Help using anUniterruptable Power supply Transformer

Discussion in 'General Electronics Chat' started by sparkfishes, May 6, 2012.

  1. sparkfishes

    sparkfishes Thread Starter New Member

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    I have been given two UPS and have taken the Transformers out with the intension of making a 12- 24 V high current power supply
    I connected the mains lead, to establish the transformer out put, and it blew the 13 A house fuse
    I double checked the white and black leads had come off the original mains in put socket and assumed the transformer was short circuit
    On trying the second, identical one but from a different UPS, it also blew the 13A fuse
    What am I missing? Why are they blowing a 13A fuse when it did run on a house plug in its original configuration?

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    Last edited: May 6, 2012
  2. #12

    #12 AAC Fanatic!

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    Hard to answer why, after doing everything correctly, the transformers do not act like they did when connectly exactly the same way. Perhaps you can reconnect them in the UPS devices and see if they still blow the fuse. If so, both are defective.
  3. BillB3857

    BillB3857 Senior Member

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    Silly question but were the UPS units designed to deliver the same output voltage as you utility mains in your house?
  4. #12

    #12 AAC Fanatic!

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    One of us misunderstood that sentence. Could you clarify whether you connected the mains to the input to establish the transformer output or you connected the mains to the output to establish the transformer output?
  5. sparkfishes

    sparkfishes Thread Starter New Member

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    I did connect the two UPS mains leads to my house mains correctly
    The photo shows the input wires white and black and very thick. These originally went to the input socket of the UPS - I double checked
    I did not have any load on the out puts when I tested it
    Last edited: May 7, 2012
  6. sparkfishes

    sparkfishes Thread Starter New Member

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    Thanks for the reply ( remember I am in the UK so some of the terms are not always clear )
    If I understand you correctly are you saying the input - via the two main(s) / primary leads should be only 34V AC? I am certain the black and white wires ( primary ) were directly to the incomming mains - in my case 240V AC.

    I intended to make the main part of the PSU as you have described BUT with out a working High Amp transformer I am sunk ( will not get to first base;) ?)

    Though not impossible it does seem improbable that both transformers have suffered the same failure mode
    I have found another transformer now but this has THREE input leads in, and the usual four out
    Of the three heavy leads it does not seem one is earth by checking the continuity. The colour coding is Blue , Yellow, and Red with yellow stripe......... I have no idea what codes these are but I do think I took it out of another UPS
    I have a 20A variac I will try that to day
    Last edited: May 7, 2012
  7. Bernard

    Bernard Senior Member

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    Did you measure lead resistance? Looks like w & B are battery side. Use highest resistance as primary or line input.
  8. sparkfishes

    sparkfishes Thread Starter New Member

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    Yes as far as I can tell - we Only have 240 Volts in the UK unless it is a Factory with 3 phase
  9. debjit625

    debjit625 Active Member

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    The thick wires didn't went to the white socket,then thin wires did.
    Here is the rule you will find thick wire winding on the low voltage side i.e.. 12V or 24V ,the secondary side ,if you are using the transformer as step down type.

    Normally in any transformer the high voltage side have thin wires as the winding needs to carry less current and the low voltage side carry high current so we use thick wire winding compared to high voltage side winding. For any transformer when you step down voltage you step up current and when you step up voltage you step down current

    On the primary side (high voltage side 220VAC) you will find thin wires winding.

    From the picture ,the 220 VAC side will be the side where the four wires blue,black,yellow and white are.

    The 220 VAC side have four wires because of buck-boost configuration.
    [​IMG]

    Good Luck

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    Last edited: May 8, 2012
  10. BillB3857

    BillB3857 Senior Member

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    I agree that the White/Black pair are the low voltage- High current winding BUT, it still needs to be determined how the 4 wires on the connector are used. It could be two 120V windings to allow connection as either a 120 or 240 volt output OR one winding could be the high voltage winding for output and the other a lower voltage feedback winding for supplying the UPS with output voltage information. Too bad the OP didn't follow the wires from the output receptacle of UPS while taking it apart.
  11. R!f@@

    R!f@@ AAC Fanatic!

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    I know how they are connected... I did it u know..!
  12. debjit625

    debjit625 Active Member

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    They are in buck-boost configuration. The OP can check back the UPS circuit or he can apply 12 VAC on the low side and read the high voltage side to determine the configuration.

    I think the OP has damaged both the transformers by applying 220 VAC at low side.
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