Hi! This is my first post on AllAboutCircuits, I hope I could learn more about electronics and have your support.

I've spent some time searching on the internet for this type of AC transformer step down that I've found in a UPS. Although I couldn't find some useful information about it. It doesn't have any model number nor specifications. The only thing it says is: 220v FS and G9948, this didn't help me much. So I'm in doubt about the type of transformer because I suppose it has 3 "outputs" wires, the blue, red and brown cables, and 4 "input" wires, one red and black and one pair of blue wires which are smaller than the red and black. I never saw this type of transformer, most have 2 wires, or 3 wires (117V-0V-117V). So I connected the 2 wires red and black to 220V AC and got the measurements below:



Sorry for the bad quality. Does the measurements suggests something? The most intriguing thing is the blue pair of wires, and they measured about 15 volts when I connected the red and black wires to the 220V. I also measured the resistance between the red and black wire and had a resistance of roughly 20 Ohm, higher than the pair of blue wires.

I hope I could hear some useful information since I don't fully understand the topic.

Best regards,
João Dias

 

My guess is that the secondary is a 6 - 0 - 6 winding and the pair of Blue Wires is a 12 or 15 volt auxiliary for some control circuitry.

 

My guess is that the secondary is a 6 - 0 - 6 winding and the pair of Blue Wires is a 12 or 15 volt auxiliary for some control circuitry.

Probably you are right, in a UPS system the 12 V battery should be charged by the transformer (after AC be converted to DC), so it doesn't seem logical having a bigger transformer. But the size of it is strange, since I had smaller transformers with bigger outputs.

Thanks for the reply!

 

In a SMPS, the transformers will be small since we are dealing with frequencies of a few Kilohertz.
This is a 50 Hz transformer and will be MUCH bigger for the same outputs.