Connect with us

Relay? help?

Discussion in 'General Electronics Discussion' started by EvergreenCM, Jan 18, 2013.

Scroll to continue with content
  1. EvergreenCM

    EvergreenCM

    2
    0
    Jan 18, 2013
    Hello,

    I need to build a flashing railroad crossing signal. I would like to use 12v trailer lights and have them flash back and forth - just like a real railroad crossing signal.

    I would like to just be able to plug it into a standard 110v outlet. I have wiring experience, just never worked with relays etc. before.

    Any ideas on how to convert etc.?

    Thanks!
     
  2. davenn

    davenn Moderator

    13,722
    1,913
    Sep 5, 2009
    Hi there
    welcome to Electronics Point forums :)

    I am assuming ( because of the lack of info) that this is for a model railway ?
    Trailer light globes would be pretty huge in physical size for such a job
    LED's would be much better and are readily available at well less than 50c each
    A simple oscillator circuit could drive the LED's to have them flashing alternately

    a 110VAC to 12VDC plugpack to power the driver circuit and LED's

    Dave
     
  3. EvergreenCM

    EvergreenCM

    2
    0
    Jan 18, 2013
    Hi Dave,

    Thanks so for your reply! t's actually for theater use. It will be about 7 feet tall.
    Any ideas for that? Thanks!
     
  4. davenn

    davenn Moderator

    13,722
    1,913
    Sep 5, 2009
    ahhh OK :)

    stick with your trailer type globes

    The power supply and oscillator can be the same
    make sure the puer supply has sufficient current rating to power the globes you decide on
    The oscillator can be a 555 timer that drives power transistors for the higher current requirements of the globes

    do a google search on 555 timer as a monostable multivibrator

    Dave
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    I've taken the liberty of designing a circuit for you!

    I guess it must be a slow night ;-)

    [​IMG]

    I've shown two versions. The first one uses high-current MOSFETs to switch the lamps, and the second one uses a grunty relay. The second one is simpler and probably more reliable, but it will make an audible clicking sound, will eventually wear out (after a few years, probably) and is slightly more expensive.

    You'll need to decide on the light bulbs you want to use, and find out how much current they draw. Then rate the power supply for at least twice that much, because incandescent bulbs draw a lot more than their rated current for a short time as they warm up each time you turn them on.

    Any other questions, just ask :)
     

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,449
    2,809
    Jan 21, 2010
    The problem with flashing incandescent bulbs is that it subjects their filaments to a lot of thermal stress. This leads to them failing very quickly (in relative terms)

    The cure is to always have some current flowing through them. Not enough to light them more than perhaps a dull red glow, but enough to keep them hot.

    This has the other beneficial effect of reducing the spike of current as they are turned on each time.

    The resistor will be different for each type of bulb, and the easy way of determining its value required a variable power supply.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Interesting and helpful advice Steve.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-