UPS Transformer.

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Hello. Just did a search and could not find anything about using Uninterupted Power Supply transformers. I just got one from a junked unit and the only marking is 40A 32V on the cables that go to the battery bank. This transformers are used backwards, they are fed a sine wave from the battery bank and output 120 VAC. My question is, can I use it the other way around? Feed 120 VAC and get 32V 40A? (I only need about 15A)

Eugenio
 
Maybe. Some UPS transformers are indeed just normal transformers used backwards, but in the interest of reducing cost and size, many cheaper UPSes use higher frequency transformers. For example, an old 300W APC operated at about 90Hz. (Modern digital power supplies can operate with input frequencies as high as 400Hz and probably even higher.) Some of the newest UPSes and inverters operate at very high frequency in the range of many kHz, rectify the output, and then put it through a H bridge to make AC. Also, the transformer might be optimized to work with square waves.

Now, for Line Interactive designs, the inverter works backwards as a charger. The transformer operates at 60Hz and also is used as an autotransformer for voltage regulation.
 
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