Picking a UPS System

With the wide variety of UPS systems available to choose from, picking the right one for your application might seem like a daunting task.  This information provides some simplified helpful information.  Print this page and fill in your requirements.  Then select the UPS that meets the requirements.

 

TYPES OF UPS SYSTEMS

		Standby UPS	Line interactive	On-line UPS
A	Battery backup for blackouts (loss of voltage)	Yes	Yes	Yes
B	Surge protection	Yes	Yes	Yes
C	Voltage correction for brownouts  (low voltage)		Yes	Yes
D	Voltage correction for over voltages		Yes	Yes
E	Pure sine wave output		Usually	Yes
F	Generator friendly settings		Some	Usually
G	Extended Battery Run-time		Some	Yes
H	Short Battery Recharge-time *			sometimes
I	Always on-line (zero transfer time)			Yes
J	Rack mount models		Some	Usually
K	Cost	minimum	intermediate	slightly higher
L	Performance & Reliability	minimum	good	best

* Battery recharge time is a consideration when frequent back-to-back power outages are likely such as in some third world countries.  For these applications look for high capacity chargers in the UPS, chargers in each battery pack, or supplemental external chargers offered with some UPS systems.

 

SUGGESTED SELECTION STEPS

1	List nameplate operating (running) Amps and Volts for each item to be powered	Item ___________________ Item ___________________ Item ___________________ Item ___________________ Item ___________________	_____A  x  _____V = _____VA _____A  x  _____V = _____VA _____A  x  _____V = _____VA _____A  x  _____V = _____VA _____A  x  _____V = _____VA
2	Calculate VA for each item by multiplying Amps and Volts
3	Sum all the VA values to get total running load (or simply turn on all the loads and measure the Amps with a meter)		Total Running         ______VA
4	Assume Watts equals VA as this will provide margin in sizing and eliminates the need to determine the power factor		Total Running         ______W
5	STEPS 5 & 6 ARE RARELY USED Are there any high inrush items such as motors to be started on the UPS? If there are then for each of them calculate the difference between the running VA and the inrush starting VA.	Item ___________________ Item ___________________ Item ___________________	_____A  x  _____V = _____VA _____A  x  _____V = _____VA _____A  x  _____V = _____VA
6	Calculate the total additional inrush VA requirement by adding all inrush values that can occur simultaneously		Total Add'l Inrush    ______VA
7	Sum the running and additional inrush VA.  Most computer-grade UPS systems do publish a short-time overload rating but they are not really designed to use this capability for starting motors. Therefore, it is recommended that the total running and inrush VA be within the continuous rating of the UPS.		Grand Total            ______VA
8	Again assume Watts equals VA as this will provide margin in sizing and eliminates the need to determine the power factor		Grand Total            ______W
9	Determine how much battery run-time you will need: I you will be using UPS software to perform an automatic file save and computer shutdown then the standard 5-8 minutes may be sufficient. Or if you have an automatic standby generator the standard 5-8 minutes should provide plenty of time for the generator to start. But if you have to perform manual steps in response to a loss of power such as saving files or manually starting and connecting backup power then more battery run-time will be required (an hour or more). Or if you want to continue computer use without generator power then even more time may be needed (several hours or more).		Battery Run-time: _____ minutes minimum _____ minutes desired
10	What UPS output Voltages are required: 120V single phase, 120/240V split phase (provides combination of 120V and 240V), 208/220/230/240V single phase high voltage only		__________ Volts
11	How will the UPS be mounted? The most common and economical is tower mounting usually on the floor. Some models are available in rack mount versions, or in a configuration for both tower and rack mounting.  Circle one at right.		tower mounting rack mounting
12	Note any special features required such as communication ports, USB or relay cards, etc.		Options:
13	Select a UPS rating equal to or greater than the Grand Total VA and W figures calculated above that also meets all the other requirements above.  Easiest place to start is at the table at the link at right.	http://www.nooutage.com/UPSSystems.htm

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