1. For downloading SimTools plugins you need a Download Package. Get it with virtual coins that you receive for forum activity or Buy Download Package - We have a zero Spam tolerance so read our forum rules first.

    Buy Download Package Now!
  2. Do not try to cheat our system and do not post an unnecessary amount of useless posts only to earn credits here. We have a zero spam tolerance policy and this will cause a ban of your user account. Otherwise we wish you a pleasant stay here! Read the forum rules
  3. We have a few rules which you need to read and accept before posting anything here! Following these rules will keep the forum clean and your stay pleasant here. Do not following these rules will lead to permanent exclusion from this website: Read the forum rules.

Question Audio capacitor for motor surge current?

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Map63Vette, Mar 10, 2020.

  1. Map63Vette

    Map63Vette Member

    Joined:
    May 19, 2016
    Messages:
    47
    Occupation:
    Mechanical Engineer
    Location:
    Lawrence, KS
    Balance:
    646Coins
    Ratings:
    +8 / 0 / -0
    So I got to thinking, I used to have a big audio capacitor sitting around that I got with a car I purchased years ago. I don't remember if I still have it or managed to sell it, but would something like that be a potentially useful addition to a motion rig? I'm talking something like this: https://www.sonicelectronix.com/cat_i201_1-1-9-farad.html. It seems like it would be able to handle surge currents better if your power supply was on the edge, but didn't know if it would cause more issues than it might help. I was already planning to oversize any power supply I get to try to avoid any current spike issues, but startup current is always going to be a hard peak, so it seemed like something like this could maybe help with that.
    • Like Like x 2
    Last edited: Mar 11, 2020
  2. Ads Master

    Ads Master

    Balance:
    Coins
    Ratings:
    +0 / 0 / -0
  3. Sam MAHENDRA

    Sam MAHENDRA mahentheman Gold Contributor

    Joined:
    Jun 24, 2019
    Messages:
    35
    Occupation:
    Electrical Engineer
    Location:
    Sydney Australia
    Balance:
    60Coins
    Ratings:
    +10 / 0 / -0
    My Motion Simulator:
    2DOF, DC motor, Arduino, Motion platform
    A capacitor when not fully charged is like a dead short circuit. So, when you turn on the power supply, it may trip the power supply via the power supply's short circuit protection circuit. Once the capacitor is partially charged, this may not happen and it will be good to go. Yes, the charged capacitor will provide the short term (we are talking of milli secs) demand, but a battery instead of a capacitor will do a better job.
    In my motion sim with Arduino, I am using the SMC3 sketch with soft-start feature to overcome the motor start-up inrush current.
  4. OZHEAT

    OZHEAT Member

    Joined:
    Oct 26, 2015
    Messages:
    156
    Location:
    Australia
    Balance:
    1,887Coins
    Ratings:
    +81 / 6 / -0
    My Motion Simulator:
    3DOF, DC motor
    Also watch out that the audio cap doesn't exceed it's Max voltage, I think it is about 18v. The back EMF of the 12v motors can easily exceed 18v.
    A cap on the supply line will also still have voltage after turning off the power supply, a farrad cap would probably take a while to bleed of to a safe level.
    As Sam said the biggest issue would be inrush current unless you use a current limiting resistor to initially charge the cap.
  5. Map63Vette

    Map63Vette Member

    Joined:
    May 19, 2016
    Messages:
    47
    Occupation:
    Mechanical Engineer
    Location:
    Lawrence, KS
    Balance:
    646Coins
    Ratings:
    +8 / 0 / -0
    Yeah, that initial hookup was the biggest question mark I had. I think it might have some of that built in as there is a small PCB on top that also has a voltage readout, but I've never really played with it. I did find it in the basement the other day though, so I do have it if I wanted to do some testing.
  6. Sam MAHENDRA

    Sam MAHENDRA mahentheman Gold Contributor

    Joined:
    Jun 24, 2019
    Messages:
    35
    Occupation:
    Electrical Engineer
    Location:
    Sydney Australia
    Balance:
    60Coins
    Ratings:
    +10 / 0 / -0
    My Motion Simulator:
    2DOF, DC motor, Arduino, Motion platform
    In another application, I used a car head light globe (12 V 100 W) instead of a resistor to limit the inrush current; then I bypassed the globe by a 2 sec delay timer circuit pulling in a 12V 200Amp Heavy Duty Relay bought from ebay (around A$10.00). You can also manually turn the relay on instead of a timer circuit.

    Attached Files:

  7. Gadget999

    Gadget999 Active Member

    Joined:
    Dec 27, 2015
    Messages:
    771
    Location:
    London
    Balance:
    5,707Coins
    Ratings:
    +172 / 4 / -0
    My Motion Simulator:
    2DOF, Arduino
    do you use batteries as well as the transformer ?

    a car battery will act as a capacitor and buffer the batteries
  8. OZHEAT

    OZHEAT Member

    Joined:
    Oct 26, 2015
    Messages:
    156
    Location:
    Australia
    Balance:
    1,887Coins
    Ratings:
    +81 / 6 / -0
    My Motion Simulator:
    3DOF, DC motor
    @Gadget999
    The biggest problem with using a battery is that it has very limited current charging capacity.
    Depending on state of charge(battery's resting voltage) it will only accept so many amps and anything above that will result in boiling the electrolyte(hydrogen production).
    Also realise that a car battery although called a 12v battery but @ 12v it is considered flat and is happy at ~13.2v - 14.7v
    SLA and gel type batteries are even worse in charging amp rate as once you boil the electrolyte it is dead.

    A capacitor will accept pretty much any amps you put to it and the voltage will rise to the source voltage unless you exceed the max voltage of the capacitor, which will result in the capacitor exploding.
  9. Sam MAHENDRA

    Sam MAHENDRA mahentheman Gold Contributor

    Joined:
    Jun 24, 2019
    Messages:
    35
    Occupation:
    Electrical Engineer
    Location:
    Sydney Australia
    Balance:
    60Coins
    Ratings:
    +10 / 0 / -0
    My Motion Simulator:
    2DOF, DC motor, Arduino, Motion platform
    Lead acid batteries has an internal resistance, typically 0.3 Ω. This internal resistance limits the current that the battery can supply. Also, it should be noted that if a high surge current is required a car battery is the one to go, compared with a deep cycle, SLA battery.