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Variac 20A AC Power Auto Transformer What can you it for examples

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    Variac 20A AC Power Auto Transformer What can you it for examples

    I just bought myself this Variac transformer I changed the very crude volt meter that it had inside it

    I would like to know what type of uses this unit could be used for

    One Would like to do is make DC power supply to try out out LED modules

    Awhile back I came across a LED module that ran off 48 volts and did not have a power supply that would do 48 volts so I had to buy a 50 volt 5 amp power supply with I seen to use quite often but it was a little pricey

    I do not want to have to buy a different power supply for testing a LED module only find out that the LED module is bad

    This brings to a question

    I would like to use a bridge rectifier with a capacitor and fuse

    400 volt 2 amp bridge rectifier
    with a 2 amp breaker
    What microfarad capacitor should I use at what voltage

    To have a dc power supply

    What else should I use,do to make this setup as safe as possible

    One note

    With the control knob turn all the way to the right the voltage is 151 volts AC


    One other question I have is what other uses does a Variac have please give examples
    Attached Files
    Last edited by sam_sam_sam; 06-16-2018, 04:42 PM.
    9 PC LCD Monitor
    6 LCD Flat Screen TV
    30 Desk Top Switching Power Supply
    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
    1 XBox 360 Switching Power Supply and M Board
    25 Servo Drives 220/460 3 Phase
    6 De-soldering Station Switching Power Supply 1 Power Supply
    1 Dell Mother Board
    15 Computer Power Supply
    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

    #2
    Re: Variac 20A AC Power Auto Transformer What can you it for examples

    use for bringing power up slowly on older electronics without switching circuits .. they are not always good for this . like valve rectifiers as they wont conduct until high voltage thats one to be aware of but still useful .
    the other is jfet audio amplifiers in particular that will self destruct being brought up on a variac .
    i mainly use mine to trim the voltage up a few volts as i have low voltage issue here . i only use for servicing amplifiers though .

    Comment


      #3
      Re: Variac 20A AC Power Auto Transformer What can you it for examples

      As above mainly I use these for slowly powering up some of the vintage refurbishment and repairs that come though the workshop, older electronics not so good on switching supplies. I also put together a rectifier and smoothing pack for this which I use for reforming vintage capacitors.

      I can look into the values if you need when I am next in the workshop.

      Comment


        #4
        Re: Variac 20A AC Power Auto Transformer What can you it for examples

        Originally posted by llonen View Post
        As above mainly I use these for slowly powering up some of the vintage refurbishment and repairs that come though the workshop, older electronics not so good on switching supplies. I also put together a rectifier and smoothing pack for this which I use for reforming vintage capacitors.

        I can look into the values if you need when I am next in the workshop.
        If you do not mind could you please provide this information

        Thanks
        9 PC LCD Monitor
        6 LCD Flat Screen TV
        30 Desk Top Switching Power Supply
        10 Battery Charger Switching Power Supply for Power Tool
        6 18v Lithium Battery Power Boards for Tool Battery Packs
        1 XBox 360 Switching Power Supply and M Board
        25 Servo Drives 220/460 3 Phase
        6 De-soldering Station Switching Power Supply 1 Power Supply
        1 Dell Mother Board
        15 Computer Power Supply
        1 HP Printer Supply & Control Board * lighting finished it *


        These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

        1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
        2 Hem Saw Computer Stack Board

        All of these had CAPs POOF
        All of the mosfet that are taken out by bad caps

        Comment


          #5
          Re: Variac 20A AC Power Auto Transformer What can you it for examples

          use it for questioning people.

          Comment


            #6
            Re: Variac 20A AC Power Auto Transformer What can you it for examples

            That is a BIG variac. Few things you should be aware of. Don't mess with the substance that may be used between the windings and brush.

            You cannot accurately check them using an ohmmeter. The brush design is such that it needs a certain amount of current through it to conduct properly. If you are going to test one, power an incandescent lamp or power resistor that won't exceed the max current rating (not so much a problem on yours but there are lots of smaller types in the field). Evaluate smooth continuous output by measuring the voltage across the load.

            Most intermittent issues on old units are caused by corrosion in the slip ring not the brush-winding contact.

            Fusing needs to be on output, due to power dissipation conditions. Primary fusing is optional.

            They are very versatile and useful equipment.

            Many techs recommend having an isolation transformer to follow a variac, for good reason such as if you are using it to power equipment you're poking around in, just good electrical common sense.

            The types that can output higher than the line in voltage are useful to make up for voltage drop in branch circuits so that equipment testing can be done at the line voltage specified in the DUT's service manual.

            There is a service available that will re-tip your brush at a fraction of the cost of new one.

            They are fun to use

            Regards, -L L-
            Why don't you mine your own Bismuth,
            Mine your own Bismuth
            Mine your own Bismuth
            Why don't you mine your own Bismuth,
            So you won't be mining mine?

            Comment

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