I got a multi-function laser printer for my home office. It replaced
an old laser printer that I had. This new printer causes the lights
to dim in the whole house when I print. While it prints, the lights
rhythmicly dim. This stops once the printer goes to sleep. My old
printer never did that. I ended up buying a new laser printer (for
unrelated reasons) and it does the same thing(if not worse).
I tried plugging it into different outlets without a difference. This
latest printer(Dell 1815dn) pulls 450 watts while printing. Here's
the spec sheet if you're interested:
Anyways, this bugs the heck out of me and my wife. Especially when my
wife prints out large pdfs while I'm reading :) I read about this
phenomenon on the group and know that it's common...
This house we're renting was built in the 1950s and so I'm sure it
doesn't have the greatest electrical service.
But my question is how to fix it. Since we're renting I don't want to
make any drastic electrical system changes(cant actually). I was
thinking a UPS would work or maybe a power conditioner since I'm
assuming that the draw from the printing is so high that the rest of
the appliances are being starved. If a UPS were in the mix to provide
this extra power then the rest of the appliances wouldn't have a
If my solution theory is correct, any idea what size UPS I will need?
I'm hoping I don't have to spend a lot of money for it but who knows.
Thanks for your help/suggestions/pointers
Does your light dim when your fridge kicks in or you use mirowave oven,
etc.? UPS = uninterrupted power supply, what makes you think UPS is
helpful? Maybe your place's wiring is at the borderline approaching max
capacity and that extra load printer is it. Laser printer has
fuser(heater which draws some current when printing).
Hi, no my fridge and microwave don't cause the lights to dim. In the
bathroom, the hair dryer does cause the lights to dim but only in that
My rational for the UPS solution was that since the printer runs at
450 watts when printing, then, say a 600 watt (1000VA) UPS battery
would act as a buffer during the high load times. Doesn't this make
Something weird. A hair dryer or electric kettle or a toaster each
take more than twice that 450 watt rating. A UPS without finding out
the real cause sounds like an expensive solution, possibly bypassing
finding the real cause of a potentially dangerous situation?
No. The printer likely does not draw enough current to drop the
voltage low enough for the UPS to switch to battery operation. So the
UPS will do precisely nothing, but the load will still cause your lights
to dim slightly. The printer probably works fine down to 95 V or so,
while your lights will visibly change in brightness with only a few
percent change in line voltage.
There are UPSes that provide line voltage regulation via a multi-tap
transformer. But they only adjust voltage for the device downstream.
The lights are upstream of the UPS, so they'll see as much voltage
change as ever.
The right way to fix your problem is to run a new circuit for the
printer, one that doesn't share wiring with any lights.
A simpler fix: print large documents just before going to bed.
That's probably referring to an "on line" UPS, which continuously
converts AC to DC, then back to AC using an inverter. This is larger
and more expensive (because the electronics have to run all the time,
not just when there's a power failure) but it still won't solve your
With an on-line UPS, the circuitry is designed to never discharge the
battery when AC power is available. So when your printer's fuser turns
on, it draws 400 W or so extra from the UPS, which will in turn draw
*more* than 400 W extra from the AC line. So it will have even more
effect on your lights.
The only way to prevent a UPS from affecting house voltage at all is to
unplug the UPS just before you start printing, so it doesn't draw any
power from the house and the batteries supply all the power. However,
you'll need a *big* UPS for this. It needs to be able to supply the
startup surge of the fuser, not just its steady-state running power.
Also note that most UPSes will operate for only 5 minutes or so fully
loaded - if you want to print long documents, you'll need one with more
battery capacity. When the batteries have been discharged, it takes
many hours for them to recharge, so you can't print very often. And,
finally, doing this very often will shorten the life of the batteries.
UPS will only cure symptoms. Worse, many UPSes in battery backup
mode output electricity so 'dirty' as to harm some small electric
motors - such as those inside a laser printer.
Those lights are dimming because wires have loose connections. The
fact that some appliances cause dimming and other don't helps to
locate a connection failure. Age of wires make no difference. Either
connection of wires is completely good OR that connection is bad and
If wires enter wall receptacles in rear, then that could be reason
for defective connections. Simply remove cover plate to look inside.
Wire must be fully wrapped around screw on side of receptacle.
Not only might some lights dim. Other lights may brighten. Which
do and don't? Well, basic facts such as what outlets share common
circuits, which on same side (phase) and different side of AC electric
mains box, etc - these facts will be necessary to answer your
A UPS is a fool's solution - a classic example of curing symptoms.
The dimming could, remotely, be an indication of a human safety
problem. Why then would you cure symptoms? Find and fix the problem.
Author is not talking about a $500 or $1000+ UPS to address light
dimming from a laser printer. Other plug-in 'solutions' that might be
implemented are even more expensive. Still that UPS would only cure a
symptom. Symptom that may also be related to a potential human safety
problem. Fix the problem. It's cheaper. It's safer. A UPS will not
solve the problem. At best, a UPS can only cure symptoms. Laser
printer must not cause oscillating light dimming. More symptoms of a
correctable wiring problem - more likely a simple and inexpensive
solution - a loose wire connection.
Most UPSes are less than $200 types. Computer grade UPSes that can
even contribute to damage of small electric motors - and again are no
solution to a wiring problem. Even a voltage regulator will cause
increase current - even worse light dimming. Still does not solve
Any discussion of a plug-in solution should have been terminated up
front. Wiring problem is probably a loose connection. Fix the
problem; do not cure symptoms.
Laser printers do draw a lot of current when starting up. They vary and
some do a lot more than others. I have two laser printers and if I put
either of them on the same circuit as my UPS they trigger it. However I
have several circuits in the area so they each are one a separate line and
the UPS-computer are on a third line. No problems. One printer will
slightly dim my overhead light and the other one dims the hall light outside
my library. Works for me.
Note: running 12 gauge wire rather than the 14 gauge that was there would
likely reduce the effect, but it does not bother me so I never bothered.
Most UPS's warn against connection to a laser printer. The new laser
printer sucks up more power than the old so it can warm up faster and get
the first page out faster. That was true of my Xerox, Brother, and Minolta
laser printers. All dimmed the lights. Interestingly, my 1 year old Epson
color laser multifunction machine (yes it is color and laser) does not cause
the same dimming.
I have a color laser printer in a
commercial building that causes the lights
to dim when it starts printing. A UPS
usually will not help because on
the UPS, the line is connected straight
through to the load (printer) until
the voltage drops below some number.
There are UPSs where the load
runs on the inverter all the time and
the AC line just keeps the voltage
across the battery .... i.e the battery
floats, as someone mentioned. But,
these are few and far between. BTW, the
aforementioned laser IS on
a UPS and the problem still occurs.
And, the laser blew up when the
line voltage jumped to 180 volts due to
a bad neutral problem in the
building. Apparently, some UPSs don't
protect against over voltage.
In the US, apparently the line loads are
not governed as much as in some
countries. I have an Allen Digital
computer organ where you can active
many electromagnets to lift or lower the
stop tabs in varying combination.
This thing does the same thing with the
lights as your laser printer. It
was so bad that I connected is to an
outlet at the other end of the room
which happens to be on a different
circuit where I don't see the problem.
I understand that Allen organs for
export don't have this problem. BTW,
The room where the organ is located is
wired with aluminum wire, so the
resistance is higher, making the problem
Properly-functioning aluminum wiring should not have any effect.
Aluminum is less conductive than copper for equal cross-section area,
so the electrical code required use of aluminum 2 gauges larger than
the copper that would be used for the same load. This makes the
resistance per unit length about the same for the two wire types, and
you *shouldn't* see any worse dimming with aluminum.
On the other hand, aluminum is notorious for connections increasing
resistance over time, so this may be an indication that you have an
aluminum wire connection that is degrading. Excessive dimming is a sign
that something is wrong, not a normal side effect of aluminum wire.
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