newbie project.

Discussion in 'The Projects Forum' started by tonymac, Jan 21, 2012.

  1. tonymac

    Thread Starter New Member

    Jan 20, 2012
    8
    0
    Hi All.I am trying to put a circuit together and could use some help.I am new to projects,but have some expierience with pcb s on boilers as i am a gas engineer.The first part of the circuit i need help with is how to reduce 240vac to 12vdc to power a latching relay and then i further need to reduce 12vdc to 3vdc to power a dual colour led.Space is limited.The whole circuit has to fit in a 1 gang x25mm deep box',inc relays. Thanks in advance,tony.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Find a switch mode power supply rated for 240 V AC, 12V DC @ 1 A or better. Current limiting for LEDs with a resistor from 12 V might be all that is needed; around 500 Ω, depending on LED colors.
     
  3. tonymac

    Thread Starter New Member

    Jan 20, 2012
    8
    0
    Thanks Bernard.Do i need to rectify {bridge rectifier}the ac to get dc?
     
  4. tonymac

    Thread Starter New Member

    Jan 20, 2012
    8
    0
    The rectifier is built into the smps,thanks,
     
  5. tonymac

    Thread Starter New Member

    Jan 20, 2012
    8
    0
    Hi again, could someone with better knowledge than mine just pass their eye over the attachment & let me know is there any problems. also will i need diodes between the resistors and dual colour led.

    The sequence of events are as follows.
    1. At rest when 240vac is applied to circuit it powers transformer and also goes through c-nc contacts of relay 1 and then to external load(maximum 3 amps) n.b relay 1 coil is 12 vdc. switch is 240 vac. Also +12vdc can pass through c-nc contact of dpdt relay and then through resistor to dual colour led(green-on)

    2. When external momentary switch is pressed the coil in the dpdt relay is energised (+12vdc). Both pair of switch contacts change for c-nc to c-no. Power comes off green dual colour led and puts it onto red( off). Power for dpdt relay is now taken through lower switch contacts. In addition relay 1 is energised changing from c-nc to c-no interupting power to external load.
    Circuit remains in this state until 240vac removed and circuit returns to at rest.

    Thanks in advance tony.
    IMG00844-20120122-2016.jpg
     
  6. hmv4u2

    New Member

    Jan 19, 2012
    5
    0
    hi tony,im a bit like you,not massively clued up but like a dabble :)-can i ask a question/make a observation ? if all this lot has got to fit in a single gang 25mm box its going to be tight . is the 'stop' button going to mounted in the boxs lid and does it have to be 12v operated-the reason i ask is because you could use 2 x 240 sub minature neons and a 240v relay instead which would save a lot of space ?
    howie
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you use AC coil relays, it looks like your relay logic would work without rectifiers with a minor modification. Most LEDs don't like having voltage applied in reverse. To get around that minor problem, just put a diode (1n4000 series) across each LED so that the LED conducts on 1/2 of the AC cycle and the diode conducts on the opposite 1/2 cycle. I assume you want to use a lower voltage than the 240VAC going to the remote switch. Otherwise, I would have to agree with humv4u2 about using a 240VAC coil relay except such discussion would violate terms of service..
     
  8. tonymac

    Thread Starter New Member

    Jan 20, 2012
    8
    0
    Thanks for your replies.I would prefer to keep the whole circuit 240vac,but have trawled the net to find a small latching relay,changeover relay and 240vac led,but without success.Could you give me a link for these components. Also getting it to fit into a 1 gang box is an issue.The push button will not form part of the 1 gang switch.tia,tony.
     
  9. hmv4u2

    New Member

    Jan 19, 2012
    5
    0
    tony,i didnt know talking about 240v ac would violate terms and conditions :confused:so mail me at howeze at gmail dot com or PM me and ill explain,its pretty straightforward
    howie
     
    Last edited: Jan 23, 2012
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