Cellulose Acetate and supercapacitors

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Prometheus posted this 4 weeks ago

Carbonized cellulose acetate has tiny pores... so tiny that they perform better than graphene or carbon nanotubes as a supercapacitor medium.

Where can you get cellulose acetate? You can make it... get a fine-grained wood and grind it to a fine dust. Then "de-lignify" it with a basic solution and heat/pressure.

Or use a brown paper bag, which is made of wood pulp and contains nearly no lignin. The binders in a brown paper bag (if any were added) might throw a wrench in the works. I've not tried it yet, but a gentle rinse in acetone should rinse out the binders. Let it dry before proceeding.

Then apply acetic anhydride. You'll have cellulose diacetate. If you used wood dust, it'll be in powder form. If you used a brown paper bag, it'll be in a sheet.

Then (if you've used wood dust) apply acetone and form the powder into whatever form you like (wafer, etc.).

Then place your wafer or whatever shape you've made into a pure nitrogen environment and heat it to 500 F for a few hours. It'll carbonize.

The carbonization process creates the tiny pores which give cellulose acetate its super supercapacitor properties.

Place your new supercapacitor medium between the plates of a cap and test it out. Be gentle with it, it'll be brittle.

Alternatively, you can grind it up into a fine powder and put it into a regular capacitor liquid dielectric or a thick oil to form a thick slurry, then paint the cap plates with the slurry.

Here's some South Korean researchers who use cigarette butts to do the same:

https://gizmodo.com/old-cigarette-butts-can-be-used-as-material-for-superca-1616437331

 

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Zanzal posted this 4 weeks ago

Nice, I do kinda like the idea of homemade capacitors. There are some ranges of voltages and capacitance where homemade caps could probably save money, but maybe difficult to know how to make capacitors for those ranges.

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Prometheus posted this 4 weeks ago

Well, cellulose acetate is highly dielectric, with a dielectric strength of ~11 kV / mm.

A brown paper bag is made from kraft paper, which is typically 125 gsm, with a thickness of ~0.127mm. Converted to cellulose acetate, that'd handle about ~1300V.

A sheet of printer paper is typically 50 lbs.-weight or 74 gsm, with a thickness of ~0.0508mm. Converted to cellulose acetate, it'd handle ~500V.

If I were making this (and I will be in the future, with my kids, as a learning exercise), I'd make two discs of cellulose acetate from printer paper, put one on each plate of a homemade capacitor, with a thin PTFE sheet in between, then vacuum seal the whole thing in plastic sheet. The PTFE sheet would be just slightly smaller than the plastic sheets, so it'd extend beyond the edges of the capacitor plates and would be pinched by the vacuum-sealed plastic sheets around the perimeter.

I wonder if I can convince my wife to let me use her vacuum food sealer for that... perhaps it's better to beg forgiveness than to get permission. laughing

Zanzal posted this 4 weeks ago

What about making negative capacitors? Feasible? Or is negative capacitance only useful for offsetting capacitance? Even something really small like -2pF would be very interesting to play with. Would probably need to be measured in parallel with an actual capacitance to see it on an LCR meter, but if such a thing were possible it could be useful in cases where you want to negate capacitance in a coil.

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Prometheus posted this 4 weeks ago

https://www.quora.com/What-is-negative-capacitance

Working with the conventional definition of capacitance, C=Q/U, a negative capacitance means a negative voltage across the capacitor if the charge is positive.

Let’s see what happens if you short circuit such a capacitor that was pre-charged to a voltage of U0. This means it starts out with a charge of Q0=-|C|*U0. Short circuiting the two plates would allow a current flow driven by the voltage, which normally would discharge the capacitor. But here, instead of discharging, the capacitor would charge up more and more; ad infinitum. This is non-physical. There is no such thing as negative capacitance.

Or is there? Let the simulation run until the time elapsed shows about 2 seconds. Note that on the lower-left power meter, positive is power flowing into the source, negative is power flowing out of the source.

 

Zanzal posted this 4 weeks ago

Looks like a glitch related to high time step aggravated by very low resistance values. Try decreasing the time step to 1u. Resistance values are likely to be higher than those chosen as well. 

But I suppose someone should inform these folks they are wasting their time:

https://phys.org/news/2017-12-negative-capacitance-efficient-transistors.html

https://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/16902/Ferroelectrics-Negative-Capacitance-and-the-Future-of-Transistors.aspx

Science fiction yesterday, fact today, obsolete tomorrow. -Otto O. Binder

I kind of assume though this can't be used to create a discrete capacitor than when introduced into the circuit lowers the capacitance. Would be very interesting if it could though.

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Prometheus posted this 4 weeks ago

Negative capacitance is a purely resonant phenomenon. Take the circuit out of resonance, and you don't get the same results. The same applies even in electrical components which exhibit negative capacitance, such as OLEDs (which experience negative capacitance as a result of there being a lower injection barrier for holes than for electrons), which exhibit lower negative capacitance as frequency increases due to low carrier mobility.

I've stepped the simulation down to 1ps (one picosecond) and used 1 Ohm resistors, and the effect remains (it took forever to run at only 1ps time step). I think it comes about as a result of the capacitors having resistors only on one side from the frame of the voltage source, thus the plate of the capacitor without the resistor can discharge faster than the plate of the capacitor with the resistor.

ie:

The top cap has no resistor on one leg and effectively 4 on the other.

The left cap has one resistor on one leg and effectively 3 on the other.

The right cap has one resistor on one leg and effectively 3 on the other.

The bottom cap has effectively 2 resistors on each leg.

This sets up a small but ever-increasing (due to the circuit being resonant) voltage differential across the facing plates of any two serially-connected (through the resistors) capacitors, which means that in reality each set of two serially-connected capacitors is really three capacitors (the two individual capacitors, and the facing plates of each of those capacitors which experience a voltage differential due to the resistor).

This, combined with the resonance, leads to a negative capacitance effect where the facing plates build up more and more of a voltage differential. Eventually this overrides the capacitance of the individual capacitors with an induced negative capacitance.

 

Zanzal posted this 4 weeks ago

I've stepped the simulation down to 1ps (one picosecond) and used 1 Ohm resistors

Wow, that's a lot of dedication. I think perhaps when I lowered the timestep I simply didn't let it run long enough to see that wasn't the issue, sorry. Presumably a confirmation bias on my part, I believed it was the issue so I didn't consider that I just hadn't let it run long enough. I feel bad that my mistake caused you to go to such extreme measures, but somewhat awed that you did so. You have great promise, that's serious dedication. Do that in your real experiments and you will likely succeed where others fail!

You are correct though timestep alone didn't change the outcome. But when I increased the resistances to 10 mOhm the effect doesn't appear for me. I ran it up to 12 seconds, perhaps I gave up to soon? Here is a link showing my results:

Prometheus' Negative Capacitance Circuit (modified by Zanzal)

Another consideration would be whether the simulator is consistent across computers. I believe it would be, but I can't be entirely certain. Falstad's does have some limitations and you may find for future simulations changing timestep and adding reasonable series resistance values (try to get close to real world values) helps address certain issues.

Perhaps though it is the other way around, that your idea works but its easy to get Falstad not to show it under some conditions. Don't let me or my opinions be a discouragement to you though. If you believe it works as you've said then you should pursue it even if I don't believe it will work.

Anyway, I feel like I'm derailing your thread so I'll stop commenting on negative capacitance and falstad. Please show us some of your DIY capacitors when they are done, I'd love to see what they can do!

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Prometheus posted this 4 weeks ago

Huh, that's weird. Perhaps it only shows up for certain configurations?

Perhaps the facing plates of each capacitor have to have a certain resonance which is in resonance with the driving frequency, which would change with different resistances? If you speed up the "Current Speed", in your configuration the current's swashing back and forth in time with the driving frequency. In my configuration, it's more 'turbulent', but I can't put my finger on the timing of it because the timestep is so low.

In your configuration, if you change the resistances to 23m, then speed up the "Current Speed" all the way, you can see that the top-most cap is flowing current first, then the right-hand one follows shortly behind it. But there's no voltage building up (or it's building up too slowly to notice... you'll note the power meter at bottom left is entirely in the positive, denoting power flowing back to the source), perhaps because the effect's not prominent enough?

If you change the resistances by 1m at a time, you can see the changes.

I think that's the genesis of the effect, though.

{EDIT}

Ahaha... I think I've uncovered something interesting. If you place the inductor into a graph, and graph its current, if you've got your resistances right, you'll see the current swashing back and forth in the inductor continually grows by a small amount.

I'm running 5us timesteps, with 1m resistors top and bottom, and 1.3m resistors right and left. This ensures the current in the lower-left graph is always above zero (ie: power is returned to the source). The inductor is increasing in current by ~0.08 pA per cycle.

I expect inductor current flow will eventually build up sufficiently to start overriding the capacitance, whereupon the voltage will start increasing. But it's slow. It's at 65 seconds time elapsed so far. I'll let it run.

{/EDIT}

 

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Prometheus posted this 3 weeks ago

Hmmm... looking at the recent ZPower video, that looks familiar.

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Zanzal posted this 3 weeks ago

Hmmm... looking at the recent ZPower video, that looks familiar.

A quick youtube search for ZPower shows this:

Was this what you are referring too? Claims seem to be:

  1. The device uses 5 different frequencies, similar claims made by Steven Marks.
  2. The device taps earth's magnetic field/schumann resonance, similar claims were made by Steven Marks.
  3. That if we saw the waveform on the oscilloscope we would immediately understand how it works.
  4. The device derives its energy from the sun but apparently not via sunlight.

I hope people don't invest money, if there is one thing people should have figured out by now is that anyone asking for "investment" money but are capable of building free energy machines are scammers. Not a single one of these investments ever pan out, that should tell us something.

Whether the device is legit or not who knows. Hope it is but, doubt anything will come of it. Video has a strong "looking for investment money" vibe, which means its a waste of time (my opinion only). 

 

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