The size of UPS units indicates their output power capacity.This rating is in VA (volt/amperes) or kVA(thousand volt amperes)which is preceded by a number like 500VA or 2kVA.To the lay person this can be confusing,because the power consumption label located on most equipment is typically rated in watts or amps,not VA.When the rating is specified in VA,it can become more confusing,as the input power factor of the equipment must also be considered.Most UPS manufacturers state the output power of their UPS products in Watts or Amps somewhere on their product box or in their published specifications.Most manufacturers make their product specifications available on their web sites.
To determine the input watts required to power a specific piece of equipment, multiply the input current (in AMPS) required operating the equipment times the utility (Supply voltage) normally 220V.In the South africa the utility voltage is 220Vac, so for a piece of equipment requiring 5 Amps, one would multiply (5 x 220) = 1100 watts.Do not confuse the input plug rating of a piece of electrical equipment, (15, 20 or 30 Amps) as the actual current required to operate the equipment.The actual input current required is usually specified on a label located somewhere on the equipment...
Determining the power requirements for computers (the simple rule of thumb).
For the majority of PC and Mac based computers having up to a combination of four hard and one CDROM drive,with one monitor (up to 19”), one network router or modem, selecting a UPS with a 350 watt output will be more than adequate.
Determining the power requirements for your computers (the absolutely safe method).
Should you have more equipment that needs to be protected, or are unsure of the previous method do the following?
1.Write down all of the stated input currents and wattage requirement for every piece of equipment to be protected and convert any current ratings to watts,add them up to determine the total wattage requirement.Be suspect of any individual current ratings that state 15 amps as it is highly unlikely that any office equipment would require that much current.This usually represents the full current rating of the typical electrical outlet found in most households and offices in the S.A. .Remember the stated input rating on computers and other electrical equipment in most cases represents the worst case requirements.
What you should know about laser printers, laser copiers and faxes machines.
Incorporating a laser printer,copier or any other equipment incorporating a heating element called a “fuser” can cause UPS unit problems.The best approach is to avoid connecting them to any UPS.The fuser randomly switches on and off, requiring a substantial amount of current with every on cycle.We have determined that to successfully power a typical laser printer requires UPS capable of more that 1200 watts.Additionally many or these devices do not work properly with a UPS that does
not have a true sinewave output. Should it be necessary to protect this type of equipment,install a separate over sized SBS or UPS that powers only that piece of equipment?
Computer with a 17"/19" monitor --- 180 watts
Servers --- 180 watts
Inkjet Printers --- 120 watts
Microwave Ovens --- 800 watts / 1200 watts
House Lights --- 40 / 100 watts each, depending on the globes
Satellite dish and decoder, television, dvd --- 300 watts