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A 12V Digital Timer using a 240v Timer Module

240V timers are very cheap these days. 12V timers are not so cheap. So why not use the "innards" out of a 240V timer and make a very flexible 12V timer?

Features

  • Simple to program and use
  • Timer for - 24hrs daily, weekday, weekend or 7 day setting
  • 10 off & 10 on programs with 1 minute increments
  • Random setting
  • Daylight saving advance function
  • Override switch
  • Countdown function
  • Battery back-up
  • On/off LED indicator
  • Power ? 12VDC
  • 5A rating (10A with thickened tracks)
  • Click for larger image
    Here's how the timer module starts out in life - as the "works" in an Arlec PC697 digital timer. The module, which is a separate assembly at the top of the timer (as seen here) is easily removed from the "case". The rest of the device isn't used - but we're sure a use will turn up for it shortly!

    With the price of imported electrical and electronics goods these days, often it simply isn’t economic to build. But there are times when those same imports can yield components which make other do-it-yourself projects viable.

    Such is the case with this project. It’s a 12V DC timer, based around a clock module that’s found in some commercial 240V mains timers. The module then becomes the heart of the timer enabling the user the flexibility to program the unit with ease. Its output controls a relay which in turn can be used to switch a low voltage such as 12 VDC.

    The project consists of the timer module, removed from an Arlec PC697 digital mains timer, which is then mounted in a Zippy box along with a simple power supply and relay interface.

    The SPDT relay contacts are rated at 10AC (120V) but we’d be loathe to try to switch this sort of current and expect any sort of longevity. A higher-rated relay should be substituted if heavy currents are to be switched. The PC board tracks should also be thickened with solder and/or wire for higher current.

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