Need help on capacitor discharge time

Discussion in 'Homework Help' started by dramos, Oct 21, 2010.

  1. dramos

    Thread Starter New Member

    Oct 21, 2010
    i need to find out what capacitor value i need to provide momentary backup power to a 1Amp load operating at 6V for 1.5 minutes.

    i am going to connect this capacitor in parallel with my 6V power supply. if for some reason, my power supply is interrupted, i'll have 1.5 minutes extra time to gracefully shutdown.

    would you please explain and let me know formula?

  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    From Wikipedia:
    In simple terms, 1 A with a voltage change of, say 6.5 to 5.5 volts for 1.5 minutes (90 seconds) is a lot. 1st order approximation is 90 F.

  3. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    Instead of a huge and expensive capacitor, maybe you should use a little inexpensive rechargeable battery.
  4. gschultens

    New Member

    Oct 23, 2010
    Yes, the amount of capacitance required is completely impractical in terms of cost and capacitance required (note that a previous poster calculated it to 90 Farads). Even those big capacitors for automotive power amplifiers (the ones with the useless electronics and LEDs on them) are only 1 Farad, and they are big. You would require a large bank (90) of capacitors to achieve the capacitance required. Note that backup power supplies for computers are big, and all are based on batteries.

    Capacitors are only used to get rid of AC ripple, or to allow for different DC voltage bias levels, and sometimes in timer circuits. In industry they are typically used for power factor correction to compensate for the inductive load of motors and flourescent lighting balasts.
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008