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How do I tell if a wall wart is regulated or unregulated?

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  • How do I tell if a wall wart is regulated or unregulated?

    I need a regulated 9 volt power supply for a label maker. There are lots of wall warts at thrift shops and electronics recycling places that have mounds of cheap wall warts in all sorts of voltages. I have purchased a few but they all seem to be unregulated and the voltage is way over 9 volts (unloaded). Is there a way to determine by the label if the wall wart is regulated? If not I will bring my DMM to the store and test them. Thanks.

  • #2
    Regulated warts are very rare.

    I suppose the simple thing is to measure the output. If it is the same as the rated voltage, it pretty much has to be regulated.

    I am surprised the unit needs that. it is generally far easier to put regulators and their heat sinks inside the equipment rather than the wart.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      I don't think you can get old linear unregulated supplies,today all you can get is switching type and they are all regulated.

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      • #4
        One spot?

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        • #5
          Originally posted by alexradium View Post
          I don't think you can get old linear unregulated supplies,today all you can get is switching type and they are all regulated.
          Well, depends on what you're willing to spend, and where you live. In the days before the internet, I had access to a number of industrial surplus stores, such as Apex, C & H Sales, Earls Supply (later called Industrial Licquidators), and a monthly swap meet...two, actually....TRW Radio Amateur's Technical Swap meet in Redondo Beach, CA and the General Dynamics Radio Ameteur's Technical Swap Meet in Pomona, CA. The swap meets had the best prices on linear power supplies, like Lambda, Power Tech, Kikisui, Hewlett-Packard and the like...lots of small metal boxes with barrier strips for connections, usually an adjustable pot to set the output voltage. The Surplus Stores, though, always charged an arm and a leg for their power supplies. OEM military hardware often built in one of the 'black-box' power supplies, and could be obtained for cheap...just had to pull them apart to get the supply out.

          Now, with Ebay, you can still find power supplies in all sizes and shapes...many a pig in a poke, but deals can be found. You're just having to pay the price + shipping, so hopefully the prize that looks right isn't across the continent!

          With the wall warts, usually the ones that are regulated don't have the built-in dual blades to occupy all of a wall outlet (or the lower of the two). Those having an attached AC mains cord and a trailing output tail with connector are normally the ones that are regulated.
          Logic is an organized way of going wrong with confidence

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          • #6
            I am currently using a BOSS 9 volt power supply. But I need that wall wart to power my guitar pedals. So that I why I want to buy a cheap $2 wall wart rather than a $25 Brother brand wall wart.

            I noticed last night that it was intermittently working so I took it apart. The problem was a break in the wires at the strain relief. So I cut the wires behind the break, soldered them to the board and installed a new strain relief.

            As you will notice from the picture, it is a very simple circuit with a few capacitors, transformer, diodes and a voltage regulator. Also in the picture is the label maker that I need to power.

            BTW the wall wart is a little unusual since the positive is on the outside shell of the plug and the negative is inside.
            Attached Files

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            • #7
              According to my research you can't get a switch mode power supply wall wart with the outer sleeve as positive. So I bought an outer sleeve negative wall wart, opened it up and reversed the wiring. BTW, You can always tell a switch mode wall wart because they are a lot lighter. Thanks for everyone's help.

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              • #8
                Originally posted by Axtman View Post
                I am currently using a BOSS 9 volt power supply. But I need that wall wart to power my guitar pedals. So that I why I want to buy a cheap $2 wall wart rather than a $25 Brother brand wall wart.

                I noticed last night that it was intermittently working so I took it apart. The problem was a break in the wires at the strain relief. So I cut the wires behind the break, soldered them to the board and installed a new strain relief.

                As you will notice from the picture, it is a very simple circuit with a few capacitors, transformer, diodes and a voltage regulator. Also in the picture is the label maker that I need to power.

                BTW the wall wart is a little unusual since the positive is on the outside shell of the plug and the negative is inside.
                That's the style I'm looking for in a 12VDC wall wart to run my handheld CEL 553 1/3 Oct SPL meter. My decent local thrift store closed, as I discovered on Black Friday, looking to replace a TV set gone bad. Can't seem to find any of these like you found with an IC regulator inside.
                Logic is an organized way of going wrong with confidence

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                • #9
                  In my city there are many electronics recycling stores. They have bins and bins filled with wall warts of all sorts of voltages.

                  You might have to fabricate one like I did. If you are going to modify the wall wart, look for one that has screws holding the two halves together. That said, they still glue the two halves together so you are going to need a sharp knife and some patience.

                  Good luck.

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                  • #10
                    First, let us distinguish between regulated and rectified, as well as between rectified and smoothed.

                    If there is no designation on the sealed black cube whether this or that contact is positive or negative, and especially if it shows a pair of wiggly parallel lines, then the output is AC. I.E., nothing has been done to the wall current, save for stepping it down.

                    However, once some distinction is made between the polarity of the two contacts at the end of the wire, you will have DC of some sort. It's the "of some sort" that is the challenge, since wallwarts are, by definition, sealed black boxes, whose inner contents are kept a mystery. Some can be pleasingly stable, with nary a trace of ripple, and a few may even be "regulated" to provide a stable and predictable output, while others can meet only the barest of criteria for "DC", and were originally supposed to power up something that had additional smoothing and regulation on-board and simply wanted to keep the transformer outside the chassis for noise or packaging reasons. The trouble is, there is no external indication on the black cube, or even the box it came in, as to where on the spectrum of filthy-to-clean-power it lies.

                    Of course, since you want it for a label-maker, I doubt that any audible ripple is of any concern, and I can't imagine the original requiring a well-regulated supply. Your primary concern is that it provide sufficient current, at the appropriate voltage, to power the label maker. My best advice would be to find something in the bin-o-wallwarts that states the appropriate specs on the outside, and has the appropriate plug, and simply splice a 470uf cap, with a voltage rating at least 1/3 - 1/2 above the output voltage (e.g., at least 16v for a 12V supply and preferably a 25V rating) between V+ and gnd to smooth things out a bit more. It's the "chicken soup" of power - may not cure but it can't hurt.

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