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Super capacitor for running DC motor

  1. Aug 7, 2014 #1

    I am planning to run a DC motor using a super capacitor. The specification of the motor are:

    • Voltage : 90V - 120 V DC
    • Current : 15 A
    • Duration : Should run for atleast 10 seconds.

    I have finalized this super capacitor from maxwell for the above operation http://www.maxwell.com/products/ultracapacitors/docs/160vmodule_ds_3000246-5.pdf

    I have planned to charge this capacitor to 120V and then discharge till 90V DC.

    I have used the formula:

    t=[C*(V0-V1)/I] where,
    t = Discharge time (sec)
    C = Capacitance (F)
    V0 = Initial Voltage (V)
    V1 = Final Voltage (V)
    I = Current (A)

    Thus applying the values to the formula:
    t ={5.8(120-90)/15} (120 - 90 is the voltage range for the motor, 15 is req. current)
    ={5.8(30)/15} (5.8 F is the capacitance of the Super cap mentioned in datasheet)
    =11.6 sec.

    11.6 sec which is more than what i require.

    I got the above formula from Elna Supercapacitor, Illinois Capacitor Inc and Maxwell (Page 2) http://www.maxwell.com/products/ultracapacitors/docs/applicationnote_maxwelltestprocedures.pdf so m pretty sure about the formula.

    So guys please help me here and let me know whether the calculations and the product i have finalized for running the motor for 10 seconds (atleast) is suitable or not. What problems i may face during this experiment. I have planned to use AC 110V supply with transformer/rectifier to charge the capacitor to 120 V. Do i need to add any other equipment between motor and supercap or a direct connection is sufficient.

    Thanks in advance. :)
  2. jcsd
  3. Aug 7, 2014 #2


    User Avatar
    Science Advisor

    C = Q / V
    Q = I * t
    ∴ t = V * C / I
    and so: dt = dv * C / I
    Your 11.6 sec is correct.

    To charge the capacitor to 120V DC you will need to rectify 120V / Sqr(2) = 85V AC

    To protect the motor insulation, you might consider a reverse biased Schottky diode across the motor to catch any inductive kick produced during switching.
  4. Aug 7, 2014 #3
    Thanks for the reply Baluncore...
    Guys all kind of suggestions are welcome...anything you want to add any modifications or any other super cap product cheaper and smaller than what i have suggested in the first post ...even if you think whatever i have posted is right, please let me know...
    Thanks alot again..
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