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Cheap Powersupply

Discussion in 'General Electronics Discussion' started by Xenobius, Jun 12, 2012.

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  1. Xenobius

    Xenobius

    125
    0
    May 15, 2012
    Hi Guys,

    I need to build a small power supply connected to 230VAC and I want it to give me 12V / 200mA at maximum (just a relay and a small IC).

    Can I get away by using a bridge rectifier, some filter caps and a potential divider?

    Or should I use a capacitor? I know I can make use of a capacitor's reactance and I found formulas and calculators but I still don't understand how I can do this.


    Thanks a lot
    Regards,
    X:
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    In most cases I would advise you to just go out and get a cheap plugpack.
     
  3. Xenobius

    Xenobius

    125
    0
    May 15, 2012
    Thanks Steve, In this case, I'd rather do it myself because it needs to fit in a small box which is very remote. A ready made transformer is not an option :(.

    Thanks
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Can't the plugpack be external you your box? That way the box can be even smaller.

    And this is why you need to give more details.

    The next solution I would advise is a small transformer, rectifier, and filter. Perhaps a regulator is you really need it. This will give you isolation from the mains.

    If you're planning to go the capacitive reactance route then you need to have a small and preferably fairly constant current load, and no inputs that aren't safe at mains potential. Same for the outputs.
     
  5. Xenobius

    Xenobius

    125
    0
    May 15, 2012
    You're right, sorry for that. Ok so basically this is the application.

    My dog drinks a lot of water and she likes to drink straight from the water tap not from her bowl :mad:

    So instead of leaving her dehydrated all day long waiting for me to open the damn water tap :p I bought a water solonoid valve and am building a small circuit which will trigger the valve open when she is infront of the tap. I installed the valve inside a plastic box which takes 230VAC. So basically I already have 230VAC inside this box and I decided to do this for 2 reasons. The first being that the solonoid valve operates at 230VAC and secondly the plastic box is water tight as it will be exposed to all elements hence cannot use an external power supply.

    So to conclude I need to step down from 230 to 12 to be inside this box too.

    Thanks again for our precious time! :cool:
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    9,887
    2,096
    Nov 17, 2011
    From your question I take it that you have limited experience with electronics. I therefore strongly recommend you buy a standard wall wart with the specified ratings. It will be safer for you and your dog - especially if you are going to use the setup in conjunction with water.

    Harald
     
  7. KMoffett

    KMoffett

    696
    68
    Jan 21, 2009
    I occasionally run into the problem of adding an internal low voltage DC power supply to a case that already has line voltage available inside. My usual solution is to hack a SMPS wall-wart. The internal PCB is light, efficient, isolated, cheap (they are free...check your junk drawer), and usually regulated.

    Example attached.

    Ken
     

    Attached Files:

  8. Xenobius

    Xenobius

    125
    0
    May 15, 2012
    lol thats awesome!! Great idea! So its just a matter of assembling it now!

    Thanks again :)
     
  9. KMoffett

    KMoffett

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    68
    Jan 21, 2009
  10. Iron Will

    Iron Will

    16
    0
    Jun 11, 2012
  11. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    I agree for low current requirements these can be hand on Ebay for a dollar or two delivered...
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,360
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    Jan 21, 2010
    The easier solution may be to get a small pond pump and recirculate the dog's water through a "tap"

    We have a commercial device just like that for our cats.

    The pump is box about 3cm on each side and pumps the water about 10 to 15 cm and then over a waterfall thing.
     
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