Supercapacitor + Battery

Discussion in 'General Electronics Chat' started by Marto, Aug 12, 2008.

  1. Marto

    Thread Starter New Member

    Oct 23, 2007
    Looking at the possibility of using a supercapacitor in conjunction with a battery to power a motor, the SC to handle the inrush current when the motor is turned on, and therby extend the batterys life cycle.

    Can anyone provide me with some direction on this?

    Is it sufficient to connect the two in parallell.
    I'm thinking not as this ensures that the battery is energising the SC everytime its charge drops and hence makes the SC roles pointless in extending the batterys life cycle.

    Do i require some sort of automated transfer switch to decide which source is feeding the load i.e. SC during inrush and then the battery during normal running of the load.

    What else do I need to look out for.
    Any help would be appreciated.
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    Here is an interesting discussion of battery life, discharge, and charging.

    In particular, the one chart (attached) shows that battery capacity increases with decreased discharge rates. That might lead one to go in the direction you propose. But notice, those are constant discharge rates.

    The second chart (attached) shows capacity with intermittent discharge. In that case, the effects are not so great. Thus, if by using a capacitor start with current limited recharge of the capacitor, you are able to increase the life of the battery, it does not appear the increase will be very much. I suspect the complexity and added weight for a large capacitor are not worth it.

  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    I suspect that while an SC has high capacitance it probably doesn't have particularly low output impedance which means it will dissipate some power as heat. The SC has to get its power from the battery, and if you want to somehow reduce the rate at which it charges from the battery (to extend battery life) then you will need a current limiting device between the two which will also waste power as heat.

    There seems to be a lot of misconceptions about capacitors and SCs in particular.

    One way to extend battery life slightly when driving a motor might be to bring it up to speed slowly via a PWM controller.