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Multi-device power supply.

Discussion in 'Power Electronics' started by Geonovast, Aug 26, 2012.

  1. Geonovast

    Geonovast

    16
    2
    Aug 26, 2012
    I have an idea to build myself a single power supply for all of my networking devices, so I don't have to have a power strip and a half sitting behind my desk just for that.

    I'd like to keep the wall warts intact, so I'm looking to start from scratch, however I'm not really sure where to start or which way to do this.

    I want to power 5 separate devices, their requirements are:
    5 Vdc, 2A
    12 Vdc, 600mA
    12 Vdc, 500mA
    3.3 Vdc, 3A
    7.5 Vdc, 700mA

    I'm looking to shove all of this into the case of a Linksys EZXS16W. I've attached a picture that should hopefully show how much room I have. I believe there should be enough for everything I need plus a small computer fan.

    Can any of you help get me started? I'm great at inferring from examples and reading schematics, this is just my first project starting from bottom up.
     

    Attached Files:

  2. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    If 'I' was doing this I would start out with a cheap 12V wall wart with a minimum 7A capacity, this is sorta cutting it close but IMO probably good enough... You can always measure the full current drain when all devices are on when complete and see if you are pushing it's limits and need to upgrade to a higher Amp rating to give you more head room...

    http://www.ebay.com/itm/AC-to-DC-po...C_Adapters&hash=item337539778e#ht_1165wt_1163

    From there you can tap off both 12V need directly... And for the other you could use cheap linear IC regulators, or get fancy and more efficient with the still low cost switching regulator modules from Asia... If you use linear regulators, I would highly suggest heat sinks...
     
  3. davenn

    davenn Moderator

    13,264
    1,749
    Sep 5, 2009
    Hi Geonovast
    welcome to the forums :)
    Not too difficult with a bunch of regulators

    Starting with a 16V 8Amp DC PSU you could then regulate that down to the various required rails

    [​IMG]

    Thats one possibility and is able to supply the required currents you need

    We can describe the various component values if you decided to go ahead
    Lets see if anyone else had any other ideas :)

    OOPS just noticed I had labelled it as Adj for 7V, that of course should be 7.5V

    Dave
     

    Attached Files:

  4. davenn

    davenn Moderator

    13,264
    1,749
    Sep 5, 2009
    haha
    I knew some one would post whilst i was busy drawing up a cct

    which is why I went for the 8 - 10 amps so the PSU wouldnt be overheating --- lots of headroom ;)




    D
     
  5. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    May I asked why initially regulate to 16V vs 12V as I suggest?
     
  6. davenn

    davenn Moderator

    13,264
    1,749
    Sep 5, 2009
    cuz you have to have headroom for the regulator


    tho I just see what you may heve been suggesting and as long as the 12V was well regulated at 8+ Amps then that wouldnt be a problem
    And a "cheap" walwart isnt likely to be well regulated ;)

    The only difference is I supplied the 12V regulation

    Dave
     
  7. Geonovast

    Geonovast

    16
    2
    Aug 26, 2012
    I'm glad we're thinking along the same lines. Tapping off of a high current brick was something I'd considered, I'm just not too familiar with switching power supplies, and I wasn't 100% on how they would handle tapping off that much. (I didn't see any specific problems with it, but research is usually better than fire.)

    I'd also done some research on high current regulators, but hadn't settled on one.

    Out of curiosity, why do you have the 7 volt regulator in a smaller case and tapped off the 12V? Why is it not pulling off the 16V with everything else?

    And naturally, even if it wasn't necessary, I was going to heatsink everything and have a fan in there. I have the room for it, I might as well.


    Another question - When adjusting the regulators, should I set them to the exact levels the device is calling for, or should I match them to the unloaded levels of the wall warts?
     
  8. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    I understood that, just curious why you didn't just drop down to a regulated 12V to start with, and skip the additional internal... Your design does allow you to use a simple unregulated transformer initially, that could save money...

    In regards to the supply for clarification I choose 12V @ 7A because that is the max capacity of the cheaper wall warts @ 12V, after 7A they jump significantly in price generally... This still gives you 84 Watts of power, and you only need 38.35 Watts, so even though the Amp rating is technically close at first glance, in the end unless you have horrible conversion to the lower voltages a 7A supply should be fine...
     
  9. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    I'll jump in before Dave :)

    Tapping off the 12V regulator that has excess head room not being used, lowers the voltage going into the 7.5V regulator thus it doesn't need to get rid of as much energy as wasted heat while dropping down to 7.5V... And your 7.5V rail doesn't require as much current... Combine that with the fact most TO-220 packages max out at about 2A, leaves you having to bump to a different package for those to get the 3A and give head room to the 2A requirements of the 3.3V and 5V rails...
     
  10. Geonovast

    Geonovast

    16
    2
    Aug 26, 2012
    I'm kinda seeing two options here.

    #1 - Pick up a 16V brick with slightly higher current, and regulate everything like in the schematic.

    Or,

    #2 - Get the 12V questionably regulated power supply, regulate the lower voltages and tap directly off the 12V.

    I'm leaning toward the second option as it seems it would produce less heat. Also, the last time I opened up a 12V Linksys wall wart, it wasn't regulated. If the ones I'm using now aren't regulated, I'll have no problem going with option 2. I can easily take them to school on Monday and see if there's any ripple. If they don't need it regulated, I think I'd be comfortable adding an addition filter cap and calling it good.

    I've considered two small additions to the project since starting the thread:
    I would like an LED on the front to light up when something is plugged into each cord(not sure how to do that), and it would be nice to have an addition supply with a 5V/7.5V/9V switch(easy enough).
     
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