This is the teardown of an APC Smart-UPS 1000VA (SUA1000RMI2U). An UPS is a device which powers other devices for a short time in case of a mains power failure. This allows the connected devices to shut down properly.


This UPS comes in the form of a 19 inch U2 rack mount case. The case is built to support the more than 18Kg of batteries and other components. There is a sticker on the back of the case which warns users about its weight.

Front panel

The front panel is a single plastic part which pops of easily when pulled back by the two tabs on its sides. There is a cutout on the right side through which the control panel is accessible. The covers up the battery pack and the connector which connects the battery pack with the device.

Front panel

Control panel

The control panel only has two buttons; an on/test button and an off button. There are sixteen LEDs; five LEDs on the left of the control panel indicate the power draw through the device, the five LEDs on the right side of the control panel indicate the charge level of the battery pack. The six remaining LEDs are these:

  • AVR Trim - The UPS is compensating for a high mains voltage.
  • Overload - Overload condition.
  • Online - The UPS is supplying mains power to the connected devices.
  • On Battery - The UPS is supplying battery power to the connected devices.
  • AVR Boost - The UPS is compensating for a low mains voltage.
  • Replace battery - The battery has failed and should be replaced.

Control panel

Back panel

The back panel is not part of the case, it is a separate panel which is screwed into the case. It has a single C13 connector for mains input and a four-way C14 connector for mains output. There is an overload protection reset switch which allows a user to manually reset the builtin overload protector.

Furthermore, here is a connector for serial communication which uses a non-standard pin-out and a standard USB-B connector. There is also a slot for expansion cards which APC called SmartSlot. Then there is a button for setting the device’s sensitivity for voltage distortions and an LED indicating said sensitivity.

Back panel

Front panel PCB

The front panel PCB is connected to the main PCB by a soldered flat flex cable. There are sixteen LEDs driven by two NXP 74HC595D 8-bit shift registers. There are two carbon pads for the on and off buttons. The light emitted from the LEDs is guided to the front of the device by a plastic light guide.

Control panel PCB

Light guide

USB breakout PCB

The USB-B port on the back of the device has its own small breakout board. This board is based on an STMicroelectronics ST72F63BK4M1 8-bit microcontroller. The microcontroller is used for providing the USB interface and is accompanied by a 24MHz crystal. The 24MHz frequency of the crystal is no coincidence, as an USB 2.0 interface run at two times that frequency: 48MHz.

USB breakout PCB

Ethernet expansion card

This UPS came with an ethernet expansion card in its SmartSlot. This card exposes a single RJ-45 ethernet connector, a 2.5mm jack for console output, and a reset switch. This expansion card is based on an APC branded chip (359-0267-Z). The chip is accompanied by a Spansion S29JL064J 64Mbit flash chip.

Ethernet card

The board has a 3.3V lithium backup battery, indicating that the main chip features a RTC. Note the neat routing of the address and data traces under the unpopulated flash chip.

Ethernet card flash chip

The physical layer of the network connection is handled by a Micrel KSZ8041NL/RNL Physical Layer Transceiver. Next to the RJ-45 connector are some unpopulated connectors. There is another version of this board that has two additional RJ-45 connectors for universal I/O and two USB-A host ports.

Ethernet card connectors

As you may have noticed in the above image, there are some small triangular exposed copper pads. These are spark gaps and protect the data lines from voltage spikes. Sparks will form across these gaps from the data line to the ground plane of the board. For more information on spark gaps, watch EEVblog video #678.

Ethernet card power section

A Texas Instruments SN65HVD230D 3.3V CAN-bus transceiver can be found right above the card’s edge connector. However, I did not find any CAN-bus related chips on the main PCB. Chances are that there are larger devices or installations made by APC that use a CAN-bus for internal communication.

The power for the components on this board is regulated by three individual regulator chips. The first one is an ON Semiconductor NCP3063B step-up/down/inverting switching regulator. The second one is an ON Semiconductor NCP5500B LDO regulator. The third one is an ON Semiconductor NCP1595C synchronous buck regulator.

Main PCB

The main PCB is the biggest board in the device. It takes care of the mains power distribution, mains power generation, and battery management. Refer to EEVblog video #504 for a proper explanation on how a UPS works.

Mains input filter

The mains power enters the board through the white two-pin connector between the yellow and blue filter capacitors. A blue varistor can be seen right behind the input connector. The varistor protects the device from voltage spikes.

Main PCB: Filter area

The input is filtered, from right to left, by a 1.0µF capacitor, a common mode choke, and another 1.0µF capacitor. One of the mains input lines is then filtered by an inductor. A second inductor, for the other mains input line, is missing. It has been replaced by a 4.8mm spade connector which is only used as a jumper. Finally, the input is filtered by a 2.2µF blue capacitor.

Mains input relay

There are multiple relays in the high voltage area of the main PCB. The black relay is rated for switching 250V AC at 12A. This relay switches both mains input lines. A current transformer sits next to the relay.

Main PCB: Input relay

Mains output relay

The mains output connector on the back panel is connected to the three pin connector. Only two of the three pins are used. This is to prevent mistakes during assembly.

Main PCB: Output relay

On the left side of the output connector are three X and Y rated capacitors. The black part right behind these capacitors is a Panasonic ZNR V14471U. This part absorbs transient and surge currents.

A Omron G2R-1-E relay is mounted on the right side of the output connector. This relay is used to switch the output on and off. On the right side of that relay sits the second current transformer (460-1501-A-Z). This transformers primary side is connected in series with one of the output lines.


The main transformer is too big to be mounted on the main PCB. Its primary side connects to the main PCB with four wires. These connect to different windings which can compensate for lower or higher mains voltages. The windings are selected with two additional relays on the main PCB.

Main transformer

There are two smaller transformers mounted directly on the main PCB. These transformers bring down the incoming 230V AC to 12V AC and 24V AC. These transformers are used for measuring the mains voltage.

Main PCB: Transformers

Serial port

The serial port is mounted in the high power section of the main PCB. The serial port has a proprietary pinout and is driven by an ON Semiconductor 361-0005V2.

Main PCB: Serial port


The microcontroller on the main PCB is an Intel 87C51FB1. This microcontroller is based on the Intel MCS-51 architecture. It has a 16MHz crystal next to it and it is connected to a ST M93C56 2kb EEPROM.

Main PCB: Microcontroller

SmartSlot connector

The SmartSlot on this device is connected with a ribbon cable to a 90 degree angled IDC connector. Next to this connector are two NXP 74HCT257 multiplexers to extend the microcontroller’s outputs.

Main PCB SmartSlot connector

Power supply

The main PCB has its own power supply for all the chips on the main PCB. This power supply seems to draw power from the 24V rail coming from the batteries. The 24V is stepped down to 5V to supply all the chips on the main PCB with power.

Main PCB: Power supply


The main PCB has a H-bridge to drive the main transformer in case of a power failure. This H-bridge is made with eight N-channel MOSFETs, which work in pairs. The H-bridge is controlled by an Intersil HIP4082IBZ.

Main PCB: H-bridge

The H-bridge is based on ST STP140NF55 N-channel MOSFETs, capable of switching 55V at 80A. When the UPS is charging its batteries, the power flows through the substrate diodes of the MOSFETs. The H-bridge acts as a rectifier in this configuration. The heatsinks are used to connect the main transformer and battery to the MOSFETs.

Main PCB: H-bride MOSFETs


The batteries were enclosed in a separate metal case. This case could be slid out of the device. This particular unit unfortunately killed its own batteries, causing them to bulge and eventually tear their own case apart, leaking acid all over the battery case and the connectors. The case contained four 12V 7.2Ah lead acid batteries, connected series parallel.