Regulating Super Capacitor Discharge voltage

Discussion in 'General Electronics Chat' started by gusmas, Jul 20, 2011.

  1. gusmas

    Thread Starter Active Member

    Sep 27, 2008
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    Hey people

    Situation(simplified):

    I need to regulate the output current and output voltage of the super caps so that the super caps will supply most of the current to the load until it cant anymore then I will disconnect the super caps from the circuit(not included in diagram) and the DC source will supply all the current again.

    Since I am having problem with simulation software i used paint to draw my circuit.

    I understand the load determines how much current will be drawn from the source(s).

    Will my idea work? There will be a control circuit that will monitor the voltage of the super caps bank and as soon as it drops below the DC supply voltage it will disconnect it.
     
  2. lokeycmos

    Active Member

    Apr 3, 2009
    432
    7
    how many volts are you working with? how much of a load? how many farads is the super cap? there are some simple regulators such as the lm317 that can be used fixed or adjustable from 1.2 to 37 volts. but i need to know the above specs before i can help you more.
     
  3. gusmas

    Thread Starter Active Member

    Sep 27, 2008
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    The dc source is actually hydrogen fuel cell, the fuel cell will be connected to a motor controller , so the volts will be around 24 volts , current 6 amps. Super caps will be 4.7 farads . I will buy a lot of them to make theire combine voltage will be above the supple voltage from the fuel cell.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,387
    1,605
    In your scheme you parallel the sources thru diodes. As diodes have a fairly sharp turn on knee, whichever supply is higher will win the war on supplying current.

    One supply will give all, the other will give none due to a below conduction voltage to a reverse bias on it's diode.

    Rarely will they share the load. So you essentially already have a turn off mechanism.
     
  5. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    239
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    Ok is there any other method to implement the super caps so it can source current aswell when the required current exceeds a certain value?
     
  6. lokeycmos

    Active Member

    Apr 3, 2009
    432
    7
    slightly off topic, someone correct me if im wrong. 24v/6a = 4ohms. 4 ohms times 4.7 farads = 18.8 second time constant. 18.8 * 5 time constants = 94 second charge and discharge time.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,387
    1,605
    Then you would wish to pull current from the cap based on the net load current; above a certain point you want to be drawing that excess current from the cap, irregardless of the voltage levels.

    That sounds like you need some sort of switching power supply controller. Load is direct off the fuel cell with the ability of converting the cap's output in parallel for load sharing.

    I could not say what topology you should use as I don't know. Someone else will have to make that recommendation.

    If I told you that was correct I would be rewarding you for hijacking some one else's thread.

    SO YOU ARE WRONG!
     
  8. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    239
    0
    Ok cool thx for the response guys. Where can I find the steps to design a buck converter? And what is a good simulation package?
     
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