Help: 12vDC motor polarity change with timer for bench test

Discussion in 'The Projects Forum' started by roc383, Apr 17, 2009.

  1. roc383

    Thread Starter New Member

    Apr 17, 2009
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    0
    I am working on a test fixture for 12VDC actuators. I am not certain the exact amperage, but I know it is well under 1amp. Somewhere around 300mA, I believe. The normal usage is to rotate a shaft which moves a plastic door. There are only two positions for the door: either end of full travel. The actuator is always powered, so when the door gets to it’s hard stop, the actuator is still powered, but stalls. I need to build a circuit that can test these actuators on a bench and run 100’s of simulated cycles by driving for a set time and then switching polarity. The normal time for full travel is roughly 4 seconds. I would like to drive the actuators on the test bench for 15 seconds (most of the time would be against a hard stop). After 15 seconds of one direction, I need to reverse polarity and drive the other way for 15 seconds. This needs to repeat endlessly until I manually end the test. It will probably run for as long as a week, non stop. I believe my best bet for changing direction is through using an H-Bridge. But, I’m not sure how setup the timer. Could anyone provide suggestions? I understand electrical circuits, but my electronics knowledge is less than basic. Thanks for any help.
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Doing a timed switch....4sec/15sec/4sec/15sec....for a week will eventually jam the actuator. Slight variations in friction and power-on/power-off timing will add creep into the actual actuator position. Better to set up two limit switches to give absolute end positions.

    Something like the attached could be done with a simple DPDT relay. This could be driven by a 19 second (4+15) LC555 astable oscillator.

    Ken
     
  3. roc383

    Thread Starter New Member

    Apr 17, 2009
    2
    0
    Thank you for the response! I just wan't to make sure I am clear - It was not my intention to have alternating drive time, 4s/15s/4s etc. I just need to drive one direction for 15s then drive the opposite direction for 15s, and repeat. Does this change your advice any? Thanks again.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    I re-read your original requirement. You "want" the actuator to jam at each end of travel for ~11 seconds and then reverse. What you need is a repeat-interval timer driving a DPDT relay. Since you "understand electrical circuits", my guess that you would prefer more off-the-shelf "electrical" components, than building electronic circuits from scratch.

    Something like this: http://www.ssac.com/catalog/HRD3Gen.pdf or http://relays.tycoelectronics.com/datasheets/VTM7.pdf

    , used to drive an external DPDT relay will work and be simple to wire up. These come in a variety of supply voltages and time ranges. They're about $70US, but it trades time for money. There are cheaper timing solutions, but will require more effort and learning on your part.

    Ken
     
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