SUA1500 Buzzing Noise Late at Night

[BillP]

I have been running a APC smart UPS SUA 1500 for just about 30 days now and have noticed in the last week that it emits a transformer-like buzzing noise every night starting at about 10:30 or 11:00 pm.; by morning the buzzing has stopped. No buzzing during the day - only at night starting at around 10:30. The UPS is running at 30% load (high sensitivity), the largest draw being a 2009 quad core MAC Pro desktop and NEC LCD monitor.

From the data log the voltage drops in the evening to about 113v while during the day it is usually at 118v but will vary between 118v and 115v until late evening when it drops to 113v and stays there. Apparently the 113v level is not low enough to trigger battery or boost operation but does seem to cause the buzzing. My question is, is this normal/expected behavior for the UPS given the line condition at my location or is this particular UPS unit defective? I have a APC 1000 XS plugged into the same outlet as the SUA1500 and it does not buzz.

Stan

[BillP]

Techie wrote:
Hi Stan,

I would like to gather some more information from you before making any comments about this issue..Has it been happening since you installed the UPS? What lights are on the front of the UPS when it is buzzing? If possible, stimulate a power failure by unplugging the UPS from the wall and see if the UPS emits the same kind of noise which is similar to the noise that you are referring to.

I have had the UPS for approx. 30 days. I only noticed the buzzing in the last week late at night. No unusual front panel lights come on during the buzzing - the load (one segment) light , on-line light and battery charge light are the only lamps lit during the buzzing. By the way, last night there was no buzzing even though the in coming voltage was consistently at about 109-110v most of the late evening (it did go as low as 108 and the boost light lit for awhile but no buzzing). I pulled the plug for about 30 seconds and no unusual noise - no buzzing - just the fan revving up a bit in response to battery power mode.

[Techie_apc]

Are you sure that the other equipment is not the source of the buzzing? I have seen in many cases that the other equipment which is plugged to the UPS caused the buzzing noise. Is the buzzing noise abnormally loud?

[BillP]

Techie wrote:
Are you sure that the other equipment is not the source of the buzzing? I have seen in many cases that the other equipment which is plugged to the UPS caused the buzzing noise. Is the buzzing noise abnormally loud?

When the buzzing occurred it was definitely coming from the UPS. How do I know? I turned off all devices except the ups. The buzz was loud enough for me to want to walk away from the workstation. At any rate I did not have the buzzing last night and do not have it now, so it is intermittent and apparently not caused by the variations in incoming line voltage. Still puzzled.

[Techie_apc]

At this time, I recommend you to monitor the UPS performance for another couple of days and see if the same kind of buzzing comes from the UPS.

secondly, It is normal for the unit to emit noise when the fan inside the unit is operating. this [k-base|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=6672] has got the reasons the fan in my Smart-UPS will come on.

[BillP · Accepted solution]

I have been running a APC smart UPS SUA 1500 for just about 30 days now and have noticed in the last week that it emits a transformer-like buzzing noise every night starting at about 10:30 or 11:00 pm.; by morning the buzzing has stopped. No buzzing during the day - only at night starting at around 10:30. The UPS is running at 30% load (high sensitivity), the largest draw being a 2009 quad core MAC Pro desktop and NEC LCD monitor.

From the data log the voltage drops in the evening to about 113v while during the day it is usually at 118v but will vary between 118v and 115v until late evening when it drops to 113v and stays there. Apparently the 113v level is not low enough to trigger battery or boost operation but does seem to cause the buzzing. My question is, is this normal/expected behavior for the UPS given the line condition at my location or is this particular UPS unit defective? I have a APC 1000 XS plugged into the same outlet as the SUA1500 and it does not buzz.

Stan