Author Topic: Storing unused ultra/super cap, keep terminals opened or shorted ?  (Read 9540 times)

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Online BravoV

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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.
 

Offline NANDBlog

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #1 on: March 23, 2016, 09:15:53 pm »
Maxwell supplies it's supercapacitor banks with a shorting strap on the terminals. I think it is all we need to know.
 

Online hayatepilot

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #2 on: March 24, 2016, 02:35:55 am »
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.
 

Online BravoV

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #3 on: March 24, 2016, 03:26:50 am »
Maxwell supplies it's supercapacitor banks with a shorting strap on the terminals. I think it is all we need to know.

Thank you, I didn't know that, and that exactly I was expecting.  :-+


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.

Regarding 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.
 

Offline zal42

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #4 on: March 24, 2016, 03:38:17 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.
 

Offline Zbig

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #5 on: March 24, 2016, 04:06:55 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

And how's 5V gonna force the lethal current through the resistance of your body, exactly? ;)
 

Offline fubar.gr

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #6 on: March 24, 2016, 04:08:50 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

But you can't have a high current without a high enough voltage.

Offline rrinker

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #7 on: March 24, 2016, 04:51:46 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

But you can't have a high current without a high enough voltage.

 Sure 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.

 

Online BravoV

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #8 on: March 24, 2016, 04:55:38 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

But you can't have a high current without a high enough voltage.

 Sure 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.

Oh .. no ,  here we go again, after voltage, current, now the "resistance" comes to play.  :-DD

C'mon guys, stop it, we already have multiple threads with gazillion posts each, arguing exactly this, please do search and post there.
 

Offline CatalinaWOW

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #9 on: March 24, 2016, 05:00:47 am »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

But you can't have a high current without a high enough voltage.

 Sure 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.

I 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.
 

Offline Shock

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #10 on: March 24, 2016, 05:07:15 am »
12V 1F, stick your tongue across this.

Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM
Oscilloscopes: Rigol DS1054Z, Phillips PM3065
 

Online SeanB

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #11 on: March 24, 2016, 05:49:58 am »
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.
 

Offline Delta

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #12 on: March 24, 2016, 06:02:22 am »
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!
 

Offline Cliff Matthews

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #13 on: March 24, 2016, 12:34:02 pm »
Regarding 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 ?

As the old saying goes, it's not the voltage that will kill you. It's the amps.

But you can't have a high current without a high enough voltage.

 Sure 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.
ElectroBOOM to the rescue!
 

Offline hamguy

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #14 on: March 24, 2016, 02:52:19 pm »
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!
I 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
 

Offline DTJ

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #15 on: March 24, 2016, 03:06:31 pm »
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.

I 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.
 

Online BravoV

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #16 on: March 24, 2016, 04:48:32 pm »
The ability to cause nasty burns due to extremely high currents as nothing to do with the ability to cause electric shocks.

Yep, 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.
 

Online hayatepilot

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #17 on: March 24, 2016, 05:22:45 pm »
I was referring the Maxwell supercap modules being safe to handle with the shorting strip.
These modules come in up to 48V and if you put multiple of them in series, things can get really dangerous really quickly.
Single cells on their own are not that worrisome.
 

Offline Psi

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #18 on: March 24, 2016, 05:35:09 pm »
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 :)
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline fubar.gr

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #19 on: March 24, 2016, 08:26:24 pm »
The ability to cause nasty burns due to extremely high currents as nothing to do with the ability to cause electric shocks.

Yep, 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.

In 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.

Offline amyk

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #20 on: March 24, 2016, 09:49:28 pm »
The ability to cause nasty burns due to extremely high currents as nothing to do with the ability to cause electric shocks.

Yep, 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.
Then don't leave them charged.
 

Offline mathsquid

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #21 on: March 25, 2016, 11:59:28 am »
12v can not cause an electric shock. Wet sponges or otherwise.  Tongues asside!
I 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...

When 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.

Offline station240

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #22 on: March 25, 2016, 02:06:23 pm »
When 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.

I'd hope your tonge isn't long enough for that to be possible  :-DD

Human 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.
 

Offline Orpheus

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #23 on: March 26, 2016, 05:42:20 am »
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
 

Online SeanB

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Re: Storing unused ultra/super cap, keep terminals opened or shorted ?
« Reply #24 on: March 26, 2016, 06:07:24 am »
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.
 


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