DIY 18 farad capacitor - Page 1
Forum section: electronics / projects

author: FrankBuss
author_rank: Unknown
timestamp: December 12, 2015, 05:10:57 am
content: This looks very interesting:If I didn't made a mistake in my calculations (see video comments), the capacitor has a capacity of 18 F. I remember when I did experiments building capacitors with aluminium and plastic foil and they where in the nanofarad range.Is this real or a fake? Has anyone independently reproduced it?

author: ataradov
author_rank: Super Contributor
timestamp: December 12, 2015, 05:41:02 am
content: Not knowing anything about this person, I feel like it is a hoax of some sort.There is just too many minor mistakes in terminology ("power supply could deliver more Amps", charging with higher voltage to compensate for insufficient current), "graphene" in the title. It all feels like one of those self-taught inventor geniuses.

author: c4757p
author_rank: Super Contributor
timestamp: December 12, 2015, 05:44:46 am
content: Quote from: ataradov on December 12, 2015, 05:41:02 amThat one feels less like a mistake in terminology and more like a fundamental misunderstanding of absolute basics. It was very hard not to just stop there. Dude has no idea what he's talking about.

author: acbern
author_rank: Frequent Contributor
timestamp: December 12, 2015, 06:56:42 am
content: Besides the fact that the guy mixes up some terms, two metal plates and an acid on a carrier inbetween is not so special. There are other videos about combining e.g. lead and alum (not an acid, but still a chemical cell). This is not working on the principles of a classic capacitor (two conductors with an insulator inbetween).Best known combination is two plates of lead and lead-oxide, and sulfuric acid inbetween, and here is your car battery. Is a little bigger, and has about 20000 Farad, depending on size.If his construction is technically usable (charge cycles, temperature behavior, stability, cost...) in an industrialized version is a totally different issue.

author: station240
author_rank: Unknown
timestamp: December 12, 2015, 07:08:55 am
content: Construction is weird, for example why use thin wire, when leaving a tab sticking out the side would allow high current (eg slide a spade connector over the aluminium).Quote from: acbern on December 12, 2015, 06:56:42 amI agree, it could simply be a chemical cell, commonly known as a battery. We never see this capacitor fully charged, or discharged.Also he hides things like, charge efficiency. Odd given he has two meters, and yet doesn't measure the power input when charging.Thinking this is closer in chemistry to a zinc carbon cell. Aluminium isn't that different to zinc.I'm always suspicious of these "I made a super capacitor using a cement mixer" videos.

author: FrankBuss
author_rank: Unknown
timestamp: December 12, 2015, 08:30:49 am
content: Right, could be just a battery. Still impressive if it charges in 10 seconds, but he has to measure how often it can be charged and discharged.

author: ataradov
author_rank: Super Contributor
timestamp: December 12, 2015, 08:33:29 am
content: Quote from: FrankBuss on December 12, 2015, 08:30:49 amWell, there is a clear jump cut and 10 seconds lasted less than a second in a video.

author: DanielS
author_rank: Frequent Contributor
timestamp: December 12, 2015, 02:46:09 pm
content: Quote from: FrankBuss on December 12, 2015, 08:30:49 amA cell that can provide an average of 30mA for 15 minutes is basically a 7.5mAh battery. You need 2.7A to charge that in 10 seconds. Seems within the realm of plausible but then again, that also makes his "invention" quite large for a 7.5mAh cell since you can get lithium cells with 10x the capacity in 1/100th the size.

author: Fungus
author_rank: Super Contributor
timestamp: December 12, 2015, 03:17:48 pm
content: If you can make them at home that easily then surely there would be commercial ones available...

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: December 12, 2015, 04:11:14 pm
content: Everybody who claims he can cook graphene in his kitchen, smear it on a foil and thus get a graphene supercap ist just a dork and shows that he doesn't even understand what graphene is.People tend to confuse graphene and graphite. Graphene is so special since it's a two-dimensional structure (one layer of atoms) and this is exactly what makes it so hard to produce capacitors or anything else from it.Keep in mind that the larger the area of a capacitor, the larger the capacitance. So to get a high capacitance you need one (2D) crystal with a very large area. If you have to combine several crystals to achieve the size, the physical properties are much worse compared to a single crystal. When the 2D-structure is completely lost by using a power, the special properties are completely lost as well and you could have used graphite in the 1st place.

author: FrankBuss
author_rank: Unknown
timestamp: December 12, 2015, 04:25:34 pm
content: You can buy graphene powder, but it is very expensive:https://graphene-supermarket.com/A-12-Graphene-Nanopowder-5g.htmlBut you are right, some other products would be more interesting, like the monolayer graphene on copper. You can get it for only $299 for a 60 mm x 40 mm copper plate:http://www.graphenea.com/collections/graphene-productsHe didn't list the graphene he was using, maybe he mixed it up with graphite.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: December 12, 2015, 04:39:01 pm
content: There might be fields of application for graphene powder - but you won't make supercaps from it. The idea of a powder somewhat contradicts the idea of a graphene monocrystal. And without the special 2D crystal structure, it's just graphite (best case) or carbon.This is the major fallacy of people who try to cook graphene at home with kitchen equipment or sellotape. Actually, you might be able to get a few microgram of graphene in a large pile of other crap, but even if you would be able to extract the graphene from the rest, you'd still have only microscopic fragments which you can't glue together to get a monocrystal.

author: FrankBuss
author_rank: Unknown
timestamp: December 12, 2015, 04:40:38 pm
content: So would it be possible to produce a very high cost capacitor, which uses layers of graphene (which is very stable and highly conductive) and layers of a good insulator between? Probably the insulator layers need to be more than one atom thick, but it would be a really high energy density capacitor.

author: gilbenl
author_rank: Regular Contributor
timestamp: December 12, 2015, 04:52:31 pm
content: Dumb. Guy needs Gen Chem, P Chem, or Wikipedia. Nice DIY/post-apocalypse carbon film cap though.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: December 12, 2015, 05:04:41 pm
content: Quote from: FrankBuss on December 12, 2015, 04:40:38 pmI don't see why it shouldn't be possible to stack layers of graphene sheets like it's already done for other (super-)caps. It's just that I somewhat doubt that you'd get a really high a capacitance this way. Graphene is special because it has very high conductivity and a high theoretical capacity per gram - due to large surface per gram. If you can't make use of that large surface because you stack little sheets I don't think the capacity will be much higher (if at all) compared to traditional approaches.Graphene is not a magic material, it just allows things that are not possible with other materials. But as long as there is no cost-effective way to use graphene in a way that makes use of its special properties, the theoretical advantages are just that: theoretical.

author: FrankBuss
author_rank: Unknown
timestamp: December 12, 2015, 06:00:14 pm
content: Graphene is stronger than steel and very conductive. With traditional approaches I guess you'll need layers which are thicker than one atom, because otherwise the ESR would be too high, or the material would break too easily. Maybe a one layer graphene layer would be possible, resulting in much more possible layers for the same height compared to normal SuperCaps (or at least much less layers than with other materials). Appropriate insulator layers would be made from diamond

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 12, 2015, 07:21:11 pm
content: Supercaps are mature technology, well understood, in standard production, and easily made at home.Making good ones at home, not so much. Mainly because you'd use activated charcoal (or some sort of graphene muck, like shown), and end up with terrible ESR. But over a long enough time scale (t >> ESR * C), the capacitance is measurable. (The voltage rating is also typically poor, because a special organic electrolyte is required to withstand 2.5V+. The same principle works in water, but is limited to 1.2V.)Tim

author: d-smes
author_rank: Regular Contributor
timestamp: December 12, 2015, 08:25:40 pm
content: I was reminded ofhttp://spectrum.ieee.org/semiconductors/materials/how-a-microscopic-supercapacitor-will-supercharge-mobile-electronicswhen reading this topic. They start out smearing graphite oxide on plastic and somehow end up with graphene after blasting (heating) it with a laser. Hope they can commercialize this (IEEE article) as it looks promising.

author: Psi
author_rank: Super Contributor
timestamp: December 12, 2015, 09:23:04 pm
content: Quote from: d-smes on December 12, 2015, 08:25:40 pmThat looks like one of the most promising technologies for improving energy storage

author: gilbenl
author_rank: Regular Contributor
timestamp: December 13, 2015, 08:32:48 pm
content: Thought this was cool. Theoretically, it looks like it is possible to make graphene using DIY materials (assuming lab-grade graphite is considered DIY). However, I don't think there's a chance in hell of getting it from activated carbon. Graphite has a "shear-able" 3D crystal, whereas activated charcoal is a similar, but highly disorganized/chaotic macrostructure. You'll just end up with multiple granules and not nice, neat monolayers.Moral of the story: Some dude in his kitchen is not going to make graphene from fish tank filter-grade activated carbon...not that anyone here has claimed this.