dvd's and cd's as capacitor plates

[hereticalhermit]

Looking to find if anyone has ever tried this? I have found only a couple of references on the web, and they were for variable capacitors of very low capacity, or using methods to join the wires to the discs that I don't believe are workable (soldering? WTF?). Here's what my thought is: these discs are abundant, and could be hopefully used to build an offgrid storage system where there is no limitation upon space. Many people want to build "high voltage" systems when making their own capacitors, but this setup wouldn't need to go over perhaps 100 volts or even less (most offgrid systems run on 12-48 volts). My thought is that if a hole were drilled in a disc and a rivet put into it to make connection with the aluminum in the polycarbonate, as well as slots being cut into the disc to accommodate the rivet/wire from the discs on either side of it, then they could be stacked normally on a spindle and hopefully get enough of them together to be able to form something that could replace batteries as a form of energy storage. Yes, I realize that it might take something the size of a car or bigger to replace one deep cycle battery, but as I said previously, I have all of the space needed available to me to do this. Does anyone care to try this with a few discs and see what kind of results they get? Thanks!

 

[Harald Kapp]

Does anyone care to try this with a few discs and see what kind of results they get?

Why don't you try it for yourself?

The CDs being rather thick will make the not very suitable for capacitors since capacitance is inversely proportional to the distance between the plates. You may achieve much higher capacitances by alternating layers of household aluminum foil and cling wrap.

this setup wouldn't need to go over perhaps 100 volts or even less (most offgrid systems run on 12-48 volts).

48 V or less can be considered relatively safe. Anything above requires you to observe safety measures. On the other hand the lower the voltage the lower the energy stored since E = 1/2 × C × V² (note that voltage contributes squared).

to replace one deep cycle battery,

Capacitors don't replace batteries. They may be used to support batteries to deliver short pulses of current.

• A battery is designed to provide a more or less constant voltage during operation. This voltage will drop significantly only when the battery is drained of most of the energy stored within.
• A capacitor's voltage will drop continuously while current is drained. So any load or attached regulator will have to deal with a constantly changing input voltage. Not impossible but more complex than using a battery.

 

[hereticalhermit]

Why don't you try it for yourself?

The CDs being rather thick will make the not very suitable for capacitors since capacitance is inversely proportional to the distance between the plates. You may achieve much higher capacitances by alternating layers of household aluminum foil and cling wrap.


48 V or less can be considered relatively safe. Anything above requires you to observe safety measures. On the other hand the lower the voltage the lower the energy stored since E = 1/2 × C × V² (note that voltage contributes squared).


Capacitors don't replace batteries. They may be used to support batteries to deliver short pulses of current.

• A battery is designed to provide a more or less constant voltage during operation. This voltage will drop significantly only when the battery is drained of most of the energy stored within.
• A capacitor's voltage will drop continuously while current is drained. So any load or attached regulator will have to deal with a constantly changing input voltage. Not impossible but more complex than using a battery.

I do intend to try it for myself when I am able to get a multimeter and other gear that I would need, but since that will be a while, it was prudent to ask if anyone else has experience with it. The goal isn't to try to maximize the capacitance, but to utilize something that is free and abundant. Yes, I understand that a voltage of around 100 v would need safety measures that wouldn't be as important at around 12 v, but a capacitor with enough energy CAN replace a battery as long as the voltage is kept above the minimum voltage that the battery would be required to operate at and the regulation is considered; part of this consideration would be using very light loads. This is intended for an offgrid use where the space available is extensive, and the weight/cost/environmental considerations of a battery would actually be a disadvantage. I'm hoping to find people who will have the right equipment to do actual tests on the capacitance so that we can get a general idea of how large such a system would need to be to provide 1 farad of storage capacity at 50 volts, and I don't have any means to measure the capacitance. Most people will automatically dismiss my idea because they are so used to doing things the way that they have become used to, but without that kind of a measurement, neither of us can actually say whether this is feasible or not.

 

[Harald Kapp]

You don't have to measure, just do some math (numbers from Wikipedia - I found the numbers in the German version only):
Area of a CD (excl. hole) A = 111.33 cm²
Thickness of a CD and therefore distance between two "plates" d = 1.2 mm
rel. permittivity of polycarbonate εr = 3.1
vacuum permittivity ε0 = 8.85 × 10^-12 As/Vm

Formula for capacitance: C = ε0 × εr × A/d = 25 nF
1 Farad requires 40000 CDs.
Mass of a single CD (with hole) = 16 g
Mass of total stack = 40000 × 16 g = 640 kg - without any wires, rivets, solder whatever...

Edit: Total mass "only" 320 kg with alternatingly stacked plates.

 

[Bluejets]

whether this is feasible or not.

Not......

 

[Martaine2005]

but a capacitor with enough energy CAN replace a battery as long as the voltage is kept above the minimum voltage that the battery would be required to operate at

A capacitor cannot replace a battery.
They are different types of storage. The capacitor discharges rapidly and stores energy physically.
The battery discharges relatively slowly and stores energy chemically.
Supercapacitors are a bit of both.
Wow, 640kg for 1 farad.
That’s a huge size for a very quick spark!.

Martin

 

[Bluejets]

That’s a huge size for a very quick spark!.

Hehehehe...yep.
Not only that but I have a sneaking suspicion the Op is not thinking of how to get it in there in the first place.
I swear by the solar panels I installed here 5 years ago BUT at a cost.
My costs have been recovered in that time but government will need to wait quite a while to get their subsidy back.

 

[Martaine2005]

Too many woo woo’s on YouTube.
“Free toast”. “Plug your toaster into a lemon”.

Martin

 

[Bluejets]

Too many woo woo’s on YouTube.
“Free toast”. “Plug your toaster into a lemon”.

Martin

How things change...used to be a potato...or a can of beer.