Watt meter

[Garry Bryant]

Hi,

Does anyone know where in Australia you can buy a watt meter for
measuring the power consumption of domestic appliances? Mainly for
personal interest use around the house, like measuring my computer in
various states of operation. I've seen units overseas like:

http://www.ccrane.com/kill_a_watt.asp

But the Dick Smiths and Jaycars don't seem to stock these types of
meters.

Thanks,

Gazza

 

[Rod Speed]

Does anyone know where in Australia you can buy a watt meter
for measuring the power consumption of domestic appliances?
http://shops.bizarsoftware.com.au/ATAShop/catalogue/category16/product120

Mainly for personal interest use around the house, like
measuring my computer in various states of operation.

Tad expensive for that sort of thing.

 

[Dave T.]

how about a decent multimeter with amp meter clamp.. then just do some
maths. Ofcourse you'll need an extension cord with the active wire able to
be seperated from the rest for measurement.

 

[cdb]

EPE magazine from the UK had in 1995/6 an electric usage meter that could be
converted to a watt meter. The software is still on their site.

Microchip have two watt meter app notes, Cypress or is AD?, anyhow have an
app note using their RMS meter IC, and somewhere out there is a Z8 app note
for a similar thing.

The most expensive part is either the LEM Hall Effect module (EPE), or the
current transformer (uChip).

Colin

 

[Phil Allison]

how about a decent multimeter with amp meter clamp.. then just do some
maths. Ofcourse you'll need an extension cord with the active wire able to
be seperated from the rest for measurement.

** Measuring the (rms) amps draw gives you the VA figure - but not the
*watts* consumed for any loads other than lighting and heating. The power
factor has to be known or measured to convert VA into watts - for lighting
and heating it is unity - but for electronic loads or motors the power
factor can be well below unity.

The SMPS in a PC may have a power factor of from 0.5 to 0.7 for example
due to the peaky shape of the AC current waveform. More recent SMPS have
power factor correction - so the figure is much closer to 1.




........... Phil

 

[Russ Verdon]

See this http://www3.telus.net/chemelec/Projects/Watt-Meter.htm


Russell

 

[David Sauer]

Hi,

Does anyone know where in Australia you can buy a watt meter for
measuring the power consumption of domestic appliances?

Turn off everything in the house, check meter has stopped turning,
turn on item and you have a watt.hour meter

Measuring how much power things like fridges use is useless since
they're an on/off item.

 

[John Saunders]

You can make a simple unit to measure VA as opposed to
watts using a 0.1 ohm 5W wire wound resistor.

Simply connect it in series with the active line, (butcher
an extension cord for this). Measure the voltage across the
resistor and this will give you amps/10.

For example if you get 0.25 volts this indicates 2.5 amps,
with a nominal 240V source (measure this too if you need
accuracy) the device is drawing 600VA.

Note that you will not be able to calculate watts as this
involves knowing the power factor. However if you have a
dual channel CRO with one input reading the voltage, and
another reading the "amps" you can measure the phase
difference and calculate the power factor.

WARNING: Be careful when measuring mains voltages. I like
to connect stuff up with the power disconnected, then stand
back and power it up. Poking around a live mains circuit
with a multimeter probe might seem OK until one day your
mind wanders, the probe slips and you get an almighy jolt
up the arm. Fortunately I lived to be wiser...

 

[Phil Allison]

You can make a simple unit to measure VA as opposed to
watts using a 0.1 ohm 5W wire wound resistor.

Simply connect it in series with the active line, (butcher
an extension cord for this). Measure the voltage across the
resistor and this will give you amps/10.

** To measure VA you have to use a "true rms" amp meter.

This will mostly matter with electronic devices.




.............. Phil

 

[The Real Andy]

** To measure VA you have to use a "true rms" amp meter.

This will mostly matter with electronic devices.

I like the hack, it sounds nice. Good enough for a rough indication. Not
good for much else, a bit like me actually.