Solid States Devices > Captret effect

Making an Electret, or several actually.

(1/5) > >>

Hello All and a happy new year.

I started a thread here at OUR a few days ago.

I hope you'll forgive me for a copy/paste introduction?

Cheers Graham.

Hello Everyone.

I have always been fascinated by Electrostatic phenomena, my father demonstrating to me as a child the famous balloon on the ceiling trick, yes it goes way back.

As many will remember I built a modern day Franklin Electrostatic motor earlier this year with the intention of testing one of our members, Smudge theories. That’s still in the pipeline, BTW.

These devices have really grabbed my attention, particularly when Verpies pointed out that the forces generated can exceed both gravity and magnetism.

Over the Christmas holidays I have been playing around with some simple experiments moving small masses by Electrostatic means, but my goal is to try and build an attraction motor that uses segmented Electrets so that no external HV supply will be required.

I have opened this thread to ask if any members here have made successful wax Electrets and to document my own attempts as well.

I have " bumped " here in the hope that some/any of the contributors here at OU.Com might be able to help me with this rather interesting area of Electrostatics.

Cheers Graham.

Here's some You Tube links to my recent Electrostatic experiments.

Hi Graham,

The effects you are describing are what my Swiss contacts claim as
the driving force of the Testatika machines.

This is best demonstrated using two Whimshurst machines
One physically rotated, the other connected in parallel
through the output terminals.
The second machine rotates by electric force.

One of our members named LidMotor has a nice collection of
experiments on his YouTube channel. A quick search there will
lead you to his channel.

Also TK shows us a few tricks he has learned.

Hope this helps.

Hi Grum. I have never made an electret, but I find this interesting about electrets:

"When the oil reaches room temperature, turn off the power supply and remove the electret. Immediately fold the aluminum foil forward over the surface in contact with the top plate, short-circuiting the electret. The foil acts as a 'keeper' and is analogous to the soft-iron bar placed across the open jaws of a horseshoe magnet to preserve the magnetic flux. Electrets properly short-circuited have kept for longer than five years without noticeable loss of charge.

Now comes the puzzler that stumps the experts. If the electret's polarity is measured directly after its manufacture, its charge will be just what theory predicts it should be. The negative surface of the electret will be that which made contact with the positively charged polarizing electrode, and vice versa. This agrees with the north-south polarity of a bar of steel magnetized by contact with a permanent magnet. In contrast with the behavior of a magnet, however, the charge on the electret begins to diminish immediately, and in about a week it will have fallen to zero. The charge then begins to build up in opposite polarity to a final value that may be several times as large as the original charge. This may take as long as three months. The negative surface of the stabilized electret will be the face that made contact with the negatively charged polarizing electrode. In other words, the charge will correspond in sign to the polarity of the high-voltage field. Just why this reversal takes place has never been satisfactorily explained."
Cited source: How to Make an Electret - the Device That Permanently Maintains an Electric Charge - by C. L. Strong - Scientific American, November, 1960

The statement that you should 'short circuit' with aluminum foil after making the electret and leave it for several months
short circuited like that, and the electret will change polarity during this period, and this reversed polarity can be even
stronger than the original charge. That is a pretty odd effect. If the charge separation is sealed into the cooled wax,
I would have thought that the electrostatic charge would remain fixed like that for a long time, but apparently the charge
somehow reverses over a period of a few months when 'shorted' with aluminum foil. Very odd effect indeed. :)

All the best...

Hi Guys.

Many thanks for the information.

Tinsel Koala linked to a nice little pdf on my thread over at OUR.

I have downloaded it myself but cannot seem to place it here from my PC.

In that article it also mentions this polarity reversal over time but they are suggesting hours rather than weeks.

Here's my " dream " copied from my post over at OUR.

“ Rotor?? “

I have an idea of a simple attraction motor. Your thoughts on how it might work, if at all, would be appreciated.

A disc of thin Aluminium sheet is covered by a slightly larger diameter of Polycarbonate. The Polycarbonate disc has got slots milled through its thickness. These slots extend from the centre point radially, just the same as the segments of a Wimshurst machine. I cook the wax mixture and pour into the slots cover with foil then pole the assembly with a positive potential applied to the base disc. I make a second one done the same way.

I then propose to mate the two discs back to back and provide an axle to be fitted into a pair of bearings mounted in a vertical fashion. The final part is a “ U “ section metal “ attractor “ ?? That goes to a good earth and is placed so that the rotor can run between the faces. Finished!

The above was written a few days ago, I have now changed my thoughts towards using circular wax Electrets inserted into a pre machined Polycarbonate rotor.

As a further update, the poling mould is virtually complete its dimensions are 50mm diameter by 10mm wide cavity. Poling voltage will be approximately 40,000 Volts DC provided by two 20KV air ionisers in series.

Cheers Graham.


[0] Message Index

[#] Next page

Go to full version