OT a bit - matching UPS with one's pc

[Yes]

I'll probably be buying a UPS for my pc soon and need to learn how to
size and match a UPS with my pc, but there's a lot of unclear info out
there.

Complicated but probably more exact method - add up the amps each
device in my pc uses to calculate the minimum size UPS. I've found
some calculators out there that follow this method.

Variation to that method - add the number of watts each of the various
devices need, add 10% as a safety margin and divide that number by 12
to derive amps needed from a UPS.

Simplistic method - My brother said use the specs posted for my pc's
PSU regarding amps and pick a UPS based on that number - his
explanation being that all the devices in the pc are ultimately powered
through the PSU and it therefore incorporates everything needed by the
individual components of the pc so that the amps it provides can be
thought of as the minimum amps that a UPS should provide.

My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A,
+5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean
much to me. If I add them together, the sum totals 123 Amps, but using
the second procedure yields roughly 50 Amps. For simplicity, call it a
100% difference.

My pc has an Asus M4A89GTD Pro mobo, an AMD Athlon II x3 440 CPU, a
Radeon 6750 video card, 4x4Gb DIMMs, a DVD and 2 500 Gb hds.

As far as my needs go, I think I want to use a UPS just for my pc and
leave my monitor and cable modem on a surge protector. I might choose
a UPS that can instruct my pc to shutdown when power goes out. My
biggest concerns in my neighborhood are rolling brownouts. It promises
to be a very hot summer. I don't need the UPS to power my pc for
extended periods of time, just enough time (minutes) to safely shut
down.

My brother's suggestion seems the most practical way (KISS) to decide
how much UPS I need, but I feel like I'm doing something wrong to add
up to 123 Amps using the PSU specs whereas dividing 550 Watts by 12 =
47 Amps.

Are there other considerations I should keep in mind?

Thanks,

John

 

[John McGaw]

I'll probably be buying a UPS for my pc soon and need to learn how to
size and match a UPS with my pc, but there's a lot of unclear info out
there.

Complicated but probably more exact method - add up the amps each
device in my pc uses to calculate the minimum size UPS. I've found
some calculators out there that follow this method.
snip...
Thanks,

John

Safe way: measure the actual power consumption of the equipment you need
for minimal functioning and work from that. This equipment would include
the computer + monitor + whatever equipment is needed to connect to the
Internet (modem, router, switch or whatever other bits your situation calls
for). Add at least 20% to that although doubling it won't hurt. Then buy
yourself a UPS which will support that load. You should not include power
hogs like printers, especially lasers.

Keep in mind that the power rating of the UPS is not terribly informative
about how well it will serve your purpose. A massive power output rating
simply means that it will put out that much power but not for how long. A
1000W UPS which only runs for one minute is not terribly useful; at the
very least the UPS needs to keep everything going for long enough to tell
the computer to shut down safely. A UPS which supports your equipment and
runs for 20 minutes would be a better value.

I have standardized on 1200W CyberPower units not because any of my
equipment consumes anything like that (maybe 350W max) but because the are
have proven to be reliable, have a good number of outlets (both battery and
surge protected), they are line-interactive and handle brownouts well and
they go on sale pretty regularly so they are affordable. I program the
shutdowns so that when the batteries have maybe 5 minutes of support left
the computer does a safe powerdown. I have 5 of these units as well as a
couple of 12VDC units supporting network infrastructure but I live in an
area with obsolete power distribution, lots of storms, and huge trees so
what seems like overkill is actually just barely enough.

 

[westom1]

I'll probably be buying a UPS for my pc soon and need to learn how to
size and match a UPS with my pc, but there's a lot of unclear info out
there.

Generally sum the amps or watts. Then remember a UPS battery typically degrades in three years. So, for example, if your system consumes 350 watts, then the UPS should be sized about 500 watts. So the the three year old battery can still provide enough power. And for other technical reasons.

Now, the power rating on the label for most engineer designed appliances is good enough. However many put 800 watt power supplies into computers that consume only 200 watts and never more that 350 watts. To get a better idea, read what others measured with their Kil-A-Watt in:
http://forums.anandtech.com/showthread.php?p=34917091#post34917091

BTW, a UPS connects your equipment directly to AC mains when not in battery backup mode. Many rumors are based in hearsay that is discussing a UPS costing on the order of $1000 or higher. Cleanest power come when the UPS connects your computer directly to AC mains.

And finally, power from a UPS in battery backup mode is so 'dirty' as to sometimes be harmful to motorized appliances. But electronics are so robust as to not care.

 

[Paul]

Generally sum the amps or watts. Then remember a UPS battery typically degrades in three years. So, for example, if your system consumes 350 watts, then the UPS should be sized about 500 watts. So the the three year old battery can still provide enough power. And for other technical reasons.

Now, the power rating on the label for most engineer designed appliances is good enough. However many put 800 watt power supplies into computers that consume only 200 watts and never more that 350 watts. To get a better idea, read what others measured with their Kil-A-Watt in:
http://forums.anandtech.com/showthread.php?p=34917091#post34917091

BTW, a UPS connects your equipment directly to AC mains when not in battery backup mode. Many rumors are based in hearsay that is discussing a UPS costing on the order of $1000 or higher. Cleanest power come when the UPS connects your computer directly to AC mains.

And finally, power from a UPS in battery backup mode is so 'dirty' as to sometimes be harmful to motorized appliances. But electronics are so robust as to not care.

I glossed over that detail.

Power rating is not the same thing as runtime.

Power rating is the maximum power it will provide, before
shutting off on an overload. A 1200W UPS could power up
to 1200W worth of electronics. You want the power rating,
to be greater than the sum of the loads.

Generally, to have a decent runtime at full load, a
larger battery is used in a 1200W UPS, than would be
used in a 450W UPS.

Then, if less than full load is used (a 200W PC on a
1200W UPS), the runtime could be 20 minutes. Runtime
is a function of the actual PC loading, as well as
being related to the size of the battery. When we
buy a 1200W UPS, not only is the power rating higher,
but most of the time, it comes with a physically bigger
battery.

But there isn't a direct proportionality or anything.
The manufacturer can make the runtime anything they
choose.

A dumb manufacturer, could use the battery from a 450W
unit, in a 1200W product. The product would be lightweight,
the shipping cost would be minimal, but then it would
only have a few minutes of runtime with a 200W load.
And if the 1200W load was applied (with that flimsy battery
in place), it would run out of juice in less than a minute.

So while there is a proportionality (bigger battery in
higher power UPS), you really need to consult the
runtime graph, to figure out the actual runtime.
Some manufacturers provide a nice graph, while
others say things like "run time 9 minutes at half
load). Which amounts to a single data point.

Paul

 

[larrymoencurly]

need to learn how to size and match a UPS with my pc,

Complicated but probably more exact method - add up the amps each
device in my pc uses to calculate the minimum size UPS. I've found
some calculators out there that follow this method.

Variation to that method - add the number of watts each of the various
devices need, add 10% as a safety margin and divide that number by 12
to derive amps needed from a UPS.

Simplistic method - My brother said use the specs posted for my pc's
PSU regarding amps and pick a UPS based on that number - his
explanation being that all the devices in the pc are ultimately powered
through the PSU and it therefore incorporates everything needed by the
individual components of the pc so that the amps it provides can be
thought of as the minimum amps that a UPS should provide.

My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A,
+5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which
doesn't really mean much to me. If I add them together, the sum totals
123 Amps, but using the second procedure yields roughly 50 Amps.

You can't just add up amps but instead have to add up powers
(amps X volts), but it's a lot more realistic to plug your computer
and monitor (but not the printer, scanner, or audio system) into a
Kill-A-Watt ($15-25) and run a worst-case power test (video game).
Then note the maximum Volt*Amp and watt numbers the Kill-A-Watt
reports. Add 50% to those numbers to get the VA and watt ratings
you'll need from a backup power supply. Generally backups have
a watt rating that's about 60% of its VA rating.

 

[philo]

I'll probably be buying a UPS for my pc soon and need to learn how to
size and match a UPS with my pc, but there's a lot of unclear info out
there.

Complicated but probably more exact method - add up the amps each
device in my pc uses to calculate the minimum size UPS. I've found
some calculators out there that follow this method.

Variation to that method - add the number of watts each of the various
devices need, add 10% as a safety margin and divide that number by 12
to derive amps needed from a UPS.

Simplistic method - My brother said use the specs posted for my pc's
PSU regarding amps and pick a UPS based on that number - his
explanation being that all the devices in the pc are ultimately powered
through the PSU and it therefore incorporates everything needed by the
individual components of the pc so that the amps it provides can be
thought of as the minimum amps that a UPS should provide.

My power supply is a 550 Watt PSU. Its output is listed as +3.3V@28A,
+5V@26A, +12V1@22A, +12V2@22A, +12V3@25A, -1 which doesn't really mean
much to me. If I add them together, the sum totals 123 Amps, but using
the second procedure yields roughly 50 Amps. For simplicity, call it a
100% difference.

My pc has an Asus M4A89GTD Pro mobo, an AMD Athlon II x3 440 CPU, a
Radeon 6750 video card, 4x4Gb DIMMs, a DVD and 2 500 Gb hds.

As far as my needs go, I think I want to use a UPS just for my pc and
leave my monitor and cable modem on a surge protector. I might choose
a UPS that can instruct my pc to shutdown when power goes out. My
biggest concerns in my neighborhood are rolling brownouts. It promises
to be a very hot summer. I don't need the UPS to power my pc for
extended periods of time, just enough time (minutes) to safely shut
down.

My brother's suggestion seems the most practical way (KISS) to decide
how much UPS I need, but I feel like I'm doing something wrong to add
up to 123 Amps using the PSU specs whereas dividing 550 Watts by 12 =
47 Amps.

Are there other considerations I should keep in mind?

Thanks,

John

Yes...UPSes are typically rated in VA (volt amp) which is not the same
as watts. If you assume a power factor of .65 a 1000VA UPS is good
for 650 watts.



http://www.rapidtables.com/convert/electric/va-to-watt.htm

 

[miso]

You are making the assumption that the UPS is one of those crappy
modified sine wave types. They should simply be avoided. I would rather
lose power than use a modified sine UPS.

I use a double conversion UPS, not all that different from the $500+
unit the other poster listed from newegg. Double conversion true sine is
the only way to go. Otherwise, don't use a UPS. Your gear SHOULD be able
to handle the crappy signal from the cheap inverter, but some devices
can be damaged. Basically the modified sine, which is practically a
square wave, causes increased surge current in the capacitors of the
computer power supply.

The thing to note with a true sine wave double conversion UPS is that it
is running all the time. It has fans and thus noise. Think of a computer
server room at a business, then imaging that in your house.

I'm using an optiups 1500b. About 4 or 5 years old at this point and
thus far no problem. It can run a desktop and a few very low power
computers. That is, 1500va is a lot of power.

Most of your computer power supplies, unless they are bargain basement
PCs, will have power factor correction. So they will look resistive to
the UPS.

http://en.wikipedia.org/wiki/Power_factor

Everything I build uses 80plus rated power supplies. But a lot of the
low power accessories will not have active power factor correction. That
shouldn't be an issue since the key phrase here is low power. But it
wouldn't be surprising for all the wall warts and such to add up to a
hundred watts.

BTW, I also agree having a Kill-A-Watt is a good idea. Get the cheapest
model since the fancy ones have features that really aren't all that useful.

http://www.newegg.com/Product/Product.aspx?Item=N82E16842107015

I see they still make it. OK unit, but I don't like how the front panel
attaches. It doesn't attach firmly. That is my only complaint. It is one
of the quieter double conversion units around since the fans are
variable speed. Still it is damn loud.

Tomshardware has review of it and a few others. Note the opti can work
off of serial or usb. The deal is if you have a number of devices on the
supply, serial is better since that one signal can be bussed around.
That is, for a UPS to be completely effective, all your attached devices
need to be able to sense the power failure signal. This can also be done
via lan instead of serial port, but the serial port scheme requires the
least brain power.

http://www.tomshardware.com/reviews...00pfclcd-tripp-lite-smart1500slt,2785-12.html

Note it has the best voltage regulation because it was the only double
conversion unit in the test. It was also the most expensive. However, it
will last hopefully for use over at least two different computer systems
for the average home user that gets a new PC every 5 years. Maybe three
if you change computers more often.

Note that the double conversion scheme gives you true surge protection
since it comes for free given the design. That is, the raw AC is
rectified then filtered. At the filter stage, you can really do decent
surge protection because you are dealing with DC. Filter the bejesus out
of it. Big ass caps are not a problem. Then you convert the DC to AC
with the true sine inverter.

 

[westom1]

Power rating is not the same thing as runtime. ...

A dumb manufacturer, could use the battery from a 450W
unit, in a 1200W product.
And if the 1200W load was applied (with that flimsy battery
in place), it would run out of juice in less than a minute.

And that unit would immediately shutdown three year later as the battery further degraded. It would not have power necessary to provide 1200 watts long enough to do anything useful.


All electronics are so robust that a modified sine wave UPS is sufficientand ideal power. Many get hyped by hearsay (as another demonstrates by not saying why power must be 'cleaner'). Spend massively for a double conversion UPS or a double conversion that still outputs 'dirty' sine waves. (Latter costs less, is double conversion, and still has a crappy output.)

Spending all that additional money accomplishes nothing useful. Since any advantage from a double conversion UPS is already done better inside electronics.

UPS is temporary and 'dirty' power during a blackout. It must be sized so that it will provide sufficient power even when seriously degraded in three years. Other engineering factors also say why a 350 watt load means a UPS maybe 500 watts or larger.

 

[miso]

The double conversion scheme is a power conditioner and UPS at the same
time. If you understand electronics, it is far easier to absorb a surge
at DC versus AC.

Seriously, those modified sine wave UPSs are so shitty it is far better
to suffer a power outage.

Look at the modified sine waveform. It is more like a modified square
wave. The steep edges will stress the power supply since i=C*DV/DT, and
the DV/DT of a square wave is infinite. Of course the modified sine
doesn't have an infinitely fast rise time, but it is faster than the
design criteria of 2*pi_60Hz.

 

[westom1]

The double conversion scheme is a power conditioner and UPS at the same
time. If you understand electronics, it is far easier to absorb a surge
at DC versus AC.

How many power supplies have you designed? Anything done by the power conditioner is routinely done inside all electronics. For example, how does that 'shitty' power become the rock solid 3, 5, and 12 volt DC. All shittypower is first converted to well over 300 volts. And then converted to higher voltage radio wave spikes. Does not matter how 'clean' that UPS poweris. Because inside all electronics, the power is then made much 'dirtier'..

What happens next? Those many hundred volt spikes are converted to rock solid 3, 5, or 12 volts DC by superior power conditioners already inside all electronics.

Why spend so much money on a $1000 UPS when all that 'cleaning' is automatically undone inside all electronics? Many have fears rather than learn how electronics work. Those fears get the naive to recommend a $1000 UPS rather than the $100 one.

If 'dirty' UPS power is harmful, then you can cite each specific part inside an appliance damaged by 'dirty' power. If you cannot, then knowledge comes from advertising and hearsay; not from designing electronics.

'Dirty' UPS power is ideal for all electronics. However is can be harmful to less robust devices such as small electric motors and power strip protectors.

Cure the problem. Spending excessively on a double conversion UPS solveswhat problem? Averts damage to what part? Making subjective claims about'shitty' power is why advertising is so profitable. What a double conversion UPS might do is already done better inside electronic appliances. Now reread those numbers. Any cleaning by a UPS is first completely undone inside electronics. And then ‘cleaned’ by superior circuits already inside each appliance.

 

[John McGaw]

The double conversion scheme is a power conditioner and UPS at the same
time. If you understand electronics, it is far easier to absorb a surge at
DC versus AC.

Seriously, those modified sine wave UPSs are so shitty it is far better to
suffer a power outage.

Look at the modified sine waveform. It is more like a modified square wave.
The steep edges will stress the power supply since i=C*DV/DT, and the DV/DT
of a square wave is infinite. Of course the modified sine doesn't have an
infinitely fast rise time, but it is faster than the design criteria of
2*pi_60Hz.

If one has a conservatively designed computer then the modified sine wave
you so fear is not a problem at all. This is especially true since it is
powering the computer for very short periods of time. As a Unix sysadmin
I've been down the road with the high-priced always-on sine wave UPS units
such as the big Toshibas and know that for the home user who suffers a few
minutes of outage every month such a thing would be throwing money away.
Doubly so since the always-on units are fairly greedy consumers of power on
their own.

I have five of the sort of UPS units you preach against and have had them
for years and from several manufacturers. I have fairly frequent short-term
power failures and occasional brownouts. I have had zero power supply
failures during this period of use. If they were as dangerous as you say,
shouldn't I have had at least one computer going up in smoke?