How realistic are home made high voltage capacitors - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 01:36:32 am
content: Hi all,how realistic is it that I can make mica capacitors which have a minimum 500v rating with perhaps a 500 Farad capacity?I have looked at a few online calculators and none come anywhere near close.Thoughts?

author: johansen
author_rank: Super Contributor
timestamp: March 24, 2014, 01:41:36 am
content: you would need a conventional capacitor about the size of a bus.wikipedia quotes super caps on the order of 3-5 watt hours per kilogram.500F at 500 volts is 6944 watt hours.you'll have to wait for the"nano graphene-based, ionic liquid-enabled supercapacitors" to show up, allegedly they are around 86 watt hours per kilogram

author: BravoV
author_rank: Super Contributor
timestamp: March 24, 2014, 01:45:25 am
content: 500 Farad ?What is the physical size of that cap ?

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 01:50:19 am
content: Thanks for the reply....Ok, don't have spare bus-size space, nor do I honestlyneed6944 Watt Hours.Do need to handle at least 500v.What is the equation for working out W/Hours and Capacitance from 5-600 volts?Was reading about the nano graphene-based caps the other day. Just wondered if I could make something at home?

author: BravoV
author_rank: Super Contributor
timestamp: March 24, 2014, 01:52:34 am
content: Quote from: Gazucha on March 24, 2014, 01:50:19 amAgain, just hate to see this thread turned into a joke, seems like you're ignoring people amazement on a 500V rated 500 "FARAD" capacitor.Are you sure its Farad (F) , not micro Farad as uF ?

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2014, 01:56:02 am
content: If you take a typical compact super capacitor, say 10 F, 2.5 V, then you can put 200 of them in series to get up to 500 V. But that will give you 0.05 F. So now you can put 10 000 of these series arrangements in parallel to get up to 500 F. That's going to be a mere two million capacitors. At $5 per super capacitor, that should only cost you about $10 million. But you can probably negotiate a discount for a volume purchase...

author: BravoV
author_rank: Super Contributor
timestamp: March 24, 2014, 01:57:40 am
content: Quote from: IanB on March 24, 2014, 01:56:02 amThat is assuming its an "electrolytic" cap, the OP wants a "mica" capacitors, you should re-calculate your numbers there.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 01:59:51 am
content: I appreciate it is an unlikely capacitor choice, and I have never seen one EVER anywhere close, but was looking at 'super-caps the other day which were around 2.7v and between 1 and 2200 Farads (not micro), and seeing none for sale ANYWHERE, just wondered if it wouldn't be possible to make something in the 'Farad' capacitance range which had a 5 or 600 volt rating?

author: BravoV
author_rank: Super Contributor
timestamp: March 24, 2014, 02:01:40 am
content: Possible, but you're lacking one most important thing ... budget ?

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 02:02:25 am
content: Quote from: IanB on March 24, 2014, 01:56:02 amGot a student discount card too.

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2014, 02:03:31 am
content: Quote from: Gazucha on March 24, 2014, 01:59:51 amYes, it would, as I explained. As long as your budget runs to millions of dollars...

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2014, 02:06:56 am
content: You can get a 10 µF capacitor at 250 V, or you can get a 10 F capacitor at 2.5 V.But you can't get a 10 F capacitor at 250 V. If the capacitance goes up, the voltage goes down. Or if the voltage goes up, the capacitance goes down.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 02:07:14 am
content: Ok,so what is the largest capacity, high voltage cap' that can be bought off the shelf by a pauper? Mica or not?

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2014, 02:10:13 am
content: You can search Digikey as well as I can.Or you can look out for disused equipment and try to salvage capacitors from them. Automatic defibrillators, laser power supplies, computer power supplies, etc.Just watch out. They are dangerous and can kill you before you realize you are dead...

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 02:13:13 am
content: Well, see I did do some searching online. Went to a couple of manufacturers but everything just seemed low capacitance.I'm looking Digikey now.

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2014, 02:18:06 am
content: In a disposable camera you may find a capacitor of about 160 µF at 300 V. If you are lucky you may find used disposable cameras available for free from photo processing labs.

author: mariush
author_rank: Super Contributor
timestamp: March 24, 2014, 02:20:16 am
content: Dude, some basic things first.if you connect capacitors in series, capacitance goes down, voltage goes up... ex 2 100uF 16v capacitors in series will act like a 50uF 32v capacitor.Supercapacitors in general can tolerate up to about 5.5v - there are supercapacitors that do more voltage but they're rare.The biggest supercapacitor you can probably buy now are maxwell 2600-3000uF 2.5-2.7v ultracapacitors :http://www.ebay.com/itm/Maxwell-2600F-2-5V-Supercapacitor-2600-Farad-Super-Ultra-Capacitor-/271429645000?pt=LH_DefaultDomain_0&hash=item3f3277b2c8http://www.ebay.com/itm/Maxwell-3000-Farad-Ultracapacitor-Supercapacitor-Super-Ultra-Capacitor-NEW-/301100054670?pt=PCA_UPS&hash=item461af6388eSome people replace their car battery with 6 of those 2600F capacitors (6 x 2.5v = 15v which is good enough, as the car's battery charger usually does 13.8-14v) .. but if you connect these in series you get a 430F 15v ultracapacitor. See how the capacitance drops?So if you want a 500v supercapacitor, you'll basically need 200 of these in series to get something like <1F (too lazy to do the math) 500v .. Imagine how much space those 200 supercaps use.

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 02:20:25 am
content: There are thousands of caps to look through which I don't have the time for right now, especially considering the first one I found - 500v 15uF ,,,,,are $411 each!!!!!!

author: mariush
author_rank: Super Contributor
timestamp: March 24, 2014, 02:23:53 am
content: Quote from: Gazucha on March 24, 2014, 02:13:13 amLots of supercapacitors here:http://www.digikey.com/product-search/en/capacitors/electric-double-layer-capacitors-supercaps/131084LotsLots of regular capacitors here:http://www.digikey.com/product-search/en/capacitors/aluminum-capacitors/131081Yeah, mica is more expensive. Who needs lots of capacitance usually resorts to electrolytics or other types.Use the columns to select 500v or higher. Though, sometimes it's better to go with 2 x 250v or more capacitors, it's cheaper that way

author: Unknown
author_rank: Unknown
timestamp: March 24, 2014, 02:30:11 am
content: Ok chaps,thank you very much for the info. I can work out a plan B without the robbing a bank.Can't really seem to get Digikey to work easily (won't apply filters) so will just look elsewhere.

author: MarkL
author_rank: Unknown
timestamp: March 24, 2014, 03:10:10 am
content: Quote from: mariush on March 24, 2014, 02:23:53 amFolks, do not put capacitors in series and expect them to have an additive voltage rating. Especially high voltage capacitors.In theory this works, but in reality the capacitors will differ slightly in internal resistance and capacitance and you will end up with an uneven distribution of voltage across the series. If you are already operating near the series maximum, you can easily exceed the voltage rating on an individual capacitor. And then if it shorts, even more voltage is across the remaining ones, and then they in turn will short even faster.This can be addressed with circuitry to balance the voltage between capacitors in the string, or more simply just parallel capacitors with the desired voltage rating in the first place.Surplus Sales of Nebraska (http://www.surplussales.com) sells a lot of high voltage capacitors, mostly from the old tube days. They may have what you need, but probably not up into Farad range.

author: electrodacus
author_rank: Super Contributor
timestamp: March 24, 2014, 03:25:55 am
content: A super-capacitor is a totally different type of capacitor compared do a normal mica, ceramic or electrolytic.It has much much higher energy density than an electrolytic about 5000 to 10000x moreIs also called EDLC (Electric double-layer capacitor).They working voltage is up to 2.7V I've seen some 3V but not higher the 5.5V are two super capacitors in series used in low discharge rate applications usually as backup power for a RTC.It uses carbon to store energy so it dose not have a traditional dielectric and the graphene will not be able to improve energy density by much since this already taking advantage of the under nanoscale structure of carbon. I will not expect more that a doubling in energy density that will still be at least 5 to 10x lower than that of lithium.I have a video on youtube about this

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 24, 2014, 04:16:21 am
content: If you actually need 500F and 500V... what ESR?It is in fact possible to make your own double layer caps at home using activated charcoal and water, but the voltage rating is a paltry 1.1V or so (due to electrolysis; if you had the ionic solvents used in real ones, you could get the same 2.7V proper supercaps achieve). And just any random preparation of charcoal is going to have monstrously high ESR, a few cubic inches being sufficient perhaps for CMOS memory backup but not even enough to illuminate with an LED (though what little it does glow will go on almost forever). Needless to say, you'll need hundreds of cells in series. It will be large, tedious, perform poorly, and probably end up costing more than other alternatives.But a far cheaper solution would be begging for used car batteries, which are like capacitors but better, and rejuvenating them enough to use (check/replenish acid, desulfating, etc... might recover up to half the amp-hours?). You'll only need 40 in series to get the voltage; you'll have to check how many in parallel you'll need for the capacity.If a car battery discharged linearly from 12V to 6V, delivering 50Ah in the process, it would be equivalent to a 30kF capacitor; 40 in series would then be 750F, so a truck-bed-ful of old/abused car batteries would probably come close.If size and weight is a bigger concern.... get an industrial 400V 3ph generator set.Can't beat the energy storage of gasoline (or diesel). A rectifier on there will get 500VDC pretty well, give or take some adjustment.Tim

author: johansen
author_rank: Super Contributor
timestamp: March 24, 2014, 06:39:10 am
content: on a serious note:the cheapest 500 volt capacitors on an energy basis, depending on other details is either:surplus electrolytic cells orsurplus motor run capacitors (240vac rated can safely run at 500vdc)for example:4 joules per dollar, paper-oil capacitor:http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/88-MFD-1200-VDC-RUN-CAPACITOR-22-1120.axd15 joules per dollar, not including shipping:http://www.ebay.com/itm/450V-1800uF-Electrolytic-Capacitors-High-Voltage-NEW-IN-BOX-60-Off-Dist-Price-/281047573998.75 joules per dollar, but still a very good deal:http://www.ebay.com/itm/MAXWELL-CAPACITOR-07-mfd-50-kV-CAPACITOR-6-/161232467688

author: electrodacus
author_rank: Super Contributor
timestamp: March 24, 2014, 07:05:49 pm
content: Quote from: johansen on March 24, 2014, 06:39:10 amThat is not even close the cheapest.The Hybrid one I used in my video was about 10$ in small quantitiesIs a 220F at 2.3V that can store a max of 582J so around 58J/dollarElectrolytic are not meant for energy storage so they have no chance in competing.It will be a bit hard to build a 500V DC out of 2.7V Supercapacitors but not impossible you will need a BMS for that mine is only good for 8 series supercapacitors.Not sure why the OP needs something like that what will he use this for ?

author: johansen
author_rank: Super Contributor
timestamp: March 24, 2014, 07:18:15 pm
content: i didn't even include super capacitors because they have orders of magnitude higher internal resistance, and lower voltage.

author: electrodacus
author_rank: Super Contributor
timestamp: March 25, 2014, 12:20:41 am
content: Quote from: johansen on March 24, 2014, 07:18:15 pmYes they have lower voltage but also much higher energy density.As for the ESR that is not that different Supercapacitors have ESR under one mohm depending on capacity and manufacturer where electrolytic are usually hundreds of mohm again depending.Then 200 or so supercapacitors in series will get to around 100mohm ESR so I will say the ESR is about the same for an equivalent voltage.

author: Unknown
author_rank: Unknown
timestamp: March 25, 2014, 03:16:45 am
content: Lot's of input so thanks to everyone for that.Quickly looking through, perhaps I should have asked a different question...?Something more along the lines of, 'which TYPE of capacitor is best for energy storage that can handle at least 500 volts?'I originally mentioned Mica because I once read a Tesla Patent where he mentioned them and it always stuck in my mind. I just don't remember ever seeing any Mica caps in anything near whole Farads!Why I was asking, is that I wish to play around with charging a large cap with static and then eventually trying to get some half-decent amperage back out of the cap.Just to see.

author: han
author_rank: Frequent Contributor
timestamp: March 25, 2014, 03:39:30 am
content: Easy,just grab one from here

author: calexanian
author_rank: Super Contributor
timestamp: March 25, 2014, 06:28:07 am
content: Yeah.. Unreasonable. I would say go back to the drawing board on that design and fundamentally change your power source...

author: casinada
author_rank: Frequent Contributor
timestamp: March 25, 2014, 04:43:55 pm
content: http://www.maxwell.com/ultracapacitors/http://www.ebay.com/bhp/maxwell-super-capacitor

author: c4757p
author_rank: Super Contributor
timestamp: March 25, 2014, 04:52:12 pm
content: Quote from: Gazucha on March 25, 2014, 03:16:45 amAn ESD event is typically 1 or 2 kV at about 100pF, or 100 to 200 nC. Assuming you can rig up a way to deliver one of those once per second, it will take you 58 to 116daysto charge a 1 F capacitor toone volt.If you want to experiment with storing static charge, try aLeyden jar.

author: electrodacus
author_rank: Super Contributor
timestamp: March 25, 2014, 07:07:26 pm
content: Quote from: Gazucha on March 25, 2014, 03:16:45 amFirst why do you need to store 500V ? Can you use less for storage and then use a step up to deliver your 500V?Why it needs to be stored in capacitors ? will you have a lot of energy that needs to be stored in a short amount of time?As for energy storage you probably did not watched my video it will answerer exactly your question and moreIt makes a comparison between supercapacitors electrolytic capacitors and lithium batteries there is a nice comparison at the end.