1. Do not share user accounts! Any account that is shared by another person will be blocked and closed. This means: we will close not only the account that is shared, but also the main account of the user who uses another person's account. We have the ability to detect account sharing, so please do not try to cheat the system. This action will take place on 04/18/2023. Read all forum rules.
    Dismiss Notice
  2. 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 Now a Download Plan!
  3. 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
  4. 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. Do not follow these rules can lead to permanent exclusion from this website: Read the forum rules.
    Are you a company? Read our company rules

DC Motor back current options

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by John Hien Nguyen, Oct 23, 2014.

  1. John Hien Nguyen

    John Hien Nguyen Member

    Joined:
    Dec 21, 2013
    Messages:
    8
    Balance:
    336Coins
    Ratings:
    +14 / 0 / -0
    Hi,

    I've been doing some research on back current from a DC motor and am wondering how everybody deals with this. Searching the forum I see posts on wiring up a battery in parallel to the PSU and also diodes are mentioned. I'd like to leverage your experiences, so please help answer my questions.

    Hardware
    - 2 x 350w 128rpm motordynamics worm drive motors (24v)
    - 2 x 24v, 40a Meanwell 24v switching power supplies

    Q1. Do you think I need both PSUs in parallel, or can I get away with one?
    Q2. Can I get away with using shottky diodes alone to deal with the motor back current? ie. no car battery?
    Q3. If I use two motorbike batteries in a series to get 24v, and wire this in parallel with a PSU, what specs should I be looking at? eg. >300cca, etc.
    Q4. Anybody got some example batteries I could use as reference?
    Q5. Does anybody have any other tips, say with wiring or such?

    Thanks guys.
  2. Alexey

    Alexey Well-Known Member

    Joined:
    Sep 23, 2014
    Messages:
    452
    Occupation:
    Electronics Technician
    Location:
    Adelaide, Australia
    Balance:
    8,060Coins
    Ratings:
    +620 / 2 / -0
    My Motion Simulator:
    3DOF, DC motor, Arduino
    I wouldn't have thought a reverse current would be an issue with this setup because when the motor spins backwards you are actually driving it in that direction rather than say an FFB steering wheel where you are physically driving it without electrical assistance at times, thus inducing a voltage.

    The thing with the batteries is to help out with large current spike so that it does not over stress the power supply into a shutdown mode. Even then you can just use a very large capacitor
    • Informative Informative x 1
  3. John Hien Nguyen

    John Hien Nguyen Member

    Joined:
    Dec 21, 2013
    Messages:
    8
    Balance:
    336Coins
    Ratings:
    +14 / 0 / -0
    • Funny Funny x 1
  4. Alexey

    Alexey Well-Known Member

    Joined:
    Sep 23, 2014
    Messages:
    452
    Occupation:
    Electronics Technician
    Location:
    Adelaide, Australia
    Balance:
    8,060Coins
    Ratings:
    +620 / 2 / -0
    My Motion Simulator:
    3DOF, DC motor, Arduino
    Well those diodes are for lightning strike protection, not current spike filtering.

    Personally I would use one of those supplies per motor and you won't have to worry about anything at all.
    Those supplies are 900 watt supplies, you could even use one supply for both motors but that might be borderline.
    It all really depends on how the motors perform and how much current they draw in different situations.
    The more expensive supplies will current limit, not current protect. Limiting means that you can almost be limit bashing the supply and it won't cut out (to a point). Where as over current protection will completely cut the supply until the fault condition is removed.

    One supply per motor will mean less stress on the supplies and less chance of inducing a fault condition (overcurrent).
    The motors would need to draw nearly 3 times their rated current to reach over current (which they can do in that fraction of a second where the motor stops to reverse direction). A good motor controller and good code should lessen this effect to the point of it not being an issue at all. Usually a power supply will have large capacitors on the output to filter out those spikes, but not all manufacturers put large enough capacitors to save costs.

    These types of questions are like asking, how far can I run? There are so many variables that's it's hard to give you
    a definitive and correct answer. I can only speculate with what information you have given me.

    So to end my babbling, one power supply per motor should be safe. But you won't know until you try.
    The battery option is like insurance. Also, those power supplies might need external cooling fans from what I get on google search of those supplies.

    Maybe someone else who has used similar equipment can comment?

    Hope it helps a little bit
    • Like Like x 1
  5. John Hien Nguyen

    John Hien Nguyen Member

    Joined:
    Dec 21, 2013
    Messages:
    8
    Balance:
    336Coins
    Ratings:
    +14 / 0 / -0
    Thanks, that information is very useful. I'll run with it and see how it goes either this weekend or next. Thanks again!