12 volt to 3 volt

Discussion in 'Wiring' started by sleepgsr, Jun 24, 2011.

  1. sleepgsr

    sleepgsr New Member

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    Hello All,

    I've been a lurker on the forum for over a year and never have posted yet That is probably because of all the topics and posts from others covered any questions I have had.

    I've added a portable hot water heater to my pup. Its an on demand type so as soon as I turn on the water, it fires up and heats the water. It runs on propane and takes two D batteries wired up in series so it uses about 3 volts. Does any one how I can use my 12 volt trailer power and reduce it to 3 volts to run this without having to use the D batteries. I am confident I can do the wiring but don't know what type of device I need to reduce from the 12 to 3 volts. Also are there any other power considerations the I need to know besides the voltage.

    Thanks for your time,
    Vince
     
  2. Twisty

    Twisty New Member

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  3. Snow

    Snow Well-Known Member

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  4. sleepgsr

    sleepgsr New Member

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    Great. Thanks alot.
     
  5. razmichael

    razmichael New Member

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    A note to keep in mind - if you use the AC/DC adapter you will only have this available when on shorepower (or a complicated 12v to 115 inverter and then back again - waste of power). Best bet is to us the DC to DC adapter so it will always run off the 12 volts whether through the converter or from a battery.

    If you have some electrical DIY skills (or interest) it is also very easy to build a voltage divider with just a couple of resistors. Quick search on the web will show how to do this. http://en.wikipedia.org/wiki/Voltage_divider explains what it is but looks far more complicated than it needs to be. A voltage divider has the negative issue that as the source voltage/current changes, the output also changes but I do not suspect this would be an issue unless the power drops too much for the igniter (I'm assuming the hot water heater uses the 3 volts for the igniter and the water pump). Better solution would be a linear voltage regulator. This is a circuit that acts like a voltage divider, but changes resistance to maintain a constant output voltage regardless of source current or voltage. These are not expensive (a few bucks) but need some wiring and soldering experience. One example at http://www.onsemi.com/pub_link/Collateral/LM317-D.PDF. Any electrical supply store (Radio Shack/The Souce) will have these. I used something like this to add 'hockey puck" LED spot lights in my PUP over the tables for more direct light when reading etc. Instead of batteries I wired in a small voltage regulator circuit into the puck and connected to the hot side of the nearest overhead light. Keep in mind that any of these solutions should include a heat sink as the energy from 12 to 3 volts is lost as heat (just get a part that has the heat sink included). A switching voltage regulator is much more efficient but overkill for this.

    You did ask if you needed to worry about anything else - I have no idea of the current (amperage) requirements for the heater. I do not suspect it is high given it is running from two D batteries but avoice any converter that cannot handle a decent amperage. I also suspect the the 3 volt requirement is not that tight so a 5 volt source would likely also work but this is always a risk.
     
  6. aeisbren

    aeisbren New Member

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  7. ogeer3

    ogeer3 New Member

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    The devices that Twisty and aeisbren suggested should do the job if you do not need more than an amp of current when it sparks. Good luck!
     
  8. eagle9252

    eagle9252 New Member

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    I have one also and just have not taken the time yet to look into it. Mine has to have a separate pump for the water so I will only need 3v for the igniter. Before I make a voltage reducer I will run it for the weekend with the D batteries to see how long it will work. If it burns through them quick, then it will also use the 12v system faster than I want to use and will have to add a switch at the sink. I would rather find out with the D’s first
     
  9. deman70

    deman70 Rob the noobie PUP camper.

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  10. screwballl

    screwballl Stimulus Package

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    Hook up a 12V car outlet/cigarette lighter then use one of the previously mentioned 12V to X volt devices. Make sure you check the ground wire from the adapter with a voltmeter/multimeter before fully hooking it up.
     

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