What UPS

[stafil]

I have a single outlet in my home office, to which I connect a floor lamp, a PC, a monitor and a space heater. When the heater turns on I can see the lamp going dim for a second or so. I assume because it's the heater draws too much current. I am afraid that this may affect the PC and Monitor and was thinking about getting a UPS for them. Question is, I am not sure if I need an online ups or if a line-interactive will be good enough. Thanks!

[tooki]

Your PC and monitor do not care. In all likelihood, they're specified to work on 100-240V, and it's unlikely your 120V is sagging all the way to 100V. 100V is the voltage used in Japan. And that 100V is just the nominal value: it's actually 100V ±10%, so as low as 90V. (This is why some power supplies even state 90V as their minimum.) If your 120V is sagging to 90V, you'd have to have massive problems in your electrical system.

Anyhow, due to how switching power supplies work, many of them work well below their rated voltage. (And on DC, too, since the first step is to rectify.) As an example, the Rigol DS1000Z series oscilloscopes are known to work on 48V DC, far below their rated AC input voltage.

If you get a UPS, get one if your power is unreliable and you have frequent blackouts or serious brownouts. Otherwise, don't bother.

[JustMeHere]

Tripp Lite.  All desktops should be hooked up to a UPS.  It helps protect data in the disk drives. With moden SSDs it might not be as big of an advantage.  If the computer knows it's on battery it will use RAM to cache disk writes.

[tooki]

Tripp Lite.  All desktops should be hooked up to a UPS.  It helps protect data in the disk drives. With moden SSDs it might not be as big of an advantage.  If the computer knows it's on battery it will use RAM to cache disk writes.

Hard disks have write buffers, and if power is lost unexpectedly, they actually use the rotational energy in the platters, running the motor as a generator, to finish writing the buffer to disk.

Obviously this won’t help on long writes, but I really don’t think a UPS is essential for most purposes anymore. Journaled file systems long ago eliminated the worst issues with improperly shut down systems.

[Jeroen3]

Is it on old incandescent of fluorescent lamp that it is changing brightness on voltage?
When you pull max current on a circuit you can expect several volts of drop. This is normal.
What you should worry about is thermally tripping the overload circuit breaker, ,that turns off your pc!

[beatman]

ups is only for back up when the main power is down you have few minutes power from the batteries on ups to close and save your work and shut down properly your pc to avoid any damage.for keep stable  the volts you need avrs automatic voltage regulator servo motor.inside is a variac transformer and cirquit that tracks the mains and when needed increase or lowering the voltage to keep in aceptable levels

[tooki]

ups is only for back up when the main power is down you have few minutes power from the batteries on ups to close and save your work and shut down properly your pc to avoid any damage.for keep stable  the volts you need avrs automatic voltage regulator servo motor.inside is a variac transformer and cirquit that tracks the mains and when needed increase or lowering the voltage to keep in aceptable levels

I kinda doubt that kind is still made.

Auto voltage regulation UPSes use an autotransformer with a couple of taps that are switched between using relays. 

The absolute gold standard in UPSes are the double-converting online type, where all incoming power is rectified, and the outputs run from an inverter at all times. This allows perfect output voltage control, and absolutely seamless transition to/from battery power. But of course this is expensive and inefficient, so it’s really only used for critical equipment. 

[james_s]

I'm not a fan of those AVR units that run the output transformer all the time, it results in significantly higher losses, though not as high as double conversion. I have one UPS with AVR that bypasses the transformer completely when the voltage is within the acceptable range, otherwise I'd rather it just switched over to battery any time the voltage goes outside of what is acceptable. Maybe it would make sense in an area that has extended brownouts or high line voltage but that has never been the case for me. 

[tooki]

As I alluded to, I don’t think it’s necessary anyway, since most switching power supplies are perfectly happy with the lower voltages. 

AVR might have made sense back in the days of omnipresent linear power supplies (or even unregulated power supplies!). But with modern SMPSes, it’s pointless. 

[james_s]

I'm actually kind of curious how wide the acceptable range is on older SMPS's like the sort in desktop PCs of the 80s and 90s. You always heard people say computers are "sensitive" but really I don't think they have been all that sensitive since the linear PSUs of the very early PC era. 

[stafil]

Is it on old incandescent of fluorescent lamp that it is changing brightness on voltage?

It's a LED bulb actually. Maybe I should stop being lazy and bring out the scope and measure..

[stafil]

ups is only for back up when the main power is down you have few minutes power from the batteries on ups to close and save your work and shut down properly your pc to avoid any damage.for keep stable  the volts you need avrs automatic voltage regulator servo motor.inside is a variac transformer and cirquit that tracks the mains and when needed increase or lowering the voltage to keep in aceptable levels

Yeah, I should have phrased my question better. Something like "Do I need a 'line-interactive' UPS, i.e. one with AVR, or an online, double-convertion, UPS"

[james_s]

None of those really. If you have a problematic load, get a pure sine UPS. I put one on my entertainment center because I have a lamp with a dimmer plugged into it and with the regular UPS the lamp would go out whenever the UPS kicked in. I replaced it with a pure sine model and now it works perfectly.

[stafil]

None of those really. If you have a problematic load, get a pure sine UPS. I put one on my entertainment center because I have a lamp with a dimmer plugged into it and with the regular UPS the lamp would go out whenever the UPS kicked in. I replaced it with a pure sine model and now it works perfectly.

"Pure-Sine" is the double-conversion?

[tooki]

Nope. Pure sine means the inverter output is a true sine wave, as opposed to an approximated one in cheaper models.

[stafil]

Nope. Pure sine means the inverter output is a true sine wave, as opposed to an approximated one in cheaper models.

Ok, but if it's a pure-sine offline UPS, will not help much... Am I wrong?

[james_s]

Double conversion UPS's are also typically true sine, but technically they don't have to be, it's two different concepts.

I think some UPS's also put out something better approximating a sine wave, like a stepped sine which would probably work fine in most applications but the ones I have are either square wave with deadtime, or pure sine.

[stafil]

None of those really. If you have a problematic load, get a pure sine UPS. I put one on my entertainment center because I have a lamp with a dimmer plugged into it and with the regular UPS the lamp would go out whenever the UPS kicked in. I replaced it with a pure sine model and now it works perfectly.

Can you recommend one? Which one did you use?

[james_s]

None of those really. If you have a problematic load, get a pure sine UPS. I put one on my entertainment center because I have a lamp with a dimmer plugged into it and with the regular UPS the lamp would go out whenever the UPS kicked in. I replaced it with a pure sine model and now it works perfectly.

Can you recommend one? Which one did you use?

The particular one I have is a CyberPower 850PFCLCD, I've had it for about a year and it has been fine so far. 

[beatman]

by ups  if you only want to protect your pc from unexpected mains power shutdown.other way you don't need.the pc and monitor is ok with undervoltage.

[Vovk_Z]

When the heater turns on I can see the lamp going dim for a second or so.
...
 and was thinking about getting a UPS for them.

I would instead think about inspecting the home electricity lines first. Neither an online UPS nor a line-interactive UPS will make electrical connections tight and made right.

[tooki]

Nope. Pure sine means the inverter output is a true sine wave, as opposed to an approximated one in cheaper models.

Ok, but if it's a pure-sine offline UPS, will not help much... Am I wrong?

Correct. As james_s says, pure sine is technically separate from double conversion.

Anyhow, as I think I’ve made clear, a UPS won’t “help” this “problem” because there’s no problem to fix, at least from the point of the computer: it doesn’t care if voltage sags for a second. (Heck, they can usually deal with very brief outages, like a 1/4 second or so, without skipping a beat.)