Don't know about the sub-woofer. But I can take a stab at the rechargeable
devices. Our house is "off-grid" and uses solar panels, battery bank,
inverter, back up generator and that whole trip. People like me pay a LOT of
attention to power usage of appliances and gadgets. So there tends to be a
lot of discussion around things like rechargeable items (which waste lots of
power).

When a rechargeable battery reaches full charge, most chargers still
maintain what is called a Float charge. All batteries self-discharge over
time. NiCad batteries are especially prone to self-discharge. They
continuously loose a little bit of charge just sitting there. The float
charge constantly flows a little bit of current into the battery so it
maintains full charge.

Additionally, the last 2% to 5% (depending on battery type) of a battery's
charging cycle tends to be fairly slow. It takes a long time to charge that
last 2-5% without overcharging (overheating) the battery. The float charge
slowly charges this last little bit and helps maintain the battery life. A
battery that never reaches full charge tends to die sooner.

Cheap rechargers as are found in many "gadgets" do a very bad job of the
float charge. The rate at which the batteries charge is related to the
difference in voltage between the charger and the battery. Cheap "slow"
chargers essentially just run at a voltage such that when the battery is
fully charged they are close to the same voltage. Many don't really adjust
themselves to the fully charged battery. Instead the battery at full charge
resists what the charger is trying to push in. These chargers still use a
fair amount of power even though the batteries are fully charged.

A slightly better method is an on/off switched charger. Battery is charged,
voltage rises to a trigger point, charger shuts off, battery voltage drops,
charger comes on again. Usually in a fairly quick cycle. Much safer and
harder to overcharge the batteries. But it still eats power,

More expensive chargers, such as so called "fast" chargers one sees for
cordless drills and other bigger tools are better still. They at least have
true "bulk" versus "float" charge settings. They pump in a lot at first
(large voltage differential). Then they sense when the batteries are
approaching full charge and cut themselves back to a true float voltage. You
will usually note such chargers do not run nearly as hot once the battery
reaches full charge. Though they still use some power maintaining the float
charge.

My best guess on the sub-woofer is it may be similar to most TV sets. The
"instant on" feature of the picture tube keeps flowing power through the
tube to keep the element warm. Most TV's which are supposedly off still use
a fair amount of power. My best guess is the sub-woofer keeps some of it's
electronics active so it is ready to respond instantly when it receives a
music signal.

Timothy Atwood
Holtenwood Computing
http://www.holtenwood.bc.ca/computing/


-----Original Message-----
From: Shahan, Ray [mailto:[log in to unmask]]
Sent: Monday, September 08, 2003 1:05 PM
To: [log in to unmask]
Subject: OT: Electricity usage


Hi all,

        Forgive the OT (and my ignorance of how electricity works), but I
couldn't seem to readily locate the answer to a question I have regarding
electricity usage.  I have several gadgets (flashlight, cordless
screwdriver, etc..) that are rechargeable and the directions to these
products state that once the product is fully charged I don't have to unplug
it.  The question I have is if there is no more electricity being used, then
why does the AC-to-DC converter remain warm (very warm)?  Doesn't the
presence of heat indicate an electrical discharge/action is taking place?

        This same question bothers me about my SRS sub-woofer...it has an
auto-on feature, so that the amp is supposed to turn off if no music signal
is present (after some elapsed time period), however, the heat sinks on the
back of the sub-woofer are still fairly warm even if it's not been used for
several days.

        TIA to anyone with the patience (and time) that can explain this to
me (in oh, let's say, 3rd grade level knowledge).   :-)

Ray Shahan

"There is so much good in the worst of us,
and so much bad in the best of us,
that it behooves none of us
to talk about the rest of us"
                  --Robert Louis Stevenson?


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