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Another Question for those who are better with transformers

Discussion in 'Datasheets, Manuals and Component Identification' started by chipperi, Jul 2, 2011.

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  1. chipperi


    Feb 17, 2011
    Ok I have yet another transformer I am having a little trouble with. It is marked:

    SEC SP-54H-6006 491-8518 PT-28A S3

    Are all the markings on the unit. A search of Google and sec's website don't pull any info. So I pulled out the DMM and started probing, there are 5 wires on the secondary there is continuity between all of them. From left to right Red Blue#1 Black Blue#2 Red

    With 120vac on the primary I got

    Red - Blue#1 18vac
    Red - Black 27.8vac
    Red - Blue#2 37.7vac
    Red - Red 55.7vac
    Blue#1 - Blue#2 19.4vac
    Blue - Black 9.7vac

    I'm just confused. From what I've seen with multiple secondaries, one is exactly half the voltage of the other, usually the 2 blues would be half of the 2 reds with no continuity between the two. Could someone tell me what I'm looking at.
  2. duke37


    Jan 9, 2011
    The black is the odd one out with no butty. This is the centre (US center) tap with 9.7V to each blue and 27V to each red. The voltages will be double red/red and blue/blue.. The voltages will drop somewhat under load, perhaps by 10%. It is probably a 25-0-25V transformer with taps at 9-0-9.
    Last edited: Jul 3, 2011
  3. duke37


    Jan 9, 2011
    To see if you are still confused, assume it is a 25-0-25V transformer tapped at 9V, what voltages can you get out of this?

    If you use bi-phase rectification with 1V diode drop and storage capacitors, what peak voltages can you get?
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