High Power Electrostatic Motor 95% Efficency

[markdansie]

Not sure if this is the right label but this is an impressive lightweight powerful motor (200grams and 100 watts)

http://revolution-green.com/high-power-electrostatic-motor-95-efficency/

[TinselKoala]

I've made some remarks about this motor before. I must say, I'm puzzled.

I have no doubts as to the efficiency of electrostatic motors in general, but the "vacuum" aspect has me puzzled. In order for a "vacuum" to be non-conductive enough to be able to stand off the high voltages needed for efficient electrostatic motor operation, the vacuum must be pretty "hard". That is, it must have a pressure that is below the "Paschen limit" , to the left of the leftmost curve in this diagram:

http://en.wikipedia.org/wiki/File:Paschen_Curves.PNG

This kind of hard laboratory vacuum is usually obtained and maintained by using several stages of pumps: a dual-stage vane pump for "roughing" and a turbo or oil-diffusion pump for pumping down to the final vacuum, low enough to be nonconductive at the voltages and spacings in the electrostatic motor.

Surely, the energetic "cost" of running the vacuum pumps must be included in an overall efficiency calculation.

As I've shown in my own primitive vacuum/high voltage systems, a "vacuum" that can be gotten with a simple 2-stage vane pump -- 30 microns or so --  just isn't low enough to provide the insulation that an electrostatic motor needs.


One would actually be better off using _higher pressure_ than atmospheric. High-power VanDeGraaff machines used in particle accelerator systems may operate under 10 atmospheres of CO2 or SF6 gas for insulation! And it's a lot easier to maintain a high pressure than a high vacuum.

[picowatt]

I've made some remarks about this motor before. I must say, I'm puzzled.

I have no doubts as to the efficiency of electrostatic motors in general, but the "vacuum" aspect has me puzzled. In order for a "vacuum" to be non-conductive enough to be able to stand off the high voltages needed for efficient electrostatic motor operation, the vacuum must be pretty "hard". That is, it must have a pressure that is below the "Paschen limit" , to the left of the leftmost curve in this diagram:

http://en.wikipedia.org/wiki/File:Paschen_Curves.PNG

This kind of hard laboratory vacuum is usually obtained and maintained by using several stages of pumps: a dual-stage vane pump for "roughing" and a turbo or oil-diffusion pump for pumping down to the final vacuum, low enough to be nonconductive at the voltages and spacings in the electrostatic motor.

Surely, the energetic "cost" of running the vacuum pumps must be included in an overall efficiency calculation.

As I've shown in my own primitive vacuum/high voltage systems, a "vacuum" that can be gotten with a simple 2-stage vane pump -- 30 microns or so --  just isn't low enough to provide the insulation that an electrostatic motor needs.


One would actually be better off using _higher pressure_ than atmospheric. High-power VanDeGraaff machines used in particle accelerator systems may operate under 10 atmospheres of CO2 or SF6 gas for insulation! And it's a lot easier to maintain a high pressure than a high vacuum.

TK,

Although we usually think of high voltage when we think of electrostatics,  electrostatic does not necessarily mean high voltage.  I work with the effects of a substantial amount of electrostatic attraction every day with a mere 100-200V applied.

I don't believe this motor's operating voltage was given, but I would not be surprised if it operates on well under 3-5KV. 


PW

[TinselKoala]

I doubt if it could stand off that much.... _unless_ the vacuum is, as I said above, hard enough to get below the glow discharge region. With a rotating shaft seal to get the mechanical power out of the box .... this will require constant pumping to maintain. A magnetic coupling through the walls of the vacuum chamber will have its own set of little problems.

Here's what happens when you try to put high voltage.... even a few hundred volts... into a "soft" vacuum. You get a nice, fairly conductive plasma.

https://www.youtube.com/watch?v=niFRhRgY_9M

[picowatt]

I doubt if it could stand off that much.... _unless_ the vacuum is, as I said above, hard enough to get below the glow discharge region. With a rotating shaft seal to get the mechanical power out of the box .... this will require constant pumping to maintain. A magnetic coupling through the walls of the vacuum chamber will have its own set of little problems.

Here's what happens when you try to put high voltage.... even a few hundred volts... into a "soft" vacuum. You get a nice, fairly conductive plasma.

https://www.youtube.com/watch?v=niFRhRgY_9M

TK,

"Well under" also includes much lower voltages...

My point is that the narrow clearances and small radii shown in the construction details tend to indicate that this is not a "high voltage" motor.

Regarding the "vacuum issue", I understand what you are saying, and dry air or SF6 would indeed be easier to maintain.  Possibly the article misspoke or lost something in translation.  Possibly this motor operates at a much lower voltage than one would might think. 

Other than the vacuum issue, what are your thoughts regarding this motor?

PW