LED to monitor current flow

Discussion in 'General Electronics Chat' started by Tomcct, Sep 29, 2009.

  1. Tomcct

    Thread Starter New Member

    Sep 29, 2009
    I would like to install an LED on an on/off switch which isolates(switches) a 12V DC water pump so I can see when the motor is running.

    The pump has a water pressure switch which normally controls the operation.
    When the water runs out, the motor will stay on and after time, overheats and burns out its in a noisy environment so cannot be heard.

    A red LED next to the switch or on the control panel which would flash or just illuminate when the pump is running would help the problem.
    Any suggestions for a simple monitoring circuit please.
    Application is RV or motor home water system. (12Volt supply available)
    Pls feel free to reply to TomGoldya@Yahoo.com
    Last edited: Sep 29, 2009
  2. Wendy


    Mar 24, 2008
    Just put a simple LED circuit across the motor, a red resistor in series with a 910Ω ¼W resistor. The hard part is getting the wires from the motor to the panel, but the LED is easy. Doesn't have to be an LED, it could also be any indicator lamp.

    You can even buy LEDs that will blink by themselves.
  3. someonesdad

    Senior Member

    Jul 7, 2009
    A more complicated fix would be to install a float switch in the water tank. I made one for my ditch pump about 20 years ago and it still works great (I originally used an old plastic syrup bottle for the float and the bottles have to be replaced every few years because they sun rot). The switch is an encapsulated mercury switch I got at Radio Shack, but it's possible you can't buy mercury switches anymore. Look in an older cheap thermostat -- they were used there too. The switch is in series with the motor and doesn't allow the motor to run unless there's enough water. Simple and reliable.
  4. BillB3857

    Senior Member

    Feb 28, 2009
    Most RVs have a monitor system that will show the level of liquid in the various tanks. Set yours up to keep the monitor active for the fresh water tank. Another option would be to put a low ohm resistor in series with the feed from the on-off switch and monitor the voltage drop across it it with an op-amp driving your indicator. Pump not running= no voltage drop Pump running = small drop but enough to fire the op amp.