Is Capacitor used as temporary batteries? - Page 1
Forum section: electronics / beginners

author: ActiveRegion
author_rank: Contributor
timestamp: February 02, 2022, 08:37:01 am
content: Hello,I am studying capacitors over the internet when i came across this article in wikipedia which itemized the application of Capacitor. In the energy storage applications it states that it is"COMMONLY used to maintain supply while battery is being changed". This is the first time ive read the capacitor being used in this application.I know capacitor can be used in a plethora of ways in a circuit but i want to confirm is it "common" to used it in this application? Emphasis on the word common. Or is it considered an exotic application? Or the article is entirely wrong.? Anyone who has an actualy experience implementing capacitor as temporary supply when the main is out? I want to know.screenshot of the article is attached.

author: Capernicus
author_rank: Frequent Contributor
timestamp: February 02, 2022, 08:50:12 am
content: On a temporary power outage, U can use a super capacitor to keep the unit alive, but it doesn't last that long. A really big super cap is 3000F and that'll only run things for about 5 mins before it'll run out of charge in general.Ordinary capacitors don't even last a second most the time, but they are a really useful anyway in a circuit. In a lot of ways you can think of them as a tiny battery that have a small amount of capacity, think of the potential of that!U can use them as little check points that take charge to deliver them to other places from there. (That's what bypass capacitors are I think.)If you put them in combinations with resistors the way they take time to charge up and give out current causes them to be able to be used as filters, which is quite amazing that it works out to be that. I never would have guessed without being shown.Ends up being a pain because u can accidentally form low pass filters in a design without meaning to, because they are so simple it pops up sometimes when u'r plugging your circuit together.If you put a cap in an ac powered circuit it acts as a resistor, because when the cap fills up it blocks the rest of the current in that direction (until it reverses polarity.), the useful thing is its really cool temperature cause caps don't dissipate current in an ideal sense, so they always stay nice and cool by themselves.They do more things too, its up to you to figure it out because ppl dont like giving away info so easily in these parts, sir.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 02, 2022, 09:14:27 am
content: That whole text is complete BS written by someone "for fun" with no idea what they are talking about, throwing random terms and words around. Ignore it in entirety.

author: Capernicus
author_rank: Frequent Contributor
timestamp: February 02, 2022, 10:48:09 am
content: Quote from: Siwastaja on February 02, 2022, 09:14:27 amOpinion entitled.Whats ur fav use of a cap? =)

author: Siwastaja
author_rank: Super Contributor
timestamp: February 02, 2022, 10:52:38 am
content: Don't know about favorite, but in number of manufactured and assembled capacitors, the most common use is to give low-impedance supply to ICs (including CPUs). In this use, exact amount of capacitance is irrelevant, and the most important parameter is low ESL. Hence, this is nanosecond (or even picosecond) scale energy storage, because even just a few centimeters of wire cannot supply the required fast change in supply current.Non-volatile SRAM storage is currently being discussed here:https://www.eevblog.com/forum/chat/why-not-cmos/Supercapacitors can be used for such purpose but it isn't very common to do so.We can of course try to guess what the author was thinking about, but it's more fruitful to just ignore such poorly written text.

author: MK14
author_rank: Super Contributor
timestamp: February 02, 2022, 11:07:36 am
content: Quote from: ActiveRegion on February 02, 2022, 08:37:01 amIn my opinion, it is a rather badly written wiki section, that you highlighted. What they seemed to be talking about, is that the settings/data stored in the ram of a device, can be temporarily maintained, if the circuit is appropriately designed, to just keep the ram powered, and not the rest of the circuitry. Using a small capacitor.The device itself (except for the CMOS ram), is not powered, when the battery is disconnected. Otherwise the capacitor would run out of power, extremely quickly (with complicated exceptions I will leave out).You might find proper electronics books (paper or internet), gives you more accurate information about capacitors.

author: PKTKS
author_rank: Super Contributor
timestamp: February 02, 2022, 11:13:41 am
content: They may be referring that today several projects are using SUPER-CAPACITORS as if they are bats (like CR2032 coins) instead.. they can hold charge for small systems while power is off for a considerable long period...But they eventually die some day as well..google for SUPER-CAPACITORsPaul

author: nali
author_rank: Frequent Contributor
timestamp: February 02, 2022, 11:35:05 am
content: I think whoever wrote that article now works for the RS components web team...Unfortunately although caps are physically simple little critters, actually understanding them or how they are used quite quickly goes down the rabbit hole of AC theory. Many years ago when I was at college I remember my lecturer started out by describing them as "like a bucket, for electrons"One thing that doesn't get mentioned much is the big difference between a battery & supercap is a battery will maintain a more or less constant voltage over the majority of its discharge cycle while current is drawn from it, whilst the voltage across a supercap decays just like any other capacitor.Quote from: Capernicus on February 02, 2022, 10:48:09 amImpedance matching. Decoupling is sooo boring....

author: tszaboo
author_rank: Super Contributor
timestamp: February 02, 2022, 11:55:54 am
content: It was one of their usage cases for programmable calculators or 1980 PDAs, that had SRAM storage.It is not commonly used for this, it was a niche application. Someone edit it please.

author: Capernicus
author_rank: Frequent Contributor
timestamp: February 02, 2022, 11:58:59 am
content: Quote from: nali on February 02, 2022, 11:35:05 amIf you put 1000 lipos in parallel, and u increase the discharge and charge speed, or you get a super cap and u discharge through a resistor, they meet in the middle the same on the curve, I think. Its got to do with the maximum output and capacitors look really unconstant because their discharge and charge speed is ideally infinite. which is the main selling point for them in my mind, plus the extra cycles /lifespan.<edit i think i got a mixed up in my head then, but if u put a resistor on a cap it flattens out the discharge curve. especially if it was going into a constant current circuit then it would be completely flat edit>NandBlog - are you the guy that does the fpga stuff and u sold an fpga board or something? I love ur videos they were really helpful thanks.

author: rpiloverbd
author_rank: Regular Contributor
timestamp: February 02, 2022, 12:14:44 pm
content: Super capacitors can be used as temporary batteries:https://www.sparkfun.com/products/746

author: MK14
author_rank: Super Contributor
timestamp: February 02, 2022, 12:17:45 pm
content: Quote from: tszaboo on February 02, 2022, 11:55:54 amThat as well, but was not really what I was trying to explain.You have a modern AA battery powered device, with an MCU at the heart of it, and perhaps the time and some user settings. So, when they change the batteries on perhaps an LCD clock/alarm/radio. It can keep the time (RTC) and basic settings (AM/PM or 24 hours + Alarm time), powered up, via a small capacitor, during the couple of minutes it takes to change the batteries.I.e. Only the real time clock and ram settings remain powered, everything else (like the radio) shuts down.Unfortunately some of the rest of that article, mentions (or implies the use of) about using super-capacitors to replace batteries, but I'm trying to answer the original HIGHLIGHTED question the OP was asking.

author: Renate
author_rank: Super Contributor
timestamp: February 04, 2022, 12:06:09 pm
content: I had a 100,000 µF "computer" cap back in the day. When the battery in my motorcycle died I used that. With the ignition off, you'd kick over the engine a few times to charge up the capacitor. Then kick it over once more turning on the ignition just as you kicked. It ran fine.

author: tszaboo
author_rank: Super Contributor
timestamp: February 04, 2022, 12:30:37 pm
content: Quote from: MK14 on February 02, 2022, 12:17:45 pmIt wasn't a reply to your post, was it?

author: radiolistener
author_rank: Super Contributor
timestamp: February 04, 2022, 12:37:39 pm
content: Quote from: ActiveRegion on February 02, 2022, 08:37:01 amyes, supercapacitors also used instead of a vehicle battery to startup engine when it's battery is discharged. You can carry it in the pocket and it allows to provide 400-600 Amps current at 12 Volts Voltage for 15-30 seconds

author: MK14
author_rank: Super Contributor
timestamp: February 04, 2022, 12:46:30 pm
content: Quote from: tszaboo on February 04, 2022, 12:30:37 pmSince there wasn't anyone quoted in that post. I made assumptions. If those assumptions were wrong, then I'm sorry.My responses in this thread, have been primarily aimed at the original poster. But they seemed to have disappeared from this thread, so far.I'm not sure if the OP is a real genuine user, or one of these current, 'funny' accounts. That just makes posts/threads then disappears, or ignores all responses. There seem to have been a number of such accounts, in recent times.

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 04, 2022, 01:52:07 pm
content: They do use super capacitor to run clock circuit and to retain memory in some devices but capacitor isn't very good replacement for battery. All battery maintain a rather constant voltage until near the end while capacitor voltage drops as it discharges.

author: tunk
author_rank: Super Contributor
timestamp: February 04, 2022, 01:56:45 pm
content: Not "... while battery is being changed", but some flashlightswith several modes use a capacitor as a battery to store thelast mode. Sometimes it has a resistor in parallell to dischargeit in a few minutes, without a resistor the last mode can bestored for a long time.

author: TimFox
author_rank: Super Contributor
timestamp: February 04, 2022, 03:01:27 pm
content: Q = I x T = C x dV

author: David Hess
author_rank: Super Contributor
timestamp: February 05, 2022, 02:41:44 am
content: Low power CMOS memory backup circuits that allow the battery to be changed include a capacitor to power the memory while the battery is being changed.

author: Watth
author_rank: Frequent Contributor
timestamp: February 07, 2022, 11:34:44 am
content: I'm a really not an expert, but have had a look on the subject.You can use a supercap to maintain minimum "vital" data and sometimes low-power operation. That is indeed for short power loss such as battery swapping or brief power failures to preserve, for example, RTC and RAM. Basic operation can be display that the system is in such a minimal mode and to alert the user that power should be restored ASAP.From what I understand, it needs:- that only the essential elements take power from the superC- or even better the ability to detect the main power is gone, so that the system shuts off all "non-vital" systems, displays a warning or saves important data on non-volatile memory, etc.