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I have lighting fixture that has two lighting halogen transformers 110VAC, 60Hz to 12VAC and 150W each in something like circular box. Their inputs are connected in parallel.

Their outputs are 12VAC, and they are not interconnected, each has its own load of several halogen bulbs.

They are connected in parallel configuration on primary sides. I am planing to take it to Europe and I will have there 220VAC input, 50Hz. May I connect these transformers in serial configuration, so then having 220VAC across both transformers in serial connection on primary side, I will have each transformers exposed to 110VAC, am I right. I know although they are the same type, they are not identical. I know that with 50Hz the transformers will not have enough core for that frequency, so possible some humming noise, right?

Then leave secondary side as is, I think I will be fine. What you think if any problem with that configuration?

Regards, Safet

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Your scheme has enough potential problems that I would not recommend it.

  1. Connecting the two transformer primary windings in SERIES is not recommended where the loads (on the secondary side) are DIFFERENT. It means that the power will NOT be equally divided between the two transformers. This will cause the voltage across one of the circuits to be too high and will put the bulb(s) at risk of burning out.
  2. The major problem with operating 60 Hz transformers on 50 Hz is HEAT, not HUM. It is possible to design transformers with enough margin to handle both 50 Hz and 60 Hz. But products designed for a 60Hz market are frequently fitted with power transformers built to a narrow budget margin that causes overheating when operated at 50 Hz.
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  • \$\begingroup\$ connecting the secondaries in parallel will fix problem 1, problem 2 is not easily solved. \$\endgroup\$ – Jasen Jun 4 '16 at 6:53
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The insufficient core volume issue that may arise when operating the 60Hz transformer on 50Hz can be safely tested out. Get those cheap thermal fuses rated to about 130 degree Celsius and slide it into the gaps (if you can find those gaps) of the transformer. Do this for each of your transformer. Connect these fuses in series with the mains and the serially connected primaries.

The parallel connected secondaries can be now loaded with those halogens and whole thing powered up.

If in case you have issues with the core volume, the temperature rise will burn the fuse, not your house.

enter image description here

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