Please help me circuit of input 100AC -240AC 50/60HZ to output 12VDC

Discussion in 'General Electronics Chat' started by mpcotuong, Oct 3, 2010.

  1. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Hi All,


    I am planning to get input from AC of 100 to 240AC and out put of 12VDC.

    Please help me circuit of input 100AC -240AC 50/60HZ to output 12VDC

    Thanks,

    Kevin
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    100...240..............12...which is which.

    U are not making any sense.

    Is it that u want to get 12VDC from mains.?
     
    Last edited: Oct 3, 2010
  3. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    Yes, I would like convert from 240AC go down to 12VDC.

    Thanks,
    Kevin
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Do u have a transformer?
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    If you plan to have a voltage range of 100 to 240 volt. I think you have to go for switch mode power supply. Probably primary switched also. Such power are not uncommon. I am holding one in my hand as we speak. However such power supply can be hard to build on your own. And the price for such do it your self project. Will be much higher than just purchasing some of the shelf unit. So unless you have to make one. Like in a school assignment. Get a standard one. As it is hard to beat mass production in this case. Parts may also hard to get in small volume
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    It is possible to get a transformer that accepts both 120 VAC and 240 VAC but a series/parallel arrangement of dual primary windings.

    What is the current that must be supplied?
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Easiest way is to use an old PC power supply that has a universal input voltage thus no switching involved.
     
  8. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    The current is 1A.
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Most PC supplies are capable of at least 10A at 12V even if they're fairly old.

    If you search the 'net you'll find several links that show how to make a general purpose power supply out of an old PC power supply. New ones can be as cheap as $15 on sale or most small PC shops will gladly give you an old one.

    They come two ways, one version has a switch to run on the 120V standard or the 240V standard, the other just self-selects which is the one you're looking for. They'll typically run just fine with an input as low as 90V
     
  10. mpcotuong

    Thread Starter Member

    Aug 26, 2010
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    I need to make one in one unit for my project. If you have any good circuit, please let me know.

    Thanks,
    Kevin
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    It will be easy to know what u can get or what u have
     
  12. tom66

    Senior Member

    May 9, 2009
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    Most cheaper PC power supplies use a voltage doubler when set on the 115 VAC range which boosts the voltage to 230 VAC. The problem with this circuit is that if you set it to the wrong voltage then Bang! goes the supply.

    If you need 1A one solution might be to use a 7812 regulator and on the output of a 240VAC -> ~12VAC transformer, put a switch to enable the voltage doubler. This way, if you do set the wrong voltage, it'll be fine, but the regulator will probably shut down to protect itself (due to excessive power dissipation.)

    Remember, a 12VAC transformer will have a peak output of 16.9 volts. Use a full wave rectifier and a big filter capacitor (around 2200µF should work), you'll have about 15.4 volts to play with.
     
  13. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Thus the reason to find one that autoranges 120/240 as most seem to do nowadays - even several of the older ones would as well.

    They use a PWM circuit on the input side that "slices" a portion of the incoming AC mains sine wave as needed.
     
  14. tom66

    Senior Member

    May 9, 2009
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    Active PFC. The advantage of this is reduced EMI and for some big electrical users (industrial users mostly) it reduces their bill. But the average user doesn't really benefit.
     
  15. R!f@@

    AAC Fanatic!

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    So PFC truly benefits the power company not the user.
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Having as close to 100% PFC really benefits everyone. The more efficiently you use the electricity the less strain on their systems, the less it costs them to generate X amount of electricity and the less ammo they have to charge the overall public more when the yearly corporation commission meetings come around.

    Most home users are not monitored for power factor, it just isn't worth it. PFC becomes an issue when you're running quite a few large inductive loads although a large excess of capacitance can also upset it.

    Tyically, when you're a large user of electricity, the power company's meter will keep an eye on your PFC and if it falls below a certain level you end up paying more per KWh used. Around here the penalty used to come into effect if you fell under 80%, as of last year they tried to get that up to 90% but the corporation commission only allowed them 85% as the breakover level.

    I probably have around 300 HP worth of motors running at any one time and of those most are 24x7. I also have a ton of fluorescent and HID lighting which involve ballasts (also inductive). When we moved into the building our PF was hanging around 81%. There were a number of PFC correction caps around the building (the closer to the offending loads the better they work) but some were unhooked and others hooked up in areas where they didn't need to be anymore. Anyhow, through what limited calculations I could make along with tweaking the existing PFCs by removing some, moving some and adding a few others I've got us up to around 99% during the winter and 96% during the summer.

    It's kind of a fine science:
    http://en.wikipedia.org/wiki/Power_factor

    It's also to my advantage. A motor that's properly corrected (or on a line that's fairly well corrected) is going to last longer for a number of reasons.
     
    Last edited: Oct 4, 2010
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Better switch to LED lighting then
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    Try here:
    http://smps.us/
    Lots of good info.

    Stay away from the "hobby" circuits; several of them are dangerous, and several others are just plain bad.
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    I bought some surplus name-brand switched-mode power supplies made for old telephone-line modems. They are 5V at 2A but the label says the voltage is adjustable with a trimpot inside. I paid $1.50 each. I paid for the cord and the power supply was free.

    Their output voltage is rock solid (a tiny amout of high frequency ripple) with an input of 85VAC to 240VAC.

    Because they operate at a high frequency then their transformer is small and light-weight.
     
  20. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Of course if you really need to build it from scratch just get a 240 VAC to 24 VAC transformer then rectify and regulate the ouput down to 12V. If you run 120V into a 240V transformer primary you get roughly half the amount out of the secondary.
     
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