DIY Lab Power Supply

Discussion in 'Power Electronics' started by bumba000, Oct 28, 2015.

  1. bumba000

    Thread Starter Member

    Oct 7, 2015
    72
    2
    Hi All,
    I am currently working on turning an old ATX power supply into a 12, 5 & 3.3v power supply. It will have plenty of current but was thinking about something like this http://www.12volt-travel.com/5-amp-12-volt-power-supply-p-4819.html , a couple of LM317's and some banana jacks. I was looking at the slightly larger one with 10amps but I really don't need that much power. Well I guess I don't need it yet. Anyways, my question is really - how well would this type of power supply work with LM317's to get 5 & 3.3v?

    Thank you, John
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,991
    3,736
    I would stick with the ATX supply. They have plenty of power on each voltage rail and make a nice project. Also, you can always find one in a dead desktop from an electronics recycling day.

    Trying to use LM317 for anything more than 500 mA means heat single and fans. Especially since you will be dropping 7 volts or 8.7 V to get to 5 and 3.3V respectively. Multiply those voltage drops by the current you want and that is the wattage that the poor little LM317 must deal with. No worries with the ATX supply.
     
  3. bumba000

    Thread Starter Member

    Oct 7, 2015
    72
    2
    I was kinda leaning towards the ATX. I have a few laying around that are known good, I already own them, and they do put out a ton of current. Only trouble is they're not very pretty.

    Guess I'm headed out to the shop with an ATX PS. Poor guy doesn't know I have in store for'em. I'll test it out when done and post a pic. Guess I'll have to find another project for these LM317's too.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,991
    3,736

    I desolder all of the extra 12, 5, 3.3 and ground wires from the board. Then the box opens up quite a bit for cooling without all the wires there. I use a fat piece if stranded wire (gauge depends on end use). Sometimes I add a little project box to the top so I have room for Banana jacks. Sometimes, I just add the LED (power) and LEd(standby) and a switch - then run my power to what ever I am powering with no jacks.


    Here is one.
    image.jpg
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    I have modified several atx psus and made some variable too, so you have best of both worlds, high current and 3v upto 25v dirt cheap.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    My ATX test load is both filaments of a H4 headlamp bulb for the 3.3 and 5V rails, and a 21W indicator bulb for the 12V output.

    Usually you have to put some sort of load on the 3.3 and 5V rails to get anything out of the 12V output.

    Some cheaper PSU boxes have nasty surprises in store!

    Before I made up a dummy load jig, I encountered a cheap one that the 3.3V sense wire had a plug pin all to itself, I didn't notice that and didn't provide a connection between it and the 3.3V feed wires. The PSU went bang as soon as I switched it on.
     
  8. bumba000

    Thread Starter Member

    Oct 7, 2015
    72
    2
    I went with an ATX power supply. It looks like shit, but it's great. I thought I had plenty of banana jacks. I reality I had only two. So I went ahead and drilled the required holes and then went to buy more banana jacks - they had only small jacks. So I had to make the holes smaller using washers and a mig welder. :smiley-sad:

    12v ~ 7.5a, 5.5v ~ 14a, 3.3v ~ 19a. Perfect!

    [​IMG]
     
  9. tom_s

    Member

    Jun 27, 2014
    285
    333
    currently using a couple to charge batteries off solar panels (modified) and definitely cheapest option (~250v from the panels)
     
  10. MrSoftware

    Member

    Oct 29, 2013
    497
    122
    There are several ATX breakout boards around, amazon has some, alibaba has them cheaper if you don't mind the wait. I've never used one myself, but they look convenient:

    http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias=aps&field-keywords=atx+breakout

    Also in regards to the Pyramid brand power supply that you posted; I'm not sure if it's the same Pyramid brand, but as teenagers we bought several Pyramid products back in the late 1980's / early 1990's and they were junk. The audio amplifiers in particular put out about 1/10 their claimed output. Based on my experience with the brand back then, I would consider that brand to be bottom of the barrel, and I would not trust their published specs.
     
  11. bumba000

    Thread Starter Member

    Oct 7, 2015
    72
    2
    I've had the same experience in the past with pyramid amplifiers. Figure the same would be true with their power supplies. I personally would rather buy direct from China via alibaba vs amazon. Lucky for me I have plenty of atx power supplies laying around and don't need to shop at either place.
     
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