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.
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.
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.
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.
That isn't what the diagram shows.
They are excellent for micro power applications, they do not self-discharge rapidly
Way more effective in some dawn to dusk solar powered lights where I replaced the nicad or nmh batteries - especially when you take into consideration that the batteries are often discharged well past their safe levels in normal use.
Well how long did you wait, then?
You could've saved us the time and deleted the picture, because it's meaningless.
Tim
Could well be. AlPo caps behave like that.
Cheers
Phil Hobbs
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.
My apologies for wasting your valuable time. Send me an invoice.
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.
That's not micropower. The issue is not if they self-discharge rapidly. The issue is if they can be charged up at all given the low power source they are being charged from. JL's diagram shows higher leakage current than the application I would be using these in.
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.
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.
Zeners protect them in the reverse direction, too.
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..
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