Triggering 230V with 12V SMS controller pulse

Discussion in 'General Electronics Chat' started by bowlingo, Jul 24, 2011.

  1. bowlingo

    Thread Starter Member

    Jun 29, 2011
    Hi all,

    I have a 8 input 8 output sms controller of which the outputs are triggered by a 12V pulse...

    I am trying to switch 230V loads up to 5A each on the outputs.

    The outputs on the controller pulse for 1 second and I thought I had the answer by using 12v-230V 8A relays of which send out a 1 second pulse then energise a staircase timer on the 230V side of which can be configured to 0.5 - 20 minutes.

    The above seems to work pretty acuratly when puttting a 230V lamp across the load side but when im putting on a 3A pond pump the staircase timer seems to go on 2 or 3 times (can hear it clicking where its supposed to stop)

    What I am looking for is a more reliable way of turning on 230V loads of which time out accuratly i.e 2 - 7 minutes but with only the 1 second 12V pulse to control them by.

    I thought I was onto a winner with these staircase timers as they only cost £7.50 each and I need 8

    Im wondering if anyone has any ideas?

  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    It sounds like the inductive load of the pump motor is causing some problems.

    I would suggest another type of relay. What might work better is a 'latching' relay. The relay will physically lock into position when you give it a pulse. You will of course need to send it another pulse to its other coil to unlatch it when it has run for as long as you want.

    We really need more information about your entire setup and plans, in order to offer any truly valuable advice.
  3. bowlingo

    Thread Starter Member

    Jun 29, 2011
    Hi Kermit..

    I have looked at the latching relays as far as to what a latching relay is but I need it to automatialy unlatch due to it being controller via a sms controller i.e send the command then it will turn on and off after a set amount of minutes.

    I am building a hydroponic automatic nutrient system...a good friend of mine from school owns a big Hydroponics shop (only one in area) and has done for 16 years. There are computer controlled systems of whihc are disgustingly expensive but he has never found one that is fully controlled via mobile phone.

    The SMS controller has 8 inputs and 8 outputs..the inputs are dry contacts (switches) of which I am going to be putting the below

    1) A normally open door contactor which will go on a door for security and when opened it will send a message saying the door has been opened then rearm itself when the door is closed (ive tested this and its working fine)

    2) A float switch at the bottom of the tank (25 gallon tank like you get in a loft) of which when the water level runs low it sends a text to say "water level low" (ive tested this and its working fine)

    3) A float switch at the top of the tank that sends you a message to say the tank has filled up (ive tested this and its working fine)

    The 8 x outputs I intend putting relays on capable of switching 230V at max 5A of which are below

    1) A normally closed solenoid valve of which when I get a message to say the water level is low I can open the valve via single command, it will then fill the tank for a specific amount of minutes then auto close the valve...there is to be a mechanical ball valve on here also that will cut off the incoming water once it reaches a level slightly above the top float switch

    2) A mixing pump (pond pump) on the bottom of the tank this will need to to be turned on for a specific amount of minutes as above (ive tested this but this is the one thats making the stair case timer misbehave) 5 minutes mixes the water nicely

    3,4,5,6 these are going to be connect to Peristaltic pumps of which will act as nutrient dosers and will deliver an exact amount of 4 types of nutrients again these need to be on timers as the pump in question will deliver 36ml per minute (if this goes wrong and decides to run for an extra 5 minutes it will be a disaster) so I need to look into some kind of circuitry for this.

    7,8 I am saving these for a way of switching heavy loads 8 x 600W lights through relays but one one command it will activate a time clock set to 18 hours on and 6 hours off and on another command it will activate a different time clock (or the same) that will make the lights go on at 12 hours on and 12 hours off..due to it being the same set of lights with 2 x time cycles controlable by a 12V 1 second pulse I have no real idea on this part yet.

  4. AnnexGR

    New Member

    Dec 2, 2010
    Probably you need a microcontroller to control all of the above.

    Once you have it programmed you can use it to switch Power MOSFETs, which would be perfect for your voltage/current requirements and can absorb some of that inductive kickback. As far as the control scheme goes, I think that is something you have to figure out.

    With MOSFETs you have no mechanical moving parts so you got the reliability right there.
  5. bowlingo

    Thread Starter Member

    Jun 29, 2011
    Thanks for your reply...

    The SMS controller comes as a complete unit that you put a sim card inside, mains power lead, battery back up, 8 input dry contacts and 8 x relay driveable outputs (source voltage so in my case 12V) the unit is very tidy and to program the commands, replies etc you plug it into a pc via RS232 serial cable using usb convertor.

    I have been having problems trying to send a 1 second 12V pulse from the outputs, through a 12v - 230v relay then through a stair case timer set to a specific amount of minutes..what was happening was it was timing out then reenergising again when i tried to run a pump on it on a transformer.

    Today I wired up one of these..


    Which is basically a 12v time delayed relay you can set to 0-60 seconds or 0-60 minutes..I put this on the 12V side then a 12v - 230v relay..tested the pump about 30 times and it didnt reenergise once :)