APC Back UPS XS 1500 output voltage reading normal?

[Anonymous user]

My APC Back UPS XS 1500 output voltage reading is usually at 117-118 and not 120 volts. Is this normal?

[Anonymous user]

Actually, in most areas 117 VAC is nominal, 120VAC is maximum. I think you are ok.

[BillP]

while the UPS is online, the UPS is just passing through the input voltage you are receiving, so yes it is normal. does your input voltage stay around 117-118v? it should match up if you view that.

also, 120v is the "nominal" voltage for a wall outlet. nominal means what is expected but of course there are fluctionations and other factors that cause the voltage from your utility source not to be 120v right on the dot.

[Anonymous user · Accepted solution]

You're never gonna see a steady 120V flow unless you measure the output of an online double conversion UPS which costs a small fortune.

It is almost impossible to keep a steady flow without generating the power locally, inside the UPS off the batteries power all day long, thats what online double coversion UPSes do. In every power grid there's small, medium and big fluctuations, it depends on many factors. Even your household appliences cause voltage fluctuations when they're turned on and turned off. If your neighbour is using a welder machine of something that draws a lot of power, it's not uncommon to notice voltage fluctiations on your wall outlet as well because you're sharing the same power transformer on the pole down the street.

What the AVR built in many UPSes do is to attenuate the voltage fluctuation, but it does this in small steps, usually two steps up and two steps down or only one step above to compensate for bigger undervoltages. The compensation steps are at a fixed number, let's say, 12V above and 12V down. The UPS will only trigger these compensations steps when the voltage goes off a pre-determined range. Let's say, 105Volts, then the UPS triggers the + 12V tap to compensate for undervoltage.

All power supplies tolarate voltage fluctuations within a relatively big range. Most SMPS (Switched Mode Power Supply) can work with anything below 25 to 30% its nominal voltage rating or 20-25% above the same nominal rating. So, do not worry about small fluctuations, this is completely normal and within your PSU tolerance.