Looks like it would be fine to stack these in series without any equalizing parts, like regular wet aluminum caps.
Measuring supercaps is an enormous pain; every step takes hours. The equivalent dielectric absorption is huge.
Leakage tempco appears to be strongly negative, but that may be an illusion.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
They self-discharge quickly, as shown in the diagram?
w.
Helmut Wabnig wrote on 5/25/2017 1:10 AM:
Wow! That's enough leakage to make them useless for micropower energy harvesting. Good to know.
-- Rick C
Nothing happens quickly on a 10F capacitor.
At the rated 2.7 volts, leakage is spec'd at 30 uA max. That's a discharge rate of 3 microvolts per second.
The leakage is specified after 72 hours at voltage. I didn't wait that long.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Thanks for sharing this!
Interesting: At 2.7V specified 30uA, measured 120uA. A x4 factor here...
Pere
Is this really going to be better after being 3 days there?
Pere
On a sunny day (Thu, 25 May 2017 09:36:51 +0200) it happened o pere o wrote in :
If we need ANY regulations at all, then I think it is about the highest time we impose regulations on China to live up to their specs. And force them to write decent English specs, where they for example have at leat the slightest idea what they talk about. It is in their own interests. Else no choice other than to avoid that country's products, no matter how much cheaper those are than say US or EU made stuff.
Well how long did you wait, then?
You could've saved us the time and deleted the picture, because it's meaningless.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Could well be. AlPo caps behave like that.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Could be. Things take a long time to settle, the equivalent of some very slow dielectric absorption. If I step up the voltage, the power supply current limits for a while, and when the voltage hits the target, the current tapers off slowly, over hours and probably days.
These things take some getting used to. Temperature changes C, and when you change a charged 10F cap connected to a power supply, things happen. So measuring leakage is complex.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
My apologies for wasting your valuable time. Send me an invoice.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
How do you conclude that? Wouldn't it depend on
Put another way, could you not draw the same conclusion if you measured the self-discharge of a single lithium battery cell vs. voltage? Yet people keep putting balancing circuits on them. I'm sure there is a reason.
In these caps, current increases nonlinearly, radically upward, with voltage, so a series pair will tend to equalize. In fact, a series pair that I tried did equalize nicely. And overvoltage makes them leak a lot but doesn't appear to damage them.
It's dangerous to put film caps in series to increase voltage rating. Ditto some polymer aluminums and ceramic caps. Wet aluminums, and this supercap, look to be self-equalizing.
Batteries are different, because the first one that runs out of coulombs can be reverse-biased by the others, and damaged. These supercaps are really unpolarized, so won't be damaged by reverse bias. And they are real capacitors, so have a linear discharge curve, not flat-topped like batteries; that makes the caps in the stack tend to have the same voltage across them.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
On a sunny day (Thu, 25 May 2017 08:23:31 -0700) it happened John Larkin wrote in :
Indeed, lipos will just go up in voltage if over charged. The 'equalizers' are sometimes just a parellel load system, like a zener, per cell, preventng the cell from going over 4.2 V. That way everything gets charged.
Tim Williams wrote on 5/25/2017 9:16 AM:
It's far from meaningless. It is just a measurement under different conditions. If your usage won't be for storing charge for over 72 hours this is a measurement that is more to your conditions.
-- Rick C
Zeners protect them in the reverse direction, too.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
On a sunny day (Thu, 25 May 2017 08:32:12 -0700) it happened John Larkin wrote in :
Real zeners would, although with -.7 or so volts I would not want to use those cells again... But usually you are talking about several amps charge current, and like Tim posted here some year ago, a transistor with a voltage sensor shorting out / limiting the voltage can be used. If it was a MOSFET with a reverse body diode, yes. Would have to be a logic level type that works far below 4.2 V Vgs on. Bipolar is nice here. No GHz :-)
On a sunny day (Thu, 25 May 2017 11:29:53 -0400) it happened rickman wrote in :
You may like this, guy leaves supercaps in over the weekend, car starts with it:
No battery..
That curve shows milliamps, not microamps. Crap capacitor.
To be fair it is 130ua at it's maximum rated voltage.
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