Utilising both transformer coils?

Discussion in 'The Projects Forum' started by Flamin_D, May 13, 2010.

  1. Flamin_D

    Thread Starter New Member

    May 3, 2010
    I have a 250v - 12v transformer with two secondary coils. I want to use them both to the same load to get the most power out of it (im assuming it works like that?). I wired each coil to its own bridge rectifier and paralleled the two BRs. I then tested it with my 20Vdc voltmeter which blew up when i powered on. Anyone know why?!?! Its baffling me.

  2. bertus


    Apr 5, 2008

    Take a look at the attached PDF.
    Be shure the phases are correct, otherwise you will burn the transformer.

    Flamin_D likes this.
  3. Flamin_D

    Thread Starter New Member

    May 3, 2010
    Thats what i thought would work - yet when i tried it my transformer started sizzling a bit ? maybe i had the primary wires backwards or something. Ill try it again. Thanks!
  4. bertus


    Apr 5, 2008
  5. SgtWookie


    Jul 17, 2007
    If your transformer is sizzling, you have something hooked up wrong.

    Make certain that you are using the AC in on the rectifiers. If you have one lead on an AC in and the other on a DC out, you will short out 1/2 cycle of the output sine wave.
  6. someonesdad

    Senior Member

    Jul 7, 2009
    I second bertus' comment about phasing. Here's a web page that can teach you how to phase check transformer windings with a scope or a digital multimeter. Go to the section second from the bottom. Also check out AAC's tutorial on transformers, especially the phasing section.

    In retrospect, some lessons others might get from your misfortune are:

    * Put fuses in line with circuits that are being tested for the first time.

    * Power up an AC circuit (where possible) with a Variac and monitor what's going on at lower voltages first.

    I loved your diagram -- and it reminded me that we all make mistakes like this occasionally. The key is to understand what went wrong and correct your mental picture of how things work. This lesson, then, will be far better ingrained in your brain than most others. Trust me, I know... :p
  7. eblc1388

    Senior Member

    Nov 28, 2008
    How that can happens? :confused:

    Regardless of the secondary winding polarity, the waveforms from the two secondary windings after the bridge rectifiers will be exactly the same.
  8. Norfindel

    Active Member

    Mar 6, 2008
    You could connect one cable from every seconday and measure the voltage on the other two cables (series connection), to see what's the polarity of the secondaries.

    You probably got 24 vac rectified at the voltmeter somehow, if it exploded.