On 15/11/13 20:04, Wayne Stallwood wrote:
As others have said VA rating has nothing to do with battery life..there is no time factor in a VA measurement so how can it.
Well, unless I'm very much mistaken (which I may be), the VA number is an indication of the amount of power the UPS stores. An indication, not an exact figure. Also by extrapolation, it gives an indication of how much power the UPS will be able to provide. If it didn't, why would they use the VA figure?
I would expect that given two UPSes from the same manufacturer, with similar electronics, and similar battery technology, providing a load within their capabilities, one with twice the VA of the other, the one with twice the VA would last roughly twice as long as the other.
There is no indication of run-time, because the run-time depends on the load. The lower the load, the longer the run-time.
Checking the APC website's quoted figures. http://www.apc.com/products/family/index.cfm?id=165&tab=models
I looked at the APC Smart-ups 750VA LCD RM 2U 230V and the APC Smart-UPS 1500VA LCD RM 2U 230V. I discounted the cheapest UPS, as it would probably be a cost-cutting version. I picked those two because one is twice the capacity of the other, and they are both LCD RM 2U 230V (whatever that means)
Load in Watts, Runtime in Minutes
Load 750 1500 Runtime Ratio 50 139 335 2.4 100 65 190 2.9 200 23 92 4
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. Or, if you want to increase the VA, you need to increase the battery capacity, either by increasing the number or size of the batteries, assuming the same battery technology. I can't see that as a coincidence at all.
, but it's possible to buy 1500VA UPS's with different runtimes.
Absolutely: different electronics, different types of battery, different manufacturers, a "cheapie" vs a "deluxe" version etc.
Not trying to sound argumentative, but what you're saying just doesn't make sense to me. Am I missing something?
Steve