I have few building sized UPS (200kw - 500kw) and dozens of small rack-mount DC UPS's (1kw - 8kw) for telco closets and such.
One question that keeps bugging me is the float voltage that the batteries are kept. On the building UPS's, strings of (40) 12v batteries (in series) are kept on a boost charge of 13.5v - for a total string voltage of 540vdc. This then feeds the inverter (when needed) to supply the UPS 480vac output. I have always believed that the battery strings were kept at 540vdc to accommodate the load inrush (a french phrase I can't recall) and how this interacted with batteries. Is that the sole reason, or does it have something to do with inverter?
The same situation applies to the small rack-mount DC UPS - 54vdc float charge when the load is supplied 48vdc (only different here being that there is no inverter... just DC to DC load).
Many thanks...
ShmoJoe
One question that keeps bugging me is the float voltage that the batteries are kept. On the building UPS's, strings of (40) 12v batteries (in series) are kept on a boost charge of 13.5v - for a total string voltage of 540vdc. This then feeds the inverter (when needed) to supply the UPS 480vac output. I have always believed that the battery strings were kept at 540vdc to accommodate the load inrush (a french phrase I can't recall) and how this interacted with batteries. Is that the sole reason, or does it have something to do with inverter?
The same situation applies to the small rack-mount DC UPS - 54vdc float charge when the load is supplied 48vdc (only different here being that there is no inverter... just DC to DC load).
Many thanks...
ShmoJoe