[Asterisk-Users] Asterisk Maintenance

[Colin Anderson]

>Also, the box is on a UPS, so I'm assuming the AC power is generated 
>from the battery and is a perfect sine wave.  But that begs the 
>question:  does a UPS system connect the mains to the output, or is the 
>input power used to charge the battery, and the battery used to generate 
>the output power?

Depends. A decent UPS is an "online" UPS meaning that the battery is
powering the output all the time. Catch is, online UPS'es are heat factories
and eat power because of AC->DC->AC conversion. Anything over 500VA that's
reasonably new should be an "online" UPS. They are better because there is
no fluctuation in the output in the event of a power failure, brown out,
etc.

The other kind is a "back" UPS with a switch that is essentially held open
by the presence of AC power. When the power fails, the switch is closed,
turning on the battery source. There is a lag, however small, between the
power failing and the battery kicking in. This messes up the sine wave and
causes problems in the case of a PC or a server. This is exacerbated by
power fluctuations such as undervoltage as the switch flip-flops back and
forth between battery and mains. I have observed this behavior with older
APC and *shudder* Tripp-Lite. Cheap Costco retail style UPS'es have this. 

If it says "back" anywhere on the UPS, get rid of it.