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battery decorations converted to mains tranformer

Discussion in 'Power Electronics' started by Henhead, Dec 17, 2015.

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  1. Henhead

    Henhead

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    Dec 17, 2015
    I want to create a Xmas scene for my fire place. I want to wire a number of battery Christmas decorations together and run it off a single multi voltage adapter.

    The decorations are led lights only (some change colour) ranging from led tree light (3 x aa) and a number colour changing snowmen (2 x aa) and snow men and robins (3 x LR44 Button)

    I wanted to create a box stand that they will be stuck down to and then wired underneath (hidden) and run off a single adapter.

    Is this possible? Safe? If so how would run the wires?

    multiple feeds off one wire or chain each positive feeding the next and same with neg?
     
  2. GPG

    GPG

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    Sep 18, 2015
    You could run them off a 4.5V wall wart all in parallel, Operating off batteries I dont think the current will be an issue
    This will need couple of diodes to drop the voltage,
     
  3. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Each light would have an led and a resistor to create a voltage drop and limit the current. (Apart from the button batteries)

    So each circuit in each light is already designed for there battery voltages. If you can create several different voltage rails for each light it would be simpler.

    If you used a single voltage for them all, you would need to find calculate which resistor is needed to create the right voltage drop for each(In addition to the resistors already in each light).

    Diodes are useful to drop the voltage slightly, but it's more practical to use a resistor.
     
    Last edited: Dec 17, 2015
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    That's not really the issue

    the plugpack will be wired into the existing battery terminals of each unit so that it still powers the unit for the colour changes etc

    As @GPG said, a diode will effectively drop the voltage enough to the lower voltage light unit

    no is isn't,. because a resistor will also current limit and in this case that also isn't an issue .... a diode is ideal :)



    Dave
     
  5. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Okay Dave, would the diode voltage drop be unreliable though depending on the current?
     
    Last edited: Dec 17, 2015
  6. Martaine2005

    Martaine2005

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    May 12, 2015
    Hi Ash,
    the diode would drop the voltage by approx 0.7v for each diode.
    The resistors are more for limiting the current.
    So two diodes at 0.7v is 1.4 volt drop immediately.
    As for reliability, rectifiers are used in all AC to DC units.
    So I would guess they are reliable.

    Martin
     
  7. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    I read somewhere before about the diode voltage drop changing when the load current changes. But I guess that doesn't apply here.

    So its be possible to use one voltage supply and create a series network of diodes to provide the necessary voltage drop
     
  8. Martaine2005

    Martaine2005

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    May 12, 2015
    I would guess that you can.. But obviously very inefficient. lots of diodes...
    But yeah, it's possible..

    Martin
     
  9. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Yeah, it doesn't feel right to use them like that..
     
    Martaine2005 likes this.
  10. Martaine2005

    Martaine2005

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    May 12, 2015
    But in this case, the OP has 4.5v and 3v. So two diodes are perfect for a voltage drop..

    Martin
     
  11. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    Yeah it would be perfect :rolleyes:
     
    Martaine2005 likes this.
  12. Martaine2005

    Martaine2005

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    May 12, 2015
    Sorry Ash, not trying to tell you how to suck eggs! I think you are more knowledgeable than I am!
    Sometimes, two heads are better than one!!

    Martin
     
    Sadlercomfort likes this.
  13. davenn

    davenn Moderator

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    Sep 5, 2009
    the current in the circuit will also vary with varying voltage and load through a limiting resistor ;)
     
  14. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    That's okay Martin!

    There's always something to learn in electronics. :D
     
    Martaine2005 and davenn like this.
  15. davenn

    davenn Moderator

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    there sure is ... am always learning new things :)
     
  16. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    I've accepted the fact that I'm never going to know everything.. but that's what keeps you open minded and makes electronics fun! :rolleyes:
     
    Martaine2005 likes this.
  17. Martaine2005

    Martaine2005

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    May 12, 2015
    Put yourself in mine and all other 'learners' shoes Dave!
    We will never know half of what you have forgotten!:p:p
    So catching up is a no go! Going forward is likely!..But not guaranteed in my case:D
    Uncle Chris only guides me after several large liquified grapes:eek:

    Martin
     
    davenn and Sadlercomfort like this.
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