240V-120V Transformer connection question

1996_USMC_RET1996_USMC_RET Posts: 1
edited 2013-08-06 - 07:38:59 in General Discussion
I replaced a Westinghouse EP Single Phase S10N05S51B 120 X 240, 12 X 24 Transformer, which was used to power our in-ground pool’s light, with a Westinghouse S10N0551A. Before disconnecting the old transformer, I took photos of the connections to be sure I connected the new one correctly which are:

H1H3 (Black In)
H2H4 (White in)
X1X3 (Black out)
X2X4 (White out)
Ground in to ground out.

I am positive I connected the new transformer exactly like the old one and, with the IN wires connected and no wires attached to the OUT side, power is being sent out through X1X3.

My problem is, every time I connect ANY wire (the actual load wires or a spare piece of wire) to X1X3 or even X2X4, the X1X3 wires stop sending power out. When I remove the wire, then X1X3 will again send power out. For the life of me I can’t figure this out. Anyone have any ideas what I’m doing wrong? :frown:


  • kwinnkwinn Posts: 8,600
    edited 2013-08-05 - 14:49:04
    This sounds like a transformer with dual input and output windings so that the input can be either 120V or 240V, and the output can be either 12V or 24V. If this is the case then the connections have to be in parallel for 120V input and 12V output, or in series for 240V input and 24V output. They also have to be connected in proper phase.

    Do you have a connection diagram with the new transformer, and do you know what input and output voltages you need?
  • Hal AlbachHal Albach Posts: 747
    edited 2013-08-05 - 15:26:14
    Thank you for your service to our country!
    What is the voltage and power requirement for the pool light(s)? If the lights are 12 volt and the total power required is less than 300 watts and your input voltage is 120 then you could easily use a landscape lighting transformer obtained at Home Depot or Lowes. Added benefit is a built in timer and photocell.
  • kwinnkwinn Posts: 8,600
    edited 2013-08-05 - 15:38:47
    Dual voltage transformer.jpg

    Here is a wiring diagram for this type of transformer. Your setup seems to be 120V in and 12V out. If that is the case use diagram 2.
    1000 x 241 - 55K
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2013-08-05 - 16:34:37
    Just to be complete:

    Dual voltage transformer.jpg

    Duane J
    1024 x 150 - 31K
    1024 x 150 - 31K
  • kwinnkwinn Posts: 8,600
    edited 2013-08-05 - 20:49:36
    OK Duane, but please correct the numbering of the images ;-)
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-08-06 - 04:16:29
    So, the foremost issue is that Westinghouse decided to create one transformer that will take either 120 or 240 VAC and output either 24 or 12 VAC.

    If you can grasp the concept, I think you will have an easier time getting from 120VAC in to 12VAC out. It is a puzzle.. plain and simple.

    The ground to ground connection completely bypasses the internal wiring of the transformer.

    What COULD BE the problem is that if the two output coils are 180 degrees out of phase... they might cancel eachother's output. A similar problem might be that the two input coils are 180 degrees out of phase. One, the other, or both.
  • kwinnkwinn Posts: 8,600
    edited 2013-08-06 - 07:24:07
    It's not really much of a puzzle. The input and output are treated independently. Connect the output windings in series and you get 24V out, connect them in parallel and you get 12V out. Same idea for the inputs. Connect them in series for 240V and parallel for 120V. Of course phase counts, but the wiring is usually printed on the transformer. It is a fairly standard item made by several manufacturers and used extensively in building controls systems.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-08-06 - 07:38:59
    Well, either it is the transformer or it is a short in the load.

    I would test the transformer output with an independent load to verify which is the offending item. It certainly seems at least one pair of transformer coils are out of phase.

    My mentioning puzzles is just a way of say one has to pay attention to all the details, not just follow diagrams.

    Your transformer and the replacement seem to be identical, but one with an A in the part number is indeed not the same as the other with a B. That may mean nothing, or may be the source of all your woes.

    You should be able to check both the old and the new transformers for continuity defects. There should be 4 independent coils without any leakage to ground. If that is NOT the case with the replacement, it is defective.

    Troubleshooting a simple swap is always annoying, but I have often found that it is the only way to finish the job.

    To make sure the 110 VAC is good, check each 12VAC separately for output, maybe with a reasonable load. If results are odd, either you have a leak to ground or the 110VAC is out of phase.

    If all is okay, you can then figure out what works for 12VAC to be wired parallel and in phase.
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