2nF Capacitor Design

Why????

Is it for a science project or school demonstration or a special high volatge appliction? ...why 2nF???

Try this...

Make a pile of long thin strips paper, foil, paper, foil, with a termiation to the two foils.

Roll it up...(But don't try to smoke it...[joke])

Secure it with thread, hotmelt glue, whatever...bish bash bosh...done.

No idea what the C will be...trial and error. Polythene would also do as a dielectric.

school project..

Make a pile of long thin strips paper, foil, paper, foil, with a termiation to the two foils.

do i pile this each on top of the bottom one?

Blimey!

Is there any other way to make a pile????

(Unless you place the first one on the ceiling and build the pile downwards?)

One on top the other in the order I specified.....!

The point being the two Ali' layers must not touch at any point, so make your paper strips a bit longer and wider. (I hope you have a DVM which measures C this will help to check it works)

If you can find copper foil it is easier to connect to with solder, connecting to Ali' foil reliably (e.g. school kid proof) may be difficult!

Have fun (excuse my catly sarcasm!)

Del

Here is a link to a web page with the formula to work out capacitance from the geometry of the plates. Bear in mind that the answer is in pF so you need your answer to come out at 2000 when you plug your numbers in. You will also have to find the relative dielectric coefficient of paper or whatever you use between your plates but I ain't doing the whole project for you. Im sure a google search will produce the goods.

Al

http://www.phptr.com/articles/article.asp?p=169477&seqNum=6&rl=1

Forget paper, unless its a must.... use cling film as its so thin you won't need much area to make 2000 pF capacitor, I would guess at about 6" x 2".

I know that with 60 micron spacing 500 mm^2 (about 1" square) gives 200 pF using mica as the dielectric u=3 to 8, air u = 1.

Where's the greek alphabet on 'ere?

John. - ζ Oooo that's a nice one! ξ δ Hey there's lots of them... why haven't I noticed them before??!!

I agree with the cling film reasoning but the original post stated paper so i didn't want to assume it wasn't important

Al

sorry but wat is cling film?

Hi 5.1.Rocks,

Why would you want to build a capacitor?

The construction technics will change drastically upon application. So, without an idea of why and the where, no one can give the CORRECT answer.

Wangito

If you had actually read this thread properly you would know that entry #2 states that it is for a school project

Al

UPPPPS... skipped it.

Wangito.

well. actually its for a school project..

The construction technics will change drastically upon application.

that's means i cant measure it with any instrument?then how am i to know if i get 2nF?

Hi maydayrocks,

First an apology, I should have seen post#2 where it clearly says School project.

Secondly because of not seeing that, the remark about constructions technics. In your case is out of place. and now to work;

1. The instrument that measures capacitance is called a capacity meter, and we will assume that you don't have one. We will have to engineer the capacitor: this is the formula you have to use: C=KA/t Where -C- is the capacity in Farads, -K- is a dielectric constant,-A- is the area of the plates, and t is the dialectic thickness.
2. Practical way to do this is to buy a two types of packaging tapes one is the clear adhesive tape, that will have a K close to Mylar® and another one will be a duct aluminium tape that will have a K of, you guessed it, Aluminium.
3. The tapes would have a 2" (5cm approx) width. and the thickness is stated on the tape itself. The thickness of the duct tape can be neglected for the moment. Now calculate the length of the tapes required based on the above formula, cut it to length, assemble the duct tape , over the clear tape, another duct layer, and another clear tape on top. Now start rolling them tight, you can use a pencil as a mandrel to give it a better mechanical strength. Make sure the two duct tapes, "The Capacitor Plates" are completely isolated from one another!!! Once done with the rolling, Leave both duct tape ends free, these will be your capacitor leads.

Don't forget , nF= is 1x10-⁹ Farad.!

K, The dielectric constant, You will have to google it for Al and Mylar-

t ,Thickness according to manufacturer specs.

Wangito

but i need to use paper.... where do i put it in this project?

You make a "sandwich" consisting of a layer of aluminum foil (which becomes one electrode of the capacitor), a layer of paper (the dielectric), and the other layer of foil (which becomes the other electrode of the capacitor). The paper must be physically larger that the foil to prevent any foil-to-foil contact from shorting out your capacitor. The amount of capacitance you obtain is proportional to the area of the foil plates - twice the area means twice the capacitance. The capacitance also scales inversely with the thickness of the paper - the thicker the paper, the lower the capacitance.

You can estimate the capacitance one you know the relative dielectric constant (k) of the paper (use about 3), the paper's thickness, and the area of one of the foil plates. The formula for determining capacitance (as well as a convenient calculator where you can plug in the parameters for YOUR capacitor) can be found here:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/pplate.html

Bert

thanks for the info, its really very detail..

really helps me understand..

thanks!!

Do let us know how you get on...maybe a pic. Else we'll all end up building our own!

Del.

I did make one yesterday after reading this thread, just for a bit of fun.....

Am I sad or what.... John

What were the results? What capacitance did you get out of it? Have you got a piccy? What did you use for dielectric?

Al

how is it?

did u manage to get the wanted value? can i have some pics? thanks^^

Make a Capacitor?

Me? - 'ow ?

You'll have better luck just twisting two insulated wires together. It's called a gimmix capacitor.

Here's a link: http://web.telia.com/~u85920178/begin/gimmik-0.htm

I've never heard it called that.... back in my youth we used twisted wires to make small and quite accurate capacitors for tuning.

Even recently, last month, I used one in a calibration capacitor where I needed just ½ pF to bring a 10000pF capacitance into calibration, just twist and snip!!

John.

Making a small paper capacitor is easy and fun if you're only going to use it with low voltages. The following site provides the capacitance for a single pair of aluminum foil plates and dielectric sheet.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/pplate.html

When you add more sets of sheets, you simply add the capacitances of each set. connect every other layer of foil together to form the a pair of output leads for the stack. You can use a "k" (relative dielectric constant) of about 3 for white paper in the above equation. Multiply the above result by the number of sheets of paper that you use to get total capacitance. You'll need to press the sheets together very tightly to eliminate as much air between the foil and the paper, and you'll probably find that you need more sheets than you calculate to get 2 nF because of trapped air. Use the construction technique similar to that shown schematically in the following site for connecting the plates:

http://www.cartage.org.lb/en/themes/Sciences/Physics/Electromagnetism/Electrostatics/Capacitors/Capacitors/Combination/ExampleMulti/ExampleMulti.htm

Good luck and have fun!

Bert

Just get one polyester/polyestreen capacitor 10nF or near about.

Open it carefully to get the aluminum foil and insulator,

This will give you a good insight of how it is made,

Unroll the aluminum foil and insulator carefully.

Measure its length. Workout how much length for 2nF is. Assemble in reverse to when you opened it.

You may need to try. You will get ultimately

Wish you best of luck

Nice way to measure is with a dc supply, big resistor, switch (that doesnt bounce too much) and a scope.

Just watch the rise time on the scope...kids will really see what it does.

Also as I said in previous post many DVMs (DMM...whatever you know what I mean! have a capacitance range..so if you are buying one look out for this feature!

Please refer to a new link.

May be more information for you.

http://cr4.globalspec.com/thread/23078/How-to-make-a-2nF-capacitor