🚀 go-pugleaf

salman@sungear.mame.mu.OZ.AU (Salman SHAMI) writes:

>I like to leave my TV and VCR in standby mode. My CD player amp and tuner
>switched on. 

>How much power does each piece of equipment use when left switched on as
>described above ? 
>Does it make any difference if the volume of the amp is turned
>up or down ?

Contrary to what others have said, typical audio amps and receivers do use
significant amounts of power, even with no signal coming through.  
I took home a power meter* and measured power on a few components at
home, including two stereo receivers, rated about 50W/channel.  They 
both consumed between 30 and 50W when on but idle.  (Of course they
used more when on loud---100W out with 50W in would be impossible,
but at "reasonable" volumes it doesn't take much above the idle power.
A few watts can drive most speakers pretty loud--the 50W/Ch is only
needed for big peaks and such).

Even without any instruments, you can tell that a receiver takes more
than a few watts when idle--it gets warm, and that heat must come from 
somewhere.

The CD player I tested used something around a watt--I will check that
number.  

A rule of thumb that is that a watt for a year costs a dollar in
electricity.  Of course that depends on your electric rate, but it is
exact if you pay 11.4 cents per kW hr.  That is a bit higher than
average, but lower than what I pay.  In your decision of what to leave
on you might also want to consider environmental effects of burning
coal or whatever.

More technical details on amplifier power usage:  If it were a class A
amplifier, it would use many times the rated power output (at least 4x,
by the back of my envelope) on idle.  Class B would theoretically use
zero power on idle.  Class AB amps can be biased at many different
levels between the extremes of A and B, 
to make compromises between distortion, idle power, thermal
stability, etc.  So the numbers I measured are not unexpected,
expecially when you factor in the fact that the power supply is 
not all that efficient, and it has its own standby losses (likely mainly core
loss in the transformer).

I have never measured a TV's standby power, but I am suspicious of the 
information someone posted saying it was only milliwatts.  My
understanding is that that mode keeps the cathode hot for fast starting.
You can't keep anything very big warm with a few milliwatts.  I would
expect more like a few watts, but I will try to measure one tonight.

Charlie Sullivan                     charless@power.berkeley.edu

*Yes, it was a real power meter, that measures the average of the
instantaneous product of v(t) and i(t).  I did not measure
current and voltage seperately and multiply, which would have given
me an error due to the power factor.  What I measured is the same
thing your usage meter integrates, and so is what you pay for.