Why does my UPS do this?

[Mixolydian]

I don't know a whole lot about how UPSes work, so I'm wondering what causes this:

I have my computer/monitor and a couple other things plugged into a UPS. I recently moved a laser printer to this setup, but it is NOT plugged into the UPS in any way - it is plugged directly into the wall. Whenever the printer starts warming up to print, the UPS starts making a humming noise and cuts power to some (but not all) of the connected devices for about 5-10 seconds, then resumes normal operation.

I could understand the printer overloading the UPS, but like I said, the printer is not plugged into the UPS at all. Any ideas?

 

[NutBucket]

Its causing enough of a power dip to cause the ups to come on to maintain power to the connected devices.

 

[greenhawk]

I would agree with the above poster, the laser printer is effecting the mains power so the UPS is tripping on to protect the connected equipment. You will also probably find that the UPS does not provide power to all outputs when the mains power is off.


depending on your UPS, you might be able to turn down it's scencativity to power fluctuations but most cheap ones will not have that option.

 

[Mixolydian]

Thanks. It is a TrippLite UPS and it does have software control, but I don't think you can adjust those kinds of parameters. Guess I'll just have to live with it.

 

[Red Squirrel]

It's a common issue I run into all the time. Depends on the house/wiring/printer/computer's PSU and UPS. Lot of variables. The printer causes a brownout on the line because it draws lot of power at startup, but the UPS does not react fast enough due to it not being a true cut black out, thus trips, but slightly too slow, and some stuff turns off. Some times it will in fact trip fast enough. Maybe it depends at what point in the AC phase it was at when the brown out occurred, that's just my theory.

You can unplug the UPS before printing to avoid it, as it will force a black out and will react faster. Sometimes plugging the printer into another outlet can help too.