Are these refurb APC pure sine units considerably louder than this CyberPower model? Anyone have experience with both?
Pure sine wave inverters produce more heat, so they need greater airflow to keep them cool (tend to use larger fans than stepped units, so lower rpm can move as much or more air). But even stepped units get loud, as the fans tend to be smaller (small fans at high rpm tend to be quite noticeable). Either way, there's noise. Personally, I find the stepped inverter units louder, but that may just be me.
Now how often you'll have to deal with this (whatever the dB level of the unit is), will depend on the type of unit. Pure Sine wave inverters are used in both Line Interactive (switches to the battery + inverter when needed; they're not used otherwise = no fan running) or Online/Double Conversion (always runs off of the inverter and batteries).
The load can matter as well, as the fans may run on a profile (speed ramps up or down, depending on the inverter's temp) rather than just on or off (what the original SMT series firmware did).
I don't need experience to tell you that YES, APC pure sine wave units will be louder than these CP models, as evidenced by repeated forum discussions across the net.
You have to pay attention to the type (see above).
Now there have been complaints on the SMT1500 (or others in that series), but APC's released a firmware update to take care of that (changed from on/off to a profile). It's a Line Interactive unit, so the inverter only runs when the wall voltage has dipped below what the stepped transformer can deal with or gone to zero. Most of the time, the system is powered off of the wall, not the inverter, so the fan's not running.
Online/Double Conversion units do run all the time, as the inverter is always active (it may shut off, but only if the load is very low, such as a router or ISP modem). The larger fans help though for tower based units. Rackmounts OTOH, aren't meant for quiet environments such as an office or home to begin with (expected to be stored in an equipment room full of racks and the necessary sound proofing and ventilation systems).
The CP unit is also a Line Interactive unit, so the same thing that unit does, the APC or other brands of the same type (Line Interactive, ...) will react the same way (fan will only kick in when the inverter goes active).
