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Author Topic: Making an Electret.  (Read 870 times)

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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'll add some extra links and pictures later as I’m currently using my tablet that has very limited capabilities.

Later, Graham.


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Ok....

This was a quick and dirty ( smelly too ) attempt at a Polycarbonate Aluminium sandwich. I took the assembly up to 200 degrees C in our domestic oven, the assembly was bedded on a sheet of heatproof glass with some Aluminium foil to make the electrical contact. I then had another foil as the " sandwich filler " then another sheet of 10 mm polycarbonate with a final Aluminium strip. My hope was to create an electret with two positive outside poles WRT the central sheet.

At 200 degrees C the Polycarbonate was quite pliable so I switched off the oven and switched on the 20 KV DC power module. I then allowed everything to cool slowly with the constantly applied voltage.

Once cold I removed the now bonded sandwich from the oven and was expecting to get zapped, hmmm, nothing doing! My scope was the only thing that could detect a minute charge that zeroed immediately, but returned, again and again. Milli volts not Kilovolts was the rather depressing outcome.

Later, Graham.


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I mentioned earlier about moving masses....

                             :)

https://www.youtube.com/watch?v=kIwHqV1NpHs

https://www.youtube.com/watch?v=-4XlD4YP5Kc

What better way to work off that excessive consumption!

TK inspired.... ;)

https://www.youtube.com/watch?v=u53Vwodew_Y


Cheers Graham.
« Last Edit: 2017-12-27, 15:34:59 by Grumage »


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Following on.

It seems the finest Electrets are made from wax, not any wax but Carnauba wax. This is also augmented with Rosin and Beeswax. The recipe is 45% Carnauba wax, 45 % Rosin and 10 % Beeswax, proportions by weight.

The ingredients are heated to around 150 degrees C and thoroughly mixed then poured into a suitable mould whilst the HT is running.

Now this is the Grey area for me, has anyone done this before?

Later, Graham.

Here's a zip file shared with me from Tinsel Koala.   O0

Hmmm... need some help here, it won't open my uploaded copy !!

« Last Edit: 2017-12-27, 17:43:51 by Grumage »


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Even at 10Megohms, the scope probe is seen as a "low impedance" load for the "high impedance" source of the electret's field.

Better is to make a super-simple electric field detector:





Pretty much any JFET can be used. 2sk170, MPF102 etc. The resistor is to protect the gate and may not be needed. Experiment!


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The Jefimenko article:  (maybe)



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The Jefimenko article:  (maybe)

Yes indeed, thank you.  O0


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Update.

Wax ingredients ordered via eBay today.

If this doesn't work out at the very least I'll have a superior furniture polish!   :)

Cheers Graham.


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Update.

Wax ingredients ordered via eBay today.

If this doesn't work out at the very least I'll have a superior furniture polish!   :)

Cheers Graham.

 O0

Hopefully you ordered pure ingredients, not the "car wax" formulations of "100 percent" carnauba wax, which contain volatile hydrocarbons to make them spreadable on automotive and aircraft finishes.


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Hi TK.

All either flake, crystal or pellets, 100% pure.

It’s always best to think about the project before actually making anything and I have decided to make a mould, circular in shape and cast/pole them one at a time. I was thinking of a vertical setup of a Polycarbonate insulator and having a slot at the top to pour the molten wax into the cavity. This will, I hope, ensure nice flat “ buttons “ that can be inserted into my prepared rotor once they have “ settled “.

“ 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.

Cheers Graham.


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Hello All.

Ok, the thread has been open for a couple of days with 250+ reads. I surmise that non of the membership has “ dabbled “ practically in this area before?

Time for some input then?

I want to make 8 by 50 mm diameter Electrets. The casting temperature is suggested at 150 degrees C. I proposed a vertical setup so that the wax could be poured through a “ sprue “ into the cavity to ensure perfectly flat discs. We all know that an open topped mould would create a “ meniscus “ to the top. I’ve been thinking about using two reasonably chunky pieces of machined Aluminium for the poling plates, these would be preheated to the working temperature to ensure the wax doesn’t freeze prematurely.

It’s the electrically insulated cavity material that I’m having trouble thinking about. We need a material that will remain dimensionally stable at 150 degrees C and also withstand the proposed 40 KV poling voltage.

Any ideas?

Cheers Graham.


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Hello All.

Ok, the thread has been open for a couple of days with 250+ reads. I surmise that non of the membership has “ dabbled “ practically in this area before?

Time for some input then?

I want to make 8 by 50 mm diameter Electrets. The casting temperature is suggested at 150 degrees C. I proposed a vertical setup so that the wax could be poured through a “ sprue “ into the cavity to ensure perfectly flat discs. We all know that an open topped mould would create a “ meniscus “ to the top. I’ve been thinking about using two reasonably chunky pieces of machined Aluminium for the poling plates, these would be preheated to the working temperature to ensure the wax doesn’t freeze prematurely.

It’s the electrically insulated cavity material that I’m having trouble thinking about. We need a material that will remain dimensionally stable at 150 degrees C and also withstand the proposed 40 KV poling voltage.

Any ideas?

Cheers Graham.

Hi Graham,
A few ideas are glass, acrylic plastic, Mylar.  Acrylic is dimensionally stable and can be used to a pretty high heat same with mylar, all 3 can take a lot of voltage, I know the 5 mill mylar I used in a HV capacitor worked to 15KV but glass is probably the best at 40KV.
Room


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Hi Room3327.

Thanks for the input, Glass would be the very best yes, but even with my extensive workshop capabilities I don’t have Diamond boring tools. I may, however have found a suitable billet of 60 mm diameter hard plastic that’ll do the job.

Thinking about a job that needs doing for a period of time usually ends up with a solution, it has! I was thinking about a complicated 3 piece mould with location pins etc. It dawned on me to just bore out to 50 mm a piece of plastic and use the electrodes as bungs, simple!

This afternoon I machined a Steel ring, 20 mm deep with a stepped bore of 50 mm for 10 mm and then opened out to 54 mm for the remaining 10 mm. I then poured in molten Zinc alloy and “ die cast “ a pair of electrodes/bungs.

I have given the electrodes a bit of substance so as not to chill the wax too quickly the idea is to put the assembly into my domestic oven bring up to 150 degrees C, remove and immediately pour the wax into the cavity. The poling voltage being applied as quickly as possible afterwards.

Well, that’s the plan, I guess we’ll have to wait and see!

Cheers Graham.


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Hi Graham,

At this link there are two old Popular Science articles included, maybe worth reading them to gather some further knowledge.

http://rexresearch.com/jefimenko/jefimenko.htm   

On the top of the long page (the above link goes to) there is a link to 

 "JEFIMENKO, Oleg : Electrostatic Motors  ~PDF copy of the out-of-print classic.  Run motors with atmospheric electricity."

but that link does not work.  Here is the correct link I figured out to download Jefimenko's book on Electrostatic Motors (15 MB PDF file):

http://rexresearch.com/jefimenko/jefimenkoesmotors.pdf

Gyula
   

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Hi Gyula.

Many thanks.   O0

I managed to prepare my mixture of resin and waxes last night. The smell wasn’t unpleasant, earthy perhaps.

Upon cooling the wax hadn’t slumped much but had really adhered to the bowl edges resulting in a loud crack when I poked at it with my finger. It then shattered into many pieces.

One thing that has become apparent is that my poling mould will need to be highly polished to prevent breaking of the seemingly fragile buttons.

More to come, cheers Graham.


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Hello Everyone.

How ( NOT ) to make an Electret. Take 1.

https://youtu.be/QEYXeuAxIqQ

                        :)

Cheers Graham.


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It's looking like " Plan B " time!   ;)


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Maybe try heating the mold, after the melt has cooled? Just enough to soften or remelt the contact surfaces... Or perhaps there is some mold release compound that doesn't mix with the wax material...


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Hi TinselKoala.

Yes those are good ideas but perhaps I’ll put another forward?

I’m thinking of thin, well 10mm deep cardboard rings cut accurately on the lathe as my formers.

These should be able to withstand 160 degrees C without charring and stay there for as long as necessary.

Now the poling surfaces. I have many Brass discs left over from metal spinning jobs that I used to do. They are flat and about 1.2 mm thick. I was thinking about wrapping a disc in Aluminium foil, neatly, then placing one underneath the cardboard ring with my Electrostatic connection. A second disc prepared in the same fashion would be pressed down upon the molten wax just before the voltage is applied.

I’m of the opinion that the wax will adhere to the foil but I hope will be able to remove it, or will it matter having metallic faces?

Thinking ahead with 40,000 volts flying about I will probably need to machine an insulating ring that fits neatly around the cardboard ring to spread the distance?

Just some thoughts, I have come to realise that this is an area that a very few have worked in and we’re all probably learning as I go. :)

Cheers Graham.


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Hello Graham,

I do not know which information you studied already but I found this one at a physics-forum here

https://www.physicsforums.com/threads/making-an-electret.180622/

https://rimstar.org/materials/electrets/


Since I ware raised as a son of a gold- and silver-smith I worked at my fathers workshop starting at the age of 8 ( in 1957 ) where
I learned some of the basic manual techniques of casting gold and silver into special moldes he was producing himself - at that
period after WWII you had to self-manufacture almost every tool.

From theses years of practical experience I can tell you that you are bound to get into problems the way you casted the wax into the mold. You need to provide different air-channels for the air to esxcape because the air must leave fast ( in addition : its expanding rapidly as it is heated up ) otherwise you will have bubbles of any size trapped in the wax which spoils the end-product.

In the above thread the technique does not use a closed mold.
And by the way pay attention to the paragraph "Testing electrets" : after the electret is cooled down and finished you need to attach an aluminium-foil on one side and fold it and attach it to the other side ( close contact ) in order to close the field-lines and thus strengthen the electret - as you would do with a permanent magnet ( attaching a iron bar across the two poles of a horseshoe-magnet)
So therefore it makes sense to use aluminium-foil in the mold to cast the wax on right during the manufacture process so that it sticks to the wax right from the beginning.

Hope this helps

Mike

Edit: did you read this on the scientific forum webseite:

"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."

List of Oleg Jefimenkos documents

http://electretscientific.com/author/jrnl.html



« Last Edit: 2018-01-05, 20:45:08 by Kator01 »
   
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Johan passed this Bit along for your peruse
   

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Quote from: kator
From theses years of practical experience I can tell you that you are bound to get into problems the way you casted the wax into the mold. You need to provide different air-channels for the air to esxcape because the air must leave fast ( in addition : its expanding rapidly as it is heated up ) otherwise you will have bubbles of any size trapped in the wax which spoils the end-product.In the above thread the technique does not use a closed mold.
And by the way pay attention to the paragraph "Testing electrets" : after the electret is cooled down and finished you need to attach an aluminium-foil on one side and fold it and attach it to the other side ( close contact ) in order to close the field-lines and thus strengthen the electret - as you would do with a permanent magnet ( attaching a iron bar across the two poles of a horseshoe-magnet)
So therefore it makes sense to use aluminium-foil in the mold to cast the wax on right during the manufacture process so that it sticks to the wax right from the beginning.

This. ^


Also a longer cooling phase may be helpful. Casting oversize and then machining down to exact size/shape also.


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