# Charging capacitors in parallel with a battery

I am trying to figure out a system to charge a series capacitor bank without too much current going through the capacitors. I had the idea of putting a battery in parallel with the series capacitor back to divide the current, but since the current through the capacitors is $i=C\dfrac{dV}{dt}$, and the battery would have a close to constant voltage making $\dfrac{dV}{dt}=0$. Would this effectively divide the current or would it all pass though the capacitors because of the constant voltage of the battery?

The rest of this is just for application specific reason and not as urgent as the main question above. Thanks for looking =)

The reason I am trying to do this is to cut the cost of buying more super capacitors when they are \$50 each because another method would be to add more capacitors in series to raise the voltage level and reduce the current. Are there any cheaper alternatives?

I have 1 kW of power being converted down to whatever voltage level I need. The capacitors I am looking at are the Maxwell K series. They have a voltage rating of 2.7V each, with C=1500F and a current rating of 97A. The cost of 4 is the upper limit of my budget.

• Have you considered what happens when you try to drain them at a current much higher than the battery can provide? – Ignacio Vazquez-Abrams Jun 18 '14 at 4:57
• I think your best option is to use a current source such as what is used to power LEDs. These things use a DC-DC converter so the efficiency is high enough, and you can precisley control the maximum current that your battery is sourcing. – Vladimir Cravero Jun 18 '14 at 7:09
• There are a number of different approaches. Do a search for "capacitor balancing" or "super capacitor balancing" and you'll find plenty of discussions of different solutions. – JimmyB Jun 18 '14 at 8:34
• There are too many unknowns. WHY limit current? What is capacitor bank used for (in general terms). A battery across the capacitors will discharge into them. etc. A fuller description of what you are trying to do and not how you are trying to do it will help get you a good answer and more rapidly. – Russell McMahon Jun 18 '14 at 10:58