There are 3 fundamental types of ups systems: standby, line interactive and online ups, which all come in various capacities.
- Standby ups
Also known as an offline ups or voltage and frequency-dependent ups, is the most common type of ups system, offering basic power protection and backup battery capabilities. Standby ups can prevent power failure, voltage surge and spike. However, they cannot regulate power drop and transient voltage. For that you would need at least a line-interactive ups.
When the main power supply is above or below the normal limit, the load is transferred to the inverter output, typically within 5-8 milliseconds. They are called "offline" or "standby ups" since the inverter is switched off by default.
Most of these units only run for 5-20 minutes to give you enough time to properly shut off your computer. Standby ups are best-suited for small, non-critical electronic devices and home/personal office use, such as 300 watt pure sine wave ups inverter.
- Line-interactive ups
Line-interactive ups systems are the next step up in power protection and cost from standby ups. In this type of ups, the inverter is always on and connected to the ups output. Line-interactive ups have automatic voltage regulation, using transformers to keep the voltage within set low/high limits. Whereas a standby ups would switch to battery power in such an instance, line-interactive ups systems do not. This can not only save battery power in the short term, but also save battery life in the long term.
Unlike standby ups systems, the ups inverters of line-interactive ups systems are part of the output and always connected. When the input AC power supply fails, the change-over switch will change the direction within 4-8 milliseconds to make the battery power flow to the ups output. It might not fit very sensitive electronics, so you may need to look to online ups.
In case of power failure, most line interactive ups systems provide pure sine wave output, making them a good match with most equipment.
- Online ups
Also called an online double-conversion ups, online ups systems provide the highest level of protection for IT equipment in hospitals and data centers. They are called double conversion because they convert the input AC into DC, and then convert the DC back to AC output through inverter.
Online UPS prevents any power transmission irregularities, protects against all potential power problems, and provides continuous and consistent power and protection in the event of power failure, surge, drop or any common power problems outlined in the above section. The output regulation is also much more precise than line-interactive ups, ensuring that connected electronics are not damaged by over or under voltage.
