Things that were mission critical required backup in case the main electrical power failed. While other equipment may have benefited from a battery backup system, reasons (like cost and lack of understanding) precluded them from being incorporated into most residential systems.

Folks in the industry may refer to battery backup systems as uninterruptible power supplies, or UPSs. For this discussion, I’ll use battery backup.

Battery backup systems are designed to wait patiently for the power to fail.

There are a variety of types and prices out there, from simple, small systems that offer a very short amount of run time for a very small amount of current draw to systems that could potentially run large loads for many hours.

As with many things, it’s important to fit the tool to the job at hand and get the correct size and type for your application.

How They Work

Simple battery backup mechanisms operate on a stand-by basis. When power fails, these devices kick in.

There will be some sort of switching lag time involved with this type of system. These devices will act to supplement electrical power when a brown out situation occurs.

More elaborate systems will act in conjunction with the AC power. When power fails, they switch over to the battery. Again, a delay is present.

Even more elaborate systems will be line interactive, where the incoming AC power is converted to DC, run through the batteries and then reconverted to AC again.

These tend to reproduce the electrical wave the most accurately and cost the most. Since the circuit runs through the battery, these don’t suffer from switching problems.

The size of the battery will be determined by how much load will be drawn by the devices plugged into the backup. Most of the time, that load will be measured in wattage, just like a conventional light bulb.

The higher the number, the more power it draws. Many manufacturers of battery backup systems will offer charts that allow you to insert the wattage consumed and present various run-time options, predicated on the size of the batteries in their units.

When to Call for Backup

Computer systems were early candidates for battery backup systems.

Power interruptions aren’t scheduled events, and the risk of losing data that hasn’t been backed up is a compelling reason to install a backup system.

I recommend installing a battery backup on top of a surge protection device that covers both AC and the external network connections. The signal path is AC power to surge protection, and then to battery backup.

Your customer typically does not need all the computer peripherals protected by the backup system, but they should be protected from surges.

Contemporary audio and video systems are now prime candidates for battery backup systems. Today’s processors and whole-house audio systems, as well as control systems, are complex systems with lots of programming options installed.

Even voltage fluctuations on complex systems can cause buggy behavior, and the line-interactive style of backup is most effectively deployed there.

Devices that do not feature latching power switches, where the unit returns to the state it was in before power was interrupted, should really be considered for battery backup.

Extra consideration for backup should be given if the system is in an area with shaky power from the serving power utility company. Distance from the job site increases motivation for backups, too.