Battery Backup Basics: An informational series about AC power management for the commercial AV and security industries.
Summary Information About Battery Backup Equipment
UPSs are seen more frequently in a required equipment list for sophisticated and mission critical systems. Following is useful information to consider when contemplating the purchase or specification of a battery back-up device.
UPS Design
There are three main categories of UPS technology: stand-by, line-interactive and on-line. Each occupies a different price point and provides different functions.
With a stand-by UPS, connected equipment is powered directly by the utility power until a blackout occurs. Then the UPS switches over to battery power. The quality of power conditioning provided by such a UPS prior to a blackout varies between models. Many of these units employ a “square wave” inverter, so the quality of the AC power can be less than needed for some electronics. Stand-by models are generally the least expensive.
Line-interactive UPSs provide automatic voltage regulation. This feature will provide more stable voltage which is good for connected equipment and can increase the voltage range in which a UPS can operate without switching to the battery.
An on-line UPS powers connected equipment directly off the UPS batteries 100% of the time. Utility wall power is used only to charge the batteries. In this way, the batteries serve as a complete buffer to isolate the load powered by the UPS from outside interference. This double conversion process provides the cleanest, most stable power.
Run Time
“Run time” refers to the amount of time a UPS will provide power once the main utility power is interrupted. Standard battery run time for a common UPS is around 5 to 10 minutes under full load and more than twice that under half load.
Run time is a function of the current load placed on the battery and the size of the battery. So, it makes sense that the smaller the load relative to the size of the battery the longer the run time. Over-sizing a UPS relative to the load is one way to get extended run time.
Most UPSs have warning indicators for loss of main utility power and for low battery power. A warning may also indicate when the battery is reaching the end of its useful life and needs to be replaced.
Some UPS models allow connection to external battery modules which provide additional battery capacity for extending the run time from several minutes to several hours, depending on model and power load.
Current Capacity
The current capacity of a UPS is expressed in terms of amperage. Most manufacturers also state the wattage capacity of their models. Because of the inefficiency of certain electrical loads it is probably best to select a UPS size based on the wattage of the UPS and the equipment to be powered. Both of these amperage and wattage figures should be stated by the UPS manufacturer. If only the amperage rating is available multiply it by the voltage (120) and power factor (approx. 0.7) to calculate the wattage that a UPS can produce. Select a UPS with a wattage rating a bit larger than the load.
Power Factor
The wattage, or real work, available from a UPS is a function of how efficiently that UPS uses electric current. That efficiency is stated as “power factor”. The higher the power factor the better. Many UPSs have a power factor of 0.70, meaning they convert 70% of available current into wattage. Models with higher power factors (0.80 or 0.90) use less power to do the same work and are, therefore, more economical and energy efficient.
Battery Life and Replacement
The typical life span for a UPS battery is three to five years. However, longer or shorter service life is possible. Proper battery care includes keeping the UPS plugged in and the batteries charged. The UPS and batteries should be kept in a cool (not hot), temperature controlled environment.
Batteries are replaceable in almost all commercial grade units. With the specification or a physical sample, generic brand replacement batteries may be available from a local battery supply business. Because of their weight, buying batteries locally may be preferable to having them shipped.
Most UPS batteries are sealed lead acid type. Some are made from lithium ion material. Batteries pose no danger with normal use. Follow printed safety instructions. Dispose of old batteries properly.
Communication
Many UPSs are capable of a communication link to a PC. This link allows remote monitoring and automated equipment shutdown as UPS power begins to drop. In more sophisticated systems it also allows integration of the UPS into a data network via RS232 or Ethernet communications protocol. Check the product specifications if it’s desired to turn UPS outlets on and off to perform a remote processor reboot on equipment powered by the UPS.
Wave Form
The waveform of normal alternating current (AC) voltage and amperage is a sine wave which can only be produced by a generator. When alternating current is derived from a battery (i.e. DC converted to AC) the waveform can be shaped by electronics to approximate a sine wave. Higher quality UPSs produce a high quality power output that appears to powered equipment as a true sine wave. Lower quality UPSs may output a “square wave” which lacks power characteristics needed by the power supplies of some electronic equipment.
Mounting
Because of their weight, rack mounting a UPS requires special consideration and hardware. Most rack mounted UPSs require additional mounting hardware which might not be included with the UPS. They should always be mounted to front and back mounting rails – probably as low in the rack as possible. Most rack mountable UPSs can also be mounted on their side as a “tower”.
Installation
For most UPS models, installation is as simple as plugging the UPS into the wall and plugging your equipment into it. Taking advantage of the monitoring and communications features of more sophisticated models requires some software loading and linking with a PC. Auxiliary battery modules come with instructions for connecting them to a UPS. Always review the owner’s manual before installing and using a UPS.
Summary
When power continuity or quality is important, define the size and nature of equipment to be powered and the role you want a UPS to serve. Then select a model with the design and battery capacity to provide that function. Contact Juice Goose for additional information or assistance.