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Smitty Two

In article ,
wrote:

On Thu, 17 Feb 2011 11:05:00 -0800, Smitty Two
wrote:

In article ,
wrote:

On Thu, 17 Feb 2011 08:50:59 -0500, Art Todesco
wrote:

I have a computer and DSL modem tied to an old UPS (with new
batteries). When I have a power failure, the computer keeps right
on ticking, but I always have to restart the DSL modem. I've even
restarted the modem while running on the UPS and after its restart,
all was fine. I am assuming here that the switch over time is
killing the modem. I looked at the modem and its walwart. It says
12 VDC. I was wondering if putting a few thousand micro farad cap
across the 12 volt line might help. Anyone have any experience with
something like this?
Using a cheap stand-by "almost" power converter?? (that's what APC
stands for)? Many of the cheap standby units have lousy transfer
times. Short of changing UPS units, the large 25 volt capacitor wouls
likely be the most effective solution. Don't whimp out and use a 12
volt. 16 would be OK, but a 25 will last a whole lot longer (you are
looking at unfiltered rectified ac, not clean DC on those power
warts).

More likely he's looking at a switching power supply in the wall wart.

Possibly - but there are a LOT that are non-regulated rectified
transformers - all the regulation is done in the device itself. Using
a 12 volt cap would be borderline, regardless. I would ALWAYS
over-rate by a minimum 25%. (which would be minimum 15 volts - closest
commercial value being 15vdc)

Down here in the U.S., the calendar reads 2011. The old linear wall
warts are all but long gone.