GoKawiilOur company has always had many UPSs around for the convenience and business case of not suddenly losing a ton of work. We've been intrigued to check them out further, but have been wary of connecting any of them to measurement equipment considering the high voltages involved. There is a serious potential they could damage equipment or ourselves.
Despite all that, we're throwing caution to the wind to check out some UPSs from around the office. There are so many directions that UPS/surge testing could go so this article will cover the test setup and interesting exploration results.
Uninterruptible supply of uninterruptible power supplies.
Test Setup
We mean this, don't try any of this at home .
Our previous reticence to measure UPSs was centered around the connection of our very nice $50,000 Rohde & Schwarz MXO58 oscilloscope directly to mains power . Those unfamiliar with oscilloscopes may not know that the "ground" pin of the probe is electrically connected directly to the ground of all other oscilloscope channels, and the ground in your wall outlet. It isn't just a convenient way to refer to the negative/reference connection of the probe, and it can create unintended circuit paths if you're not careful.
The main concern with probing this equipment is creating a giant current path through the mains connection, probe, oscilloscope, and back through the connection panel to the outlet. This unintended circuit could seriously damage any sensitive measurement equipment in the loop before a circuit breaker or ground fault circuit interrupter(GFCI) cuts off the circuit. While there are safe connections that can be made, there is no guarantee that the building wiring is connected correctly or that there isn't a voltage differential that could cause issues. This is even more complex when you consider UPS wiring, and how it can switch between supplying mains power or the battery back-up powered signal.
This can be done safely with high voltage differential probes like the R&SRT-ZHD , but we don't have any. What we do have is a Chroma 61507 , a programmable AC power source, capable of generating its own isolated Alternating Current(AC) signal. The AC signal created by the Chroma 61507 is galvanically isolated from the "earth"/ground, providing a floating source. Connecting the oscilloscope probe ground connection to the neutral output of the AC source simply references it to ground and no circuit loops are created.
To avoid sticking probes directly into outlets, we added a 2x1 Molex Mini-Fit connector to a mains cable. This setup still requires considerable caution.
Oscilloscope Probe
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