Smart-UPS 750 Problem

[Anonymous user]

I got new Smart UPS 750VA yesterday. I connected my Workstation and LCD. The load on the UPS is around 65-66%. Yet when i cut the power to the ups the workstation dies instantly and there is some hissing like noise form the ups for a second. The power is still fed from the ups because the likghts on the workstation are on. If i then try to turn the workstation on while ups is still running from battery it turns on ok but dies of after around 10 sec (when the load rises). When i tried to boot it off battery without lcd its able to boot allright, but if i cut the power to that configuration the workstation still dies on me.
i Tried sifferent PC (which gives about 20% load) and its working allright with same lcd attached.

So the question is what might be the problem here. Is the UPS too weak for my workstation and i should get it replaced for larger one, or is the UPS faulty and its not giving enough power under load while on battery power and i should replace it for another one?

[Anonymous user]

during normal operation the 440 gives about 20% and 620 about 65% but its not the same hardware theyre powering up but ill try to connect thae 620 to the lower end PC and see how it goes then. Ill let u know asap.

[Anonymous user]

thanks for cealring that up, too bad i didnt know that sooner 🙂 ill get bigger ups then as it seems it works perfectly fine with 400W PSU i have around so the UPS itself must be ok.

[TheNotoriousKMP_apc]

Does your workstation have an power factor corrected power supply? If so, the UPS may be grossly undersized for your needs.

Also you might want to check with the workstation's PSU manufacturer to find out if a 2-4 millisecond transfer time is acceptable from the UPS. If not, there's the problem, and you'll need something like an SURTA1500XL.

[Anonymous user]

Yes i checked on the manufacturer site and it appears that this PSu have Active PFC system installed. The PSU is rated at 620W but it only draws around 260-280. So i should get UPS with watt ratings over 620 then? Because i relly dont know what that active PFC system really means in terms of power consumption and needs when it comes to UPS workings, and why would it make any problems when the load is well below the rated power output of the UPS.

[TheNotoriousKMP_apc]

Hi....here's what happens when you use an undersized UPS and a PFC power supply.

Upon transfer to battery (the mere 2-4 milliseconds), the capacitors in the PFC PSU discharge to keep the system up and running. As soon as the UPS is back on battery and the PSU sees sufficient power, it will attempt to recharge all the capcitors simultaneously. This is where the maximum draw of power comes from the PSU specs. They'll reach 620 and overload the UPS or just completely drain the battery with such an increase in power draw and a decrease in runtime available.


So yeah, you would need a UPS that is capable of handling 620W plus everything else you're plugging into it.

[Anonymous user]

The Notorious K.M.P. wrote:
Hi....here's what happens when you use an undersized UPS and a PFC power supply.

Upon transfer to battery (the mere 2-4 milliseconds), the capacitors in the PFC PSU discharge to keep the system up and running. As soon as the UPS is back on battery and the PSU sees sufficient power, it will attempt to recharge all the capcitors simultaneously. This is where the maximum draw of power comes from the PSU specs. They'll reach 620 and overload the UPS or just completely drain the battery with such an increase in power draw and a decrease in runtime available.


So yeah, you would need a UPS that is capable of handling 620W plus everything else you're plugging into it.

Kevin,
The bulk storage capacitor holds the PC in both PFC and non-PFC power supplies. The type is irrelevant.
The maximum watt specs on PSU is supposed to represent the MAXIMUM OUTPUT. It has nothing to do with surge power.

OP,
I'm not sure how accurately the load tracking works on APC UPS though. What did you use to measure you're only drawing around ~250W?

What are the specs on your PC? The power supply size tells you nothing about the power consumption, but it merely represents the maximum power the PSU can supply.

[Anonymous user]

im using:
http://www.pentagram.pl/produkty/zasilacze_do_obudow/pentagram_silent_force_psf_620_a12s_p_9005_2
it have that nice little feature which is LCD display showing current power draw of PSU and it is usually between 250-300W thats why i knew what amount of power load it generates, and thats why i thought 500W UPS should be more than enough to feed ~400W power load.

[BillP]

Hello, zipper,
Coud you connect other load and check how UPS works?
For eg. just LCD while computer works from other power line?
Also, please try to install software to see data from UPS ( battery voltage, Runtime remaining,
Bat Capacity etc)

[Anonymous user]

yeah i tried different load. 400W PSU with active PFC aswell. it was running at ~20% load of the UPS and cutting power to UPS didnt kill the PC.
Power chute with my main workstation connected said it was about 65% load with 6 minutes runtime.
battery was just over 24V. It was fully charged aswell. Selftest passed without problems.

[BillP]

What will be the difference between the loads if the 400W PSU with active PFC aswell?
Any difference?

[Anonymous user]

ok i tested the bigger workstation connected to 440W active pfc psu (the one that worked fine while supplying power to older one) and the effect was the same. i cut the power, workstation dies, strange whistling sound from ups for about a second. im attaching logs from 2 trys i did.i hope someone can tell me if the ups should be able to pull that off (the 440W of the psu is well within 500@ ups rating now and nothing else was connected to it) and with lower load on the same psu it worked fine.

[BillP · Accepted solution]

Just to check the load. Could you connect a non-computer load @ 400W ( let us say classic electric lamps) or more ? Will UPS support the load?

From your data it looks like the PSU draws more then 500W ( please note the efficiency of the PSU)