Bizarre Interaction: Laser Printer - UPS

[JonM]

I have a very nice Intel "Skull Canyon" NUC that I use as a portable Linux workstation, mostly at my daughter's house where the power is somewhat unreliable. So, I replaced the UPS on my home network equipment and took the old (it could be > 10 years old) UPS to my daughter's house and placed it next to a laser printer. Apparently I had not printed anything since doing that until yesterday. Spooling a job to the printer caused the UPS to beep and the battery backed outlets to drop out very briefly, but long enough for the NUC to turn off.

The first time I did not understand what had happened, so I did it again with the same results. Moving the UPS a couple of feet away solved the problem, of course. At some point I will bring a scope and appropriate probes to see what I can observe. I'll at least be able to determine how long the AC drops out, maybe I will be able to observe a magnetic pulse as the laser printer fires up.

For the record, it's a Brother HL-L2380DW printer and an APC Back-UPS LS 700. UPS was on the right hand side of the printer.

[madires]

Is the laser printer powered by the UPS?

[kizmit99]

I have a similar setup - a Brother MFC-8840D (not on the UPS) and an APC Back-UPS XS-1500 for the computers and other gear.  When the printer spins-up there is a very noticeable "hit" on the AC line (evident by the lights dimming) and the UPS kicks in briefly.  In my situation the UPS is working as expected and protecting the rest of the gear from the weirdness on the AC.

My guesses a to what to check:
1) Is the printer plugged into the UPS?  If so, it wouldn't surprise me if the draw from the printer powering up is too much.  I would try plugging the printer directly into the wall.  Preferably a different outlet altogether (you may get lucky and be on the other hot leg).
2) Perhaps the batteries in your older UPS are simply bad and when the UPS switches they can't provide the necessary power to run the computer - resulting in a power drop out. 
3) Perhaps you plugged the computer into one of the regulated-but-not-battery-backed-up outlets on the UPS (if your UPS has those).

[IDEngineer]

Long ago I helped design laser printers (even have a long-expired patent on a motor drive concept for them). Many people do not realize that heating up the fuser in a laser printer can require a surprisingly large amount of current. Not surprised at all if your UPS is seeing that and reacting to it.

EDIT: Even less surprised if you're asking a 700VA UPS to power a laser printer.

EDIT2: On a related note, some equipment can be incredibly sensitive to events on the mains. My Hakko FX-951 soldering station refuses to run from a small gasoline generator, for example... just pops up an error on its display and will not function. Nothing else I've tried so far complains, including scopes and special-purpose full-of-tech battery chargers. That UPS may be similarly extra sensitive to mains events in its attempt to do its job, which is - after all - to protect your equipment from mains events.

[raptor1956]

Even if the printer isn't plugged into the UPS the power draw of the printer is very high and could cause voltage fluctuations that the UPS sees and responds to.  When the fuser is heating up the power draw can be over 1500W and since the power to the fuser is pulsed to maintain temp you are going to see spiking of the voltage.  You can often see this as flickering of incandescent lighting though now a-days most people use either compact florescent or LED which tends to minimize those effects.


Brian

[JonM]

The printer is not plugged into the UPS but they are plugged into the same outlet. However, the problem occurs only when the UPS is sitting very close to the side of the printer.

Moving the UPS to a desktop about two feet away, with no change in cabling, prevents the shutdown. I'm thinking that the heater turning on could generate enough of a field to affect a relay in the UPS, but I have made no measurements or done a teardown so far. The only test equipment I have with me at the moment is a 121GW. I'll have to bring a scope and maybe a 34465A with DIG & MEM options and look for transients.

Even if the printer start up pulled down the line voltage I would hope that the UPS output would stay up, that's it's job! I suppose that I should pull the UPS AC line from the wall to verify that the UPS is actually still doing it's job...
 

[madires]

My guess would be an EMI problem or the high voltage supply for the drum causing the UPS control to go crazy.

[JonM]

And.... I have verified that the UPS is not doing it's assigned duty.  Pulling the AC plug results in loss of output on the battery backed outlets even though the self-test passes and the Replace Battery LED is off.

So, the interference due to the printer start-up when the UPS is physically close may look like an AC line event and cause the UPS to go into battery powered mode which fails. I will still look for the source of the issue, but it's probably time to order another UPS.

[Halcyon]

I will still look for the source of the issue, but it's probably time to order another UPS.

Probably not a bad idea to upgrade to something a bit newer. Your EMI/laser printer issue aside, I've had a small handful of machines which are very sensitive to UPS transfer time and causing reboots, although this is going back many years now. Just about all computers and devices will survive the <10ms transfer from mains to battery and back again.

[NiHaoMike]

Even if the printer isn't plugged into the UPS the power draw of the printer is very high and could cause voltage fluctuations that the UPS sees and responds to.  When the fuser is heating up the power draw can be over 1500W and since the power to the fuser is pulsed to maintain temp you are going to see spiking of the voltage.  You can often see this as flickering of incandescent lighting though now a-days most people use either compact florescent or LED which tends to minimize those effects.

3D printers with heated beds also tend to do that, especially supersize CR-10S that have been upgraded with surplus server PSUs and aftermarket bed heaters. I have found triac dimmers to be especially sensitive to that sort of small cyclic voltage variation - my Prusa MK3 will cause the LED light on my desk to flicker if I use a dimmer with it. (Tried several different dimmable LED bulbs and two different dimmers, some combinations of which would just flicker on their own. Ended up not using a dimmer.)

[GreyWoolfe]

I have a Brother HL-L5100DN and APC smartUPS 1500s in my office and the same thing happens even though the printer is plugged into an outlet and no where near the 3 UPSs.   They have an instantaneous response so nothing shuts off.  The funny thing here is that I also have an HP LaserJet 400 color M451nw that doesn't freak out the APCs; it sits next to and it is plugged into the same dual outlet as one of the UPSs is.  I know, however that my office, which is an addition that the original owners built out of what once was a patio, was not only built by Moe, Larry and Curley, but they wired the room also.