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Join Date: Aug 2006
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Positive Charging

09/25/2007 9:47 AM

Just a quick question to you chaps.

When we "charge" something, we normally consider negatively charging (adding electrons). Is there a method to remove a lot of electrons from a body relatively quickly, to make it positively charged? I'm thinking on the scale of 10 - 20 coulombs.

Would having the body at effectively one edge of a capacitor (the other side being a she-ite load of capacitors) with a PD across the system work?

Is it even possible?

I've never done any electrical engineering in my life so excuse my bone question if the answer is obvious.

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Associate

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#1

Re: Positive Charging

09/25/2007 10:23 AM

yes you can do it just shorting the both poes using a resistance of some 100 Kohms

but u have to suggest how much time it will take to remove the electrons according to ur requirement

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#3
In reply to #1

Re: Positive Charging

09/25/2007 11:01 AM

Golly gosh, that was a quick response!

I was thinking in less than 10 secs. I thought that if a negative charge builds up on one plate of a capacitor, then the electrons are "sucked" from the other side of the circuit.

Any other sneaky methods used in the industry?

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#2

Re: Positive Charging

09/25/2007 10:55 AM

How about a Pelletron?

Or a maybe a modified Van de Graaff Generator, constructed with a plastic belt and a rubber roller (instead of a plastic roller and rubber belt).

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#8
In reply to #2

Re: Positive Charging

09/26/2007 12:00 PM

I like it. If someone tries it, let me know if it works.

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#4

Re: Positive Charging

09/25/2007 11:38 AM

I'm not sure what you're asking - whether you want to separate charges (a high voltage power supply and a big capacitor) or accumulate charge ( a big honking Van der Graaf) - but at 10 Coulombs, you're likely working with a dangerous amount of energy if you aren't familiar with electricity. I can attest that is enough to blow a Simpson multimeter into very small pieces (thank God the meter belonged to someone else).

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#5
In reply to #4

Re: Positive Charging

09/25/2007 12:15 PM

I understand how much charge this is: this is only a thought exercise! (Hence why its in the general section)

I want to separate charges, i.e. taking the charge out of a body (say, block of metal) and deposit it in the capacitor, thereby making the block of metal positively charged (as long as the supply stays on)

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Associate

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#6
In reply to #5

Re: Positive Charging

09/25/2007 12:31 PM

U mean you want to saparate both the poles

is it right

??

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#7

Re: Positive Charging

09/25/2007 7:02 PM

Having the body at effectively one edge of a capacitor (with the body itself presumably acting as the other plate of a capacitor?) would tend to pull charge to one side of the body, presuming the other plate was also charged and of the opposite sign. This arrangement will not remove charge from the body. It only separates the charges already there (approx 13,600 Coulombs of charge per cubic centimeter of copper). However, the net charge on the body remains the same.

The Van de Graaff machine mentioned earlier can be made to add electrons to an insulated conductor (a metallic sphere being the safest configuration), leaving a net negative charge, or to remove them, leaving a net positive charge. What limits the amount of charge the conductor can hold in practice includes humidity, radius of the sphere (too much charge and the sphere will literally be torn apart by electrostatic repulsion), smoothness of the sphere, and so forth.

10 - 20 Coulombs is an enormous amount amount of charge and with its own hazards. For example, say we had two very small spheres, each holding a charge of one Coulomb. If the spheres are separated by a distance of one meter, the net repulsive force between the two spheres would exceed one million tons!

You sure you wish to proceed?

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#11
In reply to #7

Re: Positive Charging

09/28/2007 9:56 AM

Hello Europium - your comment about force between charges, a couple of things.

1. Interesting that 1 Coulomb in this context produces a huge force, but in electrolysis it only liberates ~ 10-5 gm hydrogen (or 8.10-5 gm oxygen etc). I mentioned this in a thread a year or so back but nobody commented.

2. If we have a capacitor of 1 μF charged to 100 volt, charge is 10-4 coulomb. Taking a generous dielectric constant 10, and plate spacing 1mm, I make area reqd ~ 11m2 and volume 11 litre (0.38 ft3). This is obviously bigger than a regular 1 μF capacitor, but it gives an attractive force between the plates 110 MN (11000 ton) and stress 10 MPa (1450 psi) which is probably OK for dielectric material.

If the plate spacing is 0.1mm, area becomes ~ 1.1m2 and volume 0.11 litre (6.7in3) - the right sort of size. 10000 volt/cm OK for dielectric strength. But attractive force between the plates is 11000 MN (1100000 ton) and stress 10000 MPa (1450000 psi) which seems very high even for direct compression, and I'd not have thought there was that sort of stress in a capacitor. It's not quite as bad for a multi-layer capacitor, but acc to my calcs it doesn't make a big difference.

Can you (or anybody) see anything wrong with above?

Cheers........Codey

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#12
In reply to #7

Re: Positive Charging

10/09/2007 3:42 AM

I was thinking of splitting the body in two once the charges are seperated.

And this is only a thought exercise! If I tried to build a device that did this, i'm sure that health and safety would swoop on me like a flock of pidgeons to a statue!

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Guru

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#9

Re: Positive Charging

09/26/2007 3:40 PM

Now what is "she-ite load" of capacitors

10 -20 coulombs.......!

is it something to do with super capacitors ?

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Power-User

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#10

Re: Positive Charging

09/26/2007 4:13 PM

The problem is that electric charges having the same sign are repelling each other and you need to find a way to keep them together in order to accumulate such a significant quantity of electricity without falling apart.

There are free charges and bond charges. Through electrical polarization a body can get volumetric charge or surface charge.

An interesting way to separate and "freeze" electric charges in solids is to build an electret which is the electrical counterpart of a permanent magnet. A substance having polar molecules , if exposed to an intense exterior DC electric field while is melted and then cooled, can become a so-called thermo- electret. Most of such substances are ferroelectric materials (usually ceramics). There are also other types like photo-electrets to which polarization is induced by light.

These having being said, I suggest to reformulate your question or channel your interest in one practical direction.

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