"(Pete said:
I've got a half-dozen USB2 and FirwWire devices hanging on my PC.
Just plugging everything into a power strip and then plugging the strip into the
UPS works....sort of... but it seems like there ought tb something out there
that does the job automagically.
This would appear tb a legitimate UPS function....UPS knows when there's a load
above a certain level on a specified plug, then it cuts/restores power to the
others accordingly.
Seems like many years ago, there were power strips that did that - sensing the
load on a pass-through plug and turning the other on/off.
Anybody know of anything?
I tried a search on "current sensing" "power strip"
as two terms (include the quotes), and there are still products
being offered. Try your favorite search engine. Here
are the first two I found:
http://www.sousley.com/280/0121.htm
http://www.smarthomeusa.com/Shop/Hardware-Cable/Item/LCG1/
The only thing to watch for here, other than the quality of
the designs, or whether the layout of the strip is "brick
friendly", is that the current flow from a sleeping computer
is not likely to be sinusoidal. The current waveform becomes
more regular looking at high load, but not at low load (during
sleep for example). I've tried measuring sleep current with my
clamp-on ammeter, and even though my meter claims to be
"true RMS", I don't get correct readings from a sleeping computer.
(If I place an electric kettle on the same circuit as the
sleeping computer, and measure the summed current of the two
loads, then subtract the kettle by itself, the difference works
out to being closer to the correct answer, than just measuring
the computer by itself.)
One poster here, complained that his current sensing strip
didn't work properly with his computer.
You would really want a product, where the sensitivity was
adjustable, or the designers recognize that the controlling
device will be a sleeping computer. A sleeping computer can
draw up to 5V@2A, depending on how many USB devices are
receiving cable power while the computer sleeps. If the power
supply is only 50% efficient at making +5VSB, the wall plug
sees a 20W load. Your strip will have to recognize a sleeping
computer with load between say 5W to 20W, as "off".
You can look at ATX power supply input waveforms here. There
are ATX supplies without PFC, power supplies with passive PFC,
and power supplies with active PFC. The power supply with
active PFC has a near to sinusoidal current comsumption. What
I cannot tell you, is whether the active PFC power supply
continues to be sinusoidal at low currents, like when only
+5VSB is made during computer sleep. It could be, that a
PSU with active PFC, will work more reliably with a current
sensing strip, than your average non-PFC power supply.
http://www.xbitlabs.com/articles/other/display/psu-methodology_9.html
In any case, this will be a pretty expensive experiment, if
the payback is through a reduced power bill.
There are, of course, more high tech AC control technologies,
like X-10 controllers, that allow control remotely of appliance
loads throughout a house. I had a friend who had a whole house full
of X-10 switches, and the only device that was not switchable,
was his refrigerator
Paul
