Matching your UPS to a generator

If your business has critical infrastructure, you probably have at least one generator or UPS to keep you going in case of power failure; however, if you are just using a generator, should you also use a UPS?

Image Credit

Contrary to how it may appear, you should use a UPS in addition your standby generator to ensure your IT infrastructure keeps going through power failures without a hitch. Here is a brief outline of why this is the case and some tips on how to choose a UPS to pair with your generator.

Why match a UPS to a generator?

The basic reason is that business-critical IT infrastructure is very sensitive to power fluctuation. This even applies to exceptionally short drops in power, as your generator may not have time to kick in. The time it takes for a standby generator to come on is typically in the range 2-10 seconds – far longer than your server infrastructure could cope on its own.

Standby generators also provide power in a much larger range of frequencies than are normally provided, even with a good electric governor. A UPS operating between your generator and IT infrastructure normalises the power your business-critical systems receive, ensuring they keep working as you would like them to.

Image Credit

Online or offline UPS?

When pairing with a generator, the only real choice for a UPS is an online UPS, perhaps from an Eaton UPS distributor such as With the frequency issue mentioned above, any offline or hybrid UPS will not be the primary source of power for your IT infrastructure and will be receiving the fluctuating power frequencies from your generator, potentially causing problems or damage.

UPS and generator scaling

At an absolute minimum, you will want enough UPS capacity to keep your business-critical infrastructure running for about five minutes, giving your backup generator time to kick in or for your systems to be safely powered off in the worst-case scenario.

For generator sizing, you should consider your UPS capacity. Account for power loss through conversion to battery power, which is usually about 15 per cent, and consider how long your generator will typically run for. For longer power outages, you will not want to exceed 65 per cent of the maximum generator capacity or the maximum step load.