Smoothing capacitors

Discussion in 'General Electronics Chat' started by floomdoggle, Nov 8, 2008.

  1. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
    217
    2
    Hi all,
    I am making windmill generators. With the AC generators, after the bridge rectifier, is there a formula, or rule of thumb, on the size of the smoothing capacitor? I am using anywhere from 1.5 volts to 48 volts. I have lots of recovered capacitors from old vcrs and betamaxes. And 1 or more?
    Dan
     
  2. Metalfan1185

    Active Member

    Sep 12, 2008
    146
    0
    There may be, if there is i dont know what it is...

    Iwould try a few different values in paralell and use an oscilloscope to display the ripple, and then add/remove caps until you are rid of the ripple the best you can.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    For a 60Hz mains frequency and a full-wave rectifier bridge I use a graph that shows the peak-to-peak voltage of the ripple at various currents with various capacitor values. There is a formula on the graph for you to convert to a 50Hz mains frequency.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Dan,
    Those old caps, if electrolytic, are more than likely no good anymore. They're electrolytic. Electrolytic caps can sometimes be re-conditioned over several days using current limiting resistors, but the process is tedious at best. Electrolytic caps should be derated (rule of thumb) by 50% of their voltage rating; eg: if a cap is rated at 20v, it should not be used in a circuit that may have more than 10v on it.

    If you want to try to recondition some of your salvaged caps, try charging them using a 20k-30k resistor to their rated voltage, over a period of time.

    Salvaged capacitors aren't a good choice for storing energy, IMHO. Batteries are far better. Lead-acid are expensive. Nickle-iron batteries were widely used in the 1930's-1940's, and were quite inexpensive - although they didn't retain a charge like the lead-acid batteries did. Still, the nickle-iron batteries had an extremely long life cycle by comparison.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    Interesting chart, been looking for something like that myself. What is the source, if I might ask?
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I don't know where my chart came from.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    See Fig. 7 here. Looks like someone (AG?) added a line for 32000uF.
     
  8. floomdoggle

    Thread Starter Senior Member

    Sep 1, 2008
    217
    2
    Thanks for the responses. Sarge, the caps will be used to smooth rectified AC, will they work for that?
    Audioguru, I don't understand how the chart works. I'll be using 200rpm as my full charging speed.
    Dan
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    (Revolutions per second) times (pairs of poles) equals frequency.
     
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