Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What Power Supply To Purchase?

  1. Sep 8, 2013 #1
    I am trying to get ahead & learn electronics. I'm just working on my general education classes now.

    I'm in need of a power supply. I want this to last me through my schooling & beyond. This may sound like a dumb question but are PSU's only DC out?

    Anyone know one that'd suit me? I'm not sure what to look (voltage/amperage).

    Jameco seems to have the largest selection. I'd like to keep this under $200.


    I'm taking a shot in the dark. Thoughts?

  2. jcsd
  3. Sep 8, 2013 #2

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

  4. Sep 8, 2013 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    It helps to know what you intend to use the PSU for. The units at Jameco are probably intended for use in a computer system, which, believe it or not, use DC power.
  5. Sep 9, 2013 #4


    User Avatar
    Gold Member

    Don't buy a power supply until you have a specific problem to solve with it. Old wall warts are great power supplies. You never know what you are going to need in the way of power until you need it. It's amazing how many old wall warts show up at goodwill. Get two and you have +- voltage.

    That said, a lab supply with variable voltage up to +- 24 volts at a few amps could be a useful thing, but an oscilloscope will be infinitely more useful than a lab supply. You can scrounge power supplies from many sources.

    If you insist on a supply, the kit jim pointed to is a good one, and that page has a whole family of useful supply kits. (just be careful of the line "up to 1A with appropriate heatsinks")

    That's my personal view, anyway.
  6. Sep 9, 2013 #5
    I am astounded by number of bad advice on this topic!

    First of all, power supply IS one of the most important things you need to have on your test bench.
    1)If you are testing something, you need power to be available at an instant. You don't want to go trough box of old wall warts!!
    2) You must be able to see, adjust, or limit voltage and current your circuit can take. Otherwise you might fry whatever you are working on. Especially if you are measuring, you might short something with the probe of your multimeter or oscilloscope. Micro controllers and transistors die like flies.
    3) Using wall warts as a power supply is really not a good idea, if you are beginner you might injure yourself or die.
    If you overload the secondary of that 5-10W transformer, you might heat it up and cause short circuit between primary and secondary! Do not do that. Most of those wall warts are cheap Made In China devices, that probably can't survive maximum load written on them, wire is way to thin, and insulation cracks if you touch it.
    4) Don't buy kit's. If you really want to learn electronics, you need some tools.
    You will give, 30-40 dollars here, 20 dollars there, and in the end you will have bunch of crap that you can't use for anything, that is way more dangerous, without any displays to tell you what you are doing, and for the same money you could have bought yourself a nice bench supply that will serve you for the rest of your life.
    5) saying power supply is less important then oscilloscope is really strange. You can't do much testing without both, but one is not more important than the other.

    IF you can't afford some brand name power supply, or you still don't know what you need, you should go and check ebay. Just type "lab power supply" or "bench power supply" and you will find plethora of 50-60$ linear power supplies that can give you 0-30V with max 3-5Amps, just make sure they have current limiting function.
    You might find some nice used ones as well. Even those unknown ones will serve you for many years, it's not like you need them to be on 16 hours every day...
    Get two of those, and you will be able to test most of the circuits you find online.
  7. Sep 9, 2013 #6

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Myself I think that's bad advice.

    Any fool can throw money around.
    The guy who builds his own stuff learns 100X more.
    For an absolute newbie, a power supply is a good starter project.

    When picking out Wall-Warts, I always opt for the heavy ones with a transformer inside. They use split bobbin cores with physical primary-secondary winding separation. The tiny primary wire is by design a quite effective fuse.
  8. Sep 9, 2013 #7


    User Avatar
    Gold Member

    I stand by my statement:
    "That said, a lab supply with variable voltage up to +- 24 volts at a few amps could be a useful thing, but an oscilloscope will be infinitely more useful than a lab supply. You can scrounge power supplies from many sources."

    Why buy a power supply before you really need it? Do you have a scope?
  9. Sep 9, 2013 #8


    User Avatar

    Staff: Mentor

    Normally I'd agree that building a kit is great experience, and better than just buying an off-the-shelf unit. But since this kit involves 120VAC AC Mains voltages, and does not appear to have an associated metal enclosure to use with the kit, it appears too dangerous for a newbie to deal with.

    I discuss some related safety issues in posts 22-23 in this thread that is also going on now:


    I don't know what Jameco is trying to do by offering that open-frame kit. Sure doesn't look safe to me...
  10. Sep 9, 2013 #9


    User Avatar
    Science Advisor
    Homework Helper

    I'm with Berkeman on this. In the UK we have 230V mains not 120, and a rather less litigious approach to health and safety than in the US, but either way you don't want to be constructing mains-powered equipment at least until you have learned to solder competently, and understand the basics of working safely with high voltages.

    To get started, you don't need anything more than some rechargeable batteries for power, a breadboard, and a fairly cheap digital multimeter. (No point buying an expensive meter until you know how to use it without accidentally destroying it, and know which fancy options you are likely to actually USE.)

    Building a breadboard power supply that works from low voltage (e.g. from a wall wart) would be a better beginner's project - e.g. one of these: http://www.technobotsonline.com/connectors-and-headers/breadboards-and-breadboard-power-supplies.html [Broken]

    Save your $200 till you have a bit of practical experience, and a better idea of what you really want to do.
    Last edited by a moderator: May 6, 2017
  11. Sep 10, 2013 #10

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Some Hewlett-Packard printers came with a Wall-Wart transformer having a 20VAC 1 amp centertapped secondary. That'd make a mighty nice dual 12 volt hobby supply, with the safety related parts in a nicely manufactured and properly insulated enclosure.

    OP might enjoy this introduction:


    EDIT late addition

    HP part # HP 17122B


    Last edited: Sep 10, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook