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Reducing 14.8Vdc to 12Vdc

Discussion in 'General Electronics Discussion' started by Jules1963, Apr 5, 2017.

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  1. Jules1963


    Apr 5, 2017
    I have been given a household wireless alarm system that usually would run on mains electric and step down to 12v input.

    I would like if possible to use it in my motorhome running from the leisure battery but when the solar panels are charging the voltage at the battery increases to 14.8v, Is this voltage to high or is there an easy way to to reduce the voltage to 12v.

  2. ChosunOne


    Jun 20, 2010
    (1) Please, please, please, whenever possible, ALWAYS start with ;manufacturer name and model number of the device you are talking about.

    I've been working with alarm systems since the 70's, but I'm in North America and chances are that your make and model won't be familiar to me; however, with a model number I could probably look up the specs and give you an answer.

    (2) You say "...step down to 12V...". I'm going to guess it uses a transformer with a nominal output of 12VAC, but not knowing your model number and not being that familiar with input configuration across the pond, I'm just guessing.
    However, my educated guess (based on long experience with alarm panel power supplies) is that if it is a transformer rated at a nominal 12VAC output, (or even an adapter rated at 12VDC output), that the actual output is closer to 14.8 V (AC or DC) than to 12V. Meter the output, open circuit (no load) and under load (connected to panel) to get the actual operating output voltage. If the output is AC, remember that the peak voltage is...I'm not going to look it up, but I believe it's 1.4 X Actual AC voltage actually going to the panel's circuitry.
    If your device's actual input is within a volt (AC or DC) of your motorhome's output, then I'd say you're safe to connect it directly.

    That's assuming you have a reputable brand. If it's a cheap Chinese off-brand, all bets are off, even if you give it meticulously controlled voltage. Sorry, that's just been my experience.
    Arouse1973 likes this.
  3. Jules1963


    Apr 5, 2017

    Thanks for your reply, as I said the unit was given to me and unfortunately there are no inductions and I can't see a manufactures name on it.
    I have tested the AC adapter which it outputs 12.3 VDC. So my concern is that if I wire the alarm to my leisure battery which can go as high as 14.8VDC when charging from the solar panel this represents an increase in voltage of approx 20% (2.5v).
    I'm aware that automotive products are capable of higher voltages because of the alternator charging the main battery but I'm not sure this applies to what is essentially a household product.
    Because the leisure battery voltage fluctuates demanding on the time of day and other appliances in use I was hoping that there was a device that could take an input of 12-15VDC and output a more stable 12VDC.
  4. Alec_t


    Jul 7, 2015
    The simplest way to drop the voltage would be to use 3 silicon diodes in series, dropping ~2.1V to 3V depending on current. Any idea how much current your alarm system draws?
    A low drop-out regulator would be a better solution.
  5. Ben King

    Ben King

    Apr 4, 2017
    yeah just just use a 12vdc regulator; there's plenty of 'em out there, cheap too. just watch for the current(amperage) ratings on the regulator, they have to be the same as the alarm system
    I might be wrong on all this tho :D
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