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Why shouldn't I attach laser printers or scanners to a UPS?


I have an FSP EP1000 UPS.


The User's Manual says:



CAUTION: NEVER connect a laser printer or scanner to the UPS unit. This may cause the damage of the unit.



Why is this restriction?



Answer



Updated


Why you shouldn't connect a printer to a UPS


(Unless you accurately size the UPS for peak power requirements)


When turned on, Laser printers draw a high current to heat up their fuser roller. A typical UPS cannot cope with such a spike.


Descriptions of the problem by UPS manufacturers do not go into details.


The problem may be one or other of



  • The initial inrush current at start-up, This can be seven or more times the average operating current of the printer.

  • Initial power-on when the fuser is heated to the temperature needed to fuse toner. Subsequent re-heating of the fuser may be periodic or may occur when the printer switches from and idle state to full-power to satisfy a print request after a period of inactivity.


Fuser temperature is up to 200 °C (392 °F).



Printer Information


From HP specification for LaserJet 3200


Power consumption   135 watts

During Printing: At nominal line voltage.   
  Model A (120V): Maximum of 700 W, Average of 210 W 
  Model AB (240V): Maximum of 625 W, Average of 210 W

Inrush Current: (Duration: significantly < 1 second)    
  Model A  (120V): 23 A peak (20 deg C, from cold start) 
  Model AB (240V): 40 A peak (20 deg C, from cold start)

Note:


If we disregard power factors and other AC complications,



  • The (overall average?) power usage quoted at 135W at 120V would draw a little over 1 Amp.

  • The active average power usage quoted at 210W at 120V would draw just under 2 Amps.

  • The maximum active power usage quoted at 700W at 120V would draw well over 5 Amps.


The inrush current is an order of magnitude larger than average operating currents.


In conjunction with other equipment, the 700W max during printing could overload a small UPS.



UPS Information


For example Belkin say



A laser printer or scanner draws significantly more power when in use than when idle. This may overload the UPS.



APC say



APC recommends a [UPS] that is sized for the maximum power draw of the laser printer as defined by the manufacturer. This is typically a 1500va or larger UPS. Even small laser printers can have very high maximum power draws due to the nature of the technology.



Anecdotal reports say


Laser printer usage is sometimes reported as causing voltage sags in power circuits such that lights noticeably dim in the building for a brief moment.



Here is an example of power used vs time.


Brother 5250 current draw


From http://www.johndearmond.com/2008/08/04/laser-printers-and-inverters/


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