LTT Labs used a galvanically isolated Chroma 61507 AC source and R&S MXO58 oscilloscope to safely capture and compare output waveforms from APC and Eaton UPS units.
Key Takeaways
The Eaton SMART1500PSRTNC (line-interactive, pure sine wave) switches cleanly; switchover gap is variable but one test nearly matched input phase within 16 ms.
The APC BE750G produces a blocky simulated sine wave on battery – expected at its price point but causes efficiency loss, vibration, and heat in connected equipment.
One APC BN1500M2-CA unit showed severely degraded battery output that persisted even under a 60 W load, suggesting hardware failure beyond a dead battery.
A working BN1500M2-CA has ~10 ms zero-voltage gap on unplug – at the edge of what ATX PSUs can bridge at full load.
All tested units show a zero-crossing transient/hitch in their battery-generated sine waves; planned follow-ups include harmonic analysis, surge handling, and ATX PSU holdover testing.
Hacker News Comment Review
The core measurement challenge – oscilloscope ground loops through mains – and the galvanically isolated AC source workaround drew attention as the technically interesting setup detail.
One commenter argues the entire AC UPS architecture is wasteful: generating a conditioned sine wave only for connected devices to immediately rectify it back to DC; DC UPS standards (common in telecom) are rarely mainstream.
