240 volts AC to 12 volts DC

Discussion in 'The Projects Forum' started by Lightfire, Feb 12, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Hello,

    I know I might look fool or so to ask it over and over again.

    As I am a childish, I will ask these childish questions.

    1.) When I went to a mall to buy something, I saw the sales agent opening the circuit breaker before he test 12 v bulb if it will work or not. (cant understand, not necessarily to understand)))

    2.) I know there are some 240 volts to 12 volts converter. so, here are some of my questions.

    2.1 for example some of my circuit (12 v) got short circuited, the main (or the 240 volts socket) will get short circuited too??? OR just will turn off all the devices (devices of 12 v)))...

    2.2 if ever i purchased that converter, my billings is just the same??? i mean even though the operated volts is just 12 volt???

    2.3 if ever i touch the 12 volts electric wire (which is stripped or whatever you call), is there any tendency to get electric shock???

    thanks all of you guys for understanding my questions and all the members and as well as those mods/workers in this site is VERY VERY VERY nice!!!!!!!!!!!!!!!!!!!!1

    have fun!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    It's usually better form to switch electricity with a device made for that - a swich or circuit breaker - than to make a or break the connection at the load. It's not much issue for a 12v bulb, though.
    This is why we isolate circuits from each other, for instance by using a transformer. A short on the secondary (low voltage side) may be a problem but it won't directly short the primary (high voltage side).
    Worse, even, because you pay for POWER, not voltage, and a small bit of power will be wasted when converting from one voltage to another.
    Not so much, unless your skin is wet and/or salty, to allow current to flow. Touching a 9v battery to your tongue, for instance, is very unpleasant - but not dangerous for most people. You can firmly grab the poles of a 12v car battery and not feel a thing. Alternating current is easier to detect at a given voltage, and of course 120V AC is lethal if you can't get away from it.
     
  3. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    i know this is so foolish question again and again...

    so what should i do to have an 12.0 volt DC power???

    i mean it's like that...


    a power supply
    if a voltage became less than 12.0 volt, then automatically off! discharged!!!

    and so on!!!
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    I think the only safe way for you to have a 12V DC power supply is to obtain a ready-made one. From what you have said in previous posts, you may not be ready to build mains-operated equipment.

    I really don't know what your last sentence means. Are you asking about some kind of automatic circuit-breaker?
     
  5. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    No, it's not about circuit-breaker.

    I mean if battery voltage drops below than 12.0 volts, it will automatically discharged...

    But yeah, maybe you're correct, maybe it's kind of automatic circuit-breaker, but still don't know....
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You can build your own power supply, with a wall wart.

    Basic Bench Top Power Supplies

    Wall warts are a godsend to beginners and advanced users alike. Getting the power supply out of the project box solves a lot of problems.

    I asked this in another thread, but how much current are you wanting? You can get off the shelf units for a decent price that will handle 3 amps. Most of the prebuild power supplies I'm thinking about provide 13.7VDC, which is what a car with a fully charged battery provides. The voltage in cars is not very stable, it is a given.
     
  7. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21


    Hello Bill_Marsden,

    I read your topic and it directly says "creating your own battery", which I am really confusing. I mean, I think I don't want to work anymore as I need it already. :) But anyway, current? I am not sure with current. But I suppose, the battery will operate some kinds of lights, mini tv, mini electricfan, and so on... those appliances were rated 12.0 volt...

    P.S. Can I test something's voltage (for example) via voltmeter? or battery can only be test?

    Thanks!
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Your google translator is malfunctioning. Power supply is not a battery. It plugs into a wall outlet and creates DC voltage.
     
  9. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Oh, I mean power supply not battery. It's not google problem anyway...
     
  10. floomdoggle

    Senior Member

    Sep 1, 2008
    217
    2
    I'd stick with wall warts for now, until you get LOTS more experience with mains voltage. After 36 years working with electricity, I still will never cut corners. Btw, anytime you use mains voltage, even after being stepped down to 12 volts there is a chance that 240 volts will get thru.
     
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