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12-14.5v from car to replace mains 12v adapter

Discussion in 'Troubleshooting and Repair' started by Slowy, Jan 21, 2017.

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  1. Slowy

    Slowy

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    Jan 21, 2017
    I have got a Greenpacket Wimax indoor CPE that powers from an ac adapter with a steady 12.3 v. Can I power it with a 12v battery that reaches 14.5 v when charging without damaging the unit? Thanks from an off-the-grid sailor.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,446
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    Nov 17, 2011
    That's impossible to guarantee without knowing details about the CPE.
    I'd expect the CPE to have one (or even more) internal voltage regulators as modern chips operate from 5V, 3.3V or even less, but not 12 V. So it is likely that these regulators tolerate up to 14V, but as I said there's no guarantee.

    Does the manual of the CPE state anything on the allowed range of input voltages?

    Depending on the current consumption of the CPE a simple series resistor with zener diode or a low drop voltage regulator may be suitabel to limit the input voltage to the CPE.
     
  3. KTW

    KTW

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    Feb 22, 2015
    You can use a DC to AC inverter along with your existing ac adapter.
     
  4. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    I've seen requests like this come in from campers and sailors all wishing to power the equipment off-grid using usually very limited supplies.
    Using an Inverter & the supplied AC/DC adaptor will work, but is very inefficient. Not to mention that cheaper inverters can actually damage sensitive electronics if they produce a very poor sine or simply pump out a 2-step square wave...
    If you get an inverter, expect higher than necessary current draw to power your device, and please don't cheap out unless you only plan to run a light-bulb or hot-plate.

    Harald's suggestion is most likely going to be the best bet here.
    We don't know if 14.4V will harm anything... you can build a simple regulation circuit with nothing more than a resistor and zener diode.
    If you can share the current draw in mA, that would go a long way in suggesting a better alternative.
    (If current draw is too high for the simple method, you can find/buy a 'buck' type switch-mode voltage regulator that will give you a clean 12.3V output and many are adjustable.)
     
    Harald Kapp likes this.
  5. Slowy

    Slowy

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    0
    Jan 21, 2017
    Thanks guys.
    The CPE draws in the region of 1 amp. I don't like having to use the inverter as it is inefficient, noisey and battery power is vital to running the fridge and keeping the beer cold.
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    If you are drawing an amp, then if you are using a linear device to regulate the voltage, you will be wasting close to 2.5W in waste heat. This can be managed with a heat-sink of course.
    If you go with a buck (or buck-boost) type switch mode regulator, you will be able to run cooler.

    Regardless of the method you use, I strongly suggest you do some basic filtering on the input side of the regulator to prevent voltage spikes from causing damage. Automotive is notorious for noisy damaging voltage sources.
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Want to roll your own converter (9V...14 V in -> 12 V out)? Here's a reference design.
    Or buy a module. The kind the link points to willl need an additional housing.
    I support Gryd's suggestion for using a filter, e.g. like this one.
     
    Gryd3 likes this.
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