Wall charger transformer leads

Discussion in 'General Electronics Chat' started by OrionV, Jul 3, 2016.

  1. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    Hello. I wanted to use a wall charger transformer to step up some voltage but it has 7 leads on it - 3 on one side and 4 on the other. I have no idea how to connect it, if anyone can tell me which lead does what that would be great.
    Thanks.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If it's from a switch mode supply it is a high-frequency transformer, which may or may not be useful to you.
     
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  3. OrionV

    Thread Starter New Member

    Jul 3, 2016
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  4. Hypatia's Protege

    Distinguished Member

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    The image appears to be that of a ferrite core transformer of the type commonly incorporated in SMPS units --- Such transformers are generally comprised of a primary, an (often tapped) secondary and, occasionally, a feedback/auxiliary winding... Please preform a continuity 'scan' of the leads such that we may be of further assistance.

    Best regards
    HP:)
     
  5. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    Thank you for the answer but I don't know how to do that. I'm not even sure I know what it means...
     
  6. Hypatia's Protege

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    I apologize for my over-cursory treatment of the subject in my first post:oops::(...

    You may preform a continuity scan via use of a resistance indicator (e.g. A DMM set for resistance ['Ohms'] measurement) to measure and record inter-lead resistances...

    For instance, you might arbitrarily number the leads 1 through 7 then connect one test prod to lead #1 and with the other measure and record the resistance to each of 2,3,4,5,6,7 -- Then move on to lead #2 and record the resistances to each of 3,4,5,6,7 and so on until all (21) measurements have been recorded:cool:

    Very best regards
    HP:)
     
  7. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    I dont think you can use that like an ordinary wall wart transformer. That looks like it is from a switching regulated wall wart, which use higher frequency transformers. The only way you could use that is if you knew the specs of that transformer or just needed some light current perhaps.
    In any case, you have to use a higher frequency switching signal to power it, not directly from the line. I dont know if you want to do that or not.

    Back when they made regular wall warts they would consist of just a 60Hz line transformer and rectifier diodes and a filter cap. These days they make regulated wall warts that use a special switching IC chip that pulses the primary of the transformer and also regulates the output to stay within a certain percentage of the target voltage, such as 5v. These newer kinds have completely different kinds of transformers so they have to be used in a switching circuit.
     
  8. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    That is the result from the "continuity scan", I think that between 6th and 7th lead is the secondary, but I'm not sure about the primary. Any thoughts?
    Thanks.
     
  9. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    I'm not sure if I undertood you correctly but I'm using only the transformer for stepping up voltage. The higher frequency required for that to work doesn't bother me, I'm trying to use a 555 oscillator with a 9v battery, so changing some specs in the schematic should increase the frequency.
    Thank you for your answer.
     
  10. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    The 'equidistance' of the tapped winding (i.e. 1,2,3) is curious:confused: --- I can but assume such owes to the indicator's precision limitations -- What does the instrument show when the prods are 'shorted' together?

    Please give me a moment that I might compose a diagram:)

    Best regards
    HP
     
    Last edited: Jul 3, 2016
  11. Hypatia's Protege

    Distinguished Member

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    In that case 6,7 is a good choice for the secondary - bear in mind, however, that higher resistance does not necessarily = greater number of turns (though, in this case, I feel same is a safe assumption).

    You may use the tapped winding as the primary in a 'half bridge' arrangement -- however, owing to the very low resistances, the configuration of said winding must be determined by other means (e.g. an LCR indicator or merely exciting the transformer with ≈ 40kHz while measuring the 'drops')

    I'm off to work up the diagram -- Pleas stand by:D
     
  12. Hypatia's Protege

    Distinguished Member

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    Here's the (putative) schematic of the transformer -- Inductance values would allow calculation of turns/impedance ratios, etc... -- That said, I feel this should supply a good starting point -- Should you wish to use a single-ended driver, I suggest 4,5 as the primary (for its higher resistance [and, presumably, impedance] with respect to 1,2,3) -- On the other hand, 1,2,3, once 'mapped' would likely lend itself to more efficient design (used as the primary)...

    It may behoove you to consider 40kHz the minimum frequency of operation...

    Best regards
    HP:)

    xfmr.jpg
     
  13. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    It reads 0.4 ohms. It isn't the most expensive and high quality multimeter on the market :D . As for a "half-bridge arrangement" I assume that means using only the first two leads instead of the first and second?
     
  14. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    Thank you very much for the assistance, plus giving me the tip about the frequency it requires. You helped me a lot!
     
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  15. Hypatia's Protege

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    Stated plainly it means applying power to the center-tap and alternately switching the 'outer ends' to ground:cool:

    Best regards
    HP:)
     
  16. Hypatia's Protege

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    No problem!:cool: -- Please let me know should you have further questions:)

    Best regards
    HP
     
  17. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    Okay, sorry to bother you again :D but just a small final question: wouldn't it be even more efficient if I just connect 5 and 6 together and use 4 through 7 as a single coil for greater inductance?
     
  18. Hypatia's Protege

    Distinguished Member

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    First off - Please don't assume the phasing is shown correctly! - Such was not determined via resistance testing! --- But to the 'gist' of your question, you could do that (assuming you will be using 1,2,3 as the primary) howbeit it would offer only a modest increase in secondary EMF - whether or not such would be more efficient will depend upon the impedance of the load...

    Please feel free to ask should you have further questions or require clarification:)

    Best regards
    HP:cool:
     
  19. OrionV

    Thread Starter New Member

    Jul 3, 2016
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    Thank you very much for your help, you are awesome. Have a great day! :)
     
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  20. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    That sounds good then. Probably 10kHz or higher should do it.
     
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