3 phase transformers and bridge rectifiers

Discussion in 'General Electronics Chat' started by yassser, Mar 25, 2013.

  1. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
    hello,

    I constructed the following power supply to drive a dc motor

    [​IMG]

    this one worked well , then I needed to supply two motors so I constructed the following circuit

    [​IMG]

    one of the bridges blew up , is there something wrong i'm doing , what can I do to make it work
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Are you connecting any outputs from the two bridges together?
     
  3. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
    I found out that one of the caps was connected with the wrong polarity , it must have been the reason why the bridges blew up.

    I will get a new bridge and try again , do you think that there is nothing wrong with this connection ?
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,522
    Why not just use a three phase rectifier? That way you are using a balanced load on the transformer. A three phase rectifier uses six diodes instead of four like a single phase rectifier. Like shown in the attached image.
     
    PackratKing likes this.
  5. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Your loads are un-balanced across the transformer secondary. Wrong capacitor polarity is probably what caused its destruction. Using all three phases will result in much less AC ripple < 5% on the bridge rectifier output and you can do away with the capacitors.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
    ErnieM and PackratKing like this.
  6. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    If you need a common ground for the motors, then you have to connected as the circuit from shortbus provided.

    In any conditions that you can't connected the output together from two motors as your second circuit.

    Why your rectifier blew up, i think that is like this:
    Because the capacitor connected the wrong polarity, so it blew up first and it became shorted, when it shorted then the output of rectifier will overload, so it blew up too.

    You can check the capacitor.
     
    shortbus likes this.
  7. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
    so , with the second connection I mentioned , it is not possible to combine the grounds of the output from the rectifier ? because I have to combine the outputs .
     
  8. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    How can you just connected the output together and let the ground alone, if you doing so, then the current of circuit will loss the loop condition, it just go out but didn't come back, and you can't get the power from the circuit.

    The current flow from :
    city power → transformer → rectifier → capacitor → (+)Motor
    city power ← transformer ← rectifier ← capacitor ← (+)Motor

    So if you want to using the second circuit then you can't just connected two output of voltage or two ground together, it doesn't mean anything, this circuit should be used in two motors alone.

    If you want that two motors has common ground, then you can using the circuit from shortbus.
     
  9. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
    this is the complete schematic , is this connection possible or not ?

    thanks

    [​IMG]
     
  10. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
    the controller is what cobines the grounds of the rectifier outputs

    when I tried this coneection , the controller burned , and the igbt gate drivers in one of the two channels burned , what can I do to make it work ?
     
  11. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    I'm not sure the current is enough no not, but you can try the half rectifier, and it will has a common ground.

    O1 → diode → capacitor → to motor 1 power
    O2 → diode → capacitor → to motor 2 power
    The ground is common terminal for transformer and motors and controller

    Or the ground in series a diode common
    Transformer N ← (-)Diode(+) ← the common ground of motors and controller .
     
  12. yassser

    Thread Starter Member

    Jul 25, 2011
    91
    0
  13. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you look at your drawing and draw the four diodes out for the bridges, I think you will see that the lower left diode will have ground tied to both ends. Does that make any sense at all? A bridge rectifier depends upon either an input supply isolated from ground or an output isolated from ground.
     
Loading...