On 16/11/13 00:23, steve-ALUG@hst.me.uk wrote:
I must admit I'm surprised that the ratio of the larger run-time to the smaller is not constant, but in all cases it's at least double. But it confirms that same manufacturer, similar technology, bigger VA => longer run-time.
It's just coincidence that the larger models happen to have larger batteries so for the same load you'll get more runtime
How is it a coincidence? Given the same battery technology, if you double the number of batteries, you're more or less double the storage capacity, and probably the VA.
Because The VA rating has nothing directly to do with the number of batteries. It is a rating of the AC inverter and associated electronics. A double rated UPS in terms of VA may or may not have twice the battery capacity. Even within a particular VA rating you can get wildly different battery capacities,
Take two models from APC's site, Compare SUA750ICH and say SMX750I (both 750VA)
If you were comparing over different makes you CANNOT rely on there being anything like a 1:1 relationship on runtime to VA. It just happens that APC like to spec *most* of their UPS's to 5 minutes at full rated load so tend to double the batteries for a double in VA, and then you add batteries via the expansion kits if you want more. But a 750VA UPS with 2 battery expansions is still a 750VA UPS.