A line-interactive UPS regulates the mains supply voltage to make sure that the power supply to your equipment stays within a certain specified tolerance.
This has a stabilising effect, using a system sometimes called Buck/Boost, and sometimes called Automatic Voltage Regulation, to smooth out any variation in power supply voltage or frequency.
Although there is a slight delay, it is very small – on the order of milliseconds – during which time the inverter engages and starts to supply the necessary DC power from the UPS batteries, converted into usable AC power for your equipment.
In general the effect is similar to that of an online UPS, but is suited to slightly less critical applications, whereas with an online UPS the tolerance can be much tighter and the few milliseconds of delay are eliminated.
When to use a line-interactive UPS
A line-interactive UPS can be beneficial if your supply voltage is erratic – even only very slightly, but beyond a tight tolerance window.
In many cases an online UPS is more than enough to overcome this, whereas the ability for a line-interactive UPS to compensate for peaks and troughs in the supply voltage is perfectly adequate.
However, you should still diagnose any mains supply problems, as continual charging and discharging of the UPS batteries to account for repeated interruptions in the power supply can eventually lead to a loss of capacity.
Can I extend a line-interactive UPS?
If you need increased capacity from a line-interactive UPS, it may be possible to attach additional UPS batteries to it, enabling it to cater for a longer mains outage before equipment has to be powered down.
This can change the overall purpose of the UPS system, from giving you a few extra minutes to power down without data loss, to keeping equipment up and running while you put business continuity and disaster recovery plans into effect.
Once depleted, external UPS batteries will also need to be recharged ready for the next incident; however, external chargers can be attached to allow for this, so that the entire battery array does not have to be recharged via the line-interactive UPS unit itself.
This can make systems highly scalable in terms of capacity, giving you a good window of operations to take action during a power cut, and to potentially restore the mains supply without having to power down any of your electrical equipment at all.