Portable power supply

Discussion in 'General Electronics Chat' started by Dr.killjoy, Apr 14, 2015.

  1. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    I was looking into playing with a portable power supply.. I will be using it for basic bread boarding and I was wondering if you guys would use a smps or linear supply .. It just gets to be a pain to keep dragging my large power supply out when I am barely using way less than 1amp and under 12v dc.. Oh I was looking at using the
    lm2596 already built regulator from ebay if I decide to go with it .
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Buy a wall wart and make/buy a bread board supply board. Fits on one side of the breadboard. Don't recall if the voltages were adjustable, but it wouldn't be difficult to roll your own. I use linear supplies; less complicated, cause fewer issues, and I don't worry about efficiency when I'm testing.
     
  3. #12

    Expert

    Nov 30, 2010
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    I decided that I would use the 78Lxx and 79Lxx linear regulators for a 1/10th amp limit. That covers more than 90% of the little test jigs I explore. Most breadboard circuits are just, "proof of concept" tests. A couple of what-ifs and a few adjustments will demonstrate the uncertain points. I can still haul out the 8 pound Variac, but I rarely need it. Besides, pouring an amp through a little plug-in board is risking melty things.
     
  4. gerty

    AAC Fanatic!

    Aug 30, 2007
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    We use a lot of 5v cellphone chargers, the students get them from the Goodwill store for a dollar each.
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
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    The Goodwill stores in my area charge $3 for most adapters. Kind of pricey for a cellphone charger, but okay for 18VDC@1A. Best to get them when they're 50% off if you can.
     
  6. upand_at_them

    Active Member

    May 15, 2010
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  7. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Here is what I ordered from ebay ..
    http://www.ebay.com/itm/New-110V-DI...379?pt=LH_DefaultDomain_0&hash=item1c511bb42b
    [​IMG]
    US Plug 110V DIY LM317 Adjustable Voltage Power Supply Board Kit With Case

    Features:


    One way adjustable signal generator output. Convenient to provide the pulse signal
    With a logical pen function. For convenient the logic level of test circuit
    With one way buzzer. You can test the wires on and off (connect the wires to the power positive and signal input, the wire on - the buzzer sound). You can also test the low-frequency signal (input the signal from the signal input, if there is a signal, the buzzer sound)

    Specifications:

    Power: 2W
    Voltage: 110V (update in 2015-03-11)
    Plug: US plug
    Output voltage: 1.25V - 12V regulated output continuously adjustable.
    PCB board size: 7.3 x 6.8cm (W / L)
    Shell Size: 11 X 6.9 X 41.5cm (L / W / H)
    Weight: about 295g

    Package included:

    1 x DIY LM317 Kit
     
  8. #12

    Expert

    Nov 30, 2010
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    Awww...How cute!
     
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  9. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    LOL Stop making fun of me ...:)

    I just thought this would be a good project for my son and I to solder up...
     
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  10. #12

    Expert

    Nov 30, 2010
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    It IS cute! See-through case, lots of different colored LEDs, captive nut holders... :)
    If I wanted to make fun of you I would say the knob looks like an after-thought and it has a power cord, which seems incompatible with the word, "portable" (in your first post).

    I was just being my usual, honest, self. I think it's squee cute, like the avatar for Sinus23. :p
     
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  11. upand_at_them

    Active Member

    May 15, 2010
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    How did they calculate the power at only 2W?
     
  12. #12

    Expert

    Nov 30, 2010
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    Probably the usual way, P=IE
    2W = I 25V
    25V x 80 ma = 2W

    The auction is still open and there is a button to, "Ask a Question" if you want to hear from the seller.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    Wall-warts is pretty much how I do it much of the time.

    Appliances come and go, and often leave a wall-wart to go in the junk box, so its usually easy to find one that fits the job quite well.

    If you're developing a project for publication in an electronics magazine, a wall-wart as the power source avoids the need for DIY power supplies and gets out of oh - so many problems.

    99% of the time, local regulation issues can be taken care of with 78xx regulators. The old iron-cored transformer variety wall-warts are becoming increasingly rare - on the SMPSU type, the regulation ranges from not too bad to pretty good.
     
  14. upand_at_them

    Active Member

    May 15, 2010
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    The LM317 can do up to 1.5A. They should be quoting 12W or 18W. Their rating is probably based on that wimpy transformer.

    I don't like that they decided on an acrylic enclosure. May be easy for them to laser cut, but not a wise choice for a power supply. And I wonder if they isolated the regulator tab from the heatsink; the LM317T tab is connected to it's output.
     
  15. #12

    Expert

    Nov 30, 2010
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    The 317 comes in several flavors from 1/10 amp to 1.5 amp and SOT to TO-3. The limit on this one might be having more than 12 volts for Vcc and trying to deliver 1.25 volts at minimum adjustment value. Maybe 12.75V x 0.08A = 1.02 watt on the regulator chip. No, that doesn't seem right. Probably the transformer, as you said.
     
  16. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    The kit is $17.99 with free shipping.. My plan was to try it out and see what happens and if all else fails then make my own power board and use the clear case.. I figured you can't go wrong for the price..
     
  17. #12

    Expert

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    Yep. I've done that. Bought a multifunction screwdriver/nut driver for 50 cents, just to get the telescoping magnet mechanism from it.
     
  18. upand_at_them

    Active Member

    May 15, 2010
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    I got one of these a few years ago: http://www.amazon.com/Elenco-Triple-Output-Power-Supply/dp/B0002DT0GU

    Much more than $17, but: It's a kit. Has a metal enclosure. Proper banana jack outputs. Bigger heatsink, with properly isolated regulators. Larger current output. You can change the AC outputs to something useful. It doesn't have a display, but I added one for a few dollars (PIC, LCD, and op-amp).
     
  19. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Lol I wasn't sure but figured you where having fun with it ..

    Remember it's from china and at least it's in English and the specs are off but will have to wait til it's here..

    I have plenty of walwarts laying around but I want something simply for protoyping
    and proof of concept
    Whats wrong with using acrylic for a case ???



    I like it alot and that would be a pretty cool project but I already a Mastech 30v 3amp dc power supply .. My problem is that my work space is my kitchen table and it gets to be a pain to drag my power supply out for a simply circuit or for prototyping ...
     
  20. #12

    Expert

    Nov 30, 2010
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    Acrylic might not be as fireproof as steel. It also doesn't dissipate heat as well as steel. You must decide if it is proper for your safety.
     
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