An uninterruptible power supply (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. The on-battery runtime of most uninterruptible power sources is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment. A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption can cause serious problems.
In this tear-down I take a look at what is inside Trust Power Master PW-4095T – UPS – 950 VA UPS. First take a look at some basic information and the specifications on the device. This device is marketed as a reliable 950 VA UPS mains power protector for office and home usage. This device is designed to work with 230V AC voltage (can accept AC 170 – 280 V). It has Power Capacity of 950 VA. It uses line interactive UPS technology.
What is inside Trust Power Master PW-4095T – UPS – 950 VA UPS?
Here is view to the electronics.
There is main circuit board on the left. The heavy parts, battery and transformer, are on the right. The battery is clearly broken.
Here is a closer look at the main circuit board. It is interesting that the high current carrying wires going to transformer are bolted to the inverter switching transformer heatsinks. There are several relays on the circuit board, and I quess they are used to implement the input mains power transfer switch functionality and transformer tap switching for voltage regulation. The small circuit board sticking on the right is the telephone line surge protector. For mains power surge protection there seems to be a yellow VDR near mains power connector on the right.
A look at the specification of the broken battery. It looks like quite normal 12V sealed battery .The battery type is HR1234W from CSB battery. According to battery data sheet the battery has 34W @15min-rate to 1.67V per cell @25°C and maximum 130A discharge current.
Besides the battery, the transformer is also pretty big, because it needs to handle that 950 VA power.
This teardown ends here. Now some UPS theory related to this device:
According to APC white paper on different types of UPS systems Line Interactive is is the most common UPS design used for small business, Web, and departmental servers. In this design, the battery-to-AC power converter (inverter) is always connected to the output of the UPS. When the input AC power is normal, the inverter circuit works in “reverse mode” charging the batttery. When the input power fails, the transfer switch opens (disconnects the mains input connector from outputs) and the power flows from the battery to the UPS output (generates mains output waveform to output). You can find block diagrams of line ineractive UPS system from APC white paper and pcguide.com.
The inverter/converter is also normally fitted with circuitry to filter out noise and spikes. Line Interactive design usually incorporates a tap-changing transformer to provide means of voltage regulation by adjusting transformer taps as the input voltage varies. This topology is inherently very efficient. According to Line-interactive vs On-line Network UPS Systems and Which Should You Choose? article at the most basic level, line-interactive UPS systems are less expensive than on-line UPS systems (approximately 20 to 40% less, depending on the model and manufacturer), but they also provide less protection than on-line UPS systems.