Sciencemadness Discussion Board - Homemade capacitor for a power supply

Homemade capacitor for a power supply

Aqua_Fortis_100% - 2-7-2010 at 21:49

Hi,

After messing around with PC power supply for electrolytic synthesis, Im seriously considering the idea of having a better power supply to improve my synthesis.

Im thinking in the home traditional way, a modified MOT with HV secondary removed, a few turns of thick wire, diodes and capacitor, like this:

http://www.youtube.com/watch?v=Yr8HKlX4VnU
(made by the SMDB member White Rabbit)

I have little budget to buy these things, so the obvious way was to walk around scrapyards and other places to find it as cheap/free junk. I disassembled two garbage microwave ovens and collected two MOTs (plus 2 of each: magnetron, fan, plate motor (good for dance room

), HV diode, HV capacitor, thermal protection thing - I forgot the name - and fuse). In a auto repair center I acquired 3 alternator diodes for free.

The only basic thing (I think) I need is a big "beer can style" capacitor, low voltage and high capacitance. The problem is that these are very expensive here and I couldnt find anything in scrapyard that have some of these.

I was thinking in making a BIG bank of small capacitors - these caps more commom in most electronic circuits found in scrapyard - but Im afraid if that would work.. Maybe one or another cap of the bank is not very good and fail (what maybe could lead to the other capacitors to fail and even explode)..

So my mind said to me the obvious alternative: "why not make yourself?"
That approach may be very appellative to some people that have easy acess to electronics, but not to me.
Unfortunately I didnt find anything "amateur" on this.. Most amateur capacitors are low capacitance high voltage, for things like tesla coil and other things... Al foil and glass plates, bottles filled with brine (leyden jars and such), etc are the most commom...

I dont care (at least now) about homemade cap being much bigger than comercial and/or if I have to replace periodically the lost solution (evaporation), etc because it will be a part of a "fix" power supply..

The ('professional') things (like patents and such) I have read talk about to anodize Al foil with several solutions, put a paper spacer and then another foil that will be the negative terminal (cathode).

In practice was difficult to achieve anything reasonable..

I splitted the Al foil (supermarket grade) in several pieces of 5x30cm, easy to anodize and to roll.

As electrolyte, I used demineralized water, pharmaceutical grade boric acid and sodium bicarbonate. Boric acid dissolved quite fast in NaHCO3 solution.

As cathode I used another similair foil, spaced about 2-3 cm and used 12V from PC PSU.

I didnt give any prior treatment to the foil like etching and such..It was just a test..

The result of anodization is here:
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...

Very uneven anodizaton, the plate with several HOLES, each with gray borders and Al hidroxide flaking off.
Total fail..

The second, crude way, was making, in order, the following:
PTP//C//PTP//A//PTP//C//PTP
and then rolling around a piece of straw and putting it in a plastic container and filling it with electrolyte.
Where PTP stands for piece of toilet paper, C is cathode and A is future anode..

The conections with the Al of both cathodes and central anode was with modeled piece of Al paper, as you will see in the images:
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
That was run with the same 12 V of PC PSU.

Beside the entrapped gas bubble between Al foil and paper, I was thinking if this method was a slightly more pausible than previous.. After some hours I turned off the supply and disassembled the paper..

http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...

Well, today was only this.. BTW and obviously: Tried someone here to make such capacitors? Is really viable to make at home?

Thanks!

Sedit - 2-7-2010 at 23:38

OK I admit im a bit tipsy

but I can tell you how to make a HV cap on a budget due to all my ghetto work on tesla coils.

First and formost we will start with salt water caps. These are mearly just bottles of wine, beer or anyglass container , whose dielectric constant can be found online with ease and formulated into the correct calcution .

Fill these with salt water and a layer of cooking oil to prevent corona loss. one terminal is connected into the inside of the bottle while the other is in the holding container also filled with salt water. Using this setup in series you can obtain currents and voltages of large magnitude but impedences so high they can hinder some applications such as laser operation.

Then theres you basic plate glassand duel plate, look into these because I dont think I need to expain more.

because of the weight of the salt water cames and mobility I managed to devise using a piece of ABS pipe with AL inside and out as a lower impedence light weight alternative to the NaCl caps.

I would say more but Im not on my comp and the key board is hard to type on and to make it worse im in the middle of synthesiszing acetaldahyde in my body from EtOH. So if you need HV help I may not be the guy that gives you awsome numers and endless graphs but I can give you personal experiments from decades of experimentation.

GL brother peace
~Sedit

not_important - 3-7-2010 at 00:22

I suspect you used Wikipedia as a refeence, there is insufficient and misleading information there. For a bit more detail on the electrodes see http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm and also http://www.elna-america.com/tech_al_principles.php

Note the amount of work that goes into preparing the electrodes; the etching step is important and a bit tricky to get correct. The oxide film forming is also important, often done with careful control of current and slowly ramping up the voltage.

Ammonium borate commonly used as the salt in the electrolyte, other ammonium, amines, and aluminium salts are used as well; organic acids are common along with and in place of borate. The use of high boiling organic solvents is important to avoid evaporation of the electrolyte.

In short, I suspect that you will expend more money learning how to make a decnt electrolytic than it would cost you to buy one. You might do better checking businesses that specifically recycle computers and other electronics, looking for functional or dead power supplies.

Sedit - 3-7-2010 at 01:03

me wiki reference N_I? im confused...

Aqua_Fortis_100% - 3-7-2010 at 03:20

Thanks!

Sedit, I need a low voltage, high capacitance cap..I think leyden jars wouldnt be very effective for a low voltage power supply..
In anyway, thanks and have a good alcohol metabolisation!

Ah Sedit, in "wikipedia" N_I was refering to me. BTW, I look most info on this page: http://www.faradnet.com/deeley/book_ix.htm and some patents on freepatentsonline, that is a interesting info source. Anyway, that links are GREAT!

I was only making crude tests, just to be "familiar" with the technique.

I disassembled a small ruined cap right now just to see its structure:
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...

It has a strong organic smell (unlike other caps I disassembled that smelled ammonium compounds).
The anode foil is perfectly and even "dark" anodized and this foil is somewhat thicker than supermarcket grade. Also the home grade is not very pure (one of the links N_I posted says that the minimum purity for Al foil in anode is "99.99%")..
So, home grade Al foil is not the best choice for this..

Quote:

In short, I suspect that you will expend more money learning how to make a decnt electrolytic than it would cost you to buy one. You might do better checking businesses that specifically recycle computers and other electronics, looking for functional or dead power supplies.

Yeah.. Im learning that part now..
In anyway, is just great the even small possibility that I can master that technics in future.
So, maybe, the last way can be a big bank of sorted caps..
http://i242.photobucket.com/albums/ff176/tnitrato/ELETRONICA...

Aqua_Fortis_100% - 4-7-2010 at 07:33

Hello

I was thinking,
I didnt heard of people using DC pulsating current in electrolysis; The quality of smooth DC is much better, but what would be the real difference in using pulsating DC comparing to smooth DC?
All guess:
Im thinking in a lower efficience (higher bill tax), since there will be moments that the potential is lower than that is needed to drive the desired reaction, actually some moments that the potential is zero.
I dont know, but I guess that this may also stress some eletrodes and reduce its useful life..
Can anyone say if pulsating DC electrolysis is feasible to home experimentation?

Thanks!

Sedit - 4-7-2010 at 08:36

Quote: Originally posted by Aqua_Fortis_100%

Thanks!

Sedit, I need a low voltage, high capacitance cap..I think leyden jars wouldnt be very effective for a low voltage power supply..
In anyway, thanks and have a good alcohol metabolisation!

It sounds to me like your best bet if your looking for low input high output would be to setup a MMC or Multi mini capacitor bank. Very easy running them in paralle to achive a high accuracy of voltage and current being delivered to what ever its ue is.

And yes the invivo Acetaldahyde synthesis went according to plan without a hitch. There was a note of sluggishness in the reaction vessle after allowing it to settle overnight and much fluid had to be siphoned off the following morning using a hose due to excessive flooding of the reaction vessle but over all I deam that experiment a complete success.

Aqua_Fortis_100% - 4-7-2010 at 09:04

I cant escape in wasting some money on this..

I reconsidered, making a gret bank of old/sorted/junk caps would not be a very good idea..
Sedit, MMC of new, similair caps is now my best choice.. Im thinking in several 1000uF/16V-25V caps soldered in parallel to two large copper wires or even pipes... I guess that should even be less expensive (less than half cost) than a big cap and as you say, I can design the bank to give me more accuracy!

So the conclusion is that the process of home manufacture of these caps of these kind is nice only on theory

But anyway dont hurt experimentating.. At least with this..

Quote:

And yes the invivo Acetaldahyde synthesis went according to plan without a hitch. There was a note of sluggishness in the reaction vessle after allowing it to settle overnight and much fluid had to be siphoned off the following morning using a hose due to excessive flooding of the reaction vessle but over all I deam that experiment a complete success.

By that descripition, I guess you will like very much to reapeat this experiment very soon, and improve it... What we couldnt do for science, ah?

Sedit - 4-7-2010 at 14:15

There has indeed been much consideration on the scaling up my Acetaldahyde synthesis next time and seeing if the reaction proceeds as so or if the oxidation produces by product of acetone leading to a memory lapse of the chemist and failier to recall the experiment

.

There has also been an interesting reaction that has been noted in literature detailing with how when a femail chemist performs this experiment there has been many cases where there clothing has dissolved off

So that may be the next step in testing this synthesis inquestion. And I am eger to see the results.

woelen - 5-7-2010 at 13:20

Maybe this is interesting for you:

http://cgi.ebay.com/50-2200uF-10V-2200-uF-Radial-Electrolyti...

50x2200 uF makes up a BIG capacitor (110000 uF). Using many smaller capacitors has the added advantage that high currents are allowed. Maximum allowable current only is marginally affected by capacity and combining 50 of these, each allowing e.g. 3 A of current makes up a total of 150 A charge/discharge current.

Another option is to use a power cap for a car amplifier. These can be obtained with capacities up to 10 F, but they are expensive. Again, combining a few lower capacity items (e.g. 5 pieces of 1 F) may be interesting, allowing a higher charge/discharge current and probably lower total price.

Sedit - 5-7-2010 at 22:30

For smaller projects I still strongly suggest MMC because even if you blow out on you still don't have to replace the entire system only a few caps at the most which will only cost you a couple bucks at the most.

I admit I have not really read what you want them for but if you need very low impedence then you will be looking at higher cost no matterwhat you do.

12AX7 - 6-7-2010 at 20:46

Homemade electrolytics? For electrolysis? Not even no, but hell no...

Geez, you must be embarassingly cheap. If you can't afford ten bucks in capacitors, you certainly can't afford the electricity needed to power it!

13.8V 40A supply:
http://ludens.cl/Electron/PS40/PS40.html
You can add a wider range to this circuit, as well as adjustable current limit

I have a partial design for a 5V, 100A programmable power supply which I have already mentioned here.

Tim

peach - 10-7-2010 at 22:48

I was hoping someone would make 12AX7's point.

The idea of homebrewing a cap for a usable power supply and thinking it'll match a commercial electrolytic is insane.

All the homebrew methods feature horrendously low capacitances, because the dielectric has to be orders of magnitude thicker than in an electrolytic for you to not tear it during handling.

You can make caps using polythene A4 pockets, grease proof paper or cling film, using tin foil as the electrodes. But those are usually rated at tiny capacitances and huge voltages.

You're dealing the absolute opposite, low voltages and higher currents.

There is no way on earth you'll make a similar or cheap power supply for that using a HV capacitor format.

You can pull a power supply out of a PC and immediately have a 5 / 12V DC source. The tip is full of old electronics. A £5 soldering iron and I can pull a ton of transformers, fans, diodes and capacitors out in no time, for free.

Regulated supplies use things like the LM317 regulators for an adjustable DC voltage / current.

That you don't know the difference between pulsed and smooth, or why you might one or the other, and you thinking those types of capacitors will work for your supply makes me question if you should be scratch building one that'll be connected to the mains. The mains is bad enough. Add big capacitors and conductive solutions and that's a recipe for problems.

MOT's are about the most lethal electrical items in the house, along with their HV caps and the magnetron beside them. I am very familiar with the mains, but I am still incredibly careful with the cover off a microwave. The voltages and currents they output are similar to one of the cycles used for electric chairs.

Rip a supply out of a PC or buy a commercial supply.

[Edited on 11-7-2010 by peach]

chief - 4-8-2010 at 04:47

If you can't help yourself, try a cheap experiment, which I always had on mind but was too lazy for:
==> get some AL-foil, as well as some A4- or A3-Copy-paper (500 pieces) ...

Cut the Al-foil into pieces that are somewhat smaller than the paper, and then assemble the cap , layer by layer: Done in less than 2 hours ... (tha Al-foil may be obtained "cut", already in pieces ... , eg. in stores for professional cooks ...)

Now measure the capacitance ... ; should be able to calculte it too, from the involved surfaces ...

Now, to make it an electrolytic, just do the same, but soak the paper in the solution of the salt ...
==> ELectrolytics are usually "formed" (at least I think so

) by applying a DC-current and slowly increasing the voltage to the desired level ... which gives the Oxide-layer time to grow to the necessary thickness ... : Probably the leak-current would be monitored and the voltage would be adjusted to keep that current constant ... sort of ...

==> For a 500-V-Capacitor the voltage would be applied until the level of eg. 700 V ... ...

Could well be possible for the amateur to make good electrolytics himself that way ..., just not as small as the commercial ones ...

[Edited on 4-8-2010 by chief]

densest - 4-8-2010 at 07:30

In a word, no.

Commercial electrolytic capacitors have a number of advantages which would be hard for an amateur to match:

The foil is etched in a very controlled manner to get a very large surface area.

The foil is very thin in order to pack a very large area into a small space.

The oxide film on the anode foil is as thin as possible without any holes.

The electrolyte is conductive, supports the oxide film, but doesn't unnecessarily corrode the foil. A patent I randomly picked http://www.freepatentsonline.com/3547423.pdf says

Quote:

generally contain a solvent, such as ethylene glycol, and a conducting species or ionogen. The ionogen employed is typically a borate such as ammonium pentaborate or ammonium biborate or to other substituted ammonium salts such as ammonium acetate and ammonium tartrate

The patent doesn't say what other things are added... It does mention a high vapor pressure, so the capacitor must be sealed.

The crimp/weld connections to the foils are uniform and low resistance.

The paper is pure cellulose or other fiber. It contains no calcium carbonate or titanium oxide filler. Copy paper contains large quantities of fillers to make it white and uniform. The closest thing easily available to an amateur would be brown kraft paper of the type used for paper bags, etc.

An amateur built capacitor would have high leakage currents, low capacitance (1/1000 of a similar sized commercial capacitor), high equivalent series resistance, low voltage rating, and a short life.

As a piece of supporting evidence, I only remember one mention of such a capacitor in all the old "do it yourself" electrical or electronic articles and books I've ever read. I've seen many mentions of homemade oil capacitors in those sources. The closest thing I have seen are plans for electrolytic rectifiers.

I recently bought some 1000uF 35V low ESR high ripple current electrolytics for $0.25 each. In quantity one I think they were $0.42 each. It might be fun to try making one but for a usable power supply, buy the caps.

[Edited on 4-8-2010 by densest]

chief - 4-8-2010 at 23:40

It completely doesnt harm if the paper has any TiO2-filler or whatever ... : Not necessary to use "Kraft"-paper ...

The thicker Al-foil will allow higher short-circuit-currents ... thereby quicker discharges, limited by the induvtivity of the cap only ... which may bring certain applications into the range of lower voltages ...

The etching of commercial capacitors takes place after the caps are assembled: The foil & paper get rolled, soaked in electrolyte ... and then a voltage is applied (correct me if thats wrong, with _sources_, not free patents where things dont necessary have to belong to reality) ... ; times ago I read a paper on the manufacturing of such caps ... therefrom I remember it ...

So the amatuers cap will surely be quite big ..., but potentially also quite powerful ...
==> Once I had some old electrolytic capacitors from maybe the 1930s ... : Those had a volume of maybe ½ liter for 200 microFarad @ 300 V ...

=============
The interesting thing in self-manufacture would be
==> not to compete with the commercial ones in the cheap ranges ... (low voltage etc.)
==> but to go for somewhat higher voltages ... and short-circuit-discharge-currents ...

densest - 6-8-2010 at 06:39

@chief - I'm attaching a Nichicon article about their manufacturing methods. That article, and all the other articles I've found on the web, state that foils are etched before being wound into capacitors. The etching solution is usually a chloride. The electrolyte in the finished capacitor usually contains borate to prevent further etching or dissolution of the oxide layer.

Making a capacitor capable of high surge currents is somewhat tricky. Getting good contacts to the entire edge of both electrodes without ripping the foil or shorting it is hard. There are other problems as well - special electrolytes optimized for that service are required.

Making a case to contain the somewhat corrosive and unpleasant electrolyte is a project all on its own. Modern electrolytic capacitor cases are carefully engineered.

This project, like many proposed here, could be a lot of fun on its own. It's absolutely pointless as a way to save money. I paid $17 for brand new 1800uF 475V high current high temperature capacitors. They cost $2-5 from surplus sources. 10000uF 25V new surplus caps cost about the same. I'll gladly give sources to anyone via PM.

Attachment: tec1.pdf (319kB)
This file has been downloaded 986 times

[Edited on 6-8-2010 by densest]

chief - 6-8-2010 at 07:59

Anyhow the first electrolytic capacitor certainly was not carefully etched or whatever ...
==> You are talking about refined production-methods for caps which have to withstand a 5-year warranty under whatever conditions ...

The prior etching probably serves as a way to enhance the surface-area of the Al ...
==> This step cannot be the same that forms the oxide-layer ..., because one either etches the aluminum or forms an inert ocide onto it ...

So the basical way still would be:
==> Etch or not ...
==> assemble and electrically form an oxide-Layer ...

The electrolytic cap lives from 2 principles:
==> The very thin dielectric (which ist the oxide-layer) ...
==> and then the capacity may be enhanced by the etching ...

You are thereby talking about "enhanced" electrolytic caps ... ; anyhow the etching might be not too complicated either ...