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Above is transformer in question. And in case here is the datasheet: http://www.farnell.com/datasheets/2026060.pdf?_ga=1.56694762.1111228725.1474151580

As you see this is a single primary 6V dual secondary transformer. There is no center tap. And I measured with an ohmmeter that it seems like the two secondary outputs are not connected to each-other.

I'm trying to use this transformer as a center tapped one at the secondary side. The aim is to create a +6V 0 -6V split supply. If I connect B and C together would that be the center point(0) of a +6V 0 -6V transformer where A and D are the new terminals? A -6V D +6V relative to the new middle zero point(BC). I wanted to be sure before I try it and cause a possible hazard.

  • \$\begingroup\$ There is nothing in the data sheet to indicate phasing of this transformer but my guess is connecting B and C together would give you a center tap. If you have an oscilloscope you can easily see the phasing by measuring each winding. If not with your trusty voltmeter check A to B is 6V, C to D is 6V and with B connected to C that A to D is 12V. If its approximately 0V then connect B to D and use that as your center tap. \$\endgroup\$ Commented Sep 19, 2016 at 13:28

1 Answer 1


Yes, a B-to-C connection would be the obvious thing to try first. After making that connection (and before you connect anything else to A and D), measure the voltage between A and D. If it's 12V, you're all set.

If it's a very low value, then one of the windings needs to be reversed. Connect B to D and use that as your center tap, and then A and C become your "end" connections.

  • \$\begingroup\$ Im just worried to burn it up if my assumption is wrong. Should I use a fuse at one of the primary terminal at its rated current? \$\endgroup\$
    – user16307
    Commented Sep 19, 2016 at 13:22
  • \$\begingroup\$ This test cannot burn anything up. But yes, you should always use a fuse on the primary side anyway. \$\endgroup\$
    – Dave Tweed
    Commented Sep 19, 2016 at 13:24
  • \$\begingroup\$ thanks I just dont understand what it is to do with phasing? what do you mean by that in this context? could you give me a hint so that I can read about it? \$\endgroup\$
    – user16307
    Commented Sep 19, 2016 at 13:31
  • \$\begingroup\$ The output of the transformer will be an AC voltage. The voltage between A and B will vary from 0 to A positive relative to B, to zero, then B positive relative to A. Same will happen on the C-D winding. If A and C are positive at the same time, the winding voltages are "in phase". In that case, you can connect B to C to get 12 volts between A and D. \$\endgroup\$ Commented Sep 19, 2016 at 16:39
  • \$\begingroup\$ If only B to C is connected and nothing to A and D, there is no load and therfore no risk to burn up the transformer. Measuring the voltage between A and D is only a very, very small load if a voltmeter with high input resistance is used. If an acceptable load for 12 V and the VA Rating is applied to A and D there is also no risk to burn up the thing. If both windings are connected in the right direktion, we get 12 V at the load and the resulting current. If the windings are in wrong direction, the resulting voltage is very low and thus also the current is very low and would not harm. \$\endgroup\$
    – Uwe
    Commented Sep 20, 2016 at 12:46

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