[VoIP] Power backup questions

[Steph Kerman]

What you propose is certainly more efficient than inverting battery 
power back to 120VAC. Whether what you ask about is feasible first 
depends on whether the devices use AC or DC wall warts. If they use DC 
wall warts, it's technically feasible and something could at least be 
cobbled together to do the job. If they use an unregulated brute force 
12VDC wall wart, you might well be able to find something off-the-shelf. 
If they use regulated 5VDC or some other regulated voltage it may be 
more difficult to find an O-T-S solution.

If the devices use AC wall warts, feasibility is technically 
questionable. Some devices that operate from AC wall warts simply 
rectify it to DC and can be operated directly from an appropriate DC 
source. Appropriate means that an AC voltage when rectified and filtered 
yields about 1.4X the AC input voltage. So 12VAC rectifies and filters 
to ~ 17VDC. However some devices that operate from AC wall warts 
actually use the 60Hz itself for one purpose of another such as for 
deriving a very low frequency clock or for powering a voltage doubler. 
I've seen modems with RS-232 interfaces that used the AC to derive the 
(+) and (–) RS-232 signal voltages. However it's not highly likely that 
the devices you're asking about actually need the AC.

Steph

Jayson Smith wrote:
> Hi guys,
> This is mostly off-topic, but this morning we had an approx. two-hour power
> outage.  Yeah Doug, I know that's nothing next to what you just went
> through!  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.  This has
> happened before when we would have tiny power glitches during storms and the
> UPS would kick in.  I'm considering the purchase of a more expensive UPS for
> my computers, probably one of the full ones that runs on battery even when
> the power's on so there's no switchover time when the power actually does
> die.  However, I don't really want to spend several hundred dollars for
> another such UPS just for our router and DSL modem.  That seems a bit
> overkill to me.  Both these devices use the typical wall wart type power
> transformers, so they can't be using much power.  I'm just wondering if
> there's any type of inverter/something out there that could help eliminate
> the switchover effects?  E.G. a very tiny full, always on battery, UPS that
> would only actually run these things for, say, ten seconds would do the
> trick, since the switchover happens well within one second of the power
> going out and the regular UPS would then be powering it again.  Any
> thoughts?
> Thanks,
> Jayson.
>