DC power adapter V drop, amp rise?

Discussion in 'The Projects Forum' started by DreyeIce, Jul 5, 2012.

  1. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
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    Basically i understand schematics and can build circuits easily, i just cannot grasp the concept of building one from scratch.

    I have a DC wall adapter that puts out 7.5V @ 1000mAh. It needs to be at 1.2V steady and variable from 1-2A.

    can anyone direct me to a source to start constructing my own or give me a basis off what i should be doing? its for a circuit that uses a AA rechargable battery, i was hoping making a wall adapter would give me unlimited runtime plus some fine tuning on the amperage.

    Thanks guys
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    So you have a device that only uses 1 x AA battery and it requires 2 Amps of current?? Really? I doubt it..
    And I see no need for a steady 1.2V either.. A battery is never a steady voltage.

    Now having said that.. I'd suspect a simple LM317 circuit set to output 1.5 Volts with a suitable heatsink should be all you need to power your "single AA" device.
     
  3. takao21203

    Distinguished Member

    Apr 28, 2012
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    maybe it is a battery charger however they use higher voltage than 1.2V.

    Without giving information what it is, all help can only be guesswork.
     
  4. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
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    the device uses a single AA battery, it says battery can be no less than 2200mah. I know the 2.2A value is not constant, but id imagine for the time the battery lasts it peaks pretty quick and dies.

    basically the device just uses the battery to heat an element. battery dosent last very long and comes out of the device warm.

    it dosent have to be a steady 1.2v, and the amperage can be variable, really for the simplicity of the device i think anything would work.

    picture 2 copper leads connected by a steel mesh. each end of the battery is hooked up to the copper leads and that fine steel mesh gets red hot. very inefficient but thats what the device is designed to do.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Ah a vaporizer..
    A variable voltage LM317 circuit will work just fine.
    Your steel mesh is just a fixed resistor.. You can vary the voltage to change the amount of heat produced by this element. Up to a point where you melt everything around it or burn up the element so be careful.

    Lets say the resistance of steel mesh is 10 ohms..
    So with Vin=1.2V
    Power=(1.2^2)/10=.144 Watts of heat produced
    Current drawn=1.2/10=.12 Amps

    Now what if
    Vin=2V
    Power=(2^2)/10=.4 Watts of heat
    Current drawn=2/10=.2 Amps

    Now what if
    Vin=5V
    Power=(5^2)/10=2.50 Watts of heat
    Current drawn=5/10=.5 Amps

    First thing you need to do is find out the resistance of your element to ensure you don't violate the maximum ratings of your power supply circuit (LM317 or other)
     
  6. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
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    0
    yes, thats what its for. i figured if i described it the people that didnt know could help just as much as the ones that do, lol

    how would i go about seeing how much resistance the element is?

    i was thinking to hook up my multimeter in series with it and see how much current it pulls, could i find out that way?

    also, does anyone have a handle on a "dummy" AA battery? in order for this device to work the top + contact presses a pin down in the device, and with the covering stripped off the outside the battery it touches another contact making the body of the battery the -. so i would have to find an AA that has wires coming from it.
    the only reason im even doing this is the company sells thiers for 64$, and i live in canada, so getting it would be even more. i think i have enough materials here to make something similar to what they sell for a fraction of the price.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,447
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    What you should learn from this is to always give us the big picture. Never make any assumptions otherwise we're always just second guessing.
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
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    Open it up. I'd bet its nothing more than the battery hooked to each side of the mesh so you can just put your meter on the ohm setting to measure resistance and place each probe on the battery terminals.. If there is other circuitry then you will need to isolate the wires going to the mesh and measure across them.. Maybe its got a power LED or something too in there..
     
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