A question about transformer voltages and connecting it

Discussion in 'The Projects Forum' started by CRAIG VANDEKAMP, May 17, 2015.

  1. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    Hi folks

    Can I connect a (240V 50hz -> 24V AC) 120VA transformer to a circuit rated at 24V 3A 100VA and will there be any problems with overload if I do?

    Stupid Question I know but this is my first ever play around with transformers.

    Thanks for your help.

    Craig
     
  2. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    You have a transformer with a 240 VAC 50 Hz primary and a 24 VAC 50 Hz secondary which is a 120 VA transformer. That tells me it has a 24 VAC 5 Amp secondary. You want to run a load which is 24 VAC 50 Hz 3 Amp. That would be fine. I don't understand that last 100 VA you have? 24 Volts @ 3 Amps = 72 VA.

    Ron
     
  3. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    I have this transformer but I am a bit confused on the wiring instructions on it.
    I want 24V on the secondary

    [​IMG]


    I think this is right but I would like a second opinion; :)

    JUMP B to F and secondary out is A and E


    Thanks folks


    Craig
     
    Last edited: May 17, 2015
  4. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    Hi Ron; its an old japanese pachinko machine (pinball) and on the cover of the circuit board is written 24V AC 3A 100VA so I assumed this is what it requires - I'm new to electronics and still learning the formulas :)
    Here is a pic of the cover

    [​IMG]
     
    Last edited: May 17, 2015
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    Yes move the green wire to E and that will give 24VAC.

    (It's not good practice to use mains coloured wires or green/yellow earth wires for low voltage AC).
     
  6. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    Thanks for the wire color tip; any suggestions on appropriate color?
     
  7. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    You should be fine using the transformer you mentioned. Ah yes, fond memories of those pachinko machines. Generally when you see a power requirement like that it means the max power the circuit will draw. For single phase AC the VA is simply the Voltage * Current or Volts * Amps.

    Ron
     
  8. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    That will do it. :)

    Ron
     
  9. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    I tried this transformer on another pachinko rated the same and it blew out a 47V MOV so I'm reluctant to use it; Multimeter says its OK; any ideas on what may have caused this (the pachinko has been sitting for 24 years unused; but all circuitry looked fine when I checked it; looks like I'll be double checking it once I remove/replace the MOV and try again.

    Here is a piccie of the transformer

    [​IMG]

    And here is a picture of the pachinko for your nostalgia :)

    [​IMG]

    thanks mate :)

    Craig
     
  10. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    I remember that. You had a thread on it. I haven't a clue why the MOV failed. There are components, some capacitors come to mind which over time will degrade but generally MOVs don't fail unless there is a major voltage spike or surge.

    Ron
     
  11. CRAIG VANDEKAMP

    Thread Starter New Member

    May 14, 2015
    20
    0
    Thanks for all your help Ron and everyone else I'll end this thread now. see ya

    Craig
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    There is pretty much only one reason a MOV (VDR) fails is due to sustained voltage over and above the maximum rated, current increases as the voltage rises over the normal voltage operating point.
    Max.
     
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