Multiple PSU design question

Discussion in 'The Projects Forum' started by Jake4842, Apr 6, 2014.

  1. Jake4842

    Thread Starter New Member

    Apr 6, 2014
    3
    0
    Hello,

    I have an idea for something I'd like to build and I'm new to designing circuits so any feedback is greatly appreciated! I have 4 devices that each require 12v and they draw about 400-450w (33.3-37.5A). I'd like to design a power supply (or 4 separate) to power them. I'd like to be able to ensure that if one stopped working the others would continue and it would also be nice to be able to switch each one on independently. So here are my questions:

    1. Would I be able to run all 4 on a 20 Amp circuit? I think I should be able to but I don't know that for sure.

    2. Is it more worth it to only use 1 transformer? If so, would I still have control of each "channel"?

    3. I uploaded a picture of the power connection, why are there 3 wires for both 12v and gnd?

    4. Many things I've read said to double the 33.3-37.5A amps to be safe but to me that seems like it might be overkill?

    Since I'm still in the early stages of this, that's all I have for now but thanks for helping me get this going!

    Jake
     
  2. GRNDPNDR

    Member

    Mar 1, 2012
    435
    7
    For the transformer, you could use a multi-tap transformer that would give you 3x12V out then you do whatever else after that, but it sounds like you would need a fairly large transformer for 40 amps.
     
  3. #12

    Expert

    Nov 30, 2010
    16,284
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    1) That's not a picture of a power connection. That's a manual for an, "ANTMINER". Some kind of computer connected device. The power connections on page 4 have 3 holes for each side of the power supply because you can't run 35 amps through a single printed circuit trace without it smoking.

    2) A 500 watt transformer is way too big to carry around, and you're going to need 4 of them?:eek:
    Probably better off to use several switching supplies, like something intended for computers.

    3) No, I don't think you can get all that power out of one 120 VAC outlet. National Electrical Code limits design current for a 20 amp breaker to be 16 amps.
    16A x 120V = 1920 watts.
    1920W/4 devices = 480 watts each
    450W/480W = 93.75% efficiency.

    No. Not even with a switching supply design.
    Well...not legally. If your loads don't really use 450 watts continuously, etc. you might not get the power receptacle smoking for months.

    4) The "safe" side of designing for current is not 100% overkill, but 20% over design would seem reasonable to me if you want this thing to run for 10 years.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Here are some 500W 12V 41A Dell server supplies for sale on Ebay:
    http://www.ebay.com/itm/12v-41A-DC-...Control_Vehicles&hash=item3a8cf67b7c#shpCntId
    At $25/ea, they're cheap. You couldn't buy a custom power supply enclosure alone for that little; and they're just the power rating that you need. Buy some extras to have as spares. Don't operate more than three of these supplies on a 20A circuit.

    You will need to make a harness to interface between the power supplies and your boards. Use stranded wire as large as the terminals on the board will accept, and no smaller than AWG-16; AWG-12 would be much better. Don't try to "get by" with fewer than three wires for +12 and three for ground, or you will very likely damage the motherboard beyond economical repair.

    Designing an efficient, reliable and affordable high-power switching supply isn't for a neophyte; even experts will buy "off the shelf" solutions if they are reasonably close to their requirements. As far as electronics projects, start off with something relatively simple, like getting an LED to blink on and off; if that project is a failure, you're only out a very few $ worth of parts.
     
    Last edited: Apr 6, 2014
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  5. Jake4842

    Thread Starter New Member

    Apr 6, 2014
    3
    0
    Thanks for the info. I might just do the computer PSUs in the end but I'd still like to understand this better. I feel like it wouldn't be too easy to build a switching supply?

    1. Sorry about that. I tried to copy just the image you eventually found... So are they all coming from the same source to 3 different circuits on the device or would I want the Multi tap xfmr and have 3 seperate legs/rails? I read one place where they said all the amps would be on 1 "rail". What does that mean in terms of this?

    2. Most people I've seen using these do just get a computer PSU. I guess basically I was thinking that maybe it would be more efficient to build 1 supply to run the 4 of them rather than buying a new $100-150 Supply thats built to run a computer. Your recommendation would still be to just buy the PSUs?

    3. There are 2 configurations of these units one uses 2 PCIE connectors and one is like what you saw with the 6 wires (3x 12v and 3x gnd). Where would I get those wires from on a standard ATX supply?

    Thanks again!
     
  6. Jake4842

    Thread Starter New Member

    Apr 6, 2014
    3
    0
    Just checked out those Dell Server supplies! That looks great! So I see just a + and Gnd in the back correct? So if I capped the positive with 3 wires (since I need 3 @ +12v) I could just run those 3 into the unit, correct? I would do the same with the gnd? There are 3 main parts of the unit. Would the 3 sets of wires each just be powering its own separate part of the unit. Might be redundant but that's how they make sure they don't send too much power through a single trace? Split it into 3 smaller circuits that would draw something in the accepted range.

    Thanks again for all the help. I've build a bunch of little things but all of them have either been passive or I've just modded something that already had working power so now I want to try a supply myself but I want to make something that I could put to use...

    Jake
     
  7. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    Right. Find out the biggest wires you can fit in the holes on the mother board, attach 3 of them to the mother board, and connect all three to one terminal on the power supply. Rinse and repeat for the other power cable.

    and, no, you don't want to start designing these as a beginner.

    ps, it isn't 3 small circuits. It's all one circuit, but you can't throw 30 amps through .01 inches of copper plating, so somebody built in 3 connection spots.

    Pss, Wookies' supplies are 11% over sized. Considering they are professionally designed, that should be enough safety margin.
     
    Last edited: Apr 6, 2014
  8. SgtWookie

    Expert

    Jul 17, 2007
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    By the way, don't try overclocking your units when powered by those supplies; you'd likely overload them.

    You might get them to work with ATX form factor supplies, but you would need at least 750 Watt units which would cost $60 and up each, and would be very inefficient because the 5v portion would not be used - yet you would have to load it with at least 2A to get the 12v to regulate properly. The margin on the supplies I linked to are somewhat low, but they were designed/built by a reputable company for exactly the same kind of duty you want to use them for. Keep your units in a clean, cool, and dry environment.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Here's a good site for learning about switching supplies:
    http://smps.us/
    But start here:
    http://www.dos4ever.com/flyback/flyback.html
    Ronald Dekker's "Flyback Converters for Dummies" is a fantastic page to start learning about boost and flyback converters, and building your own - and learning a lot along the way. Keep in mind that the supplies shown on the page are quite low-power, and not suitable for adaptation for the kind of power you want for those antminers.
     
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