Supercaps

[Hugh Morris]

I'm a newbie hobbyist and building some small symmetrical supercaps using conductive ink ,aqueous electrolyte with a separator
They charge ok, self-discharge as expected but then go to negative charge on the meter.
Can anyone tell me why?

 

[DrG]

When they are discharged, they go to a negative charge? what does that mean?

 

[Hugh Morris]

I mean that the multimeter is showing a negative symbol ( - ) next to the voltage reading.
Having gone past zero the reading is climbing with a negative charge.

 

[DrG]

Climbing to what voltage? Are you talking about a few millivolts? and what happens if you reverse the leads?

It sounds to me like you are discharging the capacitor with the voltmeter and that it was not fully discharged. Or maybe I just don't understand, which is also possible.

Maybe you have demonstrated negative capacitance??

https://www.researchgate.net/profile/Petr_Viscor/post/What_is_negative_capacitance/attachment/59d63fa079197b807799bfe7/AS%3A428004963819521%401479055743305/download/NegativeCapacitance02.pdf

Nahhh

 

[atferrari]

I vaguely recall someone making reference to a type of electrolytic cap that when discharged below a very low level, suffered of such effect. Sorry but I do not recall the follow up of that story.

 

[unclejed613]

it may be a chemical reaction of the electrolyte and one of the plates. you said "aqueous" electrolyte, and that means it contains water, which can facilitate some kind of battery action after the cap discharges. did you use distilled water, or tap water in making the electrolyte? it makes a big difference, because of dissolved compounds in the water that may cause a lot of wild things to happen.