filter capacitor discharge

Discussion in 'Homework Help' started by suzuki, Sep 1, 2011.

  1. suzuki

    Thread Starter Member

    Aug 10, 2011
    Last edited: Oct 7, 2011
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    There is a great difference between what might be termed instantaneous power and average power. You appear to be interpreting the 1517 "Watts" as average power when it's clearly not when considered over a longer time frame. In situations where energy is released or dissipated over a very short time frame and not repeated for an extended period of time the average energy release or dissipation is quite small. If you averaged the joule loss from your 2.2uF capacitor going from 200V to 100V over a one second interval instead of 29usec the "average power" would be quite small.

    Putting it into a physical context. Suppose you tried to boil a liter of water starting at 25°C by dumping the equivalent energy from your capacitor (at 200V) entirely as heat into the liter of water. It takes 314kJ of energy to boil the liter of water from 25°C at sea level. Being extremely optimistic let's assume that no heat is lost from the water while you are recharging the capacitor for the next dump cycle. The 2.2uF cap at 200V stores 0.044 Joules.

    To boil the liter of water from 25°C adiabatically dumping the total capacitor charge (say) every 0.1 seconds would require 314,000/0.044 cycles. At 0.1 second per capacitor dump cycle this would take about 198 hours. Long wait for a cup of coffee!
    suzuki likes this.