Lowest Emissions Electric Motor

[ricko_uk]

Hi,
I don't know much about the various types of electric motors so just wondering if someone could give me some pointers...

A client asked me to design a simple stirrer (just a motor with a shaft) rotating with adjustable speeds between 50 RPM and 200 RPM. The load is just a tiny steel shaft mixing 500ml of liquids. It can take quite a bit o get up to speed too, that is not a problem.

Efficiency and power dissipation are also not a problem, so linear drive can also be used (I assume that would be less nosy than a PWM drive).

But they need it to be very low emissions (electric, magnetic and electromagnetic) because they have all sorts of sensors around the container which are extremely sensitive to all those emissions.

What type of (low-power) electric motor has the lowest electric, magnetic and electromagnetic emission?

Or, if when decreasing one, another increase (for example by decreasing the magnetic field the electric field increases) then which solution is easier to shield? I think perhaps higher voltage lower current because the electric and electromagnetic fields are easier to shield than the magnetic ones, perhaps?

Any clarifications and pointers are welcome.

Thank you

[uer166]

The lowest noise might be something that can run directly off of mains such as a shaded pole induction motor (or any kind of mains induction motor). Unfortunately this is not compatible with the variable speed requirement, any chance you can vary speed mechanically via belt or gearbox? If not, then some kind of brushless motor driven by a linear power-amplifier instead of PWM as mentioned. A good start would be quantifying the acceptable amount of magnetic/electric field leakage..

[langwadt]

who not a hydraulic or pneumatic motor? could be made of plastic for zero emmisions

[CatalinaWOW]

First question I would ask is what the sensitivities are.  Is the concern strong magnetic fields which might saturate or over bias a sensor.  Are there frequencies that must be avoided and are there any that can be allowed?

Depending on those answers you might look at a homopolar motor, which has no varying emissions in steady state operation.  The magnetic fields can be fairly well contained in the motor.  Going the other direction, a motor with very high pole count could drive the emissions up and out of the operating band of the sensors. 

If the problem is extreme, look into a hydraulic motor or an air motor.  By making the piping/hoses long enough you can get all the pumps and controllers isolated.  You could use fiber optics to couple a shaft position sensor to the remote location for speed control.

[coppercone2]

run it on a pulley from a distance


the lowest emissions would be hand powered from a pully, perhaps with a wet rope

[moffy]

Just use a brushed DC motor and feed it with a variable DC supply, speed control, for suppression put a capacitor across the brushes.

[David Hess]

A DC brushless motor will be electrically quieter than a brushed DC motor because of the lack of brushes and commutator.  Speed can be varied by changing the voltage.

[moffy]

A DC brushless motor will be electrically quieter than a brushed DC motor because of the lack of brushes and commutator.  Speed can be varied by changing the voltage.

Not sure you can generalise that, probably specifics dependant. Where I worked we got a 'dunny cart' for the australian army through its stringent emissions testing, it had a brushed DC motor for the pump, we just had to fit a capacitor across the brushes. The BLDC motor has a drive built in which could be noisy, and good commutation doesn't have to spark especially at low voltages.