July 2021

Hello Reader,

It’s July and we are in the heart of summer. I hope everyone is having time to enjoy the warmer weather.

This month we are discussing the need for a generator and if you need one when you have a UPS system, or vice versa.

If there is a topic you want to know more about, please send me an email.

As always, your feedback is welcomed and encouraged.

Thanks again for reading.

Rob

​rob@robdelauter.com​

​Catch up on past newsletters.​

Generator, UPS System, or Both?

While planning this month’s newsletter, I got a call from a customer whose critical load had just lost power. The building had experienced a power outage the night before when storms had moved through the area. As we talked about what happened, I research the last preventive maintenance. The technician found the batteries were six years old and showed signs of failure.

As has been the case several times throughout my career, the customer did not know why they had lost power to the critical load when they had a working generator.

To understand why, we need some background.

First, most of today’s IT loads, computers, servers, phones, etc, cannot lose electricity for over 1/4 of an electrical cycle, about 17 milliseconds in the USA. More than that, they shut down. The best generator systems take 10 seconds to start, reach operational status, and support the load. This is over 500 times longer than the IT load can be without power.

But this is only half of the problem.

As part of the generator system, a device called an Automatic Transfer Switch, or ATS, is used to determine which source of electricity, utility or generator, powers the building. The utility is normally known as the normal source, and the generator the emergency source. When the ATS senses a loss of electrical power, it signals the generator start. After the generator is at the proper voltage and frequency, the ATS changes position supplying emergency power to the building.

The ATS will also sense when utility power returns and after a predetermined time, it transfers back to the normal position, and the generator shuts down. During the time it takes for the switch to change between emergency and normal positions, there will be a loss of power to the building.

This is when we need our UPS System. It supplies power during these critical transfers. It is in series with the ATS and load and acts as a bridge supporting the load between the two sources (Figure 1.) Without a UPS system, or one not working, the load would lose power during these transfers.

Back to the question, do I need a generator, UPS system, or both? Well, it depends.

If you are only supporting mechanical and noncritical loads, a generator could be all you need. If you only need several minutes of battery backup time to allow you to safely shut down your IT loads, a UPS system alone would work. However, if you have critical IT loads that need to be supported for more than a few minutes, you will need both a UPS system and a generator.

You can learn more about how UPS systems and generators work together in my book, "UPS Handbook, A Layman's Guide to Uninterruptible Power Supply Systems".​