Connect two transformers parallel

Discussion in 'General Electronics Chat' started by justin77, Apr 6, 2010.

  1. justin77

    justin77 Thread Starter New Member

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    Can i connect two transformers after the AC to DC conversion in parallel as shown in the diagram.

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  2. t_n_k

    t_n_k AAC Fanatic!

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    You can - in this situation the highest output at any instant will conduct into the parallel load path - by virtue of the diodes D1 & D2.
  3. justin77

    justin77 Thread Starter New Member

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    Will the load get balanced. Will i be able to get more Amps from the combined circuit?
  4. t_n_k

    t_n_k AAC Fanatic!

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    You could probably lose the diodes (D1 & D2). The bridge rectifiers will themselves prevent backflow of current.

    Perhaps you could explain why you want to take this approach - is it for a real circuit?
  5. justin77

    justin77 Thread Starter New Member

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    Yeah this is. I need it to give power to my amplifier. One transformer is not enough as its maximum current is 2A. I need to have some method to provide 4A of current. So i was thinking of buying another 24 0 -24 V transfornmer and connet it in parallel.
  6. nomurphy

    nomurphy Distinguished Member

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    Instead of building two seperate circuits, literally place the two equally rated xfmr's in parallel to double the output current capacity. Verify the diode bridge can handle the extra current, or upgrade it.
  7. SgtWookie

    SgtWookie Expert

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    Make certain that you have the transformers connect in phase with each other.

    If you have them out of phase, you will get 0v out and a pair of smoking transformers. :eek:

    Connect the primaries to a fused and switched supply of mains power. Connect one of the ends of the secondaries together. Use a meter set to AC to test the voltage between the disconnected ends of the secondaries. If you have them in phase, you should measure very little voltage between the two. If they are out of phase, you will measure around 48vac.

    If they are out of phase, you can swap either the primary or secondary connections.
    PaulC likes this.
  8. justin77

    justin77 Thread Starter New Member

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    Do you mean to connect the AC output's of the two tranformers in parallel?

    Isn't it a risky thing to do. Isn't connecting DC outputs in parallel safer?
  9. Bychon

    Bychon Member

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    If the 2 transformers are same brand, same number, they will be perfectly happy in parallel. If they are a bit different, the use of 2 rectifier circuits (like the drawing shows) will keep them from fighting each other.

    In the real world, I have connected transformers of different brands, but both labeled 24 VAC, and they do not fight each other, so a little bit of difference doesn't seem to hurt.
  10. justin77

    justin77 Thread Starter New Member

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    what if one DC output is 33.3V and the other is 35V only the 35V output generating transformer will be active.

    Now if i draw 2A , 35V will drop to say 30V then the 33V transformer will become active. So only one transformer is ideally active at any one instance?

    Am i corect?
  11. t_n_k

    t_n_k AAC Fanatic!

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    The closer the match between the two parallel sub-circuits the better the balance of load sharing. Even small differences will lead to significant imbalances. Also the inclusion or non-inclusion of the diodes (D1 & D2) has an impact on the lower output side. No diodes means some charging current will flow back into the filter caps from one rectifier to the other. The diodes stop that happening but don't ensure equal load sharing. And you don't want to be adding power wasting series resistors to improve the load sharing. You could propose a solution using an interphase transformer + diodes arrangement. The cost of the interphase transformer would mitigate against this solution.

    In a case where one might want parallel connect two or more transformer rectifier modules, the better option might be to have active current controlled rectifiers which are dynamically regulated to balance the load current sharing - but this would also be a much more costly approach.

    The parallel transformer secondaries option [with the same transformer type] seems a better approach.

    In the long run it might really be better & simpler to 'bite the bullet' and buy (or build) a higher rated power single transformer + rectifier supply to meet your requirements.
  12. lmartinez

    lmartinez Active Member

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  13. justin77

    justin77 Thread Starter New Member

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    please answer my question
  14. justin77

    justin77 Thread Starter New Member

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    oops sorry when i clicked on this topic it bought me to the first page only. I didn't see page no 2.
  15. justin77

    justin77 Thread Starter New Member

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    its better to go for a switch mode power supply. Does anyone have a circuit diagram for a +24 0 -24 volt switch mode power supply
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