Uninterruptible Power Supply Systems come in a few basic varieties, each with its own advantages and disadvantages (such as features, cost, etc.). Below are the three main types of UPS systems:
The DC UPS 12W/9W is designed as a backup power for all kinds of DC power equipment such as routers, modems, remote monitoring systems and alarm systems. It can provide approximately four hours of backup time during a power failure and will recharge when AC power recovers.
The least expensive option, the off-line UPS charges the battery when mains power is active but is otherwise inactive until a power outage strikes. When this happens, the UPS switches to backup battery power giving the user time to either switch to a longer-term backup supply or to properly shut down the connected equipment. The off-line UPS does not provide protection from power sags and surges and therefore is not fit for applications where high availability is required or where protection from these power events is otherwise required.
This type of UPS system combines the inverter and charger in the power supply line for both the main AC power and the backup battery power. This configuration limits transient events when switching as well as speeding up the changeover from mains power supply to battery power when a power outage occurs. The line interactive UPS system provides more protection than an off-line (standby) UPS system but is also more expensive.
The on-line (double conversion) UPS provides the highest level of protection against outages and power quality problems. Rather than switching from the mains power supply to backup battery power when needed, the on-line (double conversion) UPS directly converts all AC power to DC power. Some of the DC power charges the battery while the rest is converted back to AC power to power the connected equipment. This double conversion action essentially prevents any power event from reaching the equipment therefore supplying the highest level of protection.