[VoIP] Power backup questions

[Steph Kerman]

Jayson Smith wrote:
> One thing that annoys me is that while the power's out they go "Beep, 
> beep! Beep, beep! Beep, beep!" all the time. When the battery gets low 
> they change to going more like, "Beep beep, beep beep, beepbeep, 
> beepbeep, beebeep, beebeep!" or something, you get the idea. Do more 
> expensive UPS's either not beep as often or have an option to turn 
> beeping off, at least until the battery is low?
The expensive-at-the-time 1KVA AT&T "on-line" UPSs I acquired some years 
ago provide continuous power without transfer glitches.  They accomplish 
this by putting the incoming AC line through a 3-winding ferro-resonant 
transformer.  One winding goes to the line, the second to the load and 
the third to the inverter output.  The inverter runs constantly to 
maintain phase synchronization with the line but do not deliver 
current.  When the AC fails, the inverter delivers current.

The ferro-resonant transformer cleans up the input stepped sine 
approximation waveform to a reasonably clean sine wave form.  Perhaps 
there are more modern approaches using high frequency switching 
techniques but these work pretty well.  The transformer is massive since 
it is operating at 60Hz.  They have an RS-232 output to initiate 
shut-down of the PC and like yours also beep until the ALARM RESET 
switch is pressed momentarily.  That retires the alarm until the next 
power failure.  Or perhaps until the battery voltage drops to the point 
where shut down of the UPS is imminent.
> I think the Dlink router uses five volts, probably DC. No idea about 
> the DSL modem. Guess we'd have to take a voltmeter to those 
> transformers if we wanted to cobble together a charger. Yes, Radio 
> Shack did once sell a talking multimeter!
Unregulated DC output AC adapters must be measured under actual load 
conditions.  You should buy a matching coaxial power plug and socket to 
make a cord you can insert between the adapter and load.  This will 
allow you to measure voltage under load and load current.  You might 
find that the actual load is quite a bit lower than the ratings marked 
on the adapter.

Steph
> ----- Original Message -----
> From: "Doug Alderdice" <ka2wft at arrl.net>
> To: "Voice Over IP Tandem for Analog Switches" <voip at ckts.info>
> Sent: Tuesday, October 31, 2006 4:22 PM
> Subject: Re: [VoIP] Power backup questions
>> At 10:59 AM 10/31/2006 -0500, Jayson Smith wrote:
>>> Anyway, while the inexpensive UPS's kept all our computers going, 
>>> the router and DSL modem had problems. I guess either the DSL modem 
>>> or the router just can't handle much in the way of power glitches. 
>>> They were both on a UPS, but when the power died so did our DSL 
>>> connection.