Cheaper powerpack replacement

Discussion in 'General Electronics Chat' started by Tateypot, Apr 14, 2011.

  1. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    Hi all!
    I have a piece of eqipment that needs a power supply of 2 x 18vac at 1000ma.
    The said eqipment is famous for broken down power packs, and they are almost £50 TO BUY!, so I thought that I would just build one.
    I have obtained a new transformer with 230v primary and 2 secondaries (0 - 18v).
    Is it as simple to just box this and connect?
    The equipment takes a 3 pin plug, so do i connect the 0v's together then wire to earth, and then wire the two 18v to the other 2 pins?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    Thanks Burtus,

    The tranformer I have has 2 seperate secondaries (0v - 18v 0v - 18v) so takes 4 wires, not 3 as I think is explained in the thread.
    Do I just connect the 0v lines together or have I got the wrong transformer?

    Thanks again
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you have a datasheet of the transformer you want to use?

    You need to connect the two windings in series, as in the attached schematic:

    [​IMG]

    The DOTS in the schematic show the start of the windings.

    Bertus
     
  5. Jaguarjoe

    Active Member

    Apr 7, 2010
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    90
    There are two ways that the transformer can be wired, with the correct phasing as shown above so the windings boost each other, or with opposite phasing so the windings buck each other. If they are properly phased to boost each other there will be 36 volts across both of the windings together. If not phased properly there will be 0 volts across both of the windings. Being a new transformer the data sheet for it should tell you which terminal or leadwire color is the start of each winding. If it can't be determined that way, then figure it out by trial and error- wire it up the way you think it should be then look for 36 volts. If its wrong then reverse the leads on one winding only.
     
  6. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    The transformer is a chassis transformer (not toroidal) by Vigortronix.
    I got it from Rapid Electronics. Info below.
    It has one primary input at 230v and two seperate 18v outputs.

    Order Code: 88-3932
    Manufacturer: Vigortronix
    Manufacturers Part Number: VTX-126-050-218
    50 va


    Similar to the one on the right of the picture but 50VA and the secondaries are at 18v (not 12v as the one in the picture).

    The data sheet is on thier site and the code is 88-3932.

    I need 2 x 18v output at at least at 1000ma, and I thought this would be the right transformer to choose as each secondary should give around 1.38amps.
    The problem is that although the equipment to power takes 2 x 18v, it only has 3 pins on the plug? One is to earth and the other two carry the 18v lines (0ne each), so I need one pin at 0v and two pins at 18v ac into the equipment.

    I know that I would have to run wires from the two 18v soldering points on the transformer to the two 18v pins, but what do I do with the earth pin?
    Do I join the two 0v solering points on the transformer together and then wire them to the earth pin?
    I am sorry if I am coming across as a bit unknowledgable, it's just that I am!
    Thanks again for any help.
    Please ask for further information if needed.






    230V Single Primary / Twin Secondaries​
    [​IMG]
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Make a temporary connection between the two CENTER connections (12V to 0V) of the low voltage winding. Measure the voltage from the Left Outside connector to the Right Outside connector. If you have 36VAC, then use the tie between the two center connections as the zero. If it reads very low voltage from the two outside terminals, then try connecting the two terminals marked "0" together and measure between the two open terminals for the 36VAC. It all has to do with the phasing of the two windings.
     
  8. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    Thanks
    I am sure that both windings are phased the same way.
     
  9. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    I'm very confused.
    I was of the impression (correct me please) that I could share the output amps between the two live pins and not the ouput voltage?
    I maybe have got the wrong transformer for the job.
    I thought that the transformer acted as two seperate power supplies of 18v (which I need) and all I had to do was split them.
    I thought that it acted as 2 transformers which were exactly the same but with single secondries:

    Primary input 0v and 230v
    Secondary output 0v and 18v
    25va


    I may get someone to do this for me.
    Don't want to ruin an expensive mixer.
    Maybe I should have just pulled out the £46 for a replacement power pack?

    Anyway, Thank for your help and understanding
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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    3

    What exactly is the equipment that you are trying to supply power to? Manufacturer and Model #. Have you done an internet search for the power requirements?
     
  11. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    ≈ALESIS NETZTEIL MULTIMIX FIREWIRE

    ALESIS Power Supply Multimix Firewire, for Alesis Multimix 12 FW & 16 FW, Multimix 8 & 16USB2.0, iMultimix 8USB, 18V/1000mA 3 Pin Connector.

    [​IMG]



    ----[​IMG]

    The one I have is the Alesis Multimix 16 Firewire
    On the rear of the unit it states:
    18vac (wavey line as above) 1000mA x 2

    The top pin is earthed
    The other 2 pins need 18v at 1000mA each

    So I need 2 feeds at 18vac 1000mA (or more than 1000mA) and one earth.

    I decided to get a transformer that has two secondaries that give 18v and at more than 1000mA each, as the unit is famous for blown power packs rated at 1000mA.
    The tranformer is rated at 50VA and so the 2 secondaries should give around 1.36A each at 18v. (Total out 18v 2.78A)

    Hope I have explained this well enough and hope pics help.
    Thanks again for your patience

    [​IMG]
     
  12. Tateypot

    Thread Starter New Member

    Apr 14, 2011
    12
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    Hi
    No, not 36v

    It's an Alesis Multimix 16 Firewire

    The top pin is earthed
    The other 2 pins need supplies of 18v at 1000mA (or more than 1000mA) EACH.

    So I need one wire to the earth pin.
    And 2 wires which carry 18v at 1amp EACH
    The transformer I have is rated ay 50VA so each of it's 2 secondaries should carry 18v at 1.36A.

    So I need 2 feeds at 18v 1.36A which I have, but don't know whether to join the 2 0V's on the secondaries together for the earth to complete the two circuits.

    If the circuits inside the mixer are independant, does phasing really matter?

    I should have put (18vac at 1000mA) x 2
    and not 2 x 18v at 1000mA.
    Sorry

    Thanks again
     
  13. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    Alesis Multimix 16 Firewire..

    Should have put (18v - 1000mA) x 2
     
  14. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    From what I see on Page 18in the manual (attached), you need 18.5VAC @ 700ma, which to me means that one power pin of the connector will tie to the 0 vac tabs of the transformer and the other power pin of the connector will tie to the 18vac tabs of the transformer. The Ground pin of the connector will tie to the Earth conductor of the power cable feeding the transformer. The Earth conductor of the power cable should also be connected to the frame of the transformer.

    In other words, connect the two 0 vac tabs together, the two 18 vac tabs together and connect to the cable going to the mixer with the Earth conductor carried through.
     
  15. Tateypot

    Thread Starter New Member

    Apr 14, 2011
    12
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    Hi Again
    Hope I'm not becoming a pain in the backside!

    Just found this on another site from 2008 in answer from someone asking a similar question

    Does this open up any more ideas or does it conferm your last answer?


    See Below:

    ------------------------------------------------------------

    I have a Multimix 16
    Anyway on my power supply it is:

    120VAC input
    with 2 - 18VAC output at 1000ma
    (notice it is AC output not DC)

    I measure as follows:
    pin 2 to 1 = ~20Vac
    pin 2 to 3 = ~20Vac
    pin 3 to 1 = ~40Vac

    without taking the power supply appart it appears that it is just a transformer with the power regulation done inside the mixer.


    --------------------------------------------------------------

    Same as mine but of course mine runs on 230volts.

    Thanks again
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    That opens up an entirely different scenario!. It indicates that indeed the two individual windings are in SERIES_ADDING mode. In that case, look at post #4 for the circuit and post #7 to verify proper connections. Then follow what you found to connect the cable. Pin 2 would be the 0 volt point shown in post #4.
     
  17. Tateypot

    Thread Starter New Member

    Apr 14, 2011
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    Yes, yes, yes! BillB3857
    I understand it now!
    The 40v is never used because I'm using only half the winding!
    And if I measure from pin 1 and 3 in the plug (2 being the earth from the link of the 2 windings) I'll get 40v
    Thank you, thank you, thank you! Got it in the end.

    I consider myself more educated.
     
  18. Tateypot

    Thread Starter New Member

    Apr 14, 2011
    12
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    Just wired it up and it's working perfectly.

    I can't thank you enough.
     
  19. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    It was a long road but the trip was worth it! Glad it worked out!
     
  20. Rykonen

    New Member

    Jun 5, 2011
    2
    0
    Any chance you could post some pictures of the final build? :O I am building this same power pack (115v however) and this thread was invaluable. Thanks guys!
     
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