Contact Electrification
Contact Electrification and Static Electricity
Contact electrification is the process where two dissimilar materials are touched together, and then separated, causing charged particles (electrons) to be released as bonds are broken between molecules of the two materials. A simple example of this is rubbing a balloon on your clothes so that the balloon becomes charged and is able to attract small particles or stick to walls.
Thetriboelectric seriesis used to show how well some common materials will absorb, or give up the 'free' electrons within them, and therefore becoming negatively or positively charged respectively. The table below shows how some materials become charged relative to each other, from most positive to most negative. The ability of the material to hold this charge is mainly dependent on the humidity of the surrounding air and the smoothness of the material. For example; a balloon will hold it charge for much longer than some fur because the individual points (the hairs) of the fur will cause corona discharge.
The Triboelectric Series
|
Material
|
||
|
+ Most Positive +
|
Dry Human Skin
|
+ Most Positive +
|
|
Leather
|
||
|
Rabbit Fur
|
||
|
Glass
|
||
|
Human Hair
|
||
|
Nylon
|
||
|
Wool
|
||
|
Lead
|
||
|
Cat Fur
|
||
|
Silk
|
||
|
Aluminium
|
||
|
Paper
|
||
|
Cotton
|
||
|
Steel
|
||
|
Wood
|
||
|
Amber
|
||
|
Hard Rubber
|
||
|
Nickel/Copper
|
||
|
Brass/Silver
|
||
|
Gold/Platinum
|
||
|
Polyester
|
||
|
Styrene (Styrofoam)
|
||
|
Saran Wrap
|
||
|
Polyurethane
|
||
|
Polyethylene
|
||
|
Polypropylene
|
||
|
Vinyl (PVC)
|
||
|
Silicon
|
||
|
- Most Negative -
|
Teflon
|
- Most Negative -
|
There are a number of devices that utilize contact electrification. A popular device is the Van De Graff Generator as it is very simple to construct. This device will produce very high voltage electricity at very low current. This means that they can be safe to touch, although it may make your hair stand on end! It works by using two rollers and a belt made from dissimilar materials. As the belt rotates, charge separation will continually occur at the point where the belt moves away from each roller. If a metal brush is placed near to these points then the charge can be collected or deposited. The choice of belt and roller materials will determine the polarity of the voltage produced
If a sharp point (a pin) is placed on the output of a Van De Graff generator, voltage multiplier, or other High voltage DC supply, it is easily possible to witness an interesting effect. This effect is often referred to as 'thread like streams of charged air' Logic might suggest the ion wind should spew out in all directions (because the like charges repel each other) from the tip of the pin towards objects of opposite charge. Under the right conditions the ion wind will come out as a fine thread from the tip of the pin. This seems to contradict the idea that these charged air molecules should repel each other.
High voltage electric fields seem to be the key to unlocking some of the deepest mysteries of the universe. There are may reports of anomalies when experimenting with high voltages. For more information on the weird science, see theunexplainedsection.
The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
- first i want to make a high voltage switch (about 20-30kv) without time delay or much time-energy consumption of the pulse discharged
- i have read the subject about the ignition coil driver i find it money consuming compared with a capacitor - SCR pulsator connected ot the primary - the question is how to connect them (the cap.& scr)
please please if u can't answer me here forward it to "thechaosdrone@yahoo.com"
please
If you want to switch 20-30kV with a silicon device like an SCR, you will find that this can be quite expensive. This is why a spark gap is used in most Tesla Coils.
i wanted to ask some questions about the spark gap (we talked about formerly)
just some trivial ideas wanna know if they could work or not
could applying a steady capacitive dc field from an external cicuit to the spark gap decrease its resitivity for the HV impulse
how could i calculate the spark gap resistivity
what about presetting of a very isolating material(ensures close distance) going continuous with a metal or so and moved perpindicularly very quickly in the field
instead of the air and the metallic ball offered in this side, it could be a rectangulare piece of plastic continuous with a very good conductor
very thankful for u after all
You can't really do a lot change the resistance of the spark gap because it is just a product of the voltage, spacing, and air/gas mix. You could possibly change the gas to Argon for example, but this has lower ionization voltage so the switching would be less abrupt. Another way would be to reduce the pressure inside the gap.
I don't know how you might calculate the resistance, but it will be a dynamic (changing) value. When the arc is fully formed, the resistance will be very low.
Are you describing some sort of rotary spark gap here? Insulating the spark gap electrodes will reduce leakage and allow you to trigger the spark manually (when you remove the insulation) rather than when the breakdown voltage of the air gap is reached.
One method of improving spark gap performance is to use magnetic quenching. This is where strong magnets are placed either side of the gap so the magnetic field crosses at 90 degrees to the electric field. With this setup, the arc will be pushed outward as soon as it forms. This is because when the current begins to flow it creates a magnetic field which will react against the field from the magnets. This has the effect of switching off your spark gap very quickly.
i have concluded that in the first place it does need very fast mechanical displacement wether using a magnet or my damn design , it is how fast the opposithion will decay to let the current grow , so we must start thinkin in the light of this ( iam waiting ur ideas )
i wanted to show u this image
it would be massive for ur plasma globe u formerly offered on the site the capacitor's impedance should be about 3000 ohms
but my problem in this design that where i live the dimmer switch is very expensive and am askin u for an alternative that i can make or cheap to buy ( cuz i donno how does the dimmer really work) i just know it is a sorta variable "power"inputter or so .
the whole thing about the spark gap is that a making a super capacitor and i want it to discharge so fast in nano seconds for a very powerful metal propeller .... so far i have chosen PET for the design dielectric cuz its (C*breakdown voltage) is very high about 22000 , if u can recommend me a better one please do
r u only one engineer who answer all the forums or wat cuz if u r so u must be a genius
waitin ur response
The rate at which you will be able to discharge your capacitor will mainly be determined by the inductive reactance of your system. You will need to keep wires as short, wide and straight as possible. The same for the capacitor. Use large conductors with as few bends as possible.
Most questions are answered by me but some are answered by other scientists if they can provde a better answer.
i have read an article about high voltage discarging and there were mentioned about the high voltage switch that "magnetrons" ,"klystrons" & "vircators" can be used
r those things applicable for me and how can i get make or use them (and how does they work in the first place)
about the commercial dimmer shown previously in the image -could it be used with dc input or it just works with ac
also i would be very thankful if u could give me a link or so to a site where i can fine about the breakdown voltages of substance (for the capacitpr ofcourse)
really appreciate u
A dimmer will work with an ac input. You would need a pulse width modulator for DC.
Google will adequatley answer your last question. Use "breakdown voltages of dielectrics". There's plenty of useful data there.
am now searching as u asked for but i found some interesting results as avalanche diodes (can hold up to 4kV) (could many of it be connected in series and operated "on" by an external cap of about 1kV in series) and avalanche-photodiodes wat about them ?also wat about zener breakdown ?
or could i directly force the main cap to arc by the same way and after the first arc there wouldn't be enuf energy for arcing back in the LC and it would continue to resonate
but i didn't find much about VBreakdown tables
However,can't the ignition coil be driven by resonance as does the TV flyback by winding a 2nd primary to the transistor's base-emitter circuit coil from around its exterior.(operating on a DC)
recently have fixed and modified a puffed up PC powersupply and turned it into a lab PS
it's terminals go as follows: 5V/8A , -5V/8A , 12V/20A & -12V/30A
could the 2N3055 power-transistor be powered upon these terminals & their combinations or it would just get burned(can their be Rs to prevent so) ,(would be marvellous if u have its fact sheet)
really without a bit of hipocracy ,i swear am very thankful to a massive extent ,really can't describe it
u'r just sophisticated
peace again ... by the way wat can i call u
It is possible to wrap a few turns of wire around the case of an ignition coil to be used as feedback for a flyback driver.
the 2n3055 is rated for a maximum of 15A.
can i half-wave rectify high AC voltage simply with a series of 1N4007
by the condition that every single diode adds a back-blockage of 1000 volts and all of them can pass a current less than 0.7 Amp
when measuring the outputs of the dimmer's circuit can i simply calculate it or i only have got to use a current divider and a voltage divider and a simple multimeter
about the hi voltage switch i talked about before it is a continuous cuboidal shape consisting of two equal cubes of a bad conductor and a good conductor fused together and it is moved swiftly between the high voltage electrodes.hope u can imagine it.
if it's beginning to be hard to bear u just can say it cuz am feeling so ...
Measuring the output would be more accurate ad easier.
Can you draw a diagram of your HV switch?
i have uploaded it on the following link "http://img263.imageshack.us/img263/1273/sparkyx0.jpg" as i think it will fail again in being forwarded.
the idea is to move swiftly and very rapidly the intermediate part up/down for switching , but am still thinkin about such an efficient way of movement ,Almst the same idea of obstacling by a magnet and movin it as u formerly recommended
just forgot to ask another question :
when charging the HV Cap. by the talked about diodes series how can i know when exactly is the cap voltage is equal to the source voltage (i.e:the cap is full or almost full)
can i attach a LED in sorta way or there is someother way
sorry again about the 2Mohms resistors wat is their wattage.
The current flowing from your charging supply will drop to near zero when the capacitor is charged. You could use an ammeter to indicate this.
The 2M resistors only need a low wattage rating because they are just being used to distribute the voltage and not much power. The typical 1/4 watt ones would be fine.
i have a question:
How is it possible to make a permanent magnet vibrate, i've read that a pieso-something can work, i'm trying to replicate a certain experiment of faraday i think,
thanks in advance
keep up the imaginations raving
as the high voltage switch and if i can please recommend me a particular one
if am making a voltage divider for high voltage source , wat should be the wattage of the resistances
in the dimmer circuit shown above from where should i get the ground for the high voltage output,i think of using the water tab cuz ofcourse it is AC which is going on the 2 primary coil terminals so i can use neither of them, can i ?
and thanks much
You can caluclate the watage of your resistors using Ohms/Watts law. Using the square of the voltage across each resistor divided by its resistance will give you the minimum power rating needed.
The opposite side of the secondry winding of an ignition coil is internally connected to the -ve input termainal. You can take your HV output from between this and the output terminal.
am running an electrolyte and i have to pass only a certain voltage through it ,i have tried to make a voltage divider but the pot. got burnt cuz of the high power ,and high power pot.s are expensive here , could i connect in series a low current pot with a high wattage (about 10 ohms) common resistance to dec the power load on the variable resistance or wat should i do ?
very thankful
Most voltage regulators are set to a specific voltage, but you can also get adjustable ones where you could use your low power pot to adjust its output.
wat intervals of power does it operate on ?
thanks
Google 'adjustable voltage regulator' for some examples.
This L200 regulator may work for you. The datasheet also includes example schematics.
If you want to maintain a constant rate of reaction then it is actually the current you will need to regulate. Devices for this are often called 'constant current diode'
this reaction is at a voltage range of 1-1.2volts
and never mind of the intensity
as long as it's constant, the power may range from 250-12.5w according to the power supply am using,according to the latter info can u help me in any specifications of the regulator used.
really appriciating ur help wether u can find this one or not
I simply can not continue to provide help for free for your own personal projects. I can design whatever electronic systems you desire, but you must pay for the time and resources. See the Custom Electronics page for details.
would be finer if with drawing
Dielectrics also have a very small level of conductivity so any induced voltage would leak away eventually.
Man made electrets are often formed by setting a liquid compound in the presence of a high electric field. This way the molecules align to the field and set into position when it hardens.
Thanks!
--Der Strom
Thanks again!
--Der Strom--
Also, the speed does not need to be fast. If it is melting, that probably indicates that the motor is running too fast.
We know that if a rubber balloon is rubbed with rabbit fur, the balloon becomes negatively charged. Therefore, the rubber must have gained electrons from the fur. The problem is, however, that according to the triboelectric series, rabbit fur is positively charged. If it's positive, then why would it lose electrons to the rubber?
Thanks for your help!
Der Strom
Any of the materials can be made to be positive or negatively charged. It just depends if the other contact material is above or below it in the series.
Thanks again!
Der Strom
Thank you very much for help.
The metal pin is ok as you can link it electrically to earth. Make sure your motor casing is also earthed.
4mm belt thickness is probably going to significantly impair the efficiency of your system. You might want to consider something different.
So what is a good belt material?
I have had trouble with this part for a long time and havn't really found any satisfactory answers.
What are a couple of options for rubber material, and what is the best rubber for a VDG belt? Also about how thick should it be? Thank you very much, Jason
VDG Belts