Making an electrolytic Capacitor... / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Making an electrolytic Capacitor...

1 2 next

Move Thread

LAN_403

Inducktion

Fri Jun 10 2011, 01:08PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Has anyone ever attempted to make something like an electrolytic cap? The two things I could see as problems would be getting the actual dielectric (aluminum oxide, right?) onto the plates and not scraping it off by accident...As well as figuring out what electrolyte to use. The rest of building the capacitor should be easy to do, as it's just winding the plates together in a large roll... And then you could use a soda can as the outside of the cap!

Electroplating anyone perhaps?

magnet18

Fri Jun 10 2011, 01:37PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

I don't think you can electroplate aluminum oxide. If you could get ahold of a strong oxidizing agent, however, you might be able to get the sides of an aluminum can to be plated in aluminum oxide.
It's easier to make wrapped foil caps.

cedric

Fri Jun 10 2011, 01:49PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

"The principle of the electrolytic capacitor was discovered in 1886 by Charles Pollak, as part of his research into anodizing of aluminum and other metals. Pollack discovered that due to the thinness of the aluminum oxide layer produced, there was a very high capacitance between the aluminum and the electrolyte solution. A major problem was that most electrolytes tended to dissolve the oxide layer again when the power is removed, but he eventually found that sodium perborate (borax) would allow the layer to be formed and not attack it afterwards. He was granted a patent for the borax-solution aluminum electrolytic capacitor in 1897."

there is so info on wikipedia about it,for my self I would use glass fiber fabric to keep the to aluminum electrode apart,rool around each other,one of the problem I see is how to connect the aluminum paper to the terminal (if different metal are used it can start a reaction with the aluminum and make a batteries instead of a capacitor...)

I think the process wish develop the layer of aluminum oxide is call anodizing...

Ash Small

Fri Jun 10 2011, 02:12PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

You are correct, Cedric. The aluminium is anodised the first time power is connected. I remember reading the exact prucedure somewhere years ago).

I think you need something (eg glass fibre) rolled up with the aluminium. It is then soaked in the electrolyte, power is connected, and it turns into an electrolytic capacitor.

If the terminals are reversed, the oxide layer breaks down, and it stops being a capacitor.

Inducktion

Fri Jun 10 2011, 02:16PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

So, you would need borax to make the electrolyte, aluminum foil, anndd.... Would paper would instead of glass fibre? Or would fibreglass insulation work too? (I'm assuming it WOULD since the name has "fiberglass" in it)

As for connecting the aluminum terminals, couldn't you use some sort of clamping thing, (maybe a paperclip for a poor man's version) or some sort of staple...

cedric

Fri Jun 10 2011, 02:45PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

Inducktion wrote ...

So, you would need borax to make the electrolyte, aluminum foil, anndd.... Would paper would instead of glass fibre? Or would fibreglass insulation work too? (I'm assuming it WOULD since the name has "fiberglass" in it)

As for connecting the aluminum terminals, couldn't you use some sort of clamping thing, (maybe a paperclip for a poor man's version) or some sort of staple...

I like the idea to use glass fabric because it is chemically neutral (most of the time) and liquid can pass through ,for the rest any thing could do.
for the contact ,the best is probably to get the aluminum paper to do a 90 degres turn ,to rool it on itself and to get the strip out of the solution,aluminum is a very reactive metal ,I assume it would react if it is in a electrolyte bath with an other metal...

Inducktion

Fri Jun 10 2011, 03:15PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Hm... So, I'll give this a shot once I get a chance. I need borax though, I don't think we have anything along those lines... and I can just use some of the glass insulation from my basement. Aluminum foil from my kitchen.

Wonder what kind of voltage these babies will be able to take.

Pinky's Brain

Fri Jun 10 2011, 04:08PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Need to etch the surface as well ... if you anodize plain aluminium foil you will get piss poor capacitance.

PS. I think I read somewhere you get grains of impurity though if you etch garden variety aluminium foil (which obviously won't form an oxide layer).

radiotech

Fri Jun 10 2011, 04:26PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Dangle a lead fishing weight in an aluminum pop can filled
with seawater and you will have a usable electrolytic
capacitor for AC use.( variations of this have been
used as emergency starting capacitor for induction
motors)

Also works as a rectifier for charging a battery,
(use a lightbulb as a ballast)

Sometimes you have no time to think and just do things.

Ash Small

Fri Jun 10 2011, 05:37PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Inducktion wrote ...

. I need borax though, I don't think we have anything along those lines...

You should be able to get small quantities of 'pure' (pharmaceutical grade) borax from a drugstore, etc.
(I used to have a sack full of the stuff, and a sack of boric acid)

Inducktion wrote ...

and I can just use some of the glass insulation from my basement. Aluminum foil from my kitchen.

Wonder what kind of voltage these babies will be able to take.

You should be able to get small quantities of fibre glass from an auto spares shop (used for body repairs) or from a boatyard if you have one near you.

cloth (known in the trade as 'woven rovings') will probably be much better than the usual 'chopped strand mat'. It comes in different 'weights' ie thickness. (maybe google this to get a better idea of what I mean)

There are two types, 'E' glass, and 'S' glass, but I think either will do for this application.

The aluminium needs to be cleaned with a solvent to degrease it (and then etched with something like sodium hydroxide, I think.)

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob