# I have a question about charging the 2.7 V super capacitor.

#### Duracell2

Joined Feb 13, 2017
3
Dear members, I have a question about charging the 2.7 V super capacitor.

I read that the maximal charging voltage for super capacitor should be 2.7 V.

However, sometimes I adjust my power supply to 3.5 V and charge them. Because then the current it's higher and it charges faster.
I connect a voltmeter directly to the capacitor and monitor the voltage rising from e.g. 1.5 V to 2.7 V
When the voltage reaches 2.7, i disconnect it from the power supply.

QUESTION 1: Why is power supply showing 3.5 V and the voltmeter connected to the power supply AND capacitor only 1.5 V when charging starts.
QUESTION 2: Is it wrong way to charge super caps, because I use 3.5 V on the power supply and not 2.7 V ?
QUESTION 3: If it is NOT wrong, can I even increase the voltage even more in order to charge them faster ? Use 5 V, and then disconnect the cap when it is charged to 2.7 V.

Thank you very much for your help

Moderator's Note:
This thread was split from --
I want to use a 1.5 F super capacitor as the output capacitor in an audio range power supply

#### ronv

Joined Nov 12, 2008
3,770
Dear members, I have a question about charging the 2.7 V super capacitor.

I read that the maximal charging voltage for super capacitor should be 2.7 V.

However, sometimes I adjust my power supply to 3.5 V and charge them. Because then the current it's higher and it charges faster.
I connect a voltmeter directly to the capacitor and monitor the voltage rising from e.g. 1.5 V to 2.7 V
When the voltage reaches 2.7, i disconnect it from the power supply.

QUESTION 1: Why is power supply showing 3.5 V and the voltmeter connected to the power supply AND capacitor only 1.5 V when charging starts.
QUESTION 2: Is it wrong way to charge super caps, because I use 3.5 V on the power supply and not 2.7 V ?
QUESTION 3: If it is NOT wrong, can I even increase the voltage even more in order to charge them faster ? Use 5 V, and then disconnect the cap when it is charged to 2.7 V.

Thank you very much for your help

Moderator's Note:
This thread was split from --
I want to use a 1.5 F super capacitor as the output capacitor in an audio range power supply
I'm going to make a guess that you are measuring your power supply then moving the meter to the capacitor, because the voltage should be the same at both ends of the wires going from the power supply to the capacitor unless they are very small.
So my guess is the power supply voltage is dropping from the high current needed to charge the cap.
This may be hard on your power supply, but is probably ok for the cap as long as you don't forget to disconnect it.

#### Duracell2

Joined Feb 13, 2017
3
I'm going to make a guess that you are measuring your power supply then moving the meter to the capacitor, because the voltage should be the same at both ends of the wires going from the power supply to the capacitor unless they are very small.
So my guess is the power supply voltage is dropping from the high current needed to charge the cap.
This may be hard on your power supply, but is probably ok for the cap as long as you don't forget to disconnect it.
I have tested it now. You are right.
I use a cheap CC/CV 10A power supply, so I have a voltage drop, when cap draws a lot of current.
Of course the voltage should be the same on cap and power supply (same connection points), but I was blended by the fancy LCD display of the power supply
I thought it should be constant.

Someone mentioned also a diode between.
I tried this too, with the 15 A diode in between. This is preventing only that the power supply shows the voltage of the cap, when voltage regulator of the power supply is turned down below the voltage of the capacitor.

For now is everything clear. Thank you very much for your help !

#### Duracell2

Joined Feb 13, 2017
3
I was thinking.
My adjustable power supply has a voltage drop while charging the caps.

But would what happen if I use "better" power supply. Would there be a voltage drop ?
Or even use 12 V Li Po battery and connect it to single 2.7 V super cap ???

What would happen ?

#### BobTPH

Joined Jun 5, 2013
2,538
Supercaps basically look like a short circuit when discharged. The correct way to charge them is with a constant current source. I.e. the voltage should be lower than 2.7V at first and increase as the capacitor charges up. The current source should be set to something less than the max rating of the power supply. This will charge the capacitors at maximum speed while not straining the power supply.

Bob