When the power goes out and your generator starts up, your UPS will be put to the test. Each type of UPS (Topology) will react differently.
A quick review of the major types UPSes.
- Standby UPSs allow electronics to run off utility power until the UPS detects a problem, at which point the UPS switches to battery power to protect against sags, surges, or outages. (Sold usually as “Back UPS”.. we dont sell many of them)
- Line-interactive UPSs regulate voltage by boosting input utility voltage up or moderating (bucking) it down as necessary before allowing it to pass to the protected equipment or resorting to battery power. (Sold as Smart UPS, most common unit)
- Double-conversion UPSs isolate equipment from raw utility power—converting power from AC to DC and back to AC again—to deliver the cleanest power and highest protection. (Sold as Online UPS)
Performance while on Generator Power
Since the generator may have unstable voltage and frequency during start-up the UPS must be able to handle generator output aberrations. If this is not conditioned by the UPS, the unstable power can result in shut-down of equipment.
Standby and line-interactive UPSs must first quantify the source and then synchronize the inverter to this source before switching the load over to the generator. These designs are also tend to switch back to battery operation if generator frequency or voltage deviates even slightly.
Online UPSs ensure that even if the generator experiences unstable output voltage or frequency as the generator warms up (or due to other loads cycling on and off the generator) the UPS continues to operate on the rectifier, rather than switching to battery operation.
Since only online UPSs are isolated from the power (either utility or generator) they are uniquely able to handle frequent generator use. Dell has a nice visual showing how the process works. See their complete white paper here