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Newbie help with programmable manual set timer circuits and water pump

Discussion in 'General Electronics Discussion' started by Cribey, Sep 30, 2016.

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  1. Cribey


    Sep 30, 2016
    I am designing a pump timer with 4 separate settable trimpot timers;
    • 1 timer On for X seconds
    • 1 timer On for Y seconds
    • 1 timer On for A seconds
    • 1 timer On for B seconds
    All timers are to power ON the same 12VDC (0.3A Max) pump for a separate amount of time. The setting of time I will change using a trimpot for each, from 0-20 seconds.

    I also want to be able to adjust the speed of the motor using a trimpot as well.

    I finally made the build but am having problems getting the motor pump to run.

    I purchased:
    I am using the DC power source that came with the pump (9V, 1A), and the LEDs and timers click on and go off, relays seem to be working, but I cannot get the pump to turn on.

    When I connect the power source directly to the pump it does work.

    I have tried all possible combinations with the outputs to the pump from the relay.

    Any thoughts and advice would be greatly appreciated.

    Thanks in advance,

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Welcome to EP.

    Obviously you haven't tried all possible combinations as there is surely one that works (I doubt that all 4 timer circuits are defect).

    From your picture I take it that you misunderstood the way the relay outputs on these timers work.
    What you did: Connect the wires (red and black) from the pump to the relay contacts on the timer board.
    What you should do: Follow the connection scheme shown on the ebay site in the top left picture.

    To connect all 4 timers to one pump expand the scheme as follows:
    1. connect one wire from the pump to one pole of the power supply (e.g. black wire to "-".
    2. connect another wire from the the pump to all of the timer module's relay outputs. For example use a red wire and connect to the rightmost terminal as in your picture. Use more of the red wire to connect to the same terminal on the other 3 timers.
    3. connect a third wire (I'd use the same color as in step 2, but color is technically irrelevant) from the power supply "+" to the center terminal of all the timer modules.

    Why is this?
    The relay on the timer module is simply an on/off contact. It doesn't supply power from anywhere to the output. But that's how you connected it: two wires from the relay to the pump, probbably assuming that these wires carry power from the timer to the pump.
    Being only a switch, the relay needs to be wired such that it controls the flow of power from the power source to the pump. You therefore have to insert the relay contact in line (in series) with the connection from the power supply to the pump. This is what my setup does.

    CDRIVE and hevans1944 like this.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Also make sure you are connecting to the common and the NO (normally open) or NC (normally closed) contacts on the relay, depending on whether you want the pump to operate when the relay is actuated (NO contacts) or when the relay is de-actuated (NC contacts). Nothing will happen if you accidentally wire between the NO and NC contacts because there is never a complete circuit there whether the relay is actuated or de-actuated.
    CDRIVE likes this.
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