In this teardown, we will take a look at an APC Smart-UPS 1000VA (SUA1000RMI2U). An UPS is a device that protects other devices from mains power failures by temporarily providing power from its batteries.

You'll typically find these devices connected to servers to prevent data loss. When mains power fails, the server receives a signal that a power failure occurred. The connected devices then have about 5 to 10 minutes to shut down. This time depends on the size of the battery of the UPS and the current drawn by the connected devices. In these few minutes, the server can shut down safely without data loss.

Essentially, these devices are just battery packs that wait for the mains power to fail. Put that way, it sounds like they are quite simple to design, but there is a lot more going on in these kind of devices. Lets see what goes into making these devices work!


These devices come in a variety of different shapes and sizes. This particular unit comes in the form of a 19 inch U2 rack mount case. The case is decently built, as it needs to support more than 18Kgs of batteries and other components. There is a sticker on the back side of the case that warns users that it weighs more than 18Kgs.

Front panel

The front panel is made out of a single piece of plastic. This panel pops off very easily when pulled back by the tabs on both sides. These is a cutout on the right side in which the permanently mounted control panel sits. The front panel gives access to the batteries and the connector with which the battery pack is connected to the device itself.

Front panel

Control panel

The control panel is very limited. It has only two buttons; one on/test button and one off button. The five LEDs on the left of the control panel indicate the current load on the device (how much power is drawn). The five LEDs on the right of the device indicate the charge level of the battery pack. Then there are the following LEDs (listed left to right, top to bottom):

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

Control panel

Back panel

The back panel is a separate piece of metal, as the connectors on this panel differ around the world. This panel is attached to the frame of the device by multiple screws.

There is a single C13 AC-in connector for mains in. Next to the AC-in connector sits an overload protection reset switch. This is an automatic overload protector, independent from the any overload protection on the main PCB. The four-way C14 AC-out connector is mounted next to the reset switch.

Back panel

In addition to the power connection, the back panel exposes two data ports. The first one is a serial port with a proprietary pinout. This means it is not compatible with any standard RS-232 connectors found on PCs or servers. The second data connector is an USB-B port. There is also a slot for expansion cards (called SmartSlot) and a button the set the device's sensitivity for voltage distortions with an accompanying LED to indicate the sensitivity.

Front panel PCB

The front panel PCB is the simpelest PCB in this device. It was permanently connected to the main PCB by a flat flex cable. The board itself does not contain much exiting components. There are sixteen LEDs driven by two NXP 74HC595D 8-bit shift registers. There are also two carbon pads for the on and off buttons.

Control panel PCB

The light emitted from the LEDs is guided by a specially made piece of transperant plastic.

Light guide

USB breakout PCB

The USB breakout PCB is maybe as boring as the front panel board. It has a single USB-B connector. Next to that sits a mounting bracket, used to attach the PCB to the back panel.

The only chip on this board is a ST ST72F63BK4M1 8-bit microcontroller providing the USB interface. The microcontroller uses the 24MHz crystal to generate its clock signal.

USB breakout PCB

Ethernet expansion card

This UPS came equipped with an ethernet expansion card in its SmartSlot. This card exposes a single RJ-45 etherenet connector, a 2.5mm jack for console output, and a reset switch.

Ethernet card

This expansion card is based on an APC branded chip. The part number of this chip is 359-0267-Z. I could not find any datasheets or other resources on this particular chip. The chip is accompanied by a Spansion S29JL064J 64Mbit flash chip.

The board also came with a 3.3V lithium backup battery, indicating that the main chip features a RTC. Also note the neat routing of the address and data traces under the missing 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 empty pads. There is another version of this board that does have them all populated. That board has two additional RJ-45 connectors for universal I/O and tho 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 pads form so called spark gaps. These gaps protect the data lines from large 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 most complex and therefore the most interesting part of this device. This board takes care of the power distribution and battery management. I will not be able to explain exactly how this UPS works. For a comprehensive explanation of how a similar UPS works, watch EEVblog video #504.

Mains input filter

The mains input enters the board through the white two pin connector behind the yellow filter capacitor. A TDK S14 K420 varistor can be seen, right behind the input connector. This component is connected to both input lines. It protects the device from large voltage spikes.

Main PCB filter area

The input is then filtered by a 1.0µF capacitor, the rightmost yellow part. After that, the input is filtered by a common mode choke (420-0003-Z). Then the input is filtered again by a 1.0µF capacitor.

One of the input lines is then filtered by a inductor, the other is not. There is room on the PCB for a second inductor for the other input line. Instead there is a spade connector, not intended to plug anything onto, but to provide a solid link. Then there is yet another, this time blue, capacitor over the input lines. It has a value of 2.2µF.

Mains input relay

The main PCB has multiple relays mounted in the high voltage section. The first one, seen from the input, is a Song Chuan 894H-2AH1-F-S 250V 12A relay. This relay switches both input lines and is the black component on the image below.

Main PCB input relay

A current transformer is visible next to that relay. This part is marked 460-0006-Z-01, which is an APC specific part number. The thick copper wire going through the middle of the transformer is connected in series with the large yellow 2.2µF capacitor in the background. I think this transformer is used to read the current going into the main transformer, but I am not entirely sure.

Mains output relay

The mains output to the back panel of the device is connected to a three pin connector, close to the input connector. Two of the three pins of that connector are connected together. The designers probably chose for a three pin connector so that the input and output can not be mixed up during assembly of the device.

Main PCV 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.



In addition to the power in and power out enable relays, there are two additional relays placed on the main PCB. These relays determine which windings of the main transformer are used. The used windings can be changed to correct for lower or higher mains voltages. Behind the first relay visible in the below image, you can see a part of an STD5NE10 100V 5A N-channel MOSFET used for driving the relays.


In addition to the main transformer, there are two smaller transformers soldered directly on the main PCB. These transformers have the APC part number 430-0030B-Z and transform the incoming 230V AC to 12V AC and 24V AC. The outputs of these transformers are used to measure the voltage level of the high power side. These are probably not for powering the low voltage electronics as the traces coming from these transformers are too small to carry any significant current. And as we'll later see, there is a small transformer further down the main PCB providing power the the chips on the main PCB.

Serial port

The serial port is mounted in the high power section so the connector can stick through the back panel. The serial port itself has a proprietary pinout. The serial port is driven by an ON Semiconductor 361-0005V2, which is also an APC specific part number. There is a power line going to the serial port connector. This line is regulated by an ON Semiconductor LM317T regulator. Next to the serial connector are the button and LED for sensitivity settings.

Main PCB serial port


The microcontroller on this main PCB is manufactured by Intel. Its part number is 87C51FB1.
This microcontroller is based on the Intel MCS-51 microcontroller architecture. It uses a 16MHz crystal next to it for its clock signal. The microcontroller has access to a ST M93C56 2Kb EEPROM next to it. Also visible on the image below is a Texas Instruments TLC0838C 8-bit ADC.


SmartSlot connector

The SmartSlot on this device is connected via 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 mounted on this board. This power supply seems to draw power from the +24V rail coming from the batteries. The 24 volt is then stepped down to 5 volt to supply all the chips on the main board with power.

Main PCV power supply

It looks like the 24 volt is first stepped down using the small transformer, driven by a Fairchild NDT3099 60V 4A N-channel MOSFET and a Fairchild NDT2955 -60V -2.5A P-channel MOSFET. Then, the voltage is rectified by single diode and with a capacitor to smooth the output. Then there is an ON Semiconductor NCP1117 voltage regulator outputting 5V.


The last major part of the main PCB is the H-bridge driving the main transformer in case of a power failure. An h-bridge is typically made with two N-channel and two P-channel MOSFETs. However, this h-bridge is made only with N-channel MOSFETs, as it is more efficient. To make this h-bridge work, a specialized chip made by Intersil is included. This chip, the HIP4082IBZ, is specifically designed for controlling a h-bridge made with only N-channel MOSFETs.

Main PCB H-bridge

The MOSFETs used in this H-bridge are ST STP140NF55 55V 80A N-channel MOSFETs. When the UPS is charging its batteries, the substrate diodes of the MOSFETs are used to rectify the power coming from the main transformer. The 24V is cleaned up by a single 40V 2700µF capacitor. The heatsinks on which the MOSFETs are mounted are also used for connecting the main transformer 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 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.