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Help with transformer 220V - something

  1. Sep 30, 2012 #1

    I am planning on making a PSU for my home project. I got this probably 30 year old transformer from an old machine used for printing.

    Now this machine is very big and it had pumps and all that, and this transformer was in it.

    It has no marks, no info, nothing.

    It has one small filter(that I have no idea what it does) and that information is obscure too.

    Can anybody help me determine how will I use this? How much power does it have? Is there any way of knowing that?

    Last edited: Sep 30, 2012
  2. jcsd
  3. Sep 30, 2012 #2


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    You ought to be a bit careful with it. Is is in good visual condition? I am being deliberately careful in replying because the mains can do a lot of damage if you don't treat it right!
    Do you have a current meter, to see how much current it takes off-load and things like that? You should put a crude, resistive load on it, corresponding to the power you are likely to want from it and see if it gets warm.

    Do you know which is the primary and which is/are the secondary/ies? You could try applying a low voltage (60Hz) to the primary and see what you get on the secondaries first (it will all scale up ok.). If it's as enormous as you imply then it is probably capable of giving you all the current you are likely to need - unlike a cheap one, off-the-shelf.
    Make sure you put fuses 'everywhere' to avoid cooking anything. But you need to know the output volts first. If it was feeding 'power' to something then its voltage may not be suitable (hence my suggestion of trying with a low input voltage).
    You will just have to have a careful play with it. If it gives suitable volts and doesn't get too warm, it should do the job for you.
  4. Sep 30, 2012 #3

    It is in good condition. By my judgement at least. It is really heavy. It has outputs 15 and 9. I am planning on putting them in series to get 24V.

    I know where is the primary and where is the secondary.

    So I should take this to an expert to try it?

    I got 2h of spare time tomorrow, I'll see what my faculty staff can do.

  5. Sep 30, 2012 #4
    You're looking right at the voltages. 110 in and 15 out center-tapped. The smaller metal box is an EMI filter. You don't need it.
  6. Sep 30, 2012 #5
    EMI filter? :D
  7. Sep 30, 2012 #6


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    ????? I would take the numbers written on the windings (0 - 100 - 110 - 120, 15 - 0 - 15) as indicating what primary and secondary voltages are. But I agree the data plate isn't very informative, except for "1A" (which is probably the max primary current, considering how big the device is).

    Probably you can wire the two primary coils either in series to use with a 200V to 240v volt mains supply, or in parallel for 100V to 120V.

    You can probably use the two center-tapped secondaries either in series or in parallel, or completely indepedently, as well.

    First check the DC resistance between EVERY pair of connections, to find out if some of the windings are connected together internally. If the primary windings seem to be connected to thesecondaries, just throw it away!!!!!

    Then connect a signal generator with output say 10V 50 Hz across the winding with the highest resistance (which should be one of the primaries) and check the AC voltage at all the other windings, and note whether the phase difference is 0 or 180 degrees if you want to use the windings in series or parallel.
  8. Sep 30, 2012 #7
    Other than voltages yea, it is pretty uninformative. If its rated 1A at primary how much would i get a secondary max, if I would use them in series? (24V)

    If its rated 1A primary, that is 220 Watts right? so that would be roughly 9 Amps at secondary?
  9. Sep 30, 2012 #8


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    So it' s not rusty or dripping with mould! I'm sure an 'expert' can help you. The
    24V thing is a good idea - as long as you want 24V. 15V could also be handy and you could have a switched 'option'. Not both at once, though. ;)
  10. Sep 30, 2012 #9


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    Electromagnetic interference. It's probably there to stop the printing machine putting voltage spikes back into the mains supply for the building when it was switched on and off. That's irrelevant if you use the transformer to power something else.
  11. Sep 30, 2012 #10


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    Use the basic equation for any transformer. ##V_pI_p = V_sI_s##, ignoring power loss in the core etc.
  12. Sep 30, 2012 #11
    Thank you, now I only have to find a place at my faculty to test this safely.

    As for sophie, the transformer looks in mint condition. No rust and all that.
  13. Sep 30, 2012 #12


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    It looks as though you have as much info as you could expect. If you were to 'soak test' it with as many amps as you could ever need, then you can give it a 'pass', I think, if it stays cool.
  14. Sep 30, 2012 #13
  15. Sep 30, 2012 #14
    But one thing I don't understand.

    These wires from mains go to filter, then they part into these 2 transformers.

    It is transforming from 110 to 15. So If I remove the filter and connect the transformers directly to mains, I would transform 220 V not 110 V which is rated at the primary.

    How does this dual transformer work?
  16. Sep 30, 2012 #15


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    Now I have looked at the pictures on my desk top computer (my smart phone is too much hard work), I should say that you just have two totally independent 110V transformers. each with +-15 and 9V outputs. If you connect the primaries with a common ground (and in the right phase) you will need to connect the secondaries too (in series, appropriately), which will give you +-30V and 18V out.
    You should not connect the two secondaries in parallel or, with just a few turns difference in them, you can get a lot of unwanted circulating currents (dark brown smell and hot hot hot). You might check that the secondary volts are, in fact, identical by connecting one end of each secondary winding together (in the antiphase condition and ascertain that you get Zero volts with your AC voltmeter at maximum sensitivity). Under those circs, you are allowed to connect them in parallel but it's is not standard practice!
    The transformer was clearly (I am sure) intended for connecting the two halves of a split phase supply to feed a fairly heavy pair of loads and to equalise the load over each half. It may be that the two sets of windings (and cores) were carefully matched with equal numbers of primary and secondary windings so that it could ht used as a centre tapped transformer but why would they have done it that way? It wouldn't make sense as they could have just wound a straight centre tapped 220V transformer.

    If you can use 110V then just use one half of it and get your 24V by using both secondary windings on that side. You 'could' use 15V from one side and 9V from the other if you wanted to make a point. In any case, you will need to get the polarity of the connections correct or you will get 6V out!!!.
  17. Sep 30, 2012 #16


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    Are the primaries connected in series or in parallel on the way out of the filter?
    This filter is, in fact, a red herring as far as you're concerned and shoudl not cause you any concern. You, basically, have two transformers.
  18. Sep 30, 2012 #17

    I will have to refer back to my textbooks about this.

    I am using a one main system.

    I should connect two transformers at primary in series and then load it to the mains?

    My o my there is much more to it than I thought. Can you send me to some schematics or so?
  19. Sep 30, 2012 #18
    Let me check, I am not sure, its a mess of wires. I don't know how does this filter work.

    EDIT: yes I don't know whether the filter internally splits it into parallel or series. My guess would be series because, if you would go parallel, you would get double the voltages at the output, right?
  20. Sep 30, 2012 #19

    jim hardy

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    hmmm.... the 110 volt markings on a transformer from a 220 volt part of the world is, well, curious...... as is the mechanical arrangement of the cores bolted so close together...

    do you have access to a Variac adjustable (sometimes called slider) transformer?

    a plot of primary milliamps versus primary volts(open secondary) will tell you whether it's a 110 or 220 volt winding. Current will be linear with volts until you approach core saturation when current rises dramatically and the core starts to noticeably hum. Dont stay up there long....core wants to operate comfortably below that point.

    I note there's terminals enough for two of those "0 100 110 120" volt windings on each transformer. My guess would be they are wired in series to make a 220 volt primary , grey wire from one winding's "0" to other's "110" so they'll add.
    That'd give you two separate 220 volt transformers bolted together, probably wired in parallel.

    perhaps somebody who's seen one of these before can explain their being bolted so close together. Seems like somebody wanted them to share magnetic flux in that common leg...perhaps so they'll share load current better?

    I'd be tempted to separate the transformers.
    One of them might do for your 3 amp supply and the other would make a good looking subwoofer power supply... see TDA2030 datasheet from ST, bridged split supply , it even has PC board layout (for non-bridged and a bridged layout is at eleccircuit.com)...

    old jim
    Last edited: Sep 30, 2012
  21. Sep 30, 2012 #20
    Yes they can be separated. I see tiny little bolts that can be unscrewed.

    But here me out:

    Would it better if I connect the primary in series(to transform 220V) and connect the secondary 9V+15V series to get my desired 24V AC?

    This way my supply unit would be ultra reliable since it would get the current from 2 transformers.

    Or is this an overkill?

    I don't know how much this transformer is rated in current. I will try to find the variac at my faculty.

    From what I see I have a lot of transformation options.

    I can get 30 V AC at the output from one transformer right?

    But If use the 120 V "port" I can get 27,5 V AC at the output. Question is, can this transformer be used like this?

    27,5 V AC is 38,8 V Max, (which i would rectify). Which is not bad because components would eat up those few extra volts.

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