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Clock failure

Discussion in 'General Electronics Discussion' started by Jimbo Joe, Jun 20, 2014.

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  1. Jimbo Joe

    Jimbo Joe

    3
    1
    Jun 20, 2014
    Hello all, Im new here, had a look at the site and liked it. Whilst Im no electrical expert by any means, ive had many years of professional hands on automotive mechanical and some electrical experience.

    I have a friend with a caravan who has a couple of what appear to be reasonable quality, and not cheap, 12v digital clocks fail on him. The van has an onboard 12v battery that is charged by both the towing vehicle and when 240v is applied at van parks. The clocks he fitted were made for marine use, and are rated at 9-16v, and the only spec I can find is for memory power when the display is switched off, which is 10mA. Even when on the clock should draw minimal power, although ive never measured the current draw, and cant now because the clock has failed. The clock has failed twice after quite long road journeys, which could indicate an over voltage issue, although checks conducted reveal the highest voltage to the clock to be 13.8v.

    My question is whether a simple voltage regulator could be placed in the clock circuit, bearing in mind my limited knowledge of regulators indicate there must be a 2 volt difference across the regulator?

    What do the experts say?

    I just saw I misspelled the thread title, could a Mod place an "l" in please? Sorry
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,569
    2,356
    Nov 17, 2011
    Welcome to our forum.

    The "l" is now there :)

    The clock's failure could be due to a voltage spike in the course of a load dump. Suitable overvoltage protectors are available (Google).
    Another possibility is a mechanical failure (broken solder joint etc.) due to mechanical stres during the journey (I'd expect the clocks to get more of a shock stress in a car than in a marine vessel).
     
  3. Jimbo Joe

    Jimbo Joe

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    Jun 20, 2014
    Hi, and thank you for the prompt response and fixing my spelling.

    Yes it could be a second clock failure, but the clocks both failed under the same circumstances which sounds a bit sus?
    Ill google overvoltage protection and give that a go.

    Thanks again
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    I'm not sure if this will help, but the Linear Technology LT3012 (http://www.linear.com/product/LT3012), available from Digikey (http://www.digikey.com/product-detail/en/LT3012EFE#PBF/LT3012EFE#PBF-ND/1620147) is ideal for this application, apart from its tiny, fiddly package.

    It's rated for 250 mA maximum output current, 80V maximum input voltage, and 0.4V dropout voltage, so it's ideal for automotive applications. You would probably use a MOV (varistor) across the input as well for extra safety.

    It's not an easy device to solder though - a 16-pin TSSOP with an exposed pad. You could use an SMT breakout board like this one: http://www.technologicalarts.ca/sho...ers/breakout-board,-t/ssop-to-20-pin-dip.html or do a custom hack - you could mount it onto an unetched copper board. Eleven of the 16 pins, and the pad, can be soldered directly onto the copper; five of them would have to be bent up and insulated from the board. A bit of a fiddly job though. Just a suggestion.
     
    Jimbo Joe likes this.
  5. Jimbo Joe

    Jimbo Joe

    3
    1
    Jun 20, 2014
    Thanks, that looks good.
     
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