07-31-2011, 07:30 PM
Robert M wrote:
With an online UPS, your hardware is always connected to inverter output whether or not there is a power outage. It's soemthing along these lines: Juice goes into the UPS and stored into the battery. The UPS then sends the juice from the battery to your hardware. At some point, the juice is cleaned up prior to getting to your hardware. The hardware never knows whether or not there is an outage. The only time power going to it is interrupted is when there is an outage and the juice stored in the battery finally runs out. Hopefully, power is restored prior to this taking place and/or you've shut the hardware down. If I remember correctly, APC SMARTups models are online models that produce pure sine wave output.
With an offline UPS, hardware gets juice from the battery only during an outage. At the moment of an outage, there is a brief amount of time that electricity isn't being sent to the protected hardware. That is the amount of time it takes the UPS to switch from main power to battery power. Machines with AVR always clean the juice prior to sending it to the hardware whether it's working off battery power or main power. Lower-end UPSs such as the APC Backups ES series and, if I remember correctly, the RS (and BX) series are offline UPS.
Online UPSs don't suck off the battery all the time as you suggest. The AC power is fed into an inverter which simultaneously is used to top off the battery and to feed to a second inverter which cleans up the power going to the jacks. Because the signal is actively being cleaned up in this process, an online UPS is actually less likely to hit the battery to cover a brief power-fluctuation than other kinds of UPSs.
APC's AVR tech is an online UPS design. It uses a transformer to moderate the AC output. During ordinary trim and boost operations the a UPS with AVR should never hit the battery.
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The shape of the sine wave is generally only of concern if you're running motors (power tools, refrigerators, laundry machines) or charging batteries with a very old (or cheap Chinese knockoff) charger off of your UPS. Don't worry about a "pure sine wave" if you're just using it with computer gear.