DIY capacitor

[Alberto]

Hi everyone.

I have made a high voltage capacitor using aluminum foil (only 2 plates) and layers of Mylar. I have wrapped it and it gives 17 nF.

Now I want a bigger one and I'm going to use 10 layers of aluminum foil in parallel. The question is, when you use more than 2 plates, can you wrap it too?

Thank you.

Kind regards

[klugesmith]

By "Wrapping" do you mean rolling the plates and dielectric around a tube, like new aluminum foil?

Sure, you could make a 10-plate stack and roll it up. 
Wouldn't you get the same capacitance with a long 2-plate stack, made into a roll with more turns?
Same "efficiency", if all dielectric layers have the same voltage stress.
That's how commercial capacitors have been made for about 100 years.

[MRMILSTAR]

A rolled capacitor may have significant parasitic inductance. Depending on your application this may be a significant consideration.

[Twospoons]

A rolled capacitor may have significant parasitic inductance.

That's very dependent on where the connections to the foil are made, and this is true whether the capacitor is rolled or flat. If both connections are made at the same end then the currents cancel and the only inductance results from the thickness of the dielectric  (a thicker dielectric leads to a larger loop area).  A very long length of foil will behave more like a transmission line, if the connections are at one end.

Commercially, rolled film/foil capacitors are constructed so the foils are exposed on either end of the roll, and connection is made across the entire endface.

[MRMILSTAR]

I assume that you are referring to schoopage. This is all very true for commercially-built capacitors. The problem is that the OP wants to make his own rolled capacitor. I don't think the average home builder has the capability of properly applying schoopage to a rolled capacitor. Thus he's left with simple connections to the plates of a rolled capacitor.

[klugesmith]

One way or another, when rolling your own capacitor you need to connect to aluminum foil.
It seems obviously easy to let each plate extend far beyond the dielectric on one end of the roll.

But a few minutes of Internet searching didn't find DIY-ers connecting to the spirally exposed foil (for low inductance).
Adam Munich missed that, in a project reported at Hackaday in 2011.

Why not leave enough plate exposed to twist each end?

[Zipdox]

You made something like this?

[Alberto]

Hello and sorry for not respond! The university have started and with the virus everithing is a mess!!

Thank you for all your answers.

The capacitor is only for fun and experimenting.

I have made a new one with cellulose acetate (0,2mm) and aluminium foil and the capacitance is the same when I wrap it.

It gives 58 nf (a plate of 88x29 cm).

Thank you and sorry again

[plasma]

If you want you could try mixing titanium dioxide with PVA glue and paint it onto the plastic just before you wrap it.
TiO2 has a constant between 80-450 depending the source which should increase the Farad.

[Alberto]

Thank you for your answer