# Stepping up super capacitor voltage output?

Discussion in 'General Electronics Discussion' started by imperium2335, Oct 4, 2012.

1. ### imperium2335

10
0
Sep 15, 2011
Hi,

Is it possible to boost the voltage coming out of a capacitor?

If so what is the effect on the capacitor? e.g. drains it faster, gets hotter, shortens its life etc

The reason I ask is that I have just bought a 3000 farad capacitor @ 2.7v, and even after making some big sparks and other acts of mindless destruction, it still has much of its voltage remaining.

I want to increase the amount of voltage it can provide for more practical purposes of course, but since its DC I can't just put a transformer on it. I'm still bit of a noob at electronics.

2. ### Harald KappModeratorModerator

12,463
2,987
Nov 17, 2011
The energy stored in the capacitor is W=1/2*C*V².
You can draw that much energy from the capacitor in the form of electric current. While drawing energy from the capacitor, the term "W" is reduced proportionally. Since "C" is a constant (describing the capcitance), the voltage "V" will decrease accordingly so the equation is still valid.

If you want to increase the DC voltage you nedd a step-up or boost converter (another link).
Another technology uses switched capacitors for the job.

If the output of your boost converter is regulated to a fixed voltage and you have a fixed load, The output power will remain constant (P=V*I). The input voltage of the boost converter, however, will fall due to the energy withdrawal from the capacitor (see above). Now, since you can't deliver more energy at the output than you draw from the capacitor at the input, a perfect converter could operate at Pin=Pout at best (100% efficiency). A real converter will operate only at e.g. 80% efficiency, thus Pin = Pout/0.8 . you need more input power thanm you can deliver at the output.
This input power is taken from Vcapacitor*Icapacitor. And as the voltage will drop over time (see above), the current has to rise inversely to keep the power constant. This rising current will drain the capacitor even faster, so you end up with draining (discharging) the capacitor ever faster.

While this is no secret magic, building an efficient boost converter is not trivial either.

3. ### BobK

7,682
1,689
Jan 5, 2010
You can also place two or more capacitors in series to increase the voltage, just like you would with batteries.

Bob

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