Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that
would give an instantaneous digital or analogue read-out of the power being
used by the whole house, without the need to squint at the spinning dial in
the electricity company's meter (which is outside in my case).

I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter, with a secondary winding driving a
high-impendance panel meter of some kind, or perhaps a D/A convertor
attached to a PC. A simple amplifier circuit might be required. Presumably
for a typical house the overall load would be close to resistive, so
measuring current alone would be sufficient. It would be fairly easy to
calibrate the DIY meter, using the electricity company meter.

I haven't done the sums yet, but it seems like it ought to be feasible, but
I can't find much evidence that anyone else has done it, nor can I find any
consumer units with this feature built in.

Simon wrote:
I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter,

I can't find much evidence that anyone else has done it, nor can I find any
consumer units with this feature built in.

Something like this?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=290011770617
"sensors clip directly onto your existing electricity meter's cabling"

John

"John" wrote in message
oups.com...

Simon wrote:
I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter,

I can't find much evidence that anyone else has done it, nor can I find
any
consumer units with this feature built in.

Something like this?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=290011770617
"sensors clip directly onto your existing electricity meter's cabling"

John


Thanks, that gives me some ideas.
The manufacturers have a website at http://www.electrisave.co.uk/
I've just found a DIY example at http://www.edcheung.com/automa/power.htm
but it sounds like he only gets 1mV output per amp of current into the house
from his clamp-on cores, so the job would not be entirely trivial.
If my electricity company meter was inside, I would try pointing a cheap
webcam at it and writing a bit of image processing software to extract power
figures - it's surprising how effective this approach can be.

"Simon" writes:

Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that

Somebody else suggests a webcam but it would be simpler to blue-tac
something to monitor the flashing red light that most modern meters
have. I've been thinking about doing this myself lately. Of course it
won't be using a PC because that would be unreliable and burn more
electricity that the information might be worth. However it does
involve production of a small unit to count the flashes in a
non-volatile way. Kind of like the meter does itself.

Jon

On Sat, 29 Jul 2006 14:48:12 GMT, Jonathan Schneider wrote:

"Simon" writes:

Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that

Somebody else suggests a webcam but it would be simpler to blue-tac
something to monitor the flashing red light that most modern meters
have. I've been thinking about doing this myself lately. Of course it
won't be using a PC because that would be unreliable and burn more
electricity that the information might be worth. However it does
involve production of a small unit to count the flashes in a
non-volatile way. Kind of like the meter does itself.

Jon

A small LCD counter module (e.g. RS Components 337-7151), with a phototransistor would probably do
the job.

On 2006-07-29 15:05:43 +0100, "Simon" said:

Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that
would give an instantaneous digital or analogue read-out of the power being
used by the whole house, without the need to squint at the spinning dial in
the electricity company's meter (which is outside in my case).

I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter, with a secondary winding driving a
high-impendance panel meter of some kind, or perhaps a D/A convertor
attached to a PC. A simple amplifier circuit might be required. Presumably
for a typical house the overall load would be close to resistive, so
measuring current alone would be sufficient. It would be fairly easy to
calibrate the DIY meter, using the electricity company meter.

I haven't done the sums yet, but it seems like it ought to be feasible, but
I can't find much evidence that anyone else has done it, nor can I find any
consumer units with this feature built in.

This is interesting, but will it make you take an action when the rate
of use is higher than you think it should be?

In article ,
"Simon" writes:

Thanks, that gives me some ideas.
The manufacturers have a website at http://www.electrisave.co.uk/

It looks like it only senses the current, in which case it will
have to make assumptions about the voltage and power factor to
estimate your power draw. I suppose it could be capacitively
picking up the voltage waveform too, which could be used to
help estimate the power factor, but I can't imagine that would
be any good to accurately obtain the mains voltage.

In France, new meters for 10 or more years have been digital,
and you can cycle through about 8 readings on them, such as
kWh, current, peak current (not sure over what period), voltage,
power factor, power, and probably more I've forgotten. No one
ever comes to read it -- it's read remotely.
You could try asking EDF to fit a french meter for you;-)

--
Andrew Gabriel

"Andy Hall" wrote in message
...
On 2006-07-29 15:05:43 +0100, "Simon" said:

Hello -

Having just received an electicity bill, I'm wondering whether anyone
tried
building a power meter for an entire house? In other words, something
that
would give an instantaneous digital or analogue read-out of the power
being
used by the whole house, without the need to squint at the spinning dial
in
the electricity company's meter (which is outside in my case).

I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter, with a secondary winding driving a
high-impendance panel meter of some kind, or perhaps a D/A convertor
attached to a PC. A simple amplifier circuit might be required.
Presumably
for a typical house the overall load would be close to resistive, so
measuring current alone would be sufficient. It would be fairly easy to
calibrate the DIY meter, using the electricity company meter.

I haven't done the sums yet, but it seems like it ought to be feasible,
but
I can't find much evidence that anyone else has done it, nor can I find
any
consumer units with this feature built in.

This is interesting, but will it make you take an action when the rate
of use is higher than you think it should be?


I think it would. I almost felt physical pain when I opened my electricity
bill yesterday. Electricity charges have risen sufficiently that it's now
worthwhile for me to put some time and money into reducing usage. Thanks for
all the suggestions so far. As my meter is a 20-year-old spinning disk model
in a cramped exterior box, my options for optical sensing are limited, so I
think some kind of inductive measurement will be required.

On Sat, 29 Jul 2006 17:01:19 +0100, "Simon"
wrote:

Thanks for
all the suggestions so far. As my meter is a 20-year-old spinning disk model
in a cramped exterior box, my options for optical sensing are limited, so I
think some kind of inductive measurement will be required.

Optical sensing on old meters is quite easy as they have a nice black
band on the disk. I made such a device many moons ago using that
well known optical transistor the OC72 with paint scraped off and a
pea bulb as a light source.

--
Peter Parry.
http://www.wpp.ltd.uk/

Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

on 29/07/2006, Simon supposed :
Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that
would give an instantaneous digital or analogue read-out of the power being
used by the whole house, without the need to squint at the spinning dial in
the electricity company's meter (which is outside in my case).

The instrument is called a clamp meter and has been around since
(?)....

You squeeze an arm which opens the jaws and permits it to be clamped
(hence the name) around a cable. The display shows the total current
being consumed. The used to be analogue but most these days are
digital. You just clamp it around one cable only, either live or
neutral will do - but not both as the current in one would cancel out
the other.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Sat, 29 Jul 2006 21:06:30 UTC, Harry Bloomfield
wrote:

The instrument is called a clamp meter and has been around since
(?)....

You squeeze an arm which opens the jaws and permits it to be clamped
(hence the name) around a cable. The display shows the total current
being consumed. The used to be analogue but most these days are
digital. You just clamp it around one cable only, either live or
neutral will do - but not both as the current in one would cancel out
the other.

I have one here that I've owned since about 1966.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

On 29 Jul 2006 21:34:48 GMT, "Bob Eager" wrote:

On Sat, 29 Jul 2006 21:06:30 UTC, Harry Bloomfield
wrote:

The instrument is called a clamp meter and has been around since
(?)....

You squeeze an arm which opens the jaws and permits it to be clamped
(hence the name) around a cable. The display shows the total current
being consumed. The used to be analogue but most these days are
digital. You just clamp it around one cable only, either live or
neutral will do - but not both as the current in one would cancel out
the other.

I have one here that I've owned since about 1966.

And my fairly old one reads DC as well. Handy to note my EV pulled
400A on takeoff and 200A cruising ;-(

All the best ..

T i m

You squeeze an arm which opens the jaws and permits it to be clamped
(hence the name) around a cable. The display shows the total current
being consumed. The used to be analogue but most these days are
digital. You just clamp it around one cable only, either live or
neutral will do - but not both as the current in one would cancel out
the other.

..addendum

You can get ones that go around the sheathing of 2 or 3 core cable +/or
flex. We use them all the time [sorry for the rather long link]




http://rswww.com/cgi-bin/bv/rswww/se... cacheID=ukie




--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

In article ,
"Simon" writes:

I've just found a DIY example at http://www.edcheung.com/automa/power.htm

I just took a look, out of curiosity. He uses the old Motorola
MC1495L 4-quadrant analogue multiplier to form the instantaneous
product of the voltage and current, just like I did in one I built
in the early 1980's. Trouble is that this chip is obsolete for 20
years now, and no one produces a 4-quadrant analogue multiplier
chip with differential inputs, which is what you really need for
this task. I suspect most true power meters nowadays work buy
sampling the voltage and current and multiplying digitally.

--
Andrew Gabriel

On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become of us?

Andrew Gabriel wrote:

[...] and no one produces a 4-quadrant analogue multiplier
chip with differential inputs, which is what you really need for
this task.

Analog Devices still do - AD633 etc.

I suspect most true power meters nowadays work buy
sampling the voltage and current and multiplying digitally.

Which must be a better way of doing it, given enough resolution on the
A/D converters (especially the current, which has quite a wide dynamic
range). The analogue multiplier approach needs great care with zeroing
and offsets if you want to be able to accumulate an accurate kWh count.
You've got to handle current up to 100 A RMS, with some allowance for
crest factor - but most of the time it will be measuring down in the mA
to 5 A sort of range.

--
Andy

In article ,
Andy Wade writes:
Andrew Gabriel wrote:

[...] and no one produces a 4-quadrant analogue multiplier
chip with differential inputs, which is what you really need for
this task.

Analog Devices still do - AD633 etc.

Ah, that looks interesting. It's probably more than 6 years
since I last looked for a 4-quadrant multiplier, admittedly.

I suspect most true power meters nowadays work buy
sampling the voltage and current and multiplying digitally.

Which must be a better way of doing it, given enough resolution on the
A/D converters (especially the current, which has quite a wide dynamic

Once you have the digital processing there, you can produce a
lot more information for no additional hardware too, just by
processing the data appropriately.

range). The analogue multiplier approach needs great care with zeroing
and offsets if you want to be able to accumulate an accurate kWh count.

Yes, component value drift with temperature becomes significant.
I had to include a manual set zero facility in my meter, whereas
the first iteration just had an internal trimmer.

You've got to handle current up to 100 A RMS, with some allowance for
crest factor - but most of the time it will be measuring down in the mA
to 5 A sort of range.

A log A/D converter would probably be appropriate. If you're
spending thousands on your electricity bill, you probably don't
care about the pence portion of the figure, but if you're trying
to measure the cost of running a dishwasher cycle, that's all
you care about.

--
Andrew Gabriel

"Andy Hall" wrote in message
...
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become of
us?

Don't be so negative. He is only trying to look after his ohm in a positive
way.

Andy Hall wrote:
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become of
us?

Fear not, its just the current phase we're going through.

"Simon" wrote in message
...
Hello -

Having just received an electicity bill, I'm wondering whether anyone
tried
building a power meter for an entire house? In other words, something that
would give an instantaneous digital or analogue read-out of the power
being
used by the whole house, without the need to squint at the spinning dial
in
the electricity company's meter (which is outside in my case).

I'm thinking of something like a clamp-on ferrite core around one of the
incoming cables close to the meter, with a secondary winding driving a
high-impendance panel meter of some kind, or perhaps a D/A convertor
attached to a PC. A simple amplifier circuit might be required. Presumably
for a typical house the overall load would be close to resistive, so
measuring current alone would be sufficient. It would be fairly easy to
calibrate the DIY meter, using the electricity company meter.

I haven't done the sums yet, but it seems like it ought to be feasible,
but
I can't find much evidence that anyone else has done it, nor can I find
any
consumer units with this feature built in.



I've done this using a current transformer and meter (moving iron?) from RS
with a 0-80A scale.

I removed the incoming live meter tail from the CU to feed it through the
current transformer.

Works great, been installed ~5 years so far.

Alan.

Andy Hall wrote:
On 2006-07-31 11:32:12 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become
of us?

Fear not, its just the current phase we're going through.

or perhaps the power factor?

Potentially.

On 2006-07-31 11:32:12 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become of us?

Fear not, its just the current phase we're going through.

or perhaps the power factor?

Andy Hall wrote:
On 2006-07-31 12:02:05 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-31 11:32:12 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will
become of us?

Fear not, its just the current phase we're going through.

or perhaps the power factor?

Potentially.

That could meet with some resistance....


You think people could re-Fuse to cooperate? That's a poor way to
conduct oneself.

On 2006-07-31 12:02:05 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-31 11:32:12 +0100, Richard Conway said:

Andy Hall wrote:
On 2006-07-29 20:00:58 +0100, "MikeH" said:


Dave wrote:
Know what you meant (See my
Powergen 10% + 30% rant on this ng.)
It's not only the magnitude of the increase, but the frequency :-)

Yeah, it's the frequency that hertz doesn't it :-)

Mike

Ohm my goodness, we're off on this cycle again... Watt will become of us?

Fear not, its just the current phase we're going through.

or perhaps the power factor?

Potentially.

That could meet with some resistance....

I've done this using a current transformer and meter (moving iron?) from RS
with a 0-80A scale.

I removed the incoming live meter tail from the CU to feed it through the
current transformer.

Works great, been installed ~5 years so far.

Alan.

Absolutely - what's the point in attempting to measure power when all
you really need is the current - the voltage doesn't not vary more than
a few percent whereas the current goes from effectively zero to well,
60 A and is as good a measure of the consumption as anything.

Rob

In article .com,
"robgraham" writes:


I've done this using a current transformer and meter (moving iron?) from RS
with a 0-80A scale.

I removed the incoming live meter tail from the CU to feed it through the
current transformer.

Beware of an often unrecognised danger of current transformer's -- never
leave the secondary open circuit (short it out if you aren't using it),
and never fiddle with the connections to it without first switching off
the primary. You can get thousands of volts from the secondary if it is
erronously left open circuit.

Absolutely - what's the point in attempting to measure power when all
you really need is the current - the voltage doesn't not vary more than
a few percent whereas the current goes from effectively zero to well,
60 A and is as good a measure of the consumption as anything.

Depends if you want to measure the current or the power. Many loads
nowadays are far from unity power factor, in which case the current
doesn't give you a good idea of the power.

--
Andrew Gabriel

On Mon, 31 Jul 2006 23:41:01 +0100, wrote:

On 31 Jul,
"robgraham" wrote:

Absolutely - what's the point in attempting to measure power when all
you really need is the current - the voltage doesn't not vary more than
a few percent whereas the current goes from effectively zero to well,
60 A and is as good a measure of the consumption as anything.

It's not the voltage error that causes the biggest error in consumption, it's
the power factor. loads like SMPS and ballasted flourescents (amongst others)
can cause major errors. OTOH, an ammeter gives a good indication.

Can you remember (quite) a few years back at
http://www.ryhopeengines.org.uk/ we did some experiments with a load
of small (2') fluorescents in showcases, which had no PFC? By sticking
a few microfarads across the supply we almost halved the current
consumption, reducing the popping of fuses.

--
Frank Erskine

In article ,
Frank Erskine writes:
Can you remember (quite) a few years back at
http://www.ryhopeengines.org.uk/ we did some experiments with a load
of small (2') fluorescents in showcases, which had no PFC? By sticking
a few microfarads across the supply we almost halved the current
consumption, reducing the popping of fuses.

If it was a T12 20W tube, these ran at 420mA, which will be
420mA from the mains with no PFC capacitor. If you only measure
the mains current draw, 0.420 x 240 = 100W apparent load, which
is clearly completely wrong, as the power factor is around 0.3
(there's around 10W extra lost in the ballast for this lamp).
With the correct PFC capacitor, you will drop the mains current
to around 140mA with a power factor of around 0.85, a factor of
around 3 times improvement in power factor and drop in mains
current draw, all for the same power consumption.

--
Andrew Gabriel

Simon wrote:
Hello -

Having just received an electicity bill, I'm wondering whether anyone tried
building a power meter for an entire house? In other words, something that
would give an instantaneous digital or analogue read-out of the power being
used by the whole house, without the need to squint at the spinning dial in
the electricity company's meter (which is outside in my case).

If your meter is made by http://www.econtrols.co.uk (or similar), it may
have an IEC 1107 infra-red digital interface which may be accessed to
read it. Elektor published a project doing this about a couple of years ago.

--
Adrian C