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Capacitive power transfer: how would you approach this?

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Steve Conner

Fri Jun 29 2012, 11:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I would make it so the bottom of the laptop was composed of two plates, each taking up half the surface area. Either one receiving plate and one ground plate, or two balanced receiving plates (same difference)

My reasoning is that the ground plates are on an equal basis to the "live" plates because the same current passes through both in series. Therefore if one set of plates had much smaller capacitance than the other set, that would be sub-optimal.

Ash Small

Fri Jun 29 2012, 01:54PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yes. I agree two transmitter and two reciever plates would simplify things considerably.

Steve Conner

Fri Jun 29 2012, 02:02PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

There are always two sets of plates whether you like it or not, for the reasons we just went through. I'm just acknowledging the existence of the second set, so I can optimise them.

TBJ

Fri Jun 29 2012, 07:47PM

Registered Member #5374 Joined: Mon Jun 18 2012, 06:54PM
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Posts: 10

I think the hardest part of this is going to be sourcing some suitable transformers. I assume the murata units are custom wound.

I have had a play with a CCFL inverter but seem to get very little power through capacitive coupling, though I must admit I haven't tried it as part of a tuned system.

Avalanche

Fri Jun 29 2012, 08:09PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I think you'll have to use a resonant system (at least whenever ground is going to be your return path) because most of the power from your 'transmitter' will just want to go straight to ground anyway.

A resonant system will make it easier to achieve some coupling, but it'll still be inefficient. Having said that, I've managed to shock myself by touching a non-energised Tesla coil, whilst operating another coil about 2 meters away so I might give dig them out and try it again - I have a couple of coils somewhere which are roughly on the same frequency!

radiotech

Fri Jun 29 2012, 08:15PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Think about industrial electrostatic lifters, then Tesla,

Create a rotating electrostatic field in the stationary part. Then make
receivers that are actually poly phase electrostatic rotators. Couple them
to micro alternators and take the energy from that.

The underlying idea is that with closed loop inertial coupling,
energy will not be radiated as electromagnetic waves to spaces
where it will be wasted.

You will get optimum tuning, when the torque of the load equals
the opposite torque of the source.

The whole system might even work on a nano level.

Pinky's Brain

Sat Jun 30 2012, 12:05PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Does that actually mean anything?

Ash Small

Sat Jun 30 2012, 08:17PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Pinky's Brain wrote ...

Does that actually mean anything?

Think of a stepper motor, with the coils in the transmitter, and a permanent magnet rotor in the reciever.

This 'will' require perfect alignment for any degree of efficiency, though.

(The rotor drives an alternator, one of the few occasions where using an electric motor to drive an alternator might actually make sense)

radiotech

Sat Jun 30 2012, 10:08PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Think of a maglev train, only instead of magnetic fields, electrostatic
ones are used. The topic was capacitive transfer, not magnetic.

Everyone has experienced a tissue, or scrap of paper sticking to screen of
a CRT computer monitor.

Consider this>

Capacitive transfer could save metal. Electrostatic generators are common,
like the wind-up ones used reset quartz fiber dosimeters.

BigBad

Thu Jul 05 2012, 03:47PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

I've been working on this for a while.

Pretty much everyone has already covered it.

To do it, you just need two tesla coils one in transmit mode, and the second to receive. I mean that's exactly what Tesla coils were invented for, to do precisely that. I mean we're not talking huge great big Tesla coils, just two resonant air-cored transformers with inductive taps and capacitive plates.

A normal Tesla coil basically uses the whole earth as one plate (i.e. it's grounded), but for portable stuff you need to have two plates at least on the receiver, and using two on the transmitter isn't a bad idea either if they're near to the receiver. So you have a Tesla coil with two balls on them, or two parallel plates either side of the thing you want to power is better if geometrically possible.

But you don't have to use plates. A dipole aerial should work well for the receiver if you point it along the field lines; you want maximum voltage drop and/or maximum area for the plates.

You want the highest voltage practical, particularly on the receiver if it has smaller plates, and a high Q. Also a high frequency like megahertz or so.

The reason for using Tesla coils is that you need to step up at the transmitter to generate high voltages and then the receiver needs high voltages as well and then you need a step down at the far end. Basically free space is high impedance and the step down ensures that you present the load to the primary as a very high impedance, and the step down step ensures that; otherwise you'll get horribly low efficiency or power.

You need high voltages on the receiver, because otherwise the receiver won't be able to subtract voltage from the transmitter very well. You need to do that since it enables the transmitter to pile in more power, rather than just sit bouncing just below its maximum voltage limit. The negative voltage represents power successfully transmitted.

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