Electrical Engineers (or enthusiasts)

Discussion in 'General Off-Topic Chat' started by nintendofreak, Apr 16, 2007.

Apr 16, 2007
  1. nintendofreak
    OP

    Member nintendofreak Around. Shoot me a PM.

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    well, here is the deal.

    Ive got this 12v power source, and i wanna use it to power something that uses 3v (2x AA)

    Now, how would I do that?

    I know V=IR and

    V=3
    I= ???
    R= WHAT I AM SOLVING FOR

    So... whats I? [​IMG]

    Yah, i know dumb question, but makes me wonder... [​IMG]


    Explanations would be appreciated [​IMG]

    Thankee [​IMG]
     
  2. FAST6191

    Reporter FAST6191 Techromancer

    pip
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    The back of the supply will usually have a wattage/power rating given in watts.

    Power (watts) = current (i in amps) x voltage (v in volts).

    of course you can also rearrange v=ir and throw it into p=iv to give p=i^2.r and p= v^2 / R

    Be careful if you do step down the voltage as the current that may end up flying through the device may blow it up (which if it is 3v will likely not be that much.
     
  3. nintendofreak
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    Member nintendofreak Around. Shoot me a PM.

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    Got it, easier than I thought.

    3V = I (584R)

    I= .0051369863

    So...

    Need 1,800 kOhm 1/8 watt resistor
    [​IMG]

    Thanks!
     
  4. Caoimhin

    Member Caoimhin GBAtemp Regular

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    Maybe some induction transformer? I don't really know ^^"
     
  5. noamkot

    Newcomer noamkot Advanced Member

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    You need to use a voltage regulator or step down converter.
    If you actually use a 3V voltage regulator you must make sure that you don't pass the power limit of the regulator.
     
  6. nintendofreak
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    Yes, that would be the easy way... But i prefer to home make things, it would cost me like 2 dollars to make it myself [​IMG]
     
  7. outphase

    Member outphase Custom title

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    Another way is to take the Thevenin equivalent of the load circuit. Then figure out a way to drop the voltage down with a resistor (or other impedances)
     
  8. Veho

    Global Moderator Veho The man who cried "Ni".

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    You can use the 12V to power a transistor amplifier, and set the output voltage of the amplifier to 3 V. That way you get the least losses. Any other voltage divider will have dissipation larger than the power output you need for the 3V device you're using, i.e. you'll still be using the entire power output of the source, instead of one fourth (or less) that you need.
     

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