 |
|
|
 |
|
|
How to Size a UPS
To correctly size a UPS one must understand the relationship between the load level and the run time as well as the capacity of the UPS.
The run time that a UPS provides is the number of minutes that the UPS will be able to provide power from the battery for a given load level. Since driving more equipment requires more power to be taken from the battery, driving more load will result in shorter run time. A UPS with a larger battery, or with an add-on battery pack, will provide longer run time for a given load size. Run time is critically important because it tells you how long a power outage the UPS can handle before the battery runs out. This chart shows the typical run time for the Sanyo Denki ASE model UPS based on the load.
Ambient temp 77º F (25º C)
All UPS have a nominal maximum capacity. For example, the ASE stand-alone UPS has a maximum capacity of 1000VA or 800W.
To understand these two values, one must understand the difference between apparent power, which is the power provided as input to a device, and actual power, which is the power the device actually uses. For most complex devices, these are not the same. The ratio of actual power to apparent power of a device is its power factor.
The load on a UPS cannot exceed its apparent power load limit in VA, nor can the load exceed its actual power load limit in Watts. If the ASE model UPS is driving a load that has a power factor of 80%, then the apparent and actual power limits are the same. But if the load being driven has a power factor higher than 80%, do not use the total VA limit because the watts used will be above the wattage limit. Conversely, if the power factor of your load is below 80% you will be limited by the total VA.
For most PC power supplies the power factor is around 60%, so calculations based on total VA should be correct. However, some PC power supplies are "power factor corrected" (power factor of 100%).
Unfortunately, most PC power supplies are rated in terms of their maximum combined output power in watts (e.g. "a 300 watt supply"). Most of these supplies never operate at their maximum output. Since excess capacity results in longer run times, most people choose to size UPSs fairly conservatively.
For a given UPS voltage, add all the current values in amps and multiply by the voltage. (If your load has a power factor greater than 80% you should also add up the power requirements in watts).
For example, to calculate the requirements for two PCs which each draw 1.6 amps, and one monitor that draws 2 amps - add up the currents - (5.2 A) and multiply by the voltage (120V) for a total of 624VA. This is well within the capacity of the Sanyo Denki ASE 1kVA UPS regardless of the power factor. Reference the chart above to see that the ASE could power this load for well over 10 minutes. Expansion capability is highly recommended. In this example, an additional 3 amp load could be added and still maintain over 5 minutes of run time.
Sizing for Redundancy:
Due to the true parallel operation of SANUPS modular UPS systems, it's possible to configure redundant, fault-tolerant systems Like a RAID disk array, you buy one module more than your minimum requirement. To size an "N+1" system, simply calculate your minimum requirements or N and then add one additional module. For example, to back up a load of 2.6kVA would require three ASE-H 1kVA Modular UPS; by configuring a four module ASE-H system fault-tolerance is achieved.
If you have questions or concerns about sizing your UPS, call us or send an e-mail! We can assist with all aspects of sizing and configuring your SANUPS system.
Power Systems Division
Sanyo Denki America, Inc.
468 Amapola Avenue
Torrance, CA 90501
Tel: (310) 783-5400
Fax: (310) 782-8021
power@sanyo-denki.com
