DC voltage

Firstly, DC is direct current. It’s created within a UPS system most commonly by batteries, but sometimes devices such as Supercapacitors are used. A chemical reaction within the batteries creates the direct current, which feeds the inverter.

Batteries within UPS systems are usually supplied as a 12V type. Again, this isn’t always the case and you can see 2V, 6V, etc within UPS systems from time to time.

A UPS has a set operating DC voltage or a window of operation where the UPS can be configured to work from a scale of voltage, which allows for a much more flexible solution when trying to achieve a certain runtime or autonomy. DC voltage usually scales up with UPS capacity (kW or kVA). For example, a 600VA UPS may work on a 12VDC, meaning 1x 12V battery would be sufficient to feed the inverter. Depending on the manufacturer, an 800kVA UPS may work from 480VDC which would be 40x 12V batteries linked together. Often when UPS enters the 3ph range, DC voltage will remain the same throughout a product series.

The number of batteries connected together to reach the desired DC voltage is often referred to as a string. 1x battery string may be 40x 12V batteries connected together to achieve 480VDC.

With UPS systems, extension of runtime can be achieved by adding batteries to the UPS. Some UPS do not allow for this function, but nearly all online double conversion UPS do. When wanting to extend autonomy, you can double the battery quantity to do so which is often called a 2 string solution. Tripling the original battery quantity would be a 3 string solution, etc, etc.

Of course, adding more batteries isn’t the only way to extend UPS autonomy. You can also utilise higher capacity batteries to achieve the same goals, i.e. moving from an internal set of 40x 12V 9Ah batteries to an external 40x 12V 55Ah batteries. It is worth noting that redundant battery strings can be installed, to remove the single point of failure of a single battery string, however caution should be taken when considering the DC protection devices utilised.

Whichever way you wish to work the solution, utilising experts in DC power is essential. Direct current is often considered more dangerous than AC and most electrical contractors would prefer to leave this scope of work to UPS experts. Thankfully, TheUPSTeam Ltd are here to offer that service and more. Get in touch with our sales team today to see what the best DC solution is for you and how we can help to install it safely.