the OS motors come with them built in).
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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

Oh -- any brass on the outside of the stator will, I think, divert a hefty proportion, if not the majority of, the energy that would otherwise go to spinning the motor. As a means of melting brass and making a mess, it's probably excellent. As a means of cooling a motor -- probably less so.

As for the varnishes, I dunno. Worse, it'll depend on the motor -- there's different enamels available for different applications. I'd suggest that you cut and try starting with whatever coolent most appeals to you, and go from there.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

** This poster must be mentally defective.

A 1000W motor smaller than a golf ball ?

Liquid cooling with no liquid flow ?

In what universe ....

.... Phil

Reply to
Phil Allison

No, a 1000W motor with a stator smaller than a golf ball. Most RC motors are outriggers, with the stator in the center and the rotor on the outside. The total motor size is bigger than just the stator, and the power/size ratios they're getting are pretty ridiculous.

The problem is, those motors are designed for high speed air cooling. Using them for anything else poses serious cooling problems.

Reply to
DJ Delorie

** Makes no difference to my point - a golf ball is 43mm dia.
** Ain't that some kind of a canoe ?

** Known as "outrunners".

The high powered types all have internal rotors and one can cool the case with a water jacket.

** The published numbers might be, the realty ain't.

** No worries if you submerge the lot in liquid Nitrogen.

... Phil

Reply to
Phil Allison

Which is why I want liquid cooling. I can buy water cooled outrunners but they don't spin fast enough. . Eric

Reply to
etpm

I think you'll save money overall by going with bigger motors, and blowing lots of air through them.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

Greetings Tim, I know I could save money by using a larger purpose bought spindle. At least I think I could. But I have not been able to find one small enough. I want to put a 32000 RPM spindle in my CAT 40 machine by using a CAT 40 tool holder modified to accept my spindle. So I need a lot of power in a small space. Speeders cost in the neighboorhood of $1500.00 for a used one. And many of them won't go fast enough anyway. I now have three engraving jobs coming up that would benefit greatly from the increased feed allowed by a faster spindle. Ideally the spindle will connect automatically to power and coolant when the tool change occurs. So this why I have chosen this route. Eric

Reply to
etpm

I'm not arguing against the model airplane BLDC motors -- just the use of liquid cooling. You know they work if sufficient air is rammed through them -- so ram sufficient air through them, and be happy!

--
Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

Hoping the 1000 watts is a typo... Your major cooling would be radiated heat and light...

Reply to
default

1.666 HP ?

Jamie

Reply to
Maynard A. Philbrook Jr.

I did a rudimentary test to measure the torque and rpm at the same time.Using a friction disc on the end of an 6 inch pound max torque wrench and slowing the rpm to about 30,000 rpm with the motor drawing about 40 amps at 12 volts I got about 1.2 inch pounds. That's a little over .5 hp. The motor got quite hot since it was not rushing through the air. The motor is rated at 70 amps as I recall. And 14.8 volts. The test was rudimentary, but it showed that the little motor may be able to consume 1000 watts for short periods without melting. The planes that use these motors don't fly very long at full power. I won't be able to get 1 hp out of it constantly, I think. But pretty close. Eric

Reply to
etpm

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