Transformer wiring clarification

Discussion in 'The Projects Forum' started by logans-electronics, Sep 15, 2009.

  1. logans-electronics

    Thread Starter Member

    Sep 1, 2009

    I was wondering if you could help me figure out the wiring here. I have 2 pictures attached...(Front/Back)...

    I do not understand why there are 2 primary inputs. I metered them, they are isolated from each other. On each side (Red to Blue) I get 4 ohms.

    When I connect 120 VAC to one side (red and a blue) it shows 20 volts at 60 hz on each yellow with black as a reference, which seems right. The transformer has a burning smell to it. It gets warm at the "primary label"....I have no load to this.

    Next, I connected both primary reds to the neutral and the primary blues to hot from 120vac. The breaker tripped.

    Did I possibly damaged the transformer?...I will hook up a 3 amp inline fuse to one side of the primary label and monitor the 20 volts. I never attempted to meter the back labeled +52 and -52.

    I just can't figure out why there are 2 primary inputs and why it has a warm burning smell with no load.

  2. mik3

    Senior Member

    Feb 4, 2008
    Maybe one primary is used for 120V and the other for 240V.
  3. mkbutan

    Senior Member

    Sep 30, 2008
    kindly let us know where the tr. is being used
    what is the pri. & sec. ckt of the tr.
  4. logans-electronics

    Thread Starter Member

    Sep 1, 2009
    Primary 120 VAC (household outlet)....Secondary to send to a bridge rectifier and filter caps. for a +20 and a -20v rail.

    Label on top says 300VA my max current would be 300VA/40V=7.5 total?

    Here is the concept drawing of my power supply...
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    If you have a meter, check you primary wires. The pairing may be red - blue and not red - red, blue - blue. For dual primary transformers, it is possible to run from both 240 and 120 VAC. The primaries go in series for 240, parallel for 120.
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    You are heading for the most amazing hum amplifier.

    Look up earth loops and decide how you will supply the low and high current parts of your circuitry.

    I doubt you will need much if any heatsink for your diode bridge. You will however want to add some high frequency capacitors across the reservoirs and a high(ish) resistance discharge path for shutdown.
  7. mkbutan

    Senior Member

    Sep 30, 2008

    kindly see the forum
    Transformer power supply - how to wire secondaries?

    it is still not clear the purpose of transformer
  8. mkbutan

    Senior Member

    Sep 30, 2008
    and for your PDF circuit you can use 1000mfd/50v capacitor
    and IN1001-IN1007 diodes for the bridge rectifier or can go for ready made bridge rectifier with heat sink but for 20-50v heat sink is not required
    Last edited: Sep 17, 2009
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    U know it's funny that u get a burning smell with a 120V AC input.
    The way I see it beenthere is right.
    Parallel for 120VAC
    Series for 240VAC