I have this big transformer taken from an old UPS. I wanted to use it to build a linear high current 12V power supply, so I was testing if it was suitable for the task. Unfortunately it has no ratings, but I assume it would be capable of delivering at least 10A. Here are a couple of pictures of the transformer: https://i.stack.imgur.com/92mCX.jpg
These are the resistance of the windings:
- grey-violet 1.61 ohm
- brown-blue 5.22 ohm
- black-red(right) 0.15 ohm
- white-red(left) 0.15 ohm
I connected brown-blue to the mains (230V) using a regular PC cable (rated 2.5A 250V) and took some measurements. In this configuration, both black and white with the respective reds were 13,8VAC, but grey-violet was out of range with my multimeter (UT61E).
Then I tried to connect grey-violet to the mains, and this is where the PC cable immediately burned.
My question is, why there was this big current absorption if there was no load connected (just my multimeter)? And why only when I connected grey and violet? Is this transformer still safe to use, provided that the resistance measurements remained the same and its cable show no signs of burning (maybe the 2.5A cable acted as a fuse)?