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Supercapacitor charging?

  1. Mar 22, 2015 #1
    I have supercapcitor 2.7V, 350F. I want to charge it by 0.001mA 20V power source. Is it safe?
    Thanks you!.
     
  2. jcsd
  3. Mar 22, 2015 #2

    davenn

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    hi
    welcome to the forums

    well its a 2.7V capacitor ... what do you think ?

    Dave
     
  4. Mar 23, 2015 #3

    NascentOxygen

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    What arrangement will you use to charge it? How do you know your power supply is limited to 0.001mA?
     
  5. Mar 23, 2015 #4
    A 350 F capacitor charged to 2.7 volt contains a charge of 2.7*350 = 945 Coulombs.
    If the current is really limited to 0.001mA, it would take 945 / (10^-6) = 9.45 * 10^8 seconds = 29.9 years for it to charge to 2.7 volts, so you'd be ok for a long time.
    In practice there will be a lot more leakage current than 0.001 mA and the capacitor would never charge to 2.7 volt.
     
  6. Mar 23, 2015 #5
    I'm experimenting power supply 20V for charging 27V capacitor 350F. Supercapacitor is loaded, but does know it safe???
     
  7. Mar 23, 2015 #6

    NascentOxygen

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    Is the capacitor rating 2.7V or 27V?
     
  8. Mar 24, 2015 #7
    . maxwell supercapacitor 2.7V 350F. thánks you
     
  9. Mar 24, 2015 #8

    NascentOxygen

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    You could connect a pair of resistors as a potential divider to reduce your 20V down to a safe level, say 2.2V. Then the supercapacitor could be safely left to charge unsupervised, and you'd know that in a few decades it should be almost fully charged to 2.2V

    You haven't answered why you want to charge it at 0.001mA, and I presume that is not the figure you intend.
     
  10. Mar 24, 2015 #9
    Although the voltage is 20V but only amperage 10mV (it as a leak). so, I do not want to pass any parts change any power consuming.
     
  11. Mar 24, 2015 #10

    NascentOxygen

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    10mV is not a current

    In theory, you could connect a parallel 2.2V zener diode to limit the capacitor's voltage at 2.2V, but a practical zener would have significant leakage current below a capacitor voltage of 2.2V.
     
  12. Mar 24, 2015 #11
    I'm sorry, 10mA
     
  13. Mar 24, 2015 #12

    NascentOxygen

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    So it's 10mA now!

    Up until this, it has been one-thousandth of a milliamp (0.001mA).

    Are you sure it's 10mA??
     
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