Re: Those who tried double conversion ups
Posted: 11 Oct 2025, 09:40
Not related to what you quoted but allrightFpsgamer wrote: ↑11 Oct 2025, 08:59I mean we've seen the results, it doesn't require a scientist.amorou wrote: ↑11 Oct 2025, 08:54Hmm somebody wrote in hifi forum:
As an electrical engineer I can only say none of the so called pure sine wave commercial 1 phase UPS can provide you a pure sinewave as even a small kerosene engine driven genset can. They don't turn in a magnetic field like an AC generator in a perfect circle to produce a sine wave. All of them chop the DC and serve a chowmein of harmonics whatever filter they use.
Unless you have a 3 phase isolation transformer with delta connected primary and star secondary you are not going to eliminate fully the harmonics generated by the chowmein supply feeding into your gear. And for that you need a 3 phase UPS.
Chat gpt response:
Engineer is partly right, partly exaggerating. Let’s dissect what’s true, what’s outdated, and what matters for your PC.
What they’re correct about
UPSs don’t “generate” sine waves magnetically.
True — an AC generator’s rotating magnetic field produces a naturally perfect sine waveform by physics.
A UPS inverter digitally synthesizes the sine wave from DC using pulse-width modulation (PWM).
That means the waveform is composed of many high-frequency pulses that are then filtered by inductors and capacitors.
Even the best UPS inverter will have tiny high-frequency components (tens of kHz).
These are far above 50 Hz and easily rejected by any power supply — but they do exist if you measure with an oscilloscope.
It cancels common-mode noise, shifts ground references, and blocks many harmonics.
In datacenters, it’s the “gold standard.”
What they’re wrong or overstated about
“Commercial UPSs produce chow-mein of harmonics.”
Modern double-conversion UPSs (from Eaton, APC, Vertiv, etc.) use high-frequency PWM and multi-pole LC filters.
Output THD is < 2 % with linear load, < 5 % with nonlinear load — that’s far cleaner than most household grid feeds (which are 4–6 %).
The harmonics they do have are in the 20–100 kHz band, well outside your PC PSU’s sensitivity.
Not true — single-phase UPSs can and do produce near-perfect sine waves.
The 3-phase delta-star idea is about isolation and phase cancellation, not about the purity of the sine wave itself.
For a small single-phase load (like a PC), the difference is academic.
What you can do is make sure you don't use your pc on overloaded breaker in your house and make sure your plug is connected right.
My grounding is nearly non-existent(very high resistance) and yet pc works fine.
What they’re correct about
UPSs don’t “generate” sine waves magnetically.
What they’re wrong or overstated about
“Commercial UPSs produce chow-mein of harmonics.”