home made foil and paper towel electrolytic capacitor issues.

MisterBill2

Joined Jan 23, 2018
17,850
RE: MrBill2 - its very probable, the supercaps use one or another system applying the PEO process. PEO is just the electrolysis in salts solution, BUT the voltage is 300-600 Volts while amperage is 0.5-10 Amps per square inch. Then millions of small sparks are dancing over the surface until its ready.
Please define the "PEO" acronym for those of us nay familiar with every cryptic code used by others. The language of short acronyms is unknown to me, at least in many cases. Hiding meanings is a block to understanding.
Just look at the confusion caused by the term "MCB."
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
I'm curious why standard printer paper/office paper is so bad for aluminum foil in distilled water Even if you limit the current to very low like a few microamps. You'll eventually be left with disintegrated dust/goo instead of foil. Even with very pure distilled water. with nothing else in it. No baking soda or anything.
Somehow something must be leaching out of the paper or creating a reaction that attacks the foil. instead of creating an insulating oxide layer.

Not a problem with paper towels. napkins. or even toilet paper. no degredation of the foil is seen. with no major differences.
 
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MisterBill2

Joined Jan 23, 2018
17,850
Good printer paper is a more complex material, with quite a few additives, including anti-stick, ink holding materials, dimensional stabilizers, and mechanical property enhancers. And much of it also includes anti-static materials.
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
I see. so theres probably an assortment of junk that leaches out and attacks the foil rapidly corroding and erroding it away.
 

joeyd999

Joined Jun 6, 2011
5,174
How about coffee filter paper? It's pretty tough when wet, extremely thin and porous yet dense, and I figure the FDA must have some rules about contaminant chemicals and biologicals.
 

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realflow300

Joined Jul 28, 2023
124
Coffee filter paper might work! Though I don't believe it comes in nice convenient flat rolls.
I'd be making small circular disk shaped capacitors with dozens of layers stacked up. and then that sandwiched and pressed together somehow. Not very convenient.
 

joeyd999

Joined Jun 6, 2011
5,174
Coffee filter paper might work! Though I don't believe it comes in nice convenient flat rolls.
I'd be making small circular disk shaped capacitors with dozens of layers stacked up. and then that sandwiched and pressed together somehow. Not very convenient.
Laboratory filter paper? I think it's the same stuff.
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
Maybe. still tears easily if wet though. but its very thin.
I dont think the "thin-ness" is the problem I'm having. its likely more due to contaminant problems. either from the foil itself directly from manufacturing. (trace amounts of solvents oils chemicals remaining ect. on the foil itself coating it) So the oxide layer can't fully coat the entire surface of the foil. either due to contaminants blocking or covering the foil.
OR due to some trace amounts of unwanted pollutents in the electrolyte. ect.
I have tried with 2 small pieces of foil and just an ultra super thin fine nylon wire mesh meant for air filtering purposes and still got leakage current problems.
Leakage current needs to be in the tens of microamps range. or less. for the capacitor to be efficient and not drain itself in a short period of time.
Anywhere from 1 to 10 microamps is probably acceptable for a homemade 500-5000uF capacitor at 5-16v
 

Danko

Joined Nov 22, 2017
1,823
Water can not be used in capacitor, because it reacts with aluminum, creating hydrogen and alumina hydrate (slime).
Water can not be used in capacitor, because it starts decompose to oxygen and hydrogen at voltage 1.23 V.
Baking soda can not be used in capacitor because it reacts with alumina, creating alumina hydrate (slime).
They use only organic electrolytes in capacitors.
ADDED:
Anodizing can also be performed in borate or tartrate baths in which aluminium oxide is insoluble. In these processes, the coating growth stops when the part is fully covered, and the thickness is linearly related to the voltage applied.[6] These coatings are free of pores, relative to the sulfuric and chromic acid processes.[6] This type of coating is widely used to make electrolytic capacitors because the thin aluminium films (typically less than 0.5 μm) would risk being pierced by acidic processes.[1]
These electrolytes used only for anodizing foil for capacitors, but inside capacitors only organic electrolytes used.
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf
 
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michael8

Joined Jan 11, 2015
408
from https://en.wikipedia.org/wiki/Anodising

Borate and tartrate baths
Anodizing can also be performed in borate or tartrate baths in which aluminium oxide is insoluble. In these processes, the coating growth stops when the part is fully covered, and the thickness is linearly related to the voltage applied.[6] These coatings are free of pores, relative to the sulfuric and chromic acid processes.[6] This type of coating is widely used to make electrolytic capacitors because the thin aluminium films (typically less than 0.5 μm) would risk being pierced by acidic processes.[1]
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
Mostly substances I shouldn't be messing with at all. too risky for me. and there doesn't seem to be any "reasonably safe" alternatives.
distilled water and baking soda works but the capacitors leakage current is really high. and if its not used often the oxide layer weakens.
 
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MisterBill2

Joined Jan 23, 2018
17,850
Keep in mind that the contents and materials in electrolytic capacitors are not intended for human consumption, nor even human contact. The capacitors are sealed well enough to avoid any contact.
So the mandate for "reasonably safe" materials is a serious impediment towards the creation of anything approaching the performance of commercial components.
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
The best I could reasonably do I think would be creating a bipolar capacitor and repeatedly washing and rinsing it in "fresh" electrolyte baths.
While also doing the same to its container and separator
by creating a bipolar capacitor. the leakage current becomes less dominant as an oxide layer forms on both foils. further insulating them from each other.
And it would need to extremely clean the whole time. with a one-way vent to vent any over-pressure and prevent even dust from contaminating it.

Having a large separation between the plates would also reduce leakage current and doesn't seem to hurt the capacitance value too much
(Theres capacitance to be gained from having the plates closer. but breakdown voltage occurrs much sooner and you get much higher leakage current too so the tradeoff is worth it to have the electrodes spaced further apart. while having more surface area instead.
More surface area wins out vs having the electrodes closer to each other when it comes to leakage current vs capacitance.
Also would need to use very very pure lab grade foil with no extra added elements (Not even 0.01% is acceptable)
It would need to be pure to at least several orders of magnitude better than regular conventional aluminum foil. so theres no unwanted metal to react and plate the electrode surfaces with unwanted corrosion or oxides drawing current.

An idea could be separating the sheets of foil with a 3D printed plastic structure to space out the foil layers from each other at least a centimeter or so. while having a grid/mesh of holes to allow the electrolyte and charge to flow from plate to plate. without them having any chance of contacting each other.
I think making a large container of rectangular plates in parallel would probably be the easiest way to get capacitance in a reasonable form factor.
That way its reusable easy to maintain.
Gloves must be used and regularly and often replaced through every step of the process. from beginning to end. to ensure no contaminants get on anything.

An alternative to water could be used. if ethylene glycol and baking soda are compatible. That might reduce the problem of unwanted ions and salts in the electrolyte.
Water is "too" good at dissolving unwanted ions and stuff. So if ethylene glycol is compatible with baking soda and can still create a reaction for forming the oxide layers for aluminum it could work. and the leakage current would be reduced
Would still need to be done in a clean dry process though.

if the oxide layer can only be formed with water. then that could be used at first to form the capacitors oxide layers.. Then the foil is rinsed and cleaned and dried with distilled water. then rinsed again with the ethylene glycol mixture to wash off any remaining water or anything left behind by the forming process.
Then it can be used possibly. without an excessive leakage current.
 
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Janis59

Joined Aug 21, 2017
1,822
Please define the "PEO" acronym for those of us nay familiar with every cryptic code used by others. The language of short acronyms is unknown to me, at least in many cases. Hiding meanings is a block to understanding.
Just look at the confusion caused by the term "MCB."
a) In the original I gave the scrupulously precise description what is it. Let read it before criticize. :)
b) One motion of fingers: PEO+Google+wikip = https://en.wikipedia.org/wiki/Plasma_electrolytic_oxidation
 

Thread Starter

realflow300

Joined Jul 28, 2023
124
I have now moved on from this project onto another one.
I designed a super simple battery out of distilled water baking soda and soldering wire
All the materials you need is paper towel. zip ties (or something to hold the wires)
soldering wire of course. a hot glue stick to wrap the soldering wire around.
And a way to charge it with low current (resistors or something)
it seems to charge just like a battery!
I get a very usable battery out of it! Roughly 1-2v range
Not super high power but its got more capacity mAh wise than the homemade capacitor experiment!
Can output almost half an amp shortcircuit.
and power a 2.5mAh load for over 3 minutes while holding above 1v

Edit after some more effort and cycling it its getting close to 10 minutes before the voltage reaches 1v when discharging!

i got it strong enough to power a small DC motor even!! At least for some time! Better than a capacitor!

I'm not using any sulfuric acid at all by the way. and its still working!

I found a guide for forming solid plate type lead-based batteries and the idea to reverse the polarity each time while charging and discharging seems to be working! every time it takes longer and longer. so I can nudge up the charging current a little bit after some time.
It keeps gaining capacity every cycle. its really cool how this works. and so easy you can make one with a bit of soldering wire from the spool!

Startedover from scratch and did it a lot neater and put a bunch more layers of paper towel for the separator. due to a spontaneous short that formed in my previous attempt.
Now the internal resistance is extremely low and i get a whole entire amp of short circuit current right away after charging it up! And the capacity is even higher too.
 
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