Electrostatic Induction - Capacitive Generator

[tim123]

Hi Folks,
  This is a variation on an idea I had years ago, and I'm planning to prototype this device. I'm looking for advice / comments etc. I know there have been similar devices invented in the past... Images below.

Construction

It consists of 3 main parts. All are made of tinfoil glued between perspex sheet, or similar:
- 2 square stationary 'Emitters'. Connected to the terminals of a High Voltage source.
   These are just 2 square sheets of alu foil between perspex.
   I'll be using a HV transformer I made which has 2 ignition coils in flyback mode. It makes about 1000v for each 1v of input.
   I'll be aiming for enough insulation for 20-30Kv

- 1 square stationary 'Collector'
   This has an even number of segments of tinfoil. Each segment is connected via a wire to the output circuit.

- 2 round rotors
   These alternate tinfoil segments with gaps. The segments should overlap the Collector segments alternately as they rotate.
   These segments are connected directly to the shaft - which is earthed via a slip-ring (or similar).
   There's one rotor each side of the collector.

Principle Of Operation:

- The 'Emitters' create a strong electrostatic field.
- The 'Collector' segments are alternately shielded from the 2 fields by the earthed rotor plates as it rotates.
- So each segment in the collector alternates between +ve and -ve, and there are two sets.
- The segments are connnected together via a load. I'll probably be using a Microwave Oven Transformer to step down the high voltage.
- The 2 sets of rotor plates are essentially capacitor plates.
- The rotor experiences no drag...

One interesting aspect of this design - is that it's possible to get very fast switching rates - by having more segments. A large radius machine could switch very fast - at fairly low shaft RPM.

The power output is limited by:
a) the emitter voltages (i.e. the power supply / insulation),
b) the switching speed, and
c) the surface area of all the collector segments.

However, the design is extremely thin (25-50mm), and multiple sections could easily fit into a small space.

Cheers
Tim

[truesearch]

@tim123:


I like your idea and diagrams. This isn't my area but I see some of your logic in your explanation.


Please keep us posted with your progress! 


truesearch

[TinselKoala]

You are right, all the way down until you get to this point:

"The rotor experiences no drag."

But it does. Or to put it another way, it does take work, to move the rotor into and out of the fields. The fact that you are sliding the rotor "sideways" into the fields doesn't really matter in this regard.

http://en.wikipedia.org/wiki/Electrostatic_voltmeter
The electrostatic voltmeter takes advantage of this phenomenon, in reverse.

Machines like Wimshurst and Bonetti require more and more power to turn the disks as they become charged up, even though the motion of the charged bits is at right angles to the electric field lines between the disks.

But by all means do build and experiment with your idea! I think it might make a good electrostatic generator even if it does take work to turn the rotor.

[tim123]

You are right, all the way down until you get to this point:

"The rotor experiences no drag."

But it does. Or to put it another way, it does take work, to move the rotor into and out of the fields. The fact that you are sliding the rotor "sideways" into the fields doesn't really matter in this regard.

Hi TK
  thanks for the input... I'm not sure about whether the rotor will experience drag - and very happy to discuss... I don't think the ES voltmeter is the same arrangement...

1) The rotor is earthed - so it cannot hold a charge itself. I think fact alone this means no drag (?) - at least I can't see a mechanism for drag.
2) The rotor will have a constant field on the Emitter side
3) The rotor will have a varying field on the Collector side
4) As the rotor enters a segment - the fields either side go from opposites (attracting) to the same (repelling).

I don't know what points 2-4 will mean in practise. I just don't know. Any input gratefully received...

Machines like Wimshurst and Bonetti require more and more power to turn the disks as they become charged up, even though the motion of the charged bits is at right angles to the electric field lines between the disks.

These machines have drag because the rotor is moving charges against the ES gradient. I.e. they carry -ve charges towards the -ve collector brush - so there is repulsion. All ES machines work on that principle - says Wiki.

But this isn't using that principle - i.e. no charges are being carried towards any terminals... This is more like a HV capacitor with switchable linkage... It's a bit like an Electro-Static version of an Ecklin-Brown generator...

Regards
Tim

[TinselKoala]

Well, good luck with your build, I hope it works as you plan. I'm always interested in new electrostatic devices. But I still think you are missing the place where you have to put in work to turn the rotor against the "charge pressure".
And it's not true that grounding an element prevents it from being charged. You can easily ground either side of just about any static generator I can think of and sometimes it will even work better, as the earth ground is a great source/sink for electrons. Voltage is relative.  Just don't ground both sides!