There's nothing too fancy in the analog processing department. All of the sensing and filtering is covered by a 324A chip (quadruple general-purpose operational amplifier), an LM358 (a slightly worse single general-purpose op-amp) and a handful of passives for voltage dividers and signal filtering.
The Three Stooges
As is common in better entry-level surge protectors, you get a pair of smaller, higher-voltage MOVs between ground and live/neutral, and a beefier lower-voltage MOV across live and neutral. The primary MOV is an Epcos S20K230, while the other two are GNR 14D361Ks. Although it's not visible here, there is an X-class filter capacitor hidden behind the Epcos MOV.
You're reminded of the possible presence of high voltage on your way in after pulling the battery out of its compartment. There's another reminder after pulling the PCB out from the enclosure. As before, the battery was disconnected long before you get to this point.
By the way, you can see that hidden gray X-class cap behind the MOV. You can also see a sample of those labeled connectors complete with function and wire color (always handy for re-assembly).
Simple Quality Control
A simple way to avoid boards getting etched with the wrong copper thickness or getting over-etched is to use one or more test tracks. The four pads are for what is called a Kelvin four-terminal resistance measurement. A known current is applied across the track using the end pads and the voltage across the test length is measured using the other two to accurately determine resistance. This eliminates the measurement error introduced by test leads when measuring very small resistances. Here, the markings tell us that if the board got etched correctly out of a PCB with two ounces of copper per square foot, the test track should measure 10mΩ.
There is another similar test track near the opposite board corner to check for etch and copper uniformity.
A pair of ST80NF55 FETs handle switching the inverter’s primary winding. Someone was clearly tasked with checking that those heat sink screws went in, with blue marker squiggles as proof, in addition to a few other components like the pair of 30A fuses in the bottom-right corner. If you did not already guess it from the part numbers, those N-channel FETs are rated for switching up to 80A and 55V.
How much power does the BE550G consume while plugged in? The answer is 48mARMS at 116V or 5.6VA with a power factor of 50%, which means only 2.8W of actual power dissipation. By feel, I can barely tell that the BE550G is above room temperature. This is much more reasonable than the SMART1000’s 12.4W and 40-45 °C chassis temperature.
BE550G vs. SL300
This looks a fair bit different from the LX and SMART: the BE550’s inverter output only goes to 160V instead of the other two’s 180V. Because of that, it needs a higher duty cycle (roughly 50%) to provide 118VRMS. The combination of higher duty cycle leaving input capacitors less time to discharge into the load (my 80W LED strip) and lower inverter output voltage also reduces its current peaks from 3.5A to 2A.
Out of curiosity, I plugged the output waveform data into my power analysis spreadsheet and calculated the THD of this voltage waveform to be only 41%, 4% better than stated on the label.
After seeing how many corners Tripp-Lite cut in the SMART1000, I was curious to find out if the much cheaper APC BE550G would fare better. For half the price, you get a slightly worse battery (7Ah vs. 8Ah), 77% lower standby power consumption, no built-in display and no AVR function, even though the transformer has the necessary extra winding and connectors for every wire except the battery’s negative terminal. It looks like APC doesn't shave as many pennies from its entry-level products as Tripp-Lite does from its mid-range designs.
I did find three flaws in the unit’s design: the seemingly incorrect location of the first common-mode choke, the use of a #18 jumper wire for the PCB and battery backup outlets’ ground, and, most important, the use of those unreliable flap strips for the ground contacts. Thankfully, none of the equipment I plan to connect to this UPS has ground connections, and I have no plan to use the surge-only outlets either. As a result, all three complaints become non-issues for my application. The use of second- and third-tier capacitor brands may also be a point of contention. Since the unit is covered by a three years warranty, I would expect the capacitor selection to be reasonably conservative.
Apart from my disappointment with the ground strips, the BE550G appears to be a fine little UPS.