how much standby power do ALL your appliances use? - Page 6

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Re: how much standby power do ALL your appliances use?

The instrument you are using is not precise, and I would not consider it
accurate. Watts are very difficult to measure directly because they are
a result of a number of electrical factors from the combination of
current, voltage, and the phase of the load. The simple power meter that
you bought can only measure a pure resistive load, such as a light bulb,
or a heating element that are not thyristor controlled. It cannot
measure a fluorescent lamp because it would be driven through a current
regulated reactive device called a ballast.

Most appliances including your TV, computer, and many home entertainment
systems use switching power supplies. These are complex power supplies
using high frequency inverters. Their load on the AC line cannot be
easily directly measured. They change the phase of their power
consumption depending on how they are loaded. Internally they use a
system of changing the switching duty cycle for their inverter at a very
high frequency, which really makes things more complicated.

In your list you actually have some items that are indicating 0W
consumption, and I know for a fact that they do draw some power. The
readings of the items below are make no sense at all. If you have a lit
LED panel, there has to be some power being pulled from the AC mains.
You would have to have perpetual power do have no power consumption!
Your IR activated remote has its processor working all the time in order
to know that the remote has been commanded. The phase of the loading of
these devices is fooling your Watt meter.

New fridge with LED panel lit up, compressor not running 0W (Impossible)
IR activated remote control curtains 0W (Impossible)
Toaster with 7 segment standby indicator 0W (Impossible)

I suggest you take that gadget you bought, put it back in to its box,
and send it back for a refund if you can!

There are power analysers that can make an accurate measurement, but
this type of instrument is very expensive in relation to what you would
spend for home use. These analysers can look at apparent, resistive, and
reactive power. Then they can do some calculations to determine the
actual power consumption.

What you can do is get a good quality true RMS DVM that can measure AC
Amperes (expensive). You will then have to rig up a series adaptor to
put the meter in series with the load.  Now you can take a current
measurement. From this you can then calculate an idea of the power

For most appliances that have a standby mode, disconnecting them from
the power when not in use is not a good practice. You will find that
over time you may end up with some power supply failure, and at least
you will shorten their lifespan and dependability. As for TV sets, VCR's
(if you still own one), and many other types of appliances, they have
memory set-ups. If you leave them too long without power, their internal
time keeping and set-ups will not be maintained.

The bottom line is that the numbers you came up with have no accurate



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Re: how much standby power do ALL your appliances use?

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**  Err  -  they can actually.

A typical SMPS is just another electronic load on the AC supply -  but
without the complication of a laminated iron transformer. This makes finding
the power consumption easier.

Three facts are used:

1.  Electronic loads draw the vast majority of their current ONLY  during
the peaks of the AC supply voltage,  the voltage at this time is close to
325 volts,  on average,  during the load current pulses.

2. When the supply voltage is a fixed value, the watts consumed is found by
multiplying the average value of the current drawn by that fixed voltage.
( Same as you would find the power being drawn from a battery.)

3.  Standard DMMs will read the average rectified value of an AC current  -
scaled up on the display by 1.11 to show the * rms value*  of a sine wave.

So,  putting this altogether:

All you do is find the AC current reading on a standard (ie non true rms)
DMM and multiply that number by 325 then divide by 1.11.  The result should
be the correct power in watts,  within 10%.

Remember -  this is for loads that do  NOT  use an iron transformer,  where
the magnetising current draw is almost 90 degrees out of phase with the AC

Also, any SPMS that features electronic " power factor correction"  ( PFC)
draws current that is essentially in phase with the AC voltage and of sine
wave shape.   So any DMM ( or moving coil or moving iron meter ) will give
the correct value for the load current and one just multiplies this by 240
to get the power in watts.

.....   Phil

Re: how much standby power do ALL your appliances use?
On Sat, 7 Jun 2008 12:58:19 +1000, "Phil in Melbourne"

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Hi Phil,

I have two of these meters. I spent quite a bit of time mucking about
with them.

They are fine measuring power down to about 15-25 watts but are not
accurate under that. They will definitely show a 7W light bulb as
consuming zero power.

My power consumption is about 19KWHr per day. About half of that
consumption is standy power for me. (I'm a "vampire power" King! :) )

I cut my Electricity bill by about $70/quarter by shutting down some
of my installations which were constantly consuming standby power,
since my circumstances had changed and it was no longer necessary to
run these things constantly.

Gas pilot lights can consume a lot of gas too.


Re: how much standby power do ALL your appliances use?

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These figures are obviously wrong, just below the resolution of your cheap


Re: how much standby power do ALL your appliances use?

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I made a simple Power Measuring device from a Silicon Chip Kit.
Dick Smith used to sell them , Cat 7217 was the number.
Only cost around $70 and it works really well.
Accuracy is around 1% , (can be improved if you have a srandard load)
and reads from 0.1 watts to 3750 watts.
Its based on a special Analog Devices IC ADE7756AN.
Doesnt get fooled by power factor or switchmode PS.
Think Jaycar sell em too.

Re: how much standby power do ALL your appliances use?

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I can also vouch for the SC power meter design. Have found no problems so
far, and is fairly accurate down to it's lowest resolution of 0.1W.

I got mine for something like $30 at the DSE kit fire sale :->


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