### Author Topic: How to build a capacitater  (Read 1923 times)

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#### Connecteur

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##### How to build a capacitater
« on: September 12, 2020, 05:07:56 pm »
Take a potato, cut it in half, move the two halves close together, apply a voltage differential, and presto,
you have a capacitater.

#### bob91343

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##### Re: How to build a capacitater
« Reply #1 on: September 12, 2020, 06:50:38 pm »

#### brucehoult

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##### Re: How to build a capacitater
« Reply #2 on: September 12, 2020, 10:31:37 pm »
It's real easy. Take two conductive objects and put them close together. The capacitance is equal to (or at least proportional to) the area of the objects divided by the distance between them. The more area the more capacitance. The closer together the more capacitance. But not so close that a spark can jump between them at the voltage you will use!

For a home made capacitor, try two sheets of aluminium foil with cling wrap between them. Roll it up tight, both to make it more conveniently small, and to make the gap as small as possible. (you'll need two sheets of cling wrap of course)

#### greenpossum

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##### Re: How to build a capacitater
« Reply #3 on: September 12, 2020, 10:47:34 pm »
As a bonus, if you put a high voltage across it and some one touches it, you have an incapacitater.

#### Monkeh

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##### Re: How to build a capacitater
« Reply #4 on: September 13, 2020, 12:18:33 am »
If you're going to steal a joke, you could at least source it:

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#### brucehoult

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##### Re: How to build a capacitater
« Reply #5 on: September 13, 2020, 01:48:04 am »
That video and the comment here were posted within an hour or two of each other!

#### Monkeh

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##### Re: How to build a capacitater
« Reply #6 on: September 13, 2020, 01:52:52 am »
That video and the comment here were posted within an hour or two of each other!

It went public at least an hour before the comment - and was shot at least a day before.

#### Bud

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##### Re: How to build a capacitater
« Reply #7 on: September 13, 2020, 03:28:12 am »
Do not know about "capacitaters" but Canadian government is imposing a tariff on american "capacitators".

#### Connecteur

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##### Re: How to build a capacitater
« Reply #8 on: September 13, 2020, 02:59:48 pm »
TIL: Jokes need citations.
Never heard of that before.

#### SmokedComponent

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##### Re: How to build a capacitater
« Reply #9 on: September 14, 2020, 03:16:39 pm »
Potato Semiconductor internal joke?

#### Fungus

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##### Re: How to build a capacitater
« Reply #10 on: November 01, 2020, 06:16:27 pm »
It's real easy. Take two conductive objects and put them close together. The capacitance is equal to (or at least proportional to) the area of the objects divided by the distance between them. The more area the more capacitance. The closer together the more capacitance. But not so close that a spark can jump between them at the voltage you will use!

For a home made capacitor, try two sheets of aluminium foil with cling wrap between them. Roll it up tight, both to make it more conveniently small, and to make the gap as small as possible. (you'll need two sheets of cling wrap of course)

Whoosh!

#### Connecteur

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##### Re: How to build a capacitater
« Reply #11 on: November 01, 2020, 07:39:15 pm »
It's real easy. Take two conductive objects and put them close together. The capacitance is equal to (or at least proportional to) the area of the objects divided by the distance between them. The more area the more capacitance. The closer together the more capacitance. But not so close that a spark can jump between them at the voltage you will use!

For a home made capacitor, try two sheets of aluminium foil with cling wrap between them. Roll it up tight, both to make it more conveniently small, and to make the gap as small as possible. (you'll need two sheets of cling wrap of course)

Whoosh!
Exactly.

#### Syntax Error

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##### Re: How to build a capacitater
« Reply #12 on: December 03, 2020, 10:12:53 pm »
This is how the guys at Marconi built a capacitor or condenser for their transatlantic transmitters, over 110 years ago.

Take a sheet of steel or copper measuring some 60 x 20 feet, and suspend it together with at least 200 other sheets from the roof, separating each sheet with an air gap of 6 inches to create a diaelectric. And then house all of these sheets in a very large building, so the whole building becomes the capacitor!

I have NO idea of how to even guess at how many Farads these condenser-buildings were or, how many watt-seconds they could dump into a spark gap? But this was pioneering electronic engineering on an industrial scale.

A picture here of the condenser plates at Cape Breton Island Novascotia: http://www.newscotland1398.net/marconi100/marpic10.html

Of course if your budget, and planning codes are limited, you could always go and build a Leyden Jar and try go catching lightning in a bottle. https://en.wikipedia.org/wiki/Leyden_jar

For anyone interested in discovering more about Guglielmo Marconi himself, the UK History of Science Museum has some interesting online resources here: https://hsm.ox.ac.uk/marconi-day-0

#### Ian.M

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##### Re: How to build a capacitater
« Reply #13 on: December 04, 2020, 12:48:48 am »
I have NO idea of how to even guess at how many Farads these condenser-buildings were or, how many watt-seconds they could dump into a spark gap?
Total capacitance is easy: If you put your numbers for plate area and separation into this calculator (which accepts US units),
http://www.calctool.org/CALC/eng/electronics/parallel_plate
and 1  for the dielectric constant of air (strictly 1.00059 at STP), you get 6.477nF per plate pair.  There were 288 plates at Cape Breton, so 287 6" gaps between pairs of plates (its a fencepost problem), so multiply by that and you get 1.86uF.

Energy stored is fractionally harder - you'd have to know the working voltage, then apply E = (1/2) C V2. Of course, that's stored energy and is likely to be be significantly greater than the discharge energy in the spark gap due to circuit losses.
To calculate that you'd need a good model for the spark gap and the rate the capacitor discharges into the gap.

Rate of discharge is incredibly more difficult - you'd have to have details of where the connections were and the external circuit sufficient to give you decent figures for the circuit inductance and resistance (including dynamic resistance of the gap) , and also treat the pairs of plates as transmission lines.  Without those circuit details all you can do is set an upper bound for it based on most favorable conditions i.e. zero plate resistance and discharge into matched resistance via external circuit of negligible length connected at the center of one long side of the plates, but even so, the calculation is going to be a stone bitch, best solved by modelling by Finite Element Analysis on a supercomputer.

Edit: Aagh! I forgot the parallel plate capacitance calculator link.
« Last Edit: December 05, 2020, 04:06:10 pm by Ian.M »

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#### Syntax Error

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##### Re: How to build a capacitater
« Reply #14 on: December 05, 2020, 03:47:46 pm »
What a remarkably tiny capacitance for such a vast component! Although I suspect the working voltage was somewhere in the megavolts range?

"Grandson, I remember a time when an electrolytic capacitor was the size of a warehouse. Now you can hold dozens of them in your hand."

#### Fungus

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##### Re: How to build a capacitater
« Reply #15 on: December 05, 2020, 06:31:40 pm »
What a remarkably tiny capacitance for such a vast component! Although I suspect the working voltage was somewhere in the megavolts range?

A 6 inch air gap between plates would limit it to about 450kV in dry air.

It was probably a lot less than that for safety.

http://www.kronjaeger.com/hv/hv/msr/spk/
« Last Edit: December 05, 2020, 06:35:26 pm by Fungus »

Smf