Storing unused ultra/super cap, keep terminals opened or shorted ? - Page 1
Forum section: electronics / beginners

author: BravoV
author_rank: Super Contributor
timestamp: March 23, 2016, 07:31:32 am
content: Title should be self explanatory.I mean for storing quite long period, say > 6 months.Just worry about the dielectric absorption may cause fire hazard in the future.Or am I worry too much ?Pro & con ? Discuss please.

author: tszaboo
author_rank: Super Contributor
timestamp: March 23, 2016, 10:15:53 am
content: Maxwell supplies it's supercapacitor banks with a shorting strap on the terminals. I think it is all we need to know.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: March 23, 2016, 03:35:55 pm
content: I think the shorting straps are more of a sanity check.When you see the strap connected, you can be absolutely shure that the cap is empty and can be touched without any dangers.

author: BravoV
author_rank: Super Contributor
timestamp: March 23, 2016, 04:26:50 pm
content: Quote from: NANDBlog on March 23, 2016, 10:15:53 amThank you, I didn't know that, and that exactly I was expecting.Quote from: hayatepilot on March 23, 2016, 03:35:55 pmRegarding electrocuted by touch, my caps are only 5.5 or 2.5 volt rated, don't think it will do harm at that voltage level, isn't it ?But yeah, its purely sanity check and also just a precaution, who knows in the future if its not strapped, the terminals get connected by accident.

author: zal42
author_rank: Contributor
timestamp: March 23, 2016, 04:38:17 pm
content: Quote from: BravoV on March 23, 2016, 04:26:50 pmAs the old saying goes, it's not the voltage that will kill you. It's the amps.

author: Zbig
author_rank: Frequent Contributor
timestamp: March 23, 2016, 05:06:55 pm
content: Quote from: zal42 on March 23, 2016, 04:38:17 pmAnd how's 5V gonna force the lethal current through the resistance of your body, exactly?

author: fubar.gr
author_rank: Unknown
timestamp: March 23, 2016, 05:08:50 pm
content: Quote from: zal42 on March 23, 2016, 04:38:17 pmBut you can't have a high current without a high enough voltage.

author: rrinker
author_rank: Super Contributor
timestamp: March 23, 2016, 05:51:46 pm
content: Quote from: fubar.gr on March 23, 2016, 05:08:50 pmSure you can - that's why a car battery and some wet sponges makes a great torture device. That's only 12V. With a LOT of amps.

author: BravoV
author_rank: Super Contributor
timestamp: March 23, 2016, 05:55:38 pm
content: Quote from: rrinker on March 23, 2016, 05:51:46 pmOh .. no , here we go again, after voltage, current, now the "resistance" comes to play.C'mon guys, stop it, we already have multiple threads with gazillion posts each, arguing exactly this, please do search and post there.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 23, 2016, 06:00:47 pm
content: Quote from: rrinker on March 23, 2016, 05:51:46 pmI don't even want to know how you know that.There isn't much danger to your body from these, but there is always danger to property. It may be minor, like a blown part, but could even be major if the wrong thing falls across the terminals and starts a fire.

author: Shock
author_rank: Super Contributor
timestamp: March 23, 2016, 06:07:15 pm
content: 12V 1F, stick your tongue across this.

author: SeanB
author_rank: Super Contributor
timestamp: March 23, 2016, 06:49:58 pm
content: Put your wedding ring across those terminals and see if the charge dissipates faster than the time it takes the ring to get past 60C, which is the threshold of burns forming. Past 100C your flesh boils, and past 600C it chars away.Your new nickname------ Stumpy.

author: Delta
author_rank: Super Contributor
timestamp: March 23, 2016, 07:02:22 pm
content: The ability to cause nasty burns due to extremely high currents as nothing to do with the ability to cause electric shocks.12v can not cause an electric shock. Wet sponges or otherwise. Tongues asside!

author: Cliff Matthews
author_rank: Unknown
timestamp: March 24, 2016, 01:34:02 am
content: Quote from: rrinker on March 23, 2016, 05:51:46 pmElectroBOOM to the rescue!

author: hamguy
author_rank: Newbie
timestamp: March 24, 2016, 03:52:19 am
content: Quote from: Delta on March 23, 2016, 07:02:22 pmI have often used my tongue to determine if a 9V battery is good or not. No damage to me or the battery, no incapacitating shock...The wet sponge thing comes from the movies. A Mel Gibson movie comes to mind...-g

author: DTJ
author_rank: Super Contributor
timestamp: March 24, 2016, 04:06:31 am
content: Quote from: SeanB on March 23, 2016, 06:49:58 pmI ring barked my finger when I shorted my wedding ring to the electrode. Luckily it was just a nasty burn, I have not worn a wedding ring since, much safer.

author: BravoV
author_rank: Super Contributor
timestamp: March 24, 2016, 05:48:32 am
content: Quote from: Delta on March 23, 2016, 07:02:22 pmYep, this is exactly what I was worrying about.Even my biggest one is only at 700F 2.5Volt, but with the internal resistance is about 4 mili Ohm, an accidental short across the terminals by a small conductive metal will make it glow bright red or even melt it.Definitely I don't want this to happen unattended.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: March 24, 2016, 06:22:45 am
content: I was referring the Maxwell supercap modules being safe to handle with the shorting strip.These modules come in up to 48Vand if you put multiple of them in series, things can get really dangerous really quickly.Single cells on their own are not that worrisome.

author: Psi
author_rank: Super Contributor
timestamp: March 24, 2016, 06:35:09 am
content: I left mine charged up (2.6V) and they slowly discharged to 1V after a year and a half.But from the purpose of safety it's best to leave them shorted, 2000A at 1V is still 2kW

author: fubar.gr
author_rank: Unknown
timestamp: March 24, 2016, 09:26:24 am
content: Quote from: BravoV on March 24, 2016, 05:48:32 amIn practice, single supercaps are mostly harmless.Yes, in theory they can dump hundreds of amps if shorted. But in reality at just 2.5 - 2.7 volts the short must have a really low contact resistance with the capacitor terminals for any significant current to flow. This requires some determination and is quite unlikely to happen accidentally.I tried shorting a supercap with crocodile clips, expecting the wire to become red hot in an instant. I was dissapointed when all I managed was to get it lukewarm. The wire-clips assembly had a total resistance of 0.7 ohms. That's low, but at just 2.7 Volts the result is an unimpressive 3.8 amps.Of course, if you string several caps in series and get a working voltage of 12 Volts or more, things can get really dangerous.

author: amyk
author_rank: Super Contributor
timestamp: March 24, 2016, 10:49:28 am
content: Quote from: BravoV on March 24, 2016, 05:48:32 amThen don't leave them charged.

author: mathsquid
author_rank: Frequent Contributor
timestamp: March 25, 2016, 12:59:28 am
content: Quote from: hamguy on March 24, 2016, 03:52:19 amWhen I was a kid, I reasoned that since sticking my tongue to a 9v battery doesn't hurt, sticking it to a 6v lantern battery would be even less of a shock. I was wrong, and it was quite painful. I would NOT put my tongue across the terminals of a car battery.

author: station240
author_rank: Unknown
timestamp: March 25, 2016, 03:06:23 am
content: Quote from: mathsquid on March 25, 2016, 12:59:28 amI'd hope your tonge isn't long enough for that to be possibleHuman skin is a reasonable insulator, so obviously areas without skin (eg tongue) or contact made under the skin (sharp pins, tasers etc) have a lower voltage/pain treshold.I'd store super capacitors with a bit of fuse wire across the terminals, as any residual charge could do damage to other electronics (including other super caps), or whatever box you store it in.

author: Orpheus
author_rank: Regular Contributor
timestamp: March 25, 2016, 06:42:20 pm
content: I'd imagine that a terminal strap would also provide ESD protection for these 2.5v devices.Elsewhere, you might never notice 5 or 50 or even 500V of ESD

author: SeanB
author_rank: Super Contributor
timestamp: March 25, 2016, 07:07:24 pm
content: I doubt a supercap would get an overvoltage from an ESD event, I can not think of any ESD event that would put that much energy into one without you being badly burnt in the process. The shorting will be more for preventing the dielectric absorption inside the supercap from charging it up to 2V again over time, or to a reverse voltage.

author: BravoV
author_rank: Super Contributor
timestamp: March 27, 2016, 12:28:10 pm
content: Quote from: SeanB on March 25, 2016, 07:07:24 pmExactly.I'm guessing when stored shorted doesn't have any bad long term effect right ? Especially to the electrodes, electrolytes and etc.Here mine, from now on its shorted, and separated from the series connections as its quite dangerous.This particular one, from a fully charged at rated voltage, then drained to 0 volt, if left opened just an overnight, it will bounce back to > 1 volt.

author: XOIIO
author_rank: Super Contributor
timestamp: March 27, 2016, 12:43:53 pm
content: Quote from: Shock on March 23, 2016, 06:07:15 pmThat's only one farad? Jeeze.

author: station240
author_rank: Unknown
timestamp: March 27, 2016, 12:49:52 pm
content: I've got a 2,000V capacitor from an old microwave stored with the terminals shorted.Those also have a reputation for building up a voltage from energy stored in the dialectric somewhere.As for the 1F car audio caps, many of them are pure wank.Somewhere online is a review an Australian did of various ones, what the actual values are, and what sort of ballast is inside to make up for the lack of actual capacitor.One had a huge lump of refactory brick inside.

author: SeanB
author_rank: Super Contributor
timestamp: March 27, 2016, 12:54:58 pm
content: Saw that, where one had a half kilo of sand and pitch inside, and a recycled capacitor as the rest. IIRC it was not even 10 000uF.