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H bridges capacitors (electric question)

Discussion in 'Electronic and hardware generally' started by CalSim, Nov 4, 2014.

  1. CalSim

    CalSim building things

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    Hi friends. Now I've seen several H bridges and tried them I would like to ask something about them.

    Those BIG black-plated cilinders on our bridges. I think they are called capacitors, and i've read you can add some more ( if you use long wires to mantain current )

    Well. Some chinesse MotoMonsters ( shown on Pit's thread's photos ) have 560 uF x2 cap.

    The ebay Motomonster I bought has 470 uF x2 capacitors.

    The pololu dual VHN 5019 has 47 uF x3 capacitors.


    WHY?? such diferences, workin with almost same Amps
    Why are they there?
    Is it good to add those extra cap.?

    No problem with them, just like to know how my things work.

    Thanks a lot
    CalSim, Nov 4, 2014
    #1
  2. Alexey

    Alexey Well-Known Member

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    For the most part those capacitors are there for power conditioning/filtering.
    They are there to eliminate or reduce any noise/ripple in the power line usually caused by cheap power supplies or cheap componentry.
    As for the "why such differences", well that all comes down to filter design and how well they filter the power. By adding or taking away
    capacitors you would change the characteristics of that filtering circuit.

    If it isn't broken don't fix it!

    Some light reading http://electronics.howstuffworks.com/capacitor.htm
    • Agree Agree x 1
    • Informative Informative x 1
    Alexey, Nov 4, 2014
    #2
  3. Zed

    Zed VR Simming w/Reverb Gold Contributor

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    I know this is an old thread, but CalSim asks and important question and something I learned while studying the VNH2SP30 datasheet (http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00043711.pdf).

    Alexey is right about power filtering but the data sheet also makes another point along with on page 21 in the Note under Figure 32:

    The value of the blocking capacitor (C) depends on the application conditions and defines the voltage and current ripple on the supply line at PWM operation. Stored energy from the motor inductance may fly back into the blocking capacitor if the bridge driver goes into tristate. This causes a hazardous overvoltage if the capacitor is not large enough. As a basic guideline, 500 µF per 10 A load current is recommended.

    If I understand this properly, I think it means we don't want to cut power to the motors while they are being actively driven or running a lot of hold current. Only kill motor drive when the rig is still and under no load or else you risk the flyback voltage causing damage if those caps aren't big enough.
    • Winner Winner x 1
    Zed, Apr 20, 2017
    #3