>To calculate the efficiency of an electrostatic micromotor,
>I need to define what the power in is.
>You know, generally the efficiency is defined as
>Power out/ Power in.
>However, because there is no current ideally in the electrostatic
>motor, I cannot apply the relationship of Power in=VI (voltage*current).
>
>Does anyone have an idea how to define the efficiency of electrostatic
>motors?
>To calculate the efficiency of an electrostatic micromotor,
>I need to define what the power in is.
>You know, generally the efficiency is defined as
>Power out/ Power in.
>However, because there is no current ideally in the electrostatic
>motor, I cannot apply the relationship of Power in=VI (voltage*current).
This idealization is not correct. As soon as you apply alternating
potentials to the electrodes (necessary to produce torque), you get
current flow charging and discharging the electrode capacitances.
Additionally these capacitances are changing as the rotor electrode
moves.
I would suggest analyzing a simplified 'electrostatic motor'
consisting of a parallel plate capacitor where one of the electrodes
can move and apply force to a load. Constrain the system to stepwise
operation; the load is locked in position, the capacitor is charged,
the load is allowed to move a distance and then locked, and then the
capacitor is discharged. Apply a potential, and current will flow
(following the capacitor charging equation). Energy is stored in the
capacitor and an attractive force will develop between the
electrodes. Disconnect the potential source. Permit the electrode
and load to move, doing work force*distance. As the electrodes
approach each other, the capacitance will increase, and the potential
on the plates will drop. During the movement phase, the no charge
has moved off the electrodes, the capacitance has gone up and the
voltage has gone down, and the energy stored in the capacitor has
dropped. This analysis would then be extensible (with lots of work)
to rotating members, coupling when the moving member is a conductor
which not electrically connected to any of the electrodes, but by
induction changes the capacitance between fixed electrodes, etc.
Jon Edelson
Chorus Motor plc
www.chorusmotor.com
--
Isaiah W. Cox
President * Chorus Motors * http://www.chorusmotors.gi
(c) Copyright Isaiah Cox 2001