Well, we’re here again to answer the question of how long will a UPS actually last in the event of a power cut, but first, let’s clear up one of the biggest misconceptions…
Runtime has nothing to do with the rating of the Uninterruptible Power Supply, but everything to do with the battery.
Got it? Well to help that sink in think of it this way – when running from the battery the Uninterruptible Power Supply has to get the power from somewhere right? So it follows that the bigger battery it has the more power is available and therefore the longer the system will last. Don’t get confused with the fact that a high capacity unit can deliver more power. If the power requirement is 1000W, then a 1500W rated unit with 12 battery blocks will deliver more runtime than a 3000W unit with 6 battery blocks.
It is true, however, that higher powered UPS Systems tend to have more batteries than the lower powered one’s. This is where the misconception has arisen, in that by using a larger UPS for a given application or load, you would have tended to have got more runtime due to the increase in battery capacity, not the increase in power capability.
The moral here is, in order to get the longest amount of runtime for your given application, the best solution is not necessarily to opt for the highest powered UPS within your budget, but to opt for an extended run UPS System that meets your load requirements and add in batteries to support it.
For example, let’s assume you have a small office, and you want to run a computer with some peripherals and some lights and the total loading will not exceed 250W (just an example).
The VFI3000T, rated at 2700W, will provide around 72minutes of runtime.
The VFI1000T+Cab, rated at 900W, will provide 2 hours of runtime.
Simply because the VFI1000T+Cab is a higher battery capacity.
The conclusion is, the UPS rating is to ensure it is powerful enough to drive the load, the battery is what gives you the runtime.