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I want to test this transformer

Discussion in 'General Electronics Discussion' started by jvdbossc, Jan 27, 2012.

  1. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    http://imageshack.us/photo/my-images/545/jvb8148.jpg/

    I found this in somebody junk:

    It is connected to 240V with (smaller) black and yellow whire. But this is done with tape only..

    The guy told me this psu should be good.

    I do not get any serious voltage out of this coil. Exept from the green and the red whire it gives 230V the ones low. The other wires give voltages like 1.24 at most AC. I doubt it is hooked up properly.

    Is there any way to test it with a basic multimiter where the 240V voltage should be hooked up :confused: So I can see what psu has to deliver.

    I am asking because I am building a labo psu, but the re-used amplifier psu is a bit to weak. So I took this psu out of garbage, but do not know anything about it, exept it came from a broken amplifier. The guy who kept it said it was good, the amp had some transistor failure.

    [​IMG]
     
    Last edited: Jan 27, 2012
  2. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Well first thing I would do is figure out which wires go to each coil and write down the resistances. The reason for this is to see if the coil is center tapped.

    Normally speaking in a step down transformer, the larger wires are the secondary and the smaller wires go to the primary.

    From there you should be able to test it once you have it wired up to 240V.
     
  3. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    This might be difficult, my digital multimeter goes bananas when measuring the resistance of inductances such as this so you would be better off using an analog meter.

    Measure the resistance between all wires and draw a diagram of which wires are connected together. Some windings will have just two connections, perhaps the brown ones, and some will have more than two connections. In this case you can find out the order of the connections by the resistance.

    The thick wires will be the secondaries and the thinner wires the high voltage primary. The primary may have several taps for different mains input voltages.

    One wire may be an earth screen and may be connected to the laminations.

    Take the highest resistance on the primary winding and input a lowish voltage (50V) if you have one or run from the mains with a 60W bulb in series, it should not light up. Measure the primary voltage and the secondary voltages. From these measurements you can calculate the full output voltages.

    I assume that your house is fitted with an earth leakage circuit breaker.
    Connect your wires with croc clips and keep clear when you switch on to take a measurement. REMEMBER THAT MAINS VOLTAGES CAN KILL.
     
  4. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    I think it is death...

    I did not understand both your posts as first, but I messured on a known working coil psu 2x24V and it gives 29.7 ohm on 240 hook up and 1.8 ohm on 2x24V and 48V = 1.6 ohm, my digital meter goes ... but it shows up ...

    This is probably just an indication and not an electronic law?:confused: (I studied informatics so no idea)

    (sorry no analog meter sadly around)

    Know I understand it should be low on ohms :confused: I get on this psu only Milllion ohm reading :eek: Tried wire with every whire nothing :confused:

    Should I recycle it for the weight of the metal, and buy in a second hand store another amplifier to have a cheap psu ? They go at 10 eu, and good coil cotts easily 50 Eu ex shipping here...

    I have one but it drops at 5 A and I wanted to have more since I have a 3A labo psu already - I wanted to build one myself at least at 6A at 9A. I tested a schematic in the past wich delivers up to 20 A if needed to be.

    I am going to solder a 2x24V AC x 1.4 = DC but ideally I am looking for 2x15 or 1x30.
     
  5. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    ps: thank you both for your kind answers.

    This might interest you:
    Yes we have an earth but it is not connected on most appliances. I do have two blocks they are called in Dutch "Power loss detection device" who detect power not coming back and shut power off very quickly for bathroom and lights and slowly for main house. This is law for new houses here. Older houses only have an earth.
     
  6. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    It appears that your digital meter works correctly on a transformer with a large inductance, it is better than mine.

    In the UK we can get earth leakage circuit breakers which plug in and are used as safety devices for exra protection when using power tools.

    There must be connections in your transformer, not all windings will be blown open circuit.
    Have you stripped the insulation and then cleaned off the enamel coating from the wire? It is quite tough and emery paper is perhaps the best way of removing it. You can check by measuring the resistance between two close positions on one wire.

    The bluey/grey wires are likely to be one winding and the brown wires another, start with these.

    The primary windings are probably on one end and the secondaries at the other end. This will definately be so if there are two side by side bobbins as there seems to be.
     
  7. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    Thanks, seems to be different law then in UK. My meter is an old fluke must be at least 20 years or so. I have got it myself for over 10 years.

    Ok thanks! Here is report: (scratched a bit and then soldered it)

    One red wire broke off..
    for the rest

    grey - grey on top over 800 ohms

    Thick brown on top: 0.6 ohm
    Thin Blew Green on top : 0.6 ohm
    Thin yellow yellow on top: 0.8 ohm

    Bottem medium thickness: green black 8.5 ohm

    bottom: yellow - black : to high unknown??


    So I was planning to wire my meter to brown and to wire AC to green black at 8.5 ohm, put the trafo outside - close the glass door - then switch ac on ... See what it delivers.. I take explosion is not an option?

    Since the brown wires are clearly high in amps - this is probably the only one I wan't...
     
  8. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    And then yellow red: 5.2 ohm... (bottom)
     
    Last edited: Jan 28, 2012
  9. jvdbossc

    jvdbossc

    36
    0
    Jan 27, 2012
    I need to abandon this transformer, it developed bad habits: smoking.. And then one of the automatic fuses had enough of it.. I will build my labo psu on the one that works and see how far I can push it, meanwhile looking for another cheap alternative...
     
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