In my previous post about that device I described UPS Ever Duo II Pro working with nut under Linux, along with variables it exports, battery charge and drain cycles and this UPS’ issues. This follow-up is why using this UPS for serious unattended production environment is not a good idea.
As mentioned before, I have discovered and confirmed (two devices of the same model in a row) that the device has two major flaws:
- Does not always indicate LB status to the host despite audible fast-beeping
- Can easily be rendered unusable with completely fair (non-hackish) combination of commands and real-life circumstances
Just to recap – here’s the scenario an UPS is designed for and should honor (aside from situations when the user is just there to act appropriately):
- Power is on, status OL, host system is running
- Power goes out, status OB, host system notified and running (normally or with reduced activities)
- Power is out, battery goes low (status LB), host system notified and initiating forced shutdown
- Power is out, status LB, host system shuts down to a halt and commands the UPS to turn off and come back on when the power is back
- Power is out, system is down, UPS is off
- Power comes back, UPS goes OL, system boots
At any time the power may suddenly come back:
- at  until  – system running, forced shutdown not initiated, coming OL, notified, resuming any heavy-duty activities if suspended before
- at  until  – forced shutdown started, in progress or finished; to bring the system up there is no other way now than to run the whole power-off/power-on cycle – otherwise it will just stay halted after shutdown
The first flaw (no LB indication) may hit you at  unless you trust blazer driver’s calculations along with clone driver workaround. The timing might be wrong after some time (battery degradation) causing the obvious.
The second flaw is much more serious. If you are at or after  the power may come back at any moment, and the UPS must still honor the shutdown command and shut the load off, wait, and come back. Ever Duo II Pro does not and will leave you “with your pants down” to say colloquially. It will not shut down when OL, but after a single shutdown command in OL it will be shutting down every time it goes OB and there’s no way I have discovered to revert it to a sane state. It means that it will basically stop doing its main job. Additionally when in that lock-up state – it reports false values (i.e. ups.load stuck at 11 but nothing connected) for its variables and I am pretty convinced both flaws are a firmware issue.
If I remember correctly I have had this issue already about 10 years ago with a different Megatec-compatible UPS device. Looks like the firmware is buggy for ages and seems not to be fixed even today.
To summarize: Avoid this UPS for unattended production environments. And pay attention to any other Megatec-compatible UPS you get, the firmware may be at least 10 years old, unmaintained and with major bugs. On the personal side – I am tired of the situation with poor UPS-es and probably will be heading for a proven APC-Smart (unfortunately much more expensive).