Giving an object charge using electronics

[Resistanceisfutile]

Hi,
I'm looking to give a metal object a charge (or a lack of).
I know capacitors can store charge - is there anyway you can use this to give an object a positive or negative charge?
Thanks

 

[BradtheRad]

You can give a single object a charge, by touching it to another object which has a charge on it. Electrons flow from one to the other, until they have equal charge.

Example, by connecting it to one terminal of a DC supply, then disconnecting it. Or to one terminal of a capacitor, then disconnecting it.

You can also pick up a high-voltage charge by scuffing your shoes on a rug. It works to different degrees, depending on the humidity, or what the rug is made of, or your shoes. Then by touching a metal object you can transfer a charge to it. Often a spark flies before you touch it.

 

[D.A.(Tony)Stewart]

All insulators are dielectrics . period. i.e. capacitors.

All conductors freely allow electrons to move. To charge up a conductor, you are effectively are charging up the surface insulation contacting the conductor, be a a thin coating like paint or dust particles in air.

Like the moon, the rocks are conductive but the surface is coated with a statically charged dust particles which are crystaline insulator dust particles.

High Voltage generators >100kV use an insulative friction belt to transfer electrons from the rotating conductor.
see https://en.wikipedia.org/wiki/Van_de_Graaff_generator

For impulse testing of transformers, bushings and power line equipment from 50kV to 2.5MV they use big Van deGraff generators to charge up a capacitor. They send the HV ( 50 to 150kV) to structure that resembles scaffolding. THis is called a MARX generator using capacitors with air gaps and they charge all the caps in parallel and with a trigger conduct an arc which puts all the caps in series for a nanosecond to charge a donut conductor ( which gives the best shape to be insulated with low leakage) and then string a thin wire to the device under test (DUT).

Using calibrated power resistors the size of shock absorbers to charge up rack mounted plastic capacitors, this is how they can generate high current high voltage impulses to simulate global standards for indirect withstanding lightning pulses. The RC ratios determine the rise time to crest and decay time or "tail time".

The total number of layers is a multiplier of voltage from the friction based enclosed HVDC generator.

Below is the equivalent circuit of the above equipment.


The basic insulation level (BIL) voltage rating for this insulation test determines the test it must withstand without arcing which is monitored by magnetic current transformers to ground.

By transferring charges from say a spark plug generator coil to a well insulated conductor, you can charge up the conductor in a zap. But without good "bushings" this will decay to zero. If you apply HVDC to a conductor, the paint or PVC becomes charged and will discharge readily if you brush your hand over the insulation, you will feel the static discharges. Mica tape then Rubber is a common insulator for wire, but inside transformer tanks they will use enamel magnet wire wrapped in "kraft" paper immersed in very pure oil. Dry types will use Mica tape wrapped in layers.

I've done this type of HV testing on transformers with HVDC, impulse and HVAC. HVDC is the most interesting as the paint on the outer steel tank is electrified. An AM radio picks up the discharge like distant lightning. Steel grid fences become electrified and wall mountings a hundred feet away (!) get electrified and if a sufficient small gap to ground will arc a small current every few seconds or minutes. tick tick..... This effective reach of a HVDC electric field much more.

You can get the same effect by putting XMAS tinsel or metallized plastic spagetti like strips on an old TV Tube and get the metallized plastic electrified with static from the outside with over 25kV.

The other conventional way to generate high voltage is to use rectified AC from a step up transformer then use diode/cap doublers also called Cockroft-Walton/Villard cascade multiplier. In the MArx generator the air gap triggered by a spark is the diode.

 

[jiripolivka]

Any insulated object in space can be charged, usually by mechanically touching it by another object with a known charge.

In the real world, we refer the charges to a common ground, then the measurable quantity becomes voltage of an object referred to ground.

The charge as a quantity can be considered as a number of electrons (or a lack of such number), and by a consent, electrons have a negative charge.

Objects like capacitors can accumulate certain charges, then the voltage across their terminals is proportional to the charge and capacitance.

Extreme charges can develop very high voltages as illustrated above. Well insulated objects can hold charges at voltages measured in kV. Your body can hold a charge by rubbing your shoes or clothing on a rug or a seat, then the discharge you can feel as a spark, usually to ground.

Detecting small charges can be done with neon lamps or FET voltmeters. People are stunned to see that they carry kilovolt charges on their body. Discharges can damage sensitive electronic circuits. The ESD is a scietific discipline treating such threats.