I didn't realise supercaps worked this well. - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 03:36:44 pm
content: Well, I hooked a 5mm clear red LED to a 5.5v one farad super cap, charged it to 2.1 volts before I went to sleep, and nodded off. It dimmed down to around 1.8 volts before I went to sleep, this morning I woke up, and saw a tiny red glow in the LED still, hooked up the meter, and it's still at 1.4778 volts right now after almost 10 hours, and dropping extremely slowly, I knew supercaps were good, but I am impressed, I see why they are used for memory backups.I imagine the properties capacitors have of gaining voltage back also help with this, but I need to order some more.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 08, 2014, 03:40:06 pm
content: bear in mind you will get a visible glow with only tens of microamps with some LEDs. Voltage will level off around the LED forward voltage, so you'll get a fairly steep initial slope, followed by a much flatter, low-current discharge slope.

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 03:42:38 pm
content: Quote from: mikeselectricstuff on May 08, 2014, 03:40:06 pmYeah, these ones need above 1/1.1 volts or so to light up at all.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 08, 2014, 04:08:44 pm
content: In my experience, blue LEDs and "emerald green" LEDs need the least amount of current to get a visible glow.

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 05:00:23 pm
content: 1.4709v now, LED is juuust barely visible.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 08, 2014, 05:05:38 pm
content: And even less if your eyes are dark adapted.Nothing about supercaps or LEDs (beyond their moderate quantum efficiency), just normal physics.The time constant, of course, rises exponentially, so it will never actually drop to zero volts (assuming an ideal capacitor -- might be better to try this with a film capacitor).Oh, and if you ever feel like a serious measurement on this, make absolutely sure the LED is completely pitch black dark, no external illumination whatsoever. It will act as a photocell, keeping the capacitor charged up to some voltage.The LED also need not fully become dark, either. I recall there was one of those shitty MIT press releases, years ago, where they claimed overunity light production. Well, yeah, you can get a few thermally generated electron pairs crossing a weakly biased LED junction, and get the visible photon from it. That doesn't mean nanowatts are actually usable. IIRC, the power density is such that, if you had a wall completely covered in pure, single crystal gallium phosphide, it wouldn't even be enough to read by. (In contrast, the same wall covered with hardly a gram of radium would glow enough to see at night. Um, don't lick the walls.)Tim

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 05:14:28 pm
content: Quote from: T3sl4co1l on May 08, 2014, 05:05:38 pmGasp! FREE ENERGY!

author: electronics man
author_rank: Frequent Contributor
timestamp: May 08, 2014, 07:46:37 pm
content: i had 75F wortgh of supercaps producing 5v (after a DC to DC convertor) powering an LED for 4 hours

author: Artlav
author_rank: Frequent Contributor
timestamp: May 08, 2014, 10:20:45 pm
content: Supercaps are interesting.I have a bunch of them linked up to a solar panel -http://orbides.1gb.ru/img/sc-1.jpgTwo parallel blocks of 8 in series -http://orbides.1gb.ru/img/sc-2.jpg25F total, at 18V.They power a phone charging socket (charges for 6 minutes at 5V, 500mA when the sun is down).They also power a couple of 1W LEDs, for quick light when i need to write an idea down at night -http://orbides.1gb.ru/img/sc-3.jpgThe LEDs run for quite a while, tens of minutes on full charge.They are driven with CC drivers, so no gradual dimming into nothingness, they die quite fast into darkness.I also dealt with bigger stuff -http://orbides.1gb.ru/img/sc-4.jpg11 of 350F ones in series, 32F at 27V.Two of these can power a gauss cannon that shoot a bolt through 0.5cm of plywood. For about 50 shots.200A currents straight out of the energy storage, no extra capacitors needed.And the largest ones i have -http://orbides.1gb.ru/img/sc-5.jpg6S2P battery of 3000F ones, 1000F at 15.6V total.Can provide 400A continuously, or 4000A for 5 seconds.Not sure how long it can power an LED, but if you put a crowbar across it, the crowbar is going to LOSE.Like i said, supercapacitors are interesting.

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 10:23:36 pm
content: Quote from: Artlav on May 08, 2014, 10:20:45 pm

author: Artlav
author_rank: Frequent Contributor
timestamp: May 08, 2014, 10:35:53 pm
content: Quote from: XOIIO on May 08, 2014, 10:23:36 pm$65 apiece at digikey -http://www.digikey.com/product-detail/en/BCAP3000%20P270%20K04/1182-1021-ND/3079285I got a box of 12 of them for $200 or thereabout on ebay a few years ago, which translates to $16 apiece.Not super expensive, but not exactly cheap stuff.

author: XOIIO
author_rank: Super Contributor
timestamp: May 08, 2014, 10:45:29 pm
content: Wow, talk about a good deal.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2014, 12:04:07 am
content: I should've gotten a few from Electronics Goldmine, back when they were on sale for $30/ea... last time they had a few they were $60, and they still sold out fast!Tim

author: Stonent
author_rank: Super Contributor
timestamp: May 09, 2014, 04:47:06 am
content: You can start your car with them:Or even smaller ones!

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 07:13:18 am
content: yep,I start my car with them every morningIt definitely gives the starter-motor a kick in the pants speed wise, because it gets almost the full 14V across it. i.e. there's very little series resistance to drop the voltage under load.Even with a brand new car battery you lose a few volts trying to pull out 200A. Not so with a supercap

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 09, 2014, 08:09:13 am
content: Quote from: Psi on May 09, 2014, 07:13:18 amNoice, but ey, a small 3s high C rc lipo would turn that over (i think thats a pulsar, but unsure), not too much heavy liftingI've got a pack like that with some 35mm2cable and alligator clamps that i use to help start machinery - clip it to the battery, wait 5 mins, start it up.

author: fcb
author_rank: Super Contributor
timestamp: May 09, 2014, 08:14:06 am
content: Cool!Do you have a conventional battery somewhere else? How does the alternator cope (does it even make a difference?)

author: XOIIO
author_rank: Super Contributor
timestamp: May 09, 2014, 08:29:15 am
content: Man I bet that would shock a mechanic, no pun intended

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 09:11:53 am
content: nope, i don't have any battery. Just the capsThe point was to get rid of the battery so i don't want to add one back in.The alternator is happy as long as the caps are >10V.It will start the engine down to about 7V, but below 10V the alternator instantly tries to pump it's full 40A into the caps at engine idle which will stall the engine unless you give it some extra gas for 10 sec or so (until the voltage gets back up).Yeah, the people at the vehicle testing station didn't know what to think of it.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 09, 2014, 09:12:48 am
content: Quote from: fcb on May 09, 2014, 08:14:06 amProbably not, as there is very very little voltage drop under load, they can start a car with no real issue from around 9v~, it'll take a few days for them to go that low. Once the car is started, the alternator brings them right back up - it can be quite a load on the alternator, but it isn't for that long so it doesn't really matter.

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 09:17:49 am
content: Self discharge is very small, they only lose about 0.1V a month with no load.I had to disconnect he alarm though. If i have the alarm connected it only takes 4 days to run the caps too flat to start the engine.With the alarm unplugged i never have to worry about it. The car can sit for months and start fine.

author: XOIIO
author_rank: Super Contributor
timestamp: May 09, 2014, 09:19:38 am
content: Quote from: peter.mitchell on May 09, 2014, 09:12:48 amThat seems like an awesome alternative to a battery, though they probably wouldn't work well here during the winter.

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 09:42:44 am
content: huh? Caps workmuchbetter during the winter.A normal lead acid battery has a lot of trouble supplying high current in very cold conditions and, when cold, the engine oil is super thick which requires higher than normal current to crank.Ultracaps have no problem supplying massive currents far in excess of a lead acid and they don't get effected by the cold anywhere near as much as batteries.Infact it's very common for large trucks to have a small cap bank across their battery to provide the high current push needed to get a cold engine turning over.

author: nowlan
author_rank: Frequent Contributor
timestamp: May 09, 2014, 09:46:01 am
content: Didnt that laser saber dude have a lipo top up the caps?My car battery is having a hard life in the cold lately.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 09, 2014, 10:09:07 am
content: Quote from: Psi on May 09, 2014, 09:17:49 amQQ aussie made cars QQ, my 2004 ba falcon takes about a week with just parasitics from remote central locking ect.i use them without an external battery to jump start machinery - even a flat lead acid battery will hold a float to 11v, give it some time to charge the caps, then when you crank the caps do the heavy lifting.

author: Artlav
author_rank: Frequent Contributor
timestamp: May 09, 2014, 10:12:13 am
content: Quote from: Psi on May 09, 2014, 09:11:53 amHm.Have you ran into any problems with self-discharge, or long spans of inactivity?Or, for example, sitting in the car with the engine off while waiting for someone - a few lights here and there and/or a radio might draw quite a bit.What is your contingency plan in case of overdischarge in the middle of nowhere?Quote from: Psi on May 09, 2014, 09:11:53 amIsn't that bad for the alternator?Or it's too short of a time to overheat anything?

author: XOIIO
author_rank: Super Contributor
timestamp: May 09, 2014, 10:15:06 am
content: Quote from: Psi on May 09, 2014, 09:42:44 amDo the work well in -30 or below Celsius?

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 11:36:13 am
content: Quote from: XOIIO on May 09, 2014, 10:15:06 amYep, -30C isnt' even outside of their operational temp rangeThe boostcaps i'm using in my car have an operational temp of -35C to 65C and a max discharge current of 600AAt -35C the ESR is a little higher but stillwayless than any battery.It's a static charge not a chemical reaction so low temps don't cause the same issues as in a battery.Quote from: Artlav on May 09, 2014, 10:12:13 amProbably, but yeah, it's oven in a few secondsQuote from: Artlav on May 09, 2014, 10:12:13 amNo problems with long spans of inactivity at all, my car is old and doesn't draw much, if anything, when off.I had to remove the car alarm though. It did draw too much.I don't really have a contingency plan. Jump starting it from another car is risky.Flat cap = dead shortI never got around to making it but i did intend to build a small DC/DC boost converter that could take a few AA's and recharge the caps in an emergency

author: XOIIO
author_rank: Super Contributor
timestamp: May 09, 2014, 11:43:33 am
content: Quote from: Psi on May 09, 2014, 11:36:13 amThat sounds ominous

author: cimmo
author_rank: Frequent Contributor
timestamp: May 09, 2014, 11:47:12 am
content: Those supercap banks as car battery replacements definitely sound interesting.What would you estimate (guesstimate?) their equivalent amp-hour rating to be?Say, down to 10v?Also, do you think the heat in the engine bay may adversely affect them (one post quoted a +65c rating).If so, how? Loss of charge while hot or permanent loss of capacity?I know my existing battery location gets hotter than that in summer.

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2014, 11:54:48 am
content: Quote from: cimmo on May 09, 2014, 11:47:12 amhm..Cap bank = 433FCap charged voltage = 14VCap end voltage = 7V (lowest i can start the engine from)So, picking a typical 1A discharge (because it will be easy to work out Ah later) we can calculate the dv/dt1A / 433F = 2.309mV drop per second under 1A loadUseful voltage / voltage drop per second under 1A load = number of seconds we'd get at 1A7V / 2.309mV = 3031 seconds of 1A discharge3031 seconds = 0.842hours of 1A, which is 842mAh, i think

author: rexxar
author_rank: Frequent Contributor
timestamp: May 09, 2014, 09:13:55 pm
content: Lead acid batteries are horrid things, but they've got incredible energy density. I like the idea of supercaps, especially for starting in extreme cold. However, I do a lot of waiting, listening to radio with the engine off, I'd much rather have something like a good LiPo pack for backup. And maybe I'd put some sort of current limiting on the alternator, to prevent it cooking itself (those things aren't cheap!)

author: IanB
author_rank: Super Contributor
timestamp: May 09, 2014, 11:29:50 pm
content: Quote from: Psi on May 09, 2014, 11:54:48 amCan work it out directly from the capacitor formula:Q = C(V1- V2)So,Q = 433 (14 - 7) = 3031 As3031/3600 = 0.842 Ah

author: Psi
author_rank: Super Contributor
timestamp: May 10, 2014, 01:23:32 am
content: cool, good to know the answer i got was correctQuote from: rexxar on May 09, 2014, 09:13:55 pmYeah, if you want engine-off accessory power for running things you definitely want some sort of additional battery.It only takes 5min 30seconds to discharge the caps from 14V to 7V with my headlights on.The typical battery voltage of 14V isn't quite in the right spot for having a lipo across it. Its too high for a 3S and too low for a 4S.You'd need some sort of DC/DC or a smaller gelcel

author: Fsck
author_rank: Super Contributor
timestamp: May 10, 2014, 01:27:29 am
content: Quote from: rexxar on May 09, 2014, 09:13:55 pmdepends on your definition of extreme cold. I haven't found (though I didn't search hard) any supercaps that actually do extreme cold, just moderate cold (-40C min operating temp for Maxwell's supercaps)I wonder if they'll even work at temps around -50C

author: Psi
author_rank: Super Contributor
timestamp: May 10, 2014, 01:31:00 am
content: I'm sure they would work at -50C, they would just be outside of spec.You can extrapolate the ESR curve to -60 and it the ESR would likely be ~300% which is still less than a battery.Not sure what it would do to the capacity, probably nothing.Quote from: cimmo on May 09, 2014, 11:47:12 amHeat didn't really occur to me until i read the datasheet yesterday and saw +65C max.I put them into the car as an experimenti guess we will see.They have been in there for just over a year now.

author: SeanB
author_rank: Super Contributor
timestamp: May 10, 2014, 05:32:14 am
content: Current limiting for the alternator is very easy, just add a series resistance in the supply lead from the alternator to the battery made simply using a 1m long length of 1.5mm automotive cable. As most cars have the alternator wiring direct to the battery you simply add it in series after winding it into a small flat coil. The extra 100-200mR will limit the current nicely, but still pass 40A easily enough.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 10, 2014, 02:08:40 pm
content: Quote from: Psi on May 10, 2014, 01:31:00 amI think i might put a thermocouple on my battery - i actually doubt it gets that high in there, even in summer, the air flow would keep them within working temp range, however, if they GENERATED heat they wouldn't be able to cool and thus would be out of temp range.

author: Psi
author_rank: Super Contributor
timestamp: May 11, 2014, 10:04:10 am
content: I've checked the per-cap voltage from time to time, just to see if they are staying balanced.So far balance between the caps hasn't been a problem. They're all the same +/- 0.1VAdding some zeners+fets to limit the per-cap voltage under 2.5V was something i thought i would need, but so far its been fine without it.I did a test leaving my remaining 3 caps (i bought 9) charged to 2.5V and graphed the voltage loss from general leakage over a few months.The leakage response flattened quite a bit once the cap voltage was down to 2.2V, so my guess is that the 6 pack finds its own balance since the higher voltage cap leaks more.

author: David Hess
author_rank: Super Contributor
timestamp: May 11, 2014, 07:43:05 pm
content: Double layer capacitor lifetime is reduced to like 1/10th for every 0.4 volt increase so hopefully they stay balanced. Rated lifetime at 2.2 volts is about 10 years so I would use 8 cells in series instead of just 6. Given the cost of the capacitors, I would also make some effort balance them.http://hal.archives-ouvertes.fr/docs/00/41/14/82/PDF/ESSCAP2006_Venet_2.pdf