Using a relay to switch a solenoid when a lamp blows -

Discussion in 'General Electronics Chat' started by Danny Evans, Jun 27, 2017.

  1. Danny Evans

    Thread Starter New Member

    Jun 27, 2017
    Hi, I'm not an electrical engineer but a plumbing and heating engineer.

    I'm currently struggling with a project. I have installed a UV filter for a client. The UV light filters water from a natural bore hole. The water is potable but this is a precaution to ensure that the water is safe to consume.

    The UV filter has three lamps inside. They are wired up to a PCB which has wiring to a green neon, which shows when the lamp is working. If the lamp element fails (bulb blows) the green neon goes out a red neon flashes and a beeper sounds.

    I wanted to wire this fault signal to a solenoid, so that if a bulb blows, the solenoid closes ensuring no one could ever consume water in the event of a lamp failing.

    I under estimated the difficulty of this.

    I am in the UK. We use 240Vac.

    I was unable to use the fault output to do anything as it was a tiny voltage and I couldn't find a suitable relay. I therefore used the green neon feed which is 110V to power the coil of a contacter/relay. The idea being if the green relay goes out - in a fault situation, the coil in the relay would switch off and I could then use that via the NO of the relay to close the solenoid.

    I ran into a problem. The voltage from to the neon was only 110V if I tested with my meter between Line and the neutral on the units incoming supply. If I test between the Line and Neutral from the PCB I get a much lower voltage.

    The issue now is - if I supply the coil via the Line from the PCB and the unit neutral, I get feedback. In other words, the green neon doesn't go out in a fault situation and the relay stays energised. Even if I swap out the 110V relay for a 240V.

    I figured - I could possibly run the supply from the lamps through the coil of a relay, and pick up a fault this way.....but I am running out of steam with this, and it's costing me time and money.

    I couldn't find anything on the market to automatically achieve this - which seems crazy as a buzzer in a plant room filtering water is useless if you are blissfully unaware of the buzzer and are in your home drinking untreated water.

    Any help would be so gratefully received.
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    Welcome to AAC!
    Use the fault signal to turn on a transistor, MOSFET, etc that drives the relay; or use a solid state relay.
  3. Reloadron

    Distinguished Member

    Jan 15, 2015
    Just a little clarification here. You mention Red and Green Neon. You are sure they are Neon and not a red and green LED? Low voltage you mention would be typical of a LED, not a neon bulb. Should the signal to the Green actually be a LED and the voltage is known then possibly an opto-coupler could be used. The opto-coupler drives a relay or transistor to drive a relay which controls the On/Off water supply solenoid. I only chose green because it is always on. Anyway, something similar to what I describe might work for you.

  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Any chance of a schematic of the current electrical wiring arrangement? Even a sketch.

    I want to say this should be easy...but that's the death hex on any project. ;)

    Last edited: Jun 27, 2017
  5. panic mode

    Senior Member

    Oct 10, 2011
    how about a photo?