Homemade long term electrolytic caps. Finding an electrolyte recipe.

[Refrigerator]

Strong winds came and tore my wind generator to pieces so i decided to rebuild the whole thing.
I want my generated electricity to be stored in an electrolytic capacitor but over time the generator might produce quite some electricity so big caps would be needed.
Big caps are expensive and hard to find where i'm at so i decided to make one.

I want my cap to be big so i will have to come up with a jig to wind it. But more importantly i want the cap to last.
What determines the lifetime of an electrolytic cap is of course the electrolyte.
From what i gathered most electrolytes are primarily made of borax and water/ethylene glycol.

I've watched a tutorial by rimstar.org and also tried myself the water+sodium bicarbonate electrolyte and it did function but, as a few  articles that i've read indicated, it does completely destroy the electrodes once voltage is removed.

Ethylene glycol can be easily found in anti-freeze  where it should be around 50/50 mix with water.
Polyethylene glycol is also an easy to find chemical used in DOT4 brake fluid but i'm not sure if DOT4 could be used in an electrolyte.

Pure water might seem best but during forming water based electrolyte could produce hydrogen gas and cause air pockets between the plates.

Some further experimentation might be needed to find out a stable electrolyte recipe that could be made cheaply.

Anyways it would be cool to see if anyone here has tried making electrolytic caps.

[jpanhalt]

Carbonates and borates are quite different, particularly in the way they may interact with vicinal glycols (e.g., ethylene glycol) and aluminum.  Why (what scientific basis) did you choose the carbonate route?

I suspect you read the Wikipedia article on capacitor electrolytes, so I won't link it here.  As general advice, I would put greater faith in studies by capacitor manufacturers, such as Kemet (e.g., http://www.kemet.com/Lists/TechnicalArticles/Attachments/15/2008-10%20CARTS%20-%20Al-Electrolytes%20for%20Automotive%20and%20High%20Temp%20Applications.pdf) than on YouTube-like demonstrations lacking much basis.  Can you give a link to the specific demonstration you followed?

John

[free_electron]

What makes you think you can make a better capacitor,than the existing companies ?
They dont use brake fluid as electrolyte...

[Siwastaja]

No, you are not going to be able to DIY a reliable, long-lasting electrolytic capacitor (especially if you need to ask this kind of question...). A proof-of-concept elcap is possible if you are good with chemical processes.

Billions of R&D money at chemistry industry giants have gone into the development of reliable electrolytic caps.

Once you realize this, nothing prevents you from doing it, but don't fool yourself into thinking they would be usable in projects.

Storing renewable energy in electrolytic capacitors is not viable even in the state-of-the-art technology, and there are no prospect that this would change in near future, even when zillions of $$$ is thrown at R&D of ultracaps all the time.

[Refrigerator]

@jpanhalt
this video got me interested in DIY electrolytics.


@free_electron
I'm not here to challenge the big boys but since i haven't found anyone who tried making caps that last for more than just one experiment i thought i'd give it a try.

@Siwastaja
After i make the cap only time will tell if it was usable for my projects. 

[CatalinaWOW]

I am almost as negative as everyone else about making your own capacitors.  But there is one little bit of wiggle room.   You can relax some requirements that drive the big commercial outfits.   Your capacitors, at least potentially, don't have to be space efficient.  You may have a spare barn you don't mind filling with your 100 F capacitor.  Your capacitors don't have to be transportable, so big glass vats with electrolyte recirculating pumps and automatic top off valves are an option.

Things like that might make your capacitor possible, even if it isn't practical in a commercial sense.  Do some electrode area calculations and see if you are happy with the results.

[drussell]

You may have a spare barn you don't mind filling with your 100 F capacitor.

Unless it is some ridiculously high voltage, 100 Farads isn't very much capacity when you're comparing it to a typical battery-type storage system...  A farad is only one coulomb of electrons (per volt of charge) for one second.

If you could boost-regulate all of it at 100% efficiency, you would need a 3000 F capacitor charged to 120 volts to light a 100 watt bulb for an hour.

There is a reason why capacitors are not (yet?) a substitute for electro-chemical cells...

[tautech]

Leakage is a factor that will be troublesome and potentially place DIY caps lower than current battery technologies.

In a recent thread there was talk of 100 year old batteries still functioning and those old and now suppressed technologies need further investigation and modernisation IMHO. While they may be expensive to build today their /year price compared to much of the muck today might make them attractive.

[LaserSteve]

How about nickel iron batteries... Much easier.. Leaky and self discharge over a few days, but work well in old Trolley Cars and in certain telephone applications.  Cheap to build as well, if you like glass or plastic tubes...

Steve 

[CatalinaWOW]

You may have a spare barn you don't mind filling with your 100 F capacitor.

Unless it is some ridiculously high voltage, 100 Farads isn't very much capacity when you're comparing it to a typical battery-type storage system...  A farad is only one coulomb of electrons (per volt of charge) for one second.

If you could boost-regulate all of it at 100% efficiency, you would need a 30,000 F capacitor charged to 120 volts to light a 100 watt bulb for an hour.

There is a reason why capacitors are not (yet?) a substitute for electro-chemical cells...

Totally agree on the practicality.  But!  Since I am sure a homemade cap won't use the exotic surface treatments in supercaps, several hundred volts is not out of reason.  So your 1 hour 100 W bulb is "only" a couple thousand Farads.  Again, the point isn't that this is the right way to go, just that it might be possible to build this engineering marvel.  It is kind of like the guys building microcomputers with TTL logic, or the ones building Nixie clocks.  Those projects are the wrong way to do the job in every way but the art of it.  But the art sometimes makes it worth doing.   

[Refrigerator]

What ever you guys say i'm still gonna make the cap.
I did some rough estimations and came up with about 0.336C of charge per 10m roll of tin foil.
Looking at a roll of foil right now it looks like the cap will be quite small. I do intend to make it fat enough to fill 110mm PVC tube.
Forming caps myself is also a quite convenient thing if i can get it right since i want my generator to be high voltage and low current to minimize the resistive losses, and be able to use thinner/cheaper wire. If i can successfully form a cap for high voltage then that gets rid of many problems ( eg. single cell without the need of balancing ).
I don't need to make these caps compact since they will be sitting outside zip-tied to the pole that my generator will be on top of, anyways.

[ConKbot]

What ever you guys say i'm still gonna make the cap.
I did some rough estimations and came up with about 0.336C of charge per 10m roll of tin foil.
Looking at a roll of foil right now it looks like the cap will be quite small. I do intend to make it fat enough to fill 110mm PVC tube.
Forming caps myself is also a quite convenient thing if i can get it right since i want my generator to be high voltage and low current to minimize the resistive losses, and be able to use thinner/cheaper wire. If i can successfully form a cap for high voltage then that gets rid of many problems ( eg. single cell without the need of balancing ).
I don't need to make these caps compact since they will be sitting outside zip-tied to the pole that my generator will be on top of, anyways.

I don't think you understand how big a 120V 100F electrolytic capacitor will be, regardless of home made or professional. A 25V 1F electrolytic is 4" across and 10" long(talking a Nichicon cap here, not a car stereo one). And you'd need  2500(500 parallel strings of 5) of them to get 120V, 100F.  720kJ total energy, 200 watt hours, assuming you can extract it all.

Versus something like http://www.batteryspace.com/custom-lfp-26650-battery-pack-25-6v-9-9ah-253wh-16a-rate-with-pcb-23-76.aspx

Or
https://www.amazon.com/ExpertPower-EXP12200-Rechargeable-Threaded-Terminals/dp/B00KC39BE6

If you want to play with making your own electrolytic caps, have fun. But don't expect to do anything super useful in terms of energy storage for domestic use.

If you do make a 700Kj cap bank, for the love of all that's holy please make a coil gun or rail gun too 

[Refrigerator]

Wait a minute... where did the 100F figure come from ? 
i'll make a big cap but i won't know the capacity till i'm done with my experiments.
right now i'm experimenting with 4x8 cm Al foil plates in different electrolytes.
First observation: borax + water = no bueno; 1.135V drop across cap, with 4mA current, no oxide forming even after many hours.
The foil is not sanded or textured in any way, but when i have a jig for rolling the cap it will drag the foil over some sandpaper to increase the surface area.
I wonder if i could electroplate some aluminum on carbon and then form the capacitor.
Basically make an electrolytic-supercap hybrid.

[CatalinaWOW]

Wait a minute... where did the 100F figure come from ? 

In your original post you state you want to store wind generated electricity.  One of the responses showed that it would take a 100 F capacitor to store enough energy to light a 100 W bulb for 1 hour.

That is really not much energy storage, but it is probably the smallest you could realistically think of.  By using low wattage LED lights you might be able to find your way around and do a little reading at night for a couple of windless days.  (Assuming leakage losses don't cause a problem).

Your storage needs may vary, but energy storage always seems to come out needing capacitance measured in Farads.  Lots of them.

[james_s]

The only way you are going to reliably store a reasonable amount of energy in something home made is with a lead-acid battery. Those are actually fairly simple to make, it's still easier and safer to go buy commercial batteries but you can make one yourself that does work about as well as one you can buy although not nearly as convenient.

A capacitor? Forget it, sure you can make an electrolytic capacitor at home, maybe a few tens of microfarads and if you're careful it may last a few days or weeks. Something large enough to be useful storing energy from a wind turbine though? No way, it's just not going to happen. Even if it were feasible it would be dangerous, have you calculated how much stored energy there would be? Have you seen what happens when a really big capacitor is charged up and then shorted? Stored energy is dangerous, there's no way around that.

[CatalinaWOW]

Stored energy is always dangerous.  Batteries, pumped water storage, molten salt, capacitors, gasoline you name it.  The danger comes from the total amount of energy and the rate at which it can be discharged. 

I wouldn't be surprised if the ESR and inductance of a very large home made capacitor made the discharge rate low enough to line up in danger with a lead acid battery system, but with much lower total energy.  Refrigerator will have to be careful, but the major additional danger comes from the fact that he is travelling a road not often taken so it is harder to benefit from the failures of others.   He doesn't have dozens of people warning him of the dangers of hydrogen gas accumulation, acid spills, lead contamination and the like.

[james_s]

That is a good point of course. Still I think it's important to put things into perspective here, I have not done any actual calculations but I'll take a wild assed guess and say that home made capacitor capable of storing as many Watt Hours of energy as an off the shelf deep cycle battery you can get for $100 at Walmart is going to be something around the size of a semi tractor trailer. Chemical batteries have energy density orders of magnitude higher than capacitors, and that's proper mass produced commercial capacitors. Anything that works well enough to be useful will be dangerous, difficult and expensive to build. I'm a big fan of DIY, but one still has to recognize when it makes sense to buy rather than try to build.

[CatalinaWOW]

That is a good point of course. Still I think it's important to put things into perspective here, I have not done any actual calculations but I'll take a wild assed guess and say that home made capacitor capable of storing as many Watt Hours of energy as an off the shelf deep cycle battery you can get for $100 at Walmart is going to be something around the size of a semi tractor trailer. Chemical batteries have energy density orders of magnitude higher than capacitors, and that's proper mass produced commercial capacitors. Anything that works well enough to be useful will be dangerous, difficult and expensive to build. I'm a big fan of DIY, but one still has to recognize when it makes sense to buy rather than try to build.

All true.  This only makes sense as art.  Like building your own Nixie tubes, or emulating a Pentium in TTL.

[Conrad Hoffman]

In spite of the popularity of the idea, it's hard to come up with a worse way to store energy than a capacitor. First order of business might be to go here- http://www.tinaja.com/etsamp1.shtml and read everything Don Lancaster has to say on energy. A better storage system might be to pump water into an elevated holding tank, or raise a few hundred thousand pounds of concrete a couple feet. Then power a generator as the water or cement comes back down. IMO, it's still fun to try and construct a capacitor. You'll need to etch the foil to get any reasonable value. I think the usual electrolyte formula has you bubble ammonia through the glcol-borate mixture. Maybe something useful in my collection of old Sprague cap notes here- http://conradhoffman.com/lib_item_list.htm You may find some clues on electrolytes and energy storage if you read between the lines.

[forrestc]

Strong winds came and tore my wind generator to pieces so i decided to rebuild the whole thing.
I want my generated electricity to be stored in an electrolytic capacitor but over time the generator might produce quite some electricity so big caps would be needed.

The correct 'electrolytic capacitor' for this purpose is created with sulfuric acid and lead plates.   Or better put - a lead-acid battery.   Or maybe some other battery chemistry.

As, now I look down the thread some other people have said the same thing.

People a lot smarter than you and I have been working on improving lead-acid battery storage for years.   So far, there really isn't anything which is better, although lithium-ion batteries are finally giving it a run for the money, and there's some work on various iron (aka edison) batteries as well.   Capacitors aren't even close.

[drussell]

Wait a minute... where did the 100F figure come from ? 

In your original post you state you want to store wind generated electricity.  One of the responses showed that it would take a 100 F capacitor to store enough energy to light a 100 W bulb for 1 hour.

You guys are off by more than an order of magnitude.  A 100F capacitor charged to 120 volts would light a 100 watt light bulb for only two minutes, not an hour.  You need a 3000F capacitor to get an hour.

That is, of course, assuming that your (Batteroo-Brand?) boost converter can slurp all the energy from the capacitor, over an input voltage range of 0 to 120 volts, with 100% efficiency.

A 3000F parallel-plate capacitor with a .001 inch plate spacing, aluminum oxide dielectric (dielectric constant of 8.4) requires about 400 square miles of aluminum foil.  Even once you double the effective surface area by rolling it up to use both sides of the plates (200 square miles) and increase the surface area by roughing the surface, I don't see how this idea is even remotely feasible, no matter how close you might be able to make the plate spacing.

You need electrochemical cells or pumped storage or something to even begin to be in the realm of being possible.  Even thinking about being able to store that amount of energy in an electrostatic field is pure insanity!   

[tautech]

You need electrochemical cells or pumped storage or something to even begin to be in the realm of being possible. 

Like a magnetically levitated 100K RPM flywheel ? 

[drussell]

All true.  This only makes sense as art.  Like building your own Nixie tubes, or emulating a Pentium in TTL.

LOL, I would love to see a Pentium in TTL.   

It would probably only take, what, about 75,000 7400-series chips and fill a large building or two.  Not sure how someone would power it, though. 

I'll stick with my still-functioning original Wang 2200 system from the 1970s, thanks...   It is made from 7400 series logic, uses 74181 ALUs for the main math functions.  That's plenty big enough for me... 

I really should make some videos of that system sometime. 

[nctnico]

If you want a lo-tech solution then lead-acid batteries are the simplest to make and maintain. As long as they are charged and discharged right they can last a very long time.

[Conrad Hoffman]

The nickel-iron batteries referred to above are old tech, but might well lend themselves to a DIY effort. Probably info on them in the old Audel's Electrical Guides and/or similar books.