[Asterisk-Users] Asterisk Maintenance

[Peter Svensson]

On Fri, 10 Dec 2004, Jim Van Meggelen wrote:

> > 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?
> 
> It seems to be common these days to have a relay that switches you to
> battery when the AC fails. This is supposed to happen fast enough that
> the caps in your power supply won't drain before the batteries kick in.
> Kinda disturbing in a sense, but this is very common. I think you're
> going to tend to pay a lot of money for an online UPS system.

There are a few terms that are commonly used here:
 * on line ups
 * off line ups
 * line interactive ups

An on line ups keeps the rectifier and inverter active the whole time. The
incoming power is run through the DC bus and turned to AC again. This
provides the best possible isolation of power problems in the incoming
line. Brownouts, spikes, dips, even frequency errors can be fixed. The
price is a constant low efficiency (may be as bad as 90% efficiency, even
lower on older models).

An off line ups is normally running in bypass mode. When it senses a 
problem it cuts over to the inverter and runs on the battery. Most of the 
times they have a transformer with different taps to compensate for 
over and under voltage. They have very high efficiency. There can be 
momentary problems at the time of switchover, and they do not handle 
waveform errors.

Som ups:es have a serial transformer that can compensate for errors in the 
waveform etc. They are somewhere in between the two above forms in terms 
of performance. APC uses this technology in several of their ups families.

> I have often wondered if some of the problems folks have with the TDM
> cards could be corrected with some power quality engineering. It's one
> of those things that provides measureable benefits if you have enough
> statistics, but it's hard to sell prevention. I have been asked
> questions like "why did you make us spend thousands of dollars cleaning
> up the power? This system hasn't had any of the problems you said we
> might. What a waste of money!"

One one hand the power that comes from the power lines in the wall socket 
can be quite crappy, with switching power supplies, indoor lighting etc. 
On the other hand, a properly designed audio system should not pick up 
these things. It should really _really_ be resistant to the effects of 
power line radiated fields.

Peter