# RC Charge/Discharge for Electrochemical Capacitor

• nanomoly
In summary, there are two problems with charging an electrochemical capacitor through an RC circuit- the voltage jumps up quickly and the capacitor never reaches the applied voltage. It seems like the cause of both of these problems is internal resistance. If you can reduce the internal resistance of the capacitor, you should be able to fix the jumping voltage and eventually reach the applied voltage.

#### nanomoly

I am a student working on designing an electrochemical capacitor (an area which i have limited experience). When I charge this capacitor through an RC circuit I notice two non ideal effects. I need to adress the cause of these effects if I can ever hope to correct them.

The first problem is that the voltage immediatly jumpts up to about a quarter of the applied voltage before following the exponential function expected from RC circuit theory. I have discovered that internal resistance of the capacitor is the cause of this. However, I don't understand why the internal resistance does not simply add to the resistor in series with the capcitor.

My second problem is that the capacitor never reaches the applied voltage but approaches a lower voltage. If i continue to let it charge it will eventually start discharging on its own. This observation holds true even for low applied votlages. I have a feeling this is caused by leakage but can anyone confirm this?

nanomoly said:
I am a student working on designing an electrochemical capacitor (an area which i have limited experience). When I charge this capacitor through an RC circuit I notice two non ideal effects. I need to adress the cause of these effects if I can ever hope to correct them.

The first problem is that the voltage immediatly jumpts up to about a quarter of the applied voltage before following the exponential function expected from RC circuit theory. I have discovered that internal resistance of the capacitor is the cause of this. However, I don't understand why the internal resistance does not simply add to the resistor in series with the capcitor.

My second problem is that the capacitor never reaches the applied voltage but approaches a lower voltage. If i continue to let it charge it will eventually start discharging on its own. This observation holds true even for low applied votlages. I have a feeling this is caused by leakage but can anyone confirm this?

If it jumps up initially, that means it does not have much capacitance. Recall the relationship between current and a changing voltage for a capacitor. Probably it has to do with the way your electrochemical electrolyte is working with no initial bias.

And the end result sounds like a high leakage current, again probably related to your electrochemistry.

Low capacitance causes an inital jump in voltage? My conclusion of high ESR was based on figure 7 of this pdf.