What size generator do I need with a UPS?

Do I need a UPS? The short answer, yes, and that’s not the sales team pushing me to say that. A UPS (Uninterruptible Power Supply) is needed whenever you have any electrical equipment plugged into the mains, and as such required power at all times. The UPS provides you stable power in the event of a power cut, instantly. It takes roughly 20ms, for context, it takes you around 200ms to blink. As more and more of us are working from home, a UPS is a need rather than a want, now more than ever.

In this blog we answer the typical UPS frequently asked questions. You will learn how to size a UPS (Uninterruptible Power Supply), how to size a generator when working with a UPS and much more.

What is an Uninterruptible Power Supply?

What size generator do I need with a UPS?

You will need to up size your generator, by 25-40%. For example, if your UPS requirement is 100kva, multiply this by 1.25 and this will give you your generator size, 125kva.

Why do I need to up size my generator, when working with a UPS?

When sizing, you will always need to upsize a generator, the generator size must exceed the UPS power rating. This is because the generator needs to cover the mains load and recharge the uninterruptible power supply when the batteries are depleted.

Why do generators and UPS work together?

A UPS covers the initial critical load requirement, whilst the generator is reaching its optimum running capability which is typically 15 seconds.

For example, a data centre has critical electrical equipment, which can’t afford any downtime, the UPS would take the initial load, whilst the generator turns on, once the generator reaches load it will take over the demand of the data centre and charge the UPS.

Likewise, a hospital cannot afford any downtime, so the UPS will kick in to take the initial load for the time it takes for the generator to turn on.

Generators and UPS can also split the load between them, which is called load shedding.

Can you install a UPS after a generator has been installed?

Yes, occasionally the load demand increases on a building, a UPS can be installed to expand the back power capabilities. On this occasion when calculating the size of the UPS, the generator would been to be 1.5 – 2 times higher than the UPS.