120v AC to 12v DC 20AMPs

Discussion in 'General Electronics Chat' started by cps68500, Nov 5, 2011.

  1. cps68500

    Thread Starter New Member

    Nov 5, 2011
    5
    0
    I have a small project that I need power for. I'd like to make this circuit and not use a commercial available one... This is what I need

    120v 15-20amp AC input
    12v 15-20amp DC output

    I'm still learning, so this would also be a learning project.
    Thanks!
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    IMHO, this is not a project to choose to learn on. I designed power supplies for 30 years and if I needed an off-line 250W power supply like this, I would buy one.

    If you insist on building, I will say this:

    You should do an offline switcher design.

    Best topology to choose would be half bridge.

    This is the same wattage ballpark as a PC power supply. You might be able to buy one and modify it.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
  4. cps68500

    Thread Starter New Member

    Nov 5, 2011
    5
    0
    Thank you. I already have a PC supply for a proto-type on my project but I really want to reduce the size... and not rely on a commercial version...
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ok, so here's an application note for a current-fed push-pull converter:
    http://www.ti.com/lit/ml/slup117/slup117.pdf

    The voltage input and output will be different, but it has most of the components that you will need. You'll need to understand how it works, too.

    Do you have an oscilloscope? If not, you'll need one.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    It is almost always cheaper to buy than to build, for example...

    http://www.sourcingmap.com/12v-20a-...gle&utm_medium=froogle&utm_campaign=usfroogle

    http://www.amazon.com/Regulated-Switching-Power-Supply-110-240V/dp/B004OLJHCI

    Though, if you are are going to use it near its rating you probably ought to up the amperage a bit. It is never a good idea to run equipment or parts near their ratings for any length of time, it shortens their life considerably.

    http://www.google.com/products/cata...7NG1Tu2JH6WLsgLi6K3jAw&sqi=2&ved=0CIgBEPMCMAA

    http://www.amazon.com/Universal-Cooling-Output-Switching-Supply/dp/B0052IGTP0

    Otherwise you are going to need a very big bulky transformer.

    BTW, the input current will be just over 1/10 the output current, call it 3A, since power supplies tend to convert energy (as using 140W, outputing 120W).
     
  7. cps68500

    Thread Starter New Member

    Nov 5, 2011
    5
    0
    Looks like I have some reading to do. I guess I was to make my own because I have a project that I want to some day turn around and sell... and if I use someone else's power supply I would then have pay them to use it, right?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Lots of reading.
    Switch-mode power supplies (SMPS) are a mighty complex subject for a newcomer to electronics.

    You will find that you are usually better off to incorporate a COTS solution (Commercial Off The Shelf).

    It is very expensive to design, build, test, have certified, and then tool up to go into production for something custom like this. It would be very difficult for you to arrive at a competitively-priced product in a timely fashion with such a complex assembly.

    That's why computer supplies are so attractive; widely available, standard sizes, reasonably efficient, tested, certified and reliable. They've built so many of them that design/tooling costs have been taken care of long ago. The manufacturers build them in such huge quantities that the cost of components is very low. Unless you're going to be building many thousands of your units, you'll be paying a good bit more for parts.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    No, you contract it out and buy it. Dell and HP and every other PC maker on earth do not build power supplies, they subcontract. You give the power supply vendor the specs and they build it.
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Or if you can buy exactly what you need off the shelf, but need quantity, contact the manufacturer and buy it from him. They do give quantity discounts if you ask nicely and are a serious customer.
     
  11. cps68500

    Thread Starter New Member

    Nov 5, 2011
    5
    0
    All good information. I'm liking this forum already. Everything I'm seeing is still quite big. I was hoping to trim down some of the size by building my own. Also, I was hoping to get rid of the fan ( I wasn't sure on the heat output)...
     
  12. cps68500

    Thread Starter New Member

    Nov 5, 2011
    5
    0
  13. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    The shown schematic is a linear powersupply.
    It will be big and produce quite some heat.

    Bertus
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    20A is a lot of current. Those power supplies are about the right side for the job. Even with switching efficiencies they are going to get hot.

    If you go linear you will not believe the heat generated. Think space heater.
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Radio Shack sells (sold? don't know if they discontinued) as 12V 25 A Switching supply for CB radios and such, I have one around somewhere, it's only 2" tall, 10" wide and 10" deep, and a few pounds is all.

    So the "single output 12V high current" has already been designed and marketed, several times.
     
Loading...