voltage range of step up transformer

[darmfam]

I've tried to repair a PC power backup system. I didn't take any voltage readings from the unit before it stopped working, so I don't know what to expect them to be.

When operating on AC I get a reading of 120.2 to 120.4 volts, but when the AC power is cut and the battery cuts in I get 104 to 109.4 volts. Is this normal? :roll:

 

[Sebi]

It's normal. This type of UPS - if the mains voltage existiert - only feed it via relais to output. When the input AC line cutted, started an inverter and this voltage level independent from mains voltage (and no sinus).
This UPS designed only for devices with SMPS. (PC,monitor)

 

[darmfam]

Thanks

The ups was designed for a PC and monitor, so I guess its working. I know that the PC has its own power supply which maintains voltage stability, do monitors also have such a feature?