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Regulated 9 Volt DC Power Supply

Discussion in 'Electronic Basics' started by Dave.H, Dec 28, 2007.

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  1. Dave.H

    Dave.H Guest

    Can anyone help me with information on building a 9 volt regulated
    power supply that runs off 250 volts AC mains? Any help greatly

  2. Chris

    Chris Guest

    Hi, Dave. The easiest and safest way is to buy a wall wart.
    Hobbyists and other newbies probably shouldn't be experimenting with
    line voltage.

    Mouser supplies a 9V 5 watt regulated DC output wall wart with a
    variety of snap-on outlet plugs which will operate with all
    international line voltages and frequencies for $12.82 ea. in single
    quantities. It's their part number 552-PSA-05R-090-R

  3. Dave.H

    Dave.H Guest

    I can buy a 9 v regulated wall wart, rated at 800 mA, but as I'm on a
    tight budget, I can't pay the $AU30 for it. I ALWAYS use extreme
    caution around high voltage. I've worked around high voltage in old
    valve radios, and learned to keep my hands away from energized
    equipment, I'm pretty comfortable working around mains voltage. If I
    build this PSU it will be in a plastic box.
  4. Chris

    Chris Guest

    OK, Dave. But if you're on a tight budget, you probably want to stay
    away from home brew power supplies, unless you've got most of the
    parts in your junkbox -- it'll still be more expensive to make it

    Dick Smith Electronics has a new regulated [email protected] output wall wart
    for A$7.98 as their P/N M9560. I'm sure you could scrounge something
    at a local surplus outlet for less.

    But if you're somewhat versed in electrical safety, and you've got
    enclosure, line cord with strain relief, fuse and fuseholder, DPST
    line voltage-capable switch, 12VAC secondary transformer that's good
    for at least an amp and a half, 6 amp bridge rectifier, 2200uF 25WV
    electrolytic cap and 10uF 16WV cap, you can buy an LM7809 from DSE for
    A$1.20 as their P/N Z6550 to make your regulated 9VDC supply. Oh, yes
    -- you'll also need a 6 to 10 watt heat sink for the TO-220 package,
    as well as a bit of perfboard to mount the components. And mounting
    hardware. And bumper feet for your enclosure. And some kind of light
    to display that it's on.

    Are you sure you want to go there?

  5. Dave.H

    Dave.H Guest

    Didn't think it would be that complicated. I'll have a look around to
    find the cheapest wall wart. Thanks for your help.
  6. John Fields

    John Fields Guest

  7. Dave.H

    Dave.H Guest

    I'm not exactly sure. The radio uses 6 "D" cells. I'm not sure of the
    current rating of "D" cells.
  8. amdx

    amdx Guest

    It's not hard to find wall warts that are being thrown away or sold
    for 50 cents or $1 at yard sales. I have about 25 in a box ranging from 3v
    to 24v, ac and dc.
    If you really want to build one on the cheap, start picking up discarded
    stereos, tv and microwaves, they have much of the hardware you need.
  9. robb

    robb Guest

    when i need stuff like this... cheap ! there are several sources.

    borrow one from stuff i have allready have, go to local
    salvage/second hand shop and buy it (usually small fraction of
    new cost), yard sales, flea markets any used stuff sale.

    the electronics may be useless but you get the part you are

    the second hand shops here usually have a 5 gallon (20 liter)
    (BIN/basket) full of wallwarts for 50 cents a piece and they get
    so many they dump the lot when the bin is full,
  10. You pull a suitable transformer out of a piece of junked electronic
    equipment. Take a "computer power supply", they are certainly plentiful
    in North America, and strip it down, using the box for building the
    power supply. That first piece of equipment is likely to supply a suitable
    bridge rectifier, and electrolytic capacitors.

    All that will really be needed is a 9volt regulator. An LM317 variable
    regulator may be easier to come by.

  11. That's the way I go, but I just keep an eye out for them -- when I
    actually need something I don't have and need it now, it's not so easy
    to just find the right yard sale or junk bin, quickly.

    For example, I found our local store "dumping" [email protected] transformers
    at $1.50 each. I bought six, knowing that I'd use them for students
    wanting to learn, later on, where I'd give them away. Also, got a
    largish-looking (bigger than other wall warts I'd ever seen, frankly)
    [email protected], [email protected], [email protected], [email protected] wall wart power supply (bought
    5) that cost me just a couple dollars each, in an electronics surplus
    outlet store. But if I needed something fast, I'm not sure I'd know
    where to go, right away.

    Also, keep in mind the cost of gas, these days! One can "burn up"
    one's power supply budget just driving, looking around. UPS and FedEX
    have been recently raising their rates, as well.
    If it weren't the case that so many things carry specialized ICs and
    parts, making junking them out for personal use less valuable than it
    once was, I'd begin to wonder if there might be a return to a practice
    of junking out TVs, radios, and so on.

    I definitely used to do a lot of that, in my youth -- I lived poor,
    without access to medical care and in houses without walls for some
    time as a child and worked the berry and vegetable fields for money as
    soon as I could (age 11, I think), so what electronics I did I had to
    do without any cost to speak of. Which reminds me... used to be, kids
    were allowed to work the fields for money and I definitely needed to
    do that to survive -- I suppose this is a reason why welfare [which
    didn't exist for me] is needed, since there are laws preventing
    children from working the fields, now. By the way, when a bowling
    alley was demonlished by a freak tornado in our area, as a kid I
    actually got up the gumption to call up the owner and asked him for
    permission to rummage through it for parts... and got it! I got lots
    of good, long wire and relays from that. Boxes of stuff.

    But things are different, today, in ways. I still do a cursory "go
    through" on TVs and so on before throwing them away, perhaps more out
    of old habit than anything. I make enough money today that I don't
    need to worry, but it still carries some fun for me so I do it and
    tuck away the parts in small drawers. Microwave units definitely get
    their power transformers pulled -- my daughter is profoundly autistic
    and has burned up perhaps 5 or 6 of them in the last few years, so I
    have a few sitting aside for some future use. Old habits die hard, I

    But it would not be easy to set up a nice looking 9V power supply from
    that stuff. Modifying the transformers is often doable, of course,
    but would take some dedication to eventually get right for someone who
    hasn't done it before. And that is only one step along the way.

  12. gearhead

    gearhead Guest

    Maximum battery power doesn't come into play. It matters how much the
    RADIO draws. The power supply needs enough grunt to meet the radio's
    maximum current draw while still putting out 9 volts.

    Now, old-fashioned wall warts, the kind with line frequency
    transformers in them, seldom have any sort of regulation circuitry.
    They come rated with a current. They will supply that current while
    still providing the nominal voltage. Heavier loads will drag the
    voltage down, and with lighter loads you will get a somewhat higher
    voltage. With such power supplies, voltage depends on how much power
    the device consumes, so you need to match the size of the power supply
    with the size of the device.
    An ordinary 9 volt wall wart, if it has enough heft, will run your
    radio. How big a wall wart you need depends on the size of the
    radio. A pocket transistor radio would run off the real small wall
    warts, like about one inch cube. A bigger radio would require bigger
    power supply.
    So grab a wall wart at a flea market or even out of the rubbish. See
    if it says 9 volts dc, weigh it in your hand, and take a guess at
    whether you think it has enough heft to run your radio. Then plug it
  13. But you're suggesting that people only throw away recent stuff, when
    in reality there's still lots of older things that have yet to be

    Yes, recent VCRs have switching supplies, which aren't too useful
    in themselves and certainly aren't a source of power transformers. But
    lots of VCRs have been sold over the decades, and they traditionally did
    have fancy transformers (full of multiple windings with a wide variety
    of voltages).

    A lot of consumer electronics is out there waiting to donate a transformer.
    Admittedly in this case the transformer current rating may be higher than
    a lot of equipment will supply, but transformers (and casing) are often
    one of the biggest cost items when building things, and if you can pull
    that relatively low power transformer out of that clock radio, it will
    power that little project without costing you anything (or forcing you
    to use batteries).

    And the older the equipment, the more likely you will find parts that
    can be reused. Those VCRs I keep bringing home are full of low power
    transistors that are fine for a lot of general purpose use.

    If you're starting out, the lack of parts is often a liability, since
    you have to buy every single part and aren't likely to experiment
    as a result. But again, those VCRs (and other equipment) are a great
    source to build up a supply of ceramic capacitors and even resistors.
    Forget the cost of the parts, with the local electronic store often
    a thing of the past in many locations, being able to get that needed
    capacitor to finish a project can mean the difference between finishing
    it now, and having to order lots of other parts to fill an order and

    Dot matrix printers can be a source of transformers too, though their
    time is enough in the past that the peak time for seeing them waiting
    for the garbage truck is mostly in the past.

    Inkjets are what you see a lot of nowadays, and they can be a supply
    of many power transistors. They also tend to have switching supplies
    in standalone modules (if they don't use an external supply), which
    make them easy to extract. And unlike "computer power supplies" their
    current capacity is more appropriate for the experimenter, and even
    usually provide a higher voltage (ie up to around 24vdc).

    I grab "computer power supplies" any time I see them, and I see them
    just lying by themselves often (no computer in sight). Like I said,
    the boxes are pretty useful for building things in.

    I think it's a far better time to find scrap electronics than when I
    was a kid. 35 years ago, the average household had a tv set or two
    and a few radios, and not much else. Electronics was something you
    bought and kept and had repaired. If it was tossed, it was old
    tube stuff grungy with dust attracted by the heat and high voltage.
    Now there's a lot more variety of stuff, and even if you have to
    buy it at garage sales than wait for the garbage, it will cost next
    to nothing.

    I think salvaging parts is as important for educational reasons than
    it is for saving money. Having parts around forces you to make a leap,
    instead of copying that project part by part and not understanding much,
    it requires you to know what the parts are doing and how tolerant
    each part is to variation. I also think it helps to demistify things;
    once you've taken things apart it's less of a mystery.

    It's often worth just keeping a basic set of tools with you, so when
    you see some old junk, you can extract just the things you want, without
    having to haul the whole unit home. A little bit of knowledge helps. So
    if you see a radio, and are interested in radio projects, you know to
    grab the variable capacitor and loopstick if you see a radio, and maybe
    the whole circuit board. If you've got the tools, you can easily unscrew
    it and cut the wires to get the board out. Or just pull the power
    transformer, like I said those often cost more than the parts for a small

  14. Yes, I suppose that is the case. However, just looking at me (and
    I've got a 1200 sq ft shed with "stuff" in it dating back a ways) and
    what I throw out these days, I can certainly see a lot less of easy
    use for a new hobbyist who is nearer the beginning than the end of
    their hobby.
    I tend to "part out" the easy stuff in everything electronic we throw
    away -- which deeply bugs my wife, since she can't just get rid of
    things when she is busy and doesn't want to wait for my convenience.
    And of late, I am speaking of the recent 10 year period and comparing
    it with the decade of my early hobby years from '65 to '75. I have to
    say that I'm pulling out less and less I can later use for hobby
    things... by quite a stretch... and I know how to use a wider variety
    today than I could back then.
    If you are talking about older, used VCRs, I don't have access to
    "VCRs I keep bringing home." Do you work somewhere in proximity to
    these things? I ask, because for the OP it may be nice to actually
    know where to go to get things with good stuff in them to extract. I
    was thinking about where to recommend, as a ready supply, and I'm not
    sure I have a good recommendation. Goodwill, perhaps. Or some place
    that scraps computers -- though I've actually volunteered at such a
    place a few months ago and helped out there and didn't find nearly as
    much as I'd imagined beforehand. Good motors in printers, yes. Heat
    sinks, yes. Some EEPROMs and FLASH memories, yes. I suppose the
    power supplies might have a few items. But nothing like the old
    Kaypro 286i, for example, which pre-dated the "chipset days" and had a
    board FULL of 7400 series SSI chips on them. And I'm not sure how
    easy it is to get them to let you rummage stuff -- the folks I worked
    with separated out the gold for extraction and sold other stuff, once
    sorted a bit, by the pound. But if I were to have asked to take
    stuff, I'd have had to "ask the boss" and I'm not sure how much they
    would have wanted to bother or worry about someone hauling out goodies
    while interfering with the sorting process.

    I agree, conceptually, with you. The problem is in the details of
    actually knowing where to go for setting hands on good stuff to gut at
    low/zero cost.
    This last one interests me. Where in the world can you hope to get a
    dot matrix printer, these days??? I just had someone ask me if I had
    any ideas at all where to get one. They wanted something that used a
    ribbon for the ink and supported _impact_ printing. I didn't have
    anything to offer, though I admit I assumed that he'd already searched
    on the web a bit before asking me. I could be wrong about that. But
    if you know of a source, I'll pass it on to him.
    I haven't gutted a recent PC power supply. But they seem to be much
    smaller, from seeing them on the outside. Which makes me think they
    are line-powered, chopping and using high frequency inductors with
    opto feedback to operate them -- and if that is right, there won't be
    a nice transformer there for handy hobby use. But I admit not
    looking, yet. Can you say more about the recent supplies?
    Well, I think there is a lot more "scrap electronics" around now --
    admitted. But I'm thinking also of 35-40 years back, when I was
    needing these things and I feel this is all a bit of a mixed bag --
    some good, some bad.

    I used to find quite a few ready supplies of parts in the area. We
    had at least 4 or 5 BIG warehouse-style stores in the area -- Allied
    Elec, for example, operated a huge facility here that was open to the
    public. But there were four others here in the area and they competed
    heavily with each other. I used to take several days and walk through
    these places, over the flat tables of hand-bagged items or loose parts
    these places had collected up and offered for sale. NONE of these
    retail facilities exist, today. Not one. And I've lived here my
    entire life and watched the change. Radio Shack (and I remember the
    Tandy leathercraft stores here, too, before and after the merger) used
    to be, by and large, a parts store. No more.

    On the other hand, I am greatly gratified by places like Mouser and
    Digikey, of course. And, except perhaps for Allied, I didn't have
    something like that as a kid -- though I probably couldn't have
    afforded it, either. But I did also have access to perhaps 20 or so
    suppliers of hobbyist quantities of glass of various types (a good two
    dozen types, at least, for lenses) and got copies of the five
    periodicals that used to exist for building your own telescopes -- all
    gone, now. Sky and Telescope still exists, but doesn't cater as it
    used to, of course, to that market. Of course, Heathkit is gone.

    It's a mixed bag. I LOVE much of the change. I have ready access to
    microcontrollers of every ilk and because of that I can do things that
    would have been simply impossible, back then. I can buy demo boards
    for almost nothing (in today's terms) and, instead of having to wire
    wrap like a madman, I can get a nice FPGA board and program in VHDL to
    wire up all that logic for me. I don't even need to do the floor
    planning of it, if I am just experimenting around for play. I can't
    tell you how much of a boon that is. For example, I've designed a few
    CPUs of my own and was able to test out my own code, too. And it
    didn't take long, nor was it hard work. So, there are some big pluses
    today. For some of us.

    But if I were starting out... well, ... okay, maybe you are right.
    Hard to say. But I do miss some things.
    I enjoyed reading this and perhaps you are right about the times, as
    well. But I do wonder about someone starting out these days. There
    is so much available, for so little money to buy, that the motives
    needed to do the real digging are harder to come buy. "Back in the
    day," you didn't really have a choice. You either built it, or did
    without. When the Altair 8800 came out, I bought the kit and built
    it. In fact, that was the only way I could have afforded my own
    computer. I built my own telescopes, because back then there wasn't a
    ready market for a wide variety of them and where they did exist
    pre-made, they were WAY too expensive and there was a ready supply of
    cheap materials for making your own. In fact, I'd add to what you
    wrote above and say that you really cannot understand your telescopic
    instrument well, if you haven't been through all the trouble of
    actually constructing and testing your own to near perfection. The
    process of actually seeing what light does is very important and no
    "book learning" will quite do it for most of us. Setting up knife
    edge or Ronchi gratings and going through various repeated steps of
    correction and testing and trying out various light sources and so on
    is as much an important part as anything. I'm not sure that an
    amateur really can know what they are working with, if they have never
    been through that process at least once or twice.

  15. The Energizer E95 (D cell) datasheet uses 10 ohms as the load for a
    radio example. Assuming that is correct, you are talking about
    (6x1.5V/10) or almost an amp load. But I'm sure that volume affects
    this, too. Anyway, using that as a reference I guess that a solid 1A
    or 1.5A supply would probably cover the need. Of course, that could
    indeed vary a lot from radio to radio, so of course more is better.

    Problem is, you can expect transformers delivering much more than an
    amp on their secondary, at voltages enough higher than 9V to be useful
    in linear circuits, to be expensive/big. You may be able to measure
    your current draw, with an ammeter if you have one. But my guess is
    that a largish wall wart supply should be okay for your use. I think
    you can get to around the 1A to 1.5A you are probably looking at.

    By the way, D cells are rated to operate over a range of current
    loads. They are usually selected over C or AA, not quite so much
    because they last longer (they do) but more because they are capable
    of larger current draws without serious loss of lifetime. This
    suggests that your radio really does want access to something in the
    100's of milliamps rather than something in the 10's. So you really
    do need to figure on estimating about .5-1A or so, simply because it
    uses D cells.


  16. Thrift stores, yard sales, or even Ebay. 498 listings, right now:

    Google has 2 million hits for dot matrix printer:

    I have two sitting in the shop right now to test. I have about a
    dozen IEEE-488 Commodore 4032 printers in storage.

    Banks and Credit Unions still use them to print multi-part forms. The
    OKI MICROLINE 320 is still a popular, new printer used in bamks.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  17. HapticZ

    HapticZ Guest

    i use a standard euro voltage adapter to get 120vac, then use any number of
    off-the shelf 9v ac/dc supplys
  18. Thanks, I'll let him know that folks on ebay seem to be willing to
    take money for them. ;)
    Well, that might only be people _talking_ about them. I will not send
    him towards some 2M listing on google.
    In fact, it was the Commodore printers that sprang to mind that I felt
    people might have sitting on closet shelves. I'll assume for now that
    you aren't offering, though.
    hehe. Thanks. That's a pointer for him. I'll let him know.

  19. Ian Malcolm

    Ian Malcolm Guest

    Its *not* that complicated. If you've been fixing radios you probably
    have a couple of chassis hanging around you can gut for a n enclosure,
    mains lead switch etc. and a filament transformer good for 50% more than
    you want output current. You need 12V so 2 6.3V windings in series
    should do. If the current you want is under 1/2A use a 78M09. Should
    be able to scrounge equivalent diodes and caps out of your junk box.
    78xx series regulators have Ov on the tab so you can use the chassis as
    a heatsink for moderate output currents. If you can find a 15-0-15
    transformer build up a decent bench supply with 7805, 7809 and 7812
    positive regulators and 7912 and 7909 negative regulators (not 0V on the
    tab) Then its time to think about a fully floating adjustable supply
    with variable current limit.

    I hacked an old 8bit computer PSU to make a nice +5 & +/-12V psu (with
    power LED and a 4 pole isolating switch for the outputs so I can solder
    on my circuit board without blowing anything) many years ago and its
    still in regular use. Dont use 9V much but a 7809 with its caps
    soldered to its legs and wire leads with aterminal block all on an old
    heatsink hooks up to an old CB supply if I need it.

    *collect* old good quality wallwarts. Always usefull for projects ;-)
  20. Ian Malcolm

    Ian Malcolm Guest

    How many hours does it get out of a set of Alkalines?
    Check the polarity first unless you *like* the smell of burning ICs. It
    can also be worth hooking up a 5 watt car bulb and seeing if the
    wallwart is good and can supply a bit over 300ma for an hour wihout
    burning up.
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