The PowerMan PM900 Series of UPS’s are manufactured using a double conversion design principal. The incoming mains is converted directly into DC. This DC power is used to charge the batteries and to drive the inverter, which in turn runs the load. Should the mains fail the batteries will simply carry on driving the inverter, and start to discharge as opposed to charging.
The units have a built in Static By-Pass feature which enables the machine to transfer the load to normal mains under certain conditions. There is no break on the output on transfer to or from the mains.