AC 120 V to approx. 6 to 5 V DC...

Discussion in 'General Electronics Chat' started by imzack, Aug 11, 2012.

  1. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Okay,

    I have seen some other posts about similar questions but nothing to detailed of an answer.

    Do I have to use a transformer? And how small can I get one if need be? I am working in a limited space area....

    Or voltage divider be able to work, and would it be really inefficent?

    When making the diode bridge, is there any certain diode i should get? Any certain rating to look for. I have some knowlege about them, just dont want to mess something up, esspecailly working with so high voltage levels...


    Thank you,

    Zack
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    A transformer is a must.
    It will provide the isolation from the mains.

    How much current is needed at the 5 - 6 volts side?

    Bertus
     
  3. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Current, 1.5 A, 2A max
     
  4. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    more or less im attempting to make a charger from scratch for some cell phone batteries....

    I have a palm, and found some cheap batteries for it, so want to make a device that i can put like 5 of these batteries in it, and it charges them all up... (thi8s will make me never have a dead phone, just swap out batts, or keep extra with me)...

    the first step is to get the ac from the wall power dropped down to a level that my microprocessor can work at... and also have enough current available that i can charge the batteries...

    Thats a quick overview of what im trying to accomplish.

    Thank you.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    So you are wanting to make a portable UPS or inverter?
     
  6. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    From wall output, goes to a transformer im guessing... to drop voltage down to 6 volts, from there it will power a micro controller that will know how many batteries are in teh charging unit... it will charge the battereis accodingly...

    Then when a battey is charged, you can take it out and use it in a device, such as a cellphone...

    I found the batteries for my cell phone cheap, want to make up a charger that can charge, if need be 5 batteries at a time... so i never have a dead battery...
     
  7. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    I just looked up a UPS... if i was able to know how to make this i think that might work at well... i could add a power supply to it so i could charge my phone off of this device as well possibly
     
  8. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Can I make a transformer myself? How would i know whats safe, how many windings is enough, gauge of wire, and what not....
     
  9. cork_ie

    Member

    Oct 8, 2011
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    Of course you can make your own transformer but it is a lot of work and you will need to make lots of little plates for the laminated core & drive yourself to distraction trying to wind and assemble it. You should have no problem getting a 120-6V 3A transformer . Lots of older electronics would have them, more modern stuff generally has switch mode power supplies which I wouldn't recommend for your project.It is also in breach of AAC terms of service making transformerless power supplies.
    If + 5V is sufficient for your needs you could try an old AT power supply from a computer or more difficult a more modern ATX . Make sure that the 5V supply can deliver 3A. If you don't do any modifications they are usually well protected and quite safe to use.
     
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  10. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Okay, good to know... Is there anyway to get something smaller though?

    I have a cellphone charger that plugs into the wall... It goes from wall power to usb, in a device that is the size of my thumb. How do they do that? How is it sooo small?
     
  11. cork_ie

    Member

    Oct 8, 2011
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    Because it is unlikely to be a 3A charger, more like 300-500Ma

    Switch Mode will usually be smaller and lighter.
     
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  12. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    [​IMG]

    [​IMG]

    I took that product i mentioned apart....

    Looks kinda complicated... anyone know what this is?
     
  13. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    It says its output is 5 voltas at 1 A....
     
  14. cork_ie

    Member

    Oct 8, 2011
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    Maker model & Google should supply the answer better than I can
     
  15. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    okay, ill give that a shot, hopefully i can find a schematic or soemthing! thank you
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    imzack and cork_ie like this.
  17. SgtWookie

    Expert

    Jul 17, 2007
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    The item you took apart is a small version of a switch mode power supply aka SMPS. Design and construction of a SMPS is an advanced topic; not something that a beginner should attempt; at a minimum one would need an oscilloscope for troubleshooting/debugging of an SMPS.

    A basic concept of an SMPS is that the higher the frequency, the smaller the inductor needs to be. A transformer for 50Hz to 60Hz has to be physically large and heavy due to the low frequencies involved. The supply you took apart operates at perhaps 500kHz, so the inductors can be very small by comparison.
     
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  18. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Wow, thank you for the run down on the SMPS.... I did notice it still had an inductor, but it is VERY small compared to some of the huge heavy power supplies i have taken apart in the past...

    I suppose i have alot of learning to do.... better start reading!
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    The battery in a cell phone is a Lithium type that is very dangerous because it can catch on fire (a VERY hot fire that burns hotter if water is put on it) if it is not charged properly with a battery charger IC.

    The complicated charger circuit for a cell phone battery is INSIDE THE PHONE!
    The "charger" is simply a power supply for the charger circuit.

    some power supplies for cell phones are tiny because they use a complicated high frequency circuit that uses a tiny transformer.
     
  20. ramancini8

    Member

    Jul 18, 2012
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    You want 6V @ 2A and that is 12 watts. Without a transformer and with a 120v line you need to drop about 113V @ 2A which is 226 watts. Besides being very risky because of using mains power, the dropping device (resistor, light bulb, etc.) will get very hot. NOT RECOMMENDED!!!


    A 15 watt wall wart measures 3 inch by 2 inch by 2.5 inch, so your power requirement determines the size. Consider that only one battery is allowed to full charge at a time reduces the current required to one fifth or 400 mA plus a small trickle current of about 50 mA , so the power requirement reduces to 2.7 watts. Now the wall wart size comes down to about 2 inch by 1 inch by 1.5 inch, but you have the problem of using the micro controller to limit the full charge to one battery at a time. This is accomplished by first in first charge, etc.
     
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