Linear actuator 12 vdc reduce supplied voltage

Discussion in 'Power Electronics' started by brcisna, Dec 12, 2016.

  1. brcisna

    Thread Starter New Member

    Dec 12, 2016
    2
    0
    Hello All,

    First time posting here. Hope someone can give some pointers.
    Wanting to build a bottle capper using a linear actuator , 12 VDC that the capper bell will mount on.
    From doing much reading ,on people that has built something similar using a pnuematic / air cylinder it is determined the lbs/force needed to cap bottles is 185 lbs.
    The actuator i'm going to purchase has a rated load capacity of 225 lbs. I figure if I purchase a 3 amp power supply as is max rated for this actuator it should do the job and then some. Question: What would be the cleanest way of regulating this for testing purposes until i can determine the minimum amount of force is needed to make the actuator do a solid cap and yet not too much.
    Of course have thought of going over engineering and using a reed switch,of some sort to stop travel ,once cap is done ,too,but dont want to get that involved.
    Would just 'stacking' resistors inline of power supply and trying with the actuator pressing down on a common bathroom scale get me pretty close to find the amount of resistance to get my 185 lbs of force,then do some trial runs?
    Of course safety glasses will be in use during testing phase! :)

    Thanks.
     
  2. Sensacell

    Moderator

    Jun 19, 2012
    1,906
    575
    A linear actuator is a very poor choice for this application.

    The problem is controlling the application of force, you can control the motor speed and limit the current, but what happens is the motor and gear train stores energy, in the form of rotational inertia. The level of current required to create the desired force might be consistent at a stand still, but if the motor starts to spin fast, it will exert far more force as this stored rotational energy is returned.

    It would take a very sophisticated control system to make this work- far more expensive than just buying an air compressor, which is what I assume you are trying to avoid.

    People use air or hydraulic cylinders for this application because it yields exactly the kind of controllable force you need for the job, at a very reasonable cost.
     
  3. dendad

    Well-Known Member

    Feb 20, 2016
    1,907
    486
    If you did want to see the current required, get a current limited power supply like...
    http://www.ebay.com.au/itm/DC-Power...961262?hash=item1c5fb7bcee:g:WeUAAOSwSdZWd9oi

    One of these is very handy for a lot of electronic work anyway. Although if you are driving inductive loads like a motor, it may be a good idea to add a 36V tranzorb across the terminals for extra protection.

    With this supply, or something similar, you can set the current limit and the volts see what is required to do the job. It would be well to monitor the speed of the motor and not allow it to run fast up to the "crunch" to prevent breakages. An Arduino looking at an encoder on the motor and PWMing the drive could be a way. The Arduino could monitor the current too.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,721
    4,583
    I made mine from a pneumatic cylinder. Works fine.
    If using a linear actuator you could use a ACS712 5a current detector and set the limit you want that trips the reverse relay.
    They can be had with a board and termination on ebay for a couple of $$.
    Max.
     
  5. brcisna

    Thread Starter New Member

    Dec 12, 2016
    2
    0
    Thanks for the informative replies.
    Two questions.

    dendad, The unit you supplied the link for looks like a good setup to fine tune to the minimal current/voltage needed for the required force needed by the linear actuator. I'm VERY electronics illiterate. Once i found the combination of voltage/current needed to do a capping cycle. How would i relate this once i got my actual supply power (12VDC, 3 amp)hooked up to the actuator? in other words how would i know amount of resistance, to put inline of power supply wires or?

    maxheadro, Don't quite understand the 'reverse relay' you are speaking of? Pretty sure the actuator i'm looking at just has a limiter switch for extend and return sets.? The ACS712 looks like a good learning tool if nothing else.

    Thanks.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,721
    4,583
    The limits or any external fitted limit would normally just stop the actuator, usually this then requires a user installed circuit/relay in order to effect the reversal of the DC motor.
    Either manually or automatically. The latter being preferable.
    Max.
     
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