Question about dual primary's

Discussion in 'General Electronics Chat' started by chaseBank, Jul 24, 2014.

  1. chaseBank

    Thread Starter New Member

    Dec 14, 2013
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    Hello all,

    Long time lurker and first time poster. I have just bought a 250va 50/60Hz 30+30 toroidal transformer and just opened it to realize it has two primary's. My question is, Do I connect both primary's to the same plug in? For example, the primary wire colors are blue/grey and the other brown/violet, would I connect blue and brown to side and grey and violet to the other ac channel? I can't image needing two totally separate plug inns to power this thing.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    If running it on 120Vac, the two primary windings need to be in parallel (with the appropriate phasing).

    If running on 240V, the two primary windings need to be in series (with the appropriate phasing).
     
  3. chaseBank

    Thread Starter New Member

    Dec 14, 2013
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    Can you elaborate on that. I just planned on connecting it to the 120v wall outlet. I've only dealt with one primary before in which I just soldered the primary wires to an ac wire.
     
    Last edited: Jul 24, 2014
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,542
    2,369
    For 120v If you do not have the connection details, what you could do is connect the one end of each primary pair together and connect this to one side of the 120v supply, then connect the end of ONE of the pair to the other side of the supply.
    Then measure from the single connected conductor to the one that is left unconnected and if it is close to zero, then you can connect this one to the other single conductor.
    If it is 240v then reverse one pair only and try again.
    Once you have a pair identified as zero between the single pair, connect both to the 120v supply
    Max.
     
  5. chaseBank

    Thread Starter New Member

    Dec 14, 2013
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    Something like this then, as in the 115v

    [​IMG]
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, but you need to identify 1-2 3-4 if you do not have the colour identification.
    Per my previous post you would connect 1-3 and leave 2 & 4 open, and initially only connect 2 OR 4 to the other supply
    terminal for 0v between 2-4.
    The alternative result would be 240v measured between 2-4.
    Max..
     
  7. chaseBank

    Thread Starter New Member

    Dec 14, 2013
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    My top primary is blu/gry or 1,2, and bottom primary is vio/brn or 3,4. So I would connect blu/vio and then either of the other colors. If I know colors its ok to connect them then, or still just one first and test with my DMM?
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    As a safety factor and to avoid popping the breaker/fuse you could temporarily connect a 120V incandescent bulb in series with the transformer primary. If the connections are wrong, it will light brightly. If correct, it will be dark or glow only dimly.
     
  9. chaseBank

    Thread Starter New Member

    Dec 14, 2013
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    Thanks for the replies, I think I got the gist of it. As long as I don't ruin my transformer I'll be ok.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, connect Blue & Vio and say gry across 120v, then between gry & brn you will get either ~0v or 240, if 0 then connect gry & brn, if 240v, connect blu & brn and try again.
    Max.
     
  11. chaseBank

    Thread Starter New Member

    Dec 14, 2013
    14
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    Thanks guys It worked without blowing anything up! Now I have to build my power supply for my amp project for Electronic engineering capstone
     
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