Overvoltage Problem?

[Anonymous user]

Our three APC units (one RS1500 and two NS1250's) starting beeping last night about 10:30 pm to indicate they were on battery power. Following is what I have found after 3.5 hours of troubleshooting. There is power to the outlets where the RS1500 and two NS1250's are connected. However, when I try to power on the units by pressing the power button on the front of the unit (the power button and display/hold to mute buttons are illuminated), each unit beeps once and nothing happens. I have reviewed the UPS owner's manual and am able to start the RS1500 and one of the NS1250's in "battery mode" (with the units plugged into or out of the outlet) but get no error lights indicating battery or line fault problems. However, when stepping through the seven groups of displays and messages in the "battery mode display selection" sequence, the fourth screen indicates an input voltage of 143 when the UPS unit is plugged into the outlet. I checked the voltage with two different multitesters (one analog and one digital) at the outlets where the UPS units are connected as well as at other locations in the house and am getting a reading of 140 to 140.5 volts. There is another computer running on a surge protector, not a UPS, in the same room where the described UPS units are located and it is running fine. My understanding is that the voltage should be 120 with no more than a 10% deviation (108 - 132) so could it possibly be that the UPS units are sensing an overvoltage situation and refusing to start to protect the computers that are connected to them? It is approaching 2:30 am and this seems like a bad dream. Any help much appreciated.

[Anonymous user]

JonPro - You are exactly correct. The good people from our local power company appeared here this morning about 5:15 am, checked the power at the meter, confirmed a voltage of 140, and assured us the problem was on "their side" and would be resolved today. I just got home, checked the voltage with a multimeter (it is now 121), hooked up the UPS's and the computers and everything is working normally. Bad experience - good outcome. Thank you.

[BillP]

Whew! I am thankful that nothing happened on your equipment and to the APC UPS's that you have there. I am glad to here that everything works fine now.

[BillP · Accepted solution]

Good day Tom,

One reason why the UPS's are running on battery is that it has detected a very high input voltage that could be damaging to your load. The UPS switched to battery mode in order to provide a good ~115V AC to the connected equipment. What we can try is to adjust the voltage thresholds of the UPS's, since the UPS that you are using has an LCD screen we can install PowerChute Personal Edition on a PC and adjust the high or low transfer voltages.