power box

Discussion in 'The Projects Forum' started by dk31, Dec 27, 2014.

  1. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Hi all,
    I need to build a power box for my garage bench - I have started reading all the chapters of the "textbooks" in this forum, but it's gonna take looong untill I get a good grasp of things....
    The idea is to have a 26amp 12v power supply mounted under the bench, and a metal box (power box) on the bench that will output what I need.
    What I really need for the moment is just two 12Volts 26Amps terminals and one 5Volts low consumption plug. But since I 've been reading about electronics, I thought I would add anything else that could prove usefull in the future.
    First thought was to add an adjustable voltage regulator based on LM350, found here http://www.instructables.com/id/Mak...ycled-par/step7/Making-the-voltage-regulator/.
    First question is what do I have to use to take the 12V of the power supply and output adjustable voltage 0-24V ? and up to how many Amps would be usefull (mostly for fooling around with educational circuits)?
    The thumbnails below show what I have done so far. The two monors in the last sketch are one for high power 12V and one for low power 0-24V.
    Any suggestion or usefull link would be highly appreciated. I will add a schematic and update it for any advice that will follow...
    20141004_131021.jpg 20141018_123911.jpg 20141019_170134.jpg Power Box.jpg
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
    120
    You'll need a boost convertor to step up the voltage from 12VDC to 24VDC. It's not something for the novice so I'd advise you use something off the shelf like this from ebay.
     
  3. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Thanks for the link. This one doesn't fit in the box (box is 40mm wide) but now I now what I ll be searching for: "Boost Converter"
     
  4. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    I have read about boost converters, and if I get it right, you can only get higher output voltage than the input voltage.
    In my case, I will have 12V (26Amp maximum) input and I want adjustable output 0-24V (5-10 Amp max). Is there any simple device that could output higher AND lower voltage than the input? Or a way to put a booster and a step down regulator together (the first for higher and the second for lower voltages)?
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Google buck-boost converter.
     
  6. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Thanks for providing the term. I have looked at ebay and wikipedia. I will spend some more time looking at DIY buck-boost converters and report back
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    I tinker a fair amount with a variety of things, and I cannot imagine needing more than 12V and 1A, unless I specifically have a motor, bright light, or something that needs more power. Maybe 5A max. My go-to working voltage is 5V and it is a rare project that draws more than 100mA. One big advantage of working at low voltage is that some parts may survive a hookup mistake. A mistake at 24V is more likely to be "fatal", for the parts at least.

    I appreciate wanting to cover every contingency and to future-proof your power supply, but you can do an awful lot of tinkering with nothing more than an old computer PSU. They're free, have all sorts of regulation and protection built in, and are tough to beat.
     
  8. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Yes, the metal case of the power box will be hard to modify later.
    I found this at ebay:
    http://www.ebay.com/itm/400821372308?_trksid=p2060778.m1438.l2649&ssPageName=STRK:MEBIDX:IT
    I think it will be ok for the project (if I replace the Volt adjusting pot with a panel mount pot).
    I have also spent some time reading how you could make one yourself, but it's not something for the novice (as paulktreg put it)...
     
  9. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Here is a schematic of the project, incorporating the 8A buck-boost converter (limitied to 5A by a fuse).
    Should I connect (ground) the black wire and the metal case and if yes, should it be about at the point where the black wire enters the case?
    Any comment on the schematic would be highly appreciated as I am very new to the world of circuits.
    Some comments:
    -The layout is based on the physical layout of components, so sorry if it looks chaotic
    -Colours of the wires of the 2 Ammeters are based on the instuctions they came with.
    -The thin 12V red/black wires coming out of the PSU are just there, so I thought to make use of them to power the Ammeters just to save me a few "Y" links.
    -The left part of the circuit will only display Volt/Amp values of the 12V line. The 5V line (limited to 2A with the fuse) is there for quick access to 5volts (I use 5V frequently)


    PB3.jpg PB1.jpg PB2.jpg
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,511
    2,369
    Normally a PC P.S. is already connected to earth ground at the power common point.
    Max.
     
  11. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    The PS is grounded (the PS case too) - I opened the case and checked. My only source of knowledge on "grounding" is the textbooks of this forum (Direct Current/Safety chapter). If I got it right, grounding the Power box matel case would serve in case a hot (red) wire inside became loose and touched the metal case. That would mean that by touching the case you got current passing through your body and the floor under your feet (floor being common to ground). Don't know much on the subject, but the textbook description sounds logical.
     
  12. dk31

    Thread Starter Member

    Oct 30, 2014
    36
    0
    Hi again,
    The power box is almost ready, I only have to fix the step up/step down module.
    I got this one : http://www.ebay.com/itm/400821372308?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT
    and it has two pots, one for adjusting voltage (I tried it from 1v to 25v) and I guess the other is for adjusting current (?). How can I be sure that I have set the current pot to maximum before I burry it in the box?
    I will post some pictures when it's ready.
     
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