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Discussion in 'Electronic Design' started by RealInfo, Apr 7, 2013.

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  1. RealInfo

    RealInfo Guest

    Hi all

    In case I use some super capacitors with very high capacitance
    like 10s of farads in parallel and those capacitors
    can be charged to 2.7 volts max, how do I step up that low volt to constant 24 vdc , high currnet ?

    The main problem is that the 2,7 volt decreases to almost zero gradually .

    So how I keep a constant 24 vdc while capacitor voltage goes down ?

  2. Bill Sloman

    Bill Sloman Guest–Walton_generator

    It's a bit tricky to get much current out. A transformer-based
    inverter can work a whole lot better.
  3. What is "high current"? Your input current will be 10 times as high as
    that, so consider if this is at all practical.
    You would need a "boost converter". Some of the products marketed as
    "energy harvesting" work down to very low input voltages. You might be
    able to find something that works in one stage, otherwise two cascaded
    boost converters.
  4. Robert Baer

    Robert Baer Guest

    Maybe 10 mega-amps for 10 femtoseconds?
  5. some are pretty darn low.

    I just got some maxwell 2 or 300F 2.7 volts caps, which are about the size
    of a D-cell and called "D Cells" or something silly like that.

    I shorted one with a multimeter lead and it melted the tip almost

    Interestingly, these caps sound like they're full of liquid, but are
    extremely light.

    there's no question they're dangerous and have an extremely low ESR. It's
    quite the contrast from the standard memory caps which do nothing if you
    short them out.
  6. Guest

    If the capacitor would be loaded with a constant current load, the
    voltage drop would be linear.

    However, if you need a constant current on the 24 V side (i.e. a
    constant power load), the current drawn from the capacitor must
    increase as the capacitor voltage goes down. This will further
    accelerate the voltage drop rate and thus, there is not much point in
    trying to use close to zero capacitor voltages.
  7. Bill Sloman

    Bill Sloman Guest

    Putting capacitors in series works a lot better with tight-tolerance capacitors.

    Typical electrolytics with tolerances in the range +80%/-20% can't be relied on to divide the series voltage equally. Three +80% tolerance parts in series with one -20% tolerance part would put 43% of the total voltage drop across the -20% part.
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