UPS lower wattage than PSU

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paulchinnz

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#205862 30-Nov-2016 01:23

I understand the UPS wattage needs to at least match the PSU wattage (assuming the system is drawing upon entire PSU) for UPS to work during an electrical outage.

But here's the question: when there isn't an outage, will the system run properly if it's connected to UPS with less watts than the PSU? (e.g. say 600W PSU and 500W UPS)

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#1679886 30-Nov-2016 02:08

Are you actually pulling 600w on the system? Unless you have a SLI titan setup or 10+ HDD's, probably not. The UPS should report the actual load in its software and an estimated run time.

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#1679890 30-Nov-2016 05:14

i have a 750w PSU and a APC smart ups rated at 500w/750VA.

i have the phone, modem, access point and computer (i5 2500k with 6HDD's and GFX card) with the 750w PSU plugged in and its idling at 14% on the UPS and its used max 50% according to the UPS.

i get about 10 mins from the computer and then im left with about 70% battery power as the PC shuts its self down as i have the ups running as a battery so the computer thinks its a laptop.

timmmay

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#1679902 30-Nov-2016 07:22

I have a 500W PSU, but the peak I've seen it draw is 150W, mostly under 100W. People oversize PSUs.

paulchinnz

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#1679924 30-Nov-2016 08:09

Hi thanks everyone.

Yes good point about whether the system is actually drawing all of the PSU.

I probably should've stated my question is hypothetical, and I'm thinking of getting a UPS, so don't have one to test yet. Assuming the wattage the system draws from the PSU exceeds the wattage of the UPS, will I see problems only when there's an outage, or even when the mains electricity is working?

i.e. does the UPS wattage constrain the max draw of the PSU from the mains electricity?

timmmay

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#1679934 30-Nov-2016 08:32

UPS draws whatever it needs to charge the battery and power the connected devices.

Just buy the UPS, rated for a bit over your maximum draw (not your PSU wattage).

paulchinnz

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#1679936 30-Nov-2016 08:38

timmmay:
UPS draws whatever it needs to charge the battery and power the connected devices.

Just buy the UPS, rated for a bit over your maximum draw (not your PSU wattage).

Thanks. If later I add components (eg 3 sli 1080) and the draw on the PSU exceeds the UPS wattage, will I only see problems during an outage or all the time?

timmmay

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#1679942 30-Nov-2016 08:56

paulchinnz:
timmmay:

UPS draws whatever it needs to charge the battery and power the connected devices.

Just buy the UPS, rated for a bit over your maximum draw (not your PSU wattage).

Thanks. If later I add components (eg 3 sli 1080) and the draw on the PSU exceeds the UPS wattage, will I only see problems during an outage or all the time?

I don't know the answer to that. I suspect if you try to use more power than the UPS can supply it'll shut down or something.

I have a small UPS that was powering my computer, but I got rid of it, for a few key reasons:

- Standby power use was a bit over 20W, which affects power bill (not much). Because of that I turned it off when computer was off, which got annoying.

- It has a fan that made an annoying use.

- I don't really care if I have power in an outage, my phone is good enough. I was mostly using it as a power conditioner. Given it's not a critical machine, and because it's backed up well, I figure if it breaks I'll just replace it, or use a laptop.

An APC UPS I bought maybe 5 years ago made an intolerable high pitched noise. I returned it, the supplier accepted this with a 15% restocking fee, with the note "not many people can hear that noise".

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richms

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#1679946 30-Nov-2016 09:03

Depends if it's a line interactive one or just switches over to an inverter and uses battery in a failure. Switching over will just be the fuse or circuit breaker to worry about till it needs to cut over.

But they will often cut over to load test the battery periodically so not just an issue when there is an outage.

One of mine beeps annoyingly when it's near its limit which made it beep occasionally when the machine woke up and all the drives spun up at the same time.

Richard rich.ms

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#1680000 30-Nov-2016 11:44

paulchinnz:

I probably should've stated my question is hypothetical, and I'm thinking of getting a UPS,

Some of the UPS manufacturers have calculators on their website to help with what size UPS you need.
Lower VA will just give less runtime on batts. It wont melt down if its a bit underspecced :-)
Chances are , if its just a single pc it will be OK . Its mainly just to give you time to shut down the PC when theres a power
cut . You wont be playing games using all 3 NV vid cards if theres a power cut, you'll be shutting down as the UPC beeps at you.

Keep in mind that the will be some BS with the spec's on the cheap & nasty brands.
Also, dont connect laser printers to it.

paulchinnz

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#1680147 30-Nov-2016 15:48

Thanks all.
In terms of working out the system draw is https://www.mitre10.co.nz/shop/elto-power-meter/p/103559 expected to be any good?

1101

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#1680533 1-Dec-2016 09:37

paulchinnz: Thanks all.
In terms of working out the system draw is https://www.mitre10.co.nz/shop/elto-power-meter/p/103559 expected to be any good?

Youre overthinking things. That money would be better spent on a higher spec'ed UPS . Will that meter even give an accurate reading with switching power supplies ?
Just use one of the online calculators , or buy a 1000VA .

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#1680546 1-Dec-2016 09:44

Don't forget to factor in battery replacements. My APC units are lasting quite a while between needing to replace batteries.

I've had nothing but good experience with APC - so I tend to stick with APC (That and the interface is quite well known, so I know whatever OS I'm using, generally it will talk to it)

The other thing to consider (if you have a laser printer, or other high draw appliances) is that some UPSes provide a filtered only output.

Cheers

paulchinnz

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#1680684 1-Dec-2016 13:32

1101:

paulchinnz: Thanks all.
In terms of working out the system draw is https://www.mitre10.co.nz/shop/elto-power-meter/p/103559 expected to be any good?

Youre overthinking things. That money would be better spent on a higher spec'ed UPS . Will that meter even give an accurate reading with switching power supplies ?
Just use one of the online calculators , or buy a 1000VA .

Thanks.

I understand online calculators aren't accurate because based on manufacturers' 'ideal estimates' as opposed to real world.

Please recommend me an online calculator?

paulchinnz

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#1680686 1-Dec-2016 13:33

wazzageek:

Don't forget to factor in battery replacements. My APC units are lasting quite a while between needing to replace batteries.

I've had nothing but good experience with APC - so I tend to stick with APC (That and the interface is quite well known, so I know whatever OS I'm using, generally it will talk to it)

The other thing to consider (if you have a laser printer, or other high draw appliances) is that some UPSes provide a filtered only output.

Cheers

Thanks yes I've heard good things about APC and Cyberpower. No high draw appliance fortunately.

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#1680718 1-Dec-2016 14:27

wazzageek:

Don't forget to factor in battery replacements. My APC units are lasting quite a while between needing to replace batteries.

I've had nothing but good experience with APC - so I tend to stick with APC (That and the interface is quite well known, so I know whatever OS I'm using, generally it will talk to it)

<snip>

I have 3 x APC UPS units - 750, 1000, and 1500VA (2 to 10 years old).

All are excellent. Totally reliable. Worth the money.

With normal usage replace batteries every three years.

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