Frequently Asked Questions
What size UPS system do I need and how long do I need it to run for?
UPS Rating/Size:
UPS systems are typically rated in either kilowatts (kW), volts amps (VA), or kilo-volt-amperes (kVA). While VA or kVA power rating represents the power limitation accepted by the UPS, the watts rating is the power output of the UPS and determines the unit’s ‘real power.’
How to size a UPS:
To size a UPS system, you can calculate the total power requirement for the equipment (load) you want to protect and then multiply that number by a factor to account for growth:
- List equipment: Make a list of all the equipment that will be connected to the UPS
- Find power consumption: For each piece of equipment, find the voltage (e.g 230V and amperage (eg. 3A) from the nameplate or technical data sheet.
- Calculate watts rating: Multiply the voltage and amperage to get the wattage (w or kW) rating for each piece of equipment.
- Add up all the watts or kW ratings to get the total watts requirement.
- Multiply your power requirement by a factor: Multiply the total watts or VA requirement by a factor like 1.15 or 1.25 to account for growth and headroom.
When you plug your UPS into the mains supply power (AC) it reduces the available power (watts) to apparent power (volt-amperes or VA).
The ratio of these two numbers is called the power factor. Power factors differ depending on the UPS. All our UPS data is available in both watts and VA, so be sure to use the watts rating of the UPS (or if you want to calculate the VA you will need to calculate the volts x amps x power factor (this is shown on the datasheet) of the UPS).
Under sizing a UPS can cause immediate problems; while oversizing it will waste energy and space. The load on a UPS should not exceed 75–80% of the UPS’s capacity.
How long do I need the UPS batteries to run for?
While the load is the total equipment the UPS will be tasked with protecting, you also need to determine how much time you want that load to stay up and running for during a power failure. This is the UPS runtime. Most UPS have an internal battery that will supply a limited amount of power if mains power isn’t available. Many UPS models can also incorporate additional battery packs to increase runtime by minutes or hours. The battery capacity is measured in AH or Amp-hrs.
If you just want a solution that gives you enough time for your building’s generator to come online or to save work and safely shutdown all the connected equipment, then a UPS with an internal battery with 10-15mins will be sufficient.
NB – There are also software options available for most systems that will perform these actions in the event the systems requiring saving and shutdown are unmanned. If you don’t have a generator and you require the power to remain up and running during an extended outage, then you must rely solely on UPS batteries and may want to consider longer battery run times.
How to Calculate UPS Runtime:
You can calculate the load by gathering measurements and completing a series of simple steps. It is important to note that while adding more batteries to a UPS can increase the battery runtime to support the load, it does not increase the capacity of the UPS. You must first ensure that the UPS is adequately sized for your load, and then add batteries to accommodate your runtime needs.
The Socomec UPS sizing tool is available here
Or if you want to calculate the runtime manually you can:
- Multiply the battery rating (in Ah) × the battery rating (in V) × the number of batteries × the battery efficiency. (This information can be found on the applicable UPS datasheets)
- Then divide that number by the load in watts (w).
What if I still don’t know what I need?
Focus Power engineers are here to help you. If you need advice specifying your UPS, then please give us a call or drop us an email. We will be happy to talk you through it, or if you have a bigger project then we can come to you to conduct a completely free, no obligation site survey. We offer completely independent guidance and will only offer you the right equipment for you based on your unique requirements and budgets.
