Does anyone know of an energy monitor for the electricity that I could
use without having to sign up for a smart meter ?

I see lots of "smart plugs", but want to monitor the whole house. not one
socket.

From memory the difference in voltage and current phasing is a function
off loading, so in theory it's a possibility.

On 20/11/2022 11:12, Jethro_uk wrote:
> Does anyone know of an energy monitor for the electricity that I could
> use without having to sign up for a smart meter ?
>
> I see lots of "smart plugs", but want to monitor the whole house. not one
> socket.
>
> From memory the difference in voltage and current phasing is a function
> off loading, so in theory it's a possibility.

They do exist. Using clamp on current and a voltage probe for the volts

--
Truth welcomes investigation because truth knows investigation will lead
to converts. It is deception that uses all the other techniques.

Jethro_uk <jethro_uk@hotmailbin.com> wrote:
> Does anyone know of an energy monitor for the electricity that I could
> use without having to sign up for a smart meter ?
>
> I see lots of "smart plugs", but want to monitor the whole house. not one
> socket.
>
> From memory the difference in voltage and current phasing is a function
> off loading, so in theory it's a possibility.

Typically a current clamp and then a plug-in device to get the voltage. You
can get various depending on whether you have power near your meter or
whether it needs to send the current reading to another box.

I would normally recommend looking at:
https://openenergymonitor.org/
as they have various solutions, but they seem to have gone up in price a lot
and have stock issues.

You can also find various options on ebay, as offered by eg British Gas
before the smart meter rollout. The 'Owl' range was popular, and they can
be picked up fairly cheap. Typically they're just sending data to a home
display - some have a USB stick option for PC access, although I'm not sure
what the software side of that looks like.

Theo

On 20 Nov 2022 11:52:32 +0000 (GMT)
Theo <theom+news@chiark.greenend.org.uk> wrote:

> You can also find various options on ebay, as offered by eg British
> Gas before the smart meter rollout. The 'Owl' range was popular, and
> they can be picked up fairly cheap. Typically they're just sending
> data to a home display - some have a USB stick option for PC access,
> although I'm not sure what the software side of that looks like.

I have an 'Owl' that I got some years ago from SSE. It does not have a
voltage probe, nor any output option, but it gives a readout of current
amps.
It has been ignored for months, years even.

--
Davey.

On 20/11/2022 11:12, Jethro_uk wrote:

> Does anyone know of an energy monitor for the electricity that I could
> use without having to sign up for a smart meter ?

If you are happy to cobble something together, then it is a fairly
straight forward build... by coincidence I was experimenting for a very
basic device that gives a "whole house" instant display of total
voltage, current, pF, power etc. (kind of like a DIY smart meter live
readout)[1]

Kit required: one Arduino dev board, a LCD display (preferably with i2c
interface module on it), a current transformer, a 9V AC/AC power adaptor
(old modem power adaptors are often good), and a USB power supply for
the microcontroller, plus a few passive components to scale and offset
the waveforms you read from the the AC PSU and the CT, so they can be
safely fed into the Arduino ADCs 0-5V range. (prolly £20 all in from
AliExpress)

The CT will let you read a real time current waveform. The AC/AC adaptor
will let you read a proxy for the mains voltage. The rest is just some
number crunching (the EmonLib library already has all you need).

In fact, looking that the library example code gives an idea of the
complexity:

// EmonLibrary examples openenergymonitor.org, Licence GNU GPL V3

#include "EmonLib.h" // Include Emon Library
EnergyMonitor emon1; // Create an instance

void setup()
{ Serial.begin(9600);

emon1.voltage(2, 234.26, 1.7); // Voltage: input pin, calibration,
phase_shift
emon1.current(1, 111.1); // Current: input pin, calibration.
}

void loop()
{ emon1.calcVI(20,2000); // Calculate all. No.of half
wavelengths (crossings), time-out
emon1.serialprint(); // Print out all variables (realpower,
apparent power, Vrms, Irms, power factor)

float realPower = emon1.realPower; //extract Real Power
into variable
float apparentPower = emon1.apparentPower; //extract Apparent
Power into variable
float powerFActor = emon1.powerFactor; //extract Power
Factor into Variable
float supplyVoltage = emon1.Vrms; //extract Vrms into
Variable
float Irms = emon1.Irms; //extract Irms into
Variable
}

So all you would need to add would be a bit at the end to format those
variable into output strings, and update a 16x2 line LCD or similar...
(again, load appropriate LCD library - so about 5 lines of code to
initialise it, clear the screen, position the cursor, and output the
formatted text).

[1] At some point when I can find the right shape of tuit, I was
thinking of doing a multi channel version that could log data to a
database for more in depth analysis on a circuit by circuit basis.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

Jethro_uk <jethro_uk@hotmailbin.com> wrote:
> Does anyone know of an energy monitor for the electricity that I could
> use without having to sign up for a smart meter ?
>
> I see lots of "smart plugs", but want to monitor the whole house. not one
> socket.
>
> From memory the difference in voltage and current phasing is a function
> off loading, so in theory it's a possibility.
>

You can certainly get units which go ‘in line’ with your supply, some fit
in the consumer unit, which measure and display consumption.

When my middle daughter bought her house, the previous owner had a ‘spur’
for the shed / garden office. It had a dedicated consumer unit with one
fitted. They had it all removed - the shed was a bit dilapidated etc.

I expect you can get ‘ smart ‘ ones now with Wi-Fi / Bluetooth etc.

On Sun, 20 Nov 2022 14:04:01 +0000, Brian wrote:

> Jethro_uk <jethro_uk@hotmailbin.com> wrote:
>> Does anyone know of an energy monitor for the electricity that I could
>> use without having to sign up for a smart meter ?
>>
>> I see lots of "smart plugs", but want to monitor the whole house. not
>> one socket.
>>
>> From memory the difference in voltage and current phasing is a function
>> off loading, so in theory it's a possibility.
>>
>>
> You can certainly get units which go ‘in line’ with your supply, some
> fit in the consumer unit, which measure and display consumption.
>
> When my middle daughter bought her house, the previous owner had a
> ‘spur’
> for the shed / garden office. It had a dedicated consumer unit with one
> fitted. They had it all removed - the shed was a bit dilapidated etc.
>
> I expect you can get ‘ smart ‘ ones now with Wi-Fi / Bluetooth etc.

I had one about ten years ago that transmitted from a current clamp to a
plug in display in the living room, they were being given away by one of
the big power companies.

On 20/11/2022 12:32, Davey wrote:
> On 20 Nov 2022 11:52:32 +0000 (GMT)
> Theo <theom+news@chiark.greenend.org.uk> wrote:
>
>> You can also find various options on ebay, as offered by eg British
>> Gas before the smart meter rollout. The 'Owl' range was popular, and
>> they can be picked up fairly cheap. Typically they're just sending
>> data to a home display - some have a USB stick option for PC access,
>> although I'm not sure what the software side of that looks like.
>
> I have an 'Owl' that I got some years ago from SSE. It does not have a
> voltage probe, nor any output option, but it gives a readout of current
> amps.
> It has been ignored for months, years even.

There was an Owl II with USB capability. But the ancient basic Owl is
good enough to show you where the vampire power usage is going. Their
website still exists but the products apparently do not.

https://www.amazon.co.uk/CM160-Electricity-Monitor-Compatible-Windows/dp/B004BDNR84

Still seems to be available from RS components though...

https://uk.rs-online.com/web/p/energy-meters/8724666

Having one of these saved our village hall a fortune by preventing
people from leaving the immersion heater, ovens or other power hogs on!

Other brands are available Energenie being the current brand du jour.

https://www.amazon.co.uk/Energenie-MIHO006-Whole-Energy-Monitor/dp/B00V52HLEK/

--
Regards,
Martin Brown

On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:

>
>I had one about ten years ago that transmitted from a current clamp to a
>plug in display in the living room, they were being given away by one of
>the big power companies.

I have one of these, an Eon meter, and it is basically misleading:

1) Switched everything off in the house (took a while as I forgot
things like alarm system and security light).

2) The Eon meter read 13 watts in use, but the rotating disc in the
real meter didn't move in 15 minutes.

3) Unclipped the cable current clamp, meter read zero, put it back -
13 watts

4) Switched the security light back on - it didn't light as it was
daylight. The meter now read 0 watts!

5) Switched it off - back to 13 watts. Back on again = 0 watts.

6) The gutter press states microwaves cost a fortune when in standby.
So switched the Panasonic on, display illuminated - Eon meter now
reads 18 watts. But the disc in the real meter didn't move in 10
minutes.

7) Opened the microwave door, light came on and Eon reading increased
by 16 watts. The disc is now rotating slowly as expected.

Hmm!

GrahamC

Graham C <grahamcrisp@btopenworld.com> wrote:
> On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:
>
> >
> >I had one about ten years ago that transmitted from a current clamp to a
> >plug in display in the living room, they were being given away by one of
> >the big power companies.
>
> I have one of these, an Eon meter, and it is basically misleading:

The current clamp is presumably sized for 100A maximum load. 13W is 54mA,
which is 1800x less than the maximum current. I'm not surprised that
accuracy suffers at that end of the scale. I wouldn't be using a 100A clamp
meter to chase loads that small - it isn't really sized for that.

Also, if it doesn't have a voltage input (eg an AC transformer) it's only
reading current and you probably have some devices with a non-unity power
factor. It can't tell that the current is out of phase with the voltage and
so it records as consumption, even though the reactive device returns the
power back again in the other half of the mains cycle.

Theo

On 21/11/2022 13:09, Graham C wrote:
> On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:
>
>>
>> I had one about ten years ago that transmitted from a current clamp to a
>> plug in display in the living room, they were being given away by one of
>> the big power companies.
>
> I have one of these, an Eon meter, and it is basically misleading:
>
> 1) Switched everything off in the house (took a while as I forgot
> things like alarm system and security light).
>
> 2) The Eon meter read 13 watts in use, but the rotating disc in the
> real meter didn't move in 15 minutes.
>
> 3) Unclipped the cable current clamp, meter read zero, put it back -
> 13 watts
>
> 4) Switched the security light back on - it didn't light as it was
> daylight. The meter now read 0 watts!
>
> 5) Switched it off - back to 13 watts. Back on again = 0 watts.
>
> 6) The gutter press states microwaves cost a fortune when in standby.
> So switched the Panasonic on, display illuminated - Eon meter now
> reads 18 watts. But the disc in the real meter didn't move in 10
> minutes.

About 5W sounds reasonable for a microwave with a timer display
illuminated. Many consumer items have standby power <0.5W now.

Some older TVs and set top boxes tend to be power hogs.
>
> 7) Opened the microwave door, light came on and Eon reading increased
> by 16 watts. The disc is now rotating slowly as expected.
>
> Hmm!

I suspect what it actually tells us is that your ancient spinning disk
meter has bearing stiction and doesn't move at all for loads under 15W!

--
Regards,
Martin Brown

On 21/11/2022 13:09, Graham C wrote:
> On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:
>
>>
>> I had one about ten years ago that transmitted from a current clamp to a
>> plug in display in the living room, they were being given away by one of
>> the big power companies.
>
> I have one of these, an Eon meter, and it is basically misleading:
>
> 1) Switched everything off in the house (took a while as I forgot
> things like alarm system and security light).
>
> 2) The Eon meter read 13 watts in use, but the rotating disc in the
> real meter didn't move in 15 minutes.

Mmm. Wattless current?

13 watts on 230v is 50mA

>
> 3) Unclipped the cable current clamp, meter read zero, put it back -
> 13 watts
>
It was measuring something then

> 4) Switched the security light back on - it didn't light as it was
> daylight. The meter now read 0 watts!
>
> 5) Switched it off - back to 13 watts. Back on again = 0 watts.
>
Sounds like some sort of mains filter issue

> 6) The gutter press states microwaves cost a fortune when in standby.
> So switched the Panasonic on, display illuminated - Eon meter now
> reads 18 watts. But the disc in the real meter didn't move in 10
> minutes.
>
> 7) Opened the microwave door, light came on and Eon reading increased
> by 16 watts. The disc is now rotating slowly as expected.
>
> Hmm!
>
> GrahamC

Since electricity is now about the same price as oil per actual Kwh, I
am not bothered about electricity heating the house.

--
“There are two ways to be fooled. One is to believe what isn’t true; the
other is to refuse to believe what is true.”

—Soren Kierkegaard

On 20/11/2022 16:28, jon wrote:
>
> I had one about ten years ago that transmitted from a current clamp to a
> plug in display in the living room, they were being given away by one of
> the big power companies.
So did I, used it until I did have a Smart Meter fitted.

It was pretty good I thought (for a 'giveaway' device). I'm sure not
super accurate, but gave good enough 'ball park' figures

On 21/11/2022 13:36, The Natural Philosopher wrote:
> On 21/11/2022 13:09, Graham C wrote:
>> On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:
>>
>>>
>>> I had one about ten years ago that transmitted from a current clamp to a
>>> plug in display in the living room, they were being given away by one of
>>> the big power companies.
>>
>> I have one of these, an Eon meter, and it is basically misleading:
>>
>> 1)  Switched everything off in the house (took a while as I forgot
>> things like alarm system and security light).
>>
>> 2)  The Eon meter read 13 watts in use, but the rotating disc in the
>> real meter didn't move in 15 minutes.
>
> Mmm. Wattless current?
>
> 13 watts on 230v is 50mA
>
>>
>> 3)  Unclipped the cable current clamp, meter read zero, put it back -
>> 13 watts
>>
> It was measuring something then

It could well be reactive power.

>> 4)  Switched the security light back on - it didn't light as it was
>> daylight.  The meter now read 0 watts!
>>
>> 5)  Switched it off - back to 13 watts.  Back on again = 0 watts.
>>
> Sounds like some sort of mains filter issue
>
>> 6)  The gutter press states microwaves cost a fortune when in standby.
>> So switched the Panasonic on, display illuminated - Eon meter now
>> reads 18 watts.  But the disc in the real meter didn't move in 10
>> minutes.
>>
>> 7)  Opened the microwave door, light came on and Eon reading increased
>> by 16 watts.  The disc is now rotating slowly as expected.
>>
>> Hmm!
>>
>> GrahamC
>
> Since electricity is now about the same price as oil per actual Kwh, I
> am not bothered about electricity heating the house.
>

On 21/11/2022 13:09, Graham C wrote:
> On Sun, 20 Nov 2022 16:28:59 -0000 (UTC), jon <jon@nospam.cn> wrote:
>
>>
>> I had one about ten years ago that transmitted from a current clamp to a
>> plug in display in the living room, they were being given away by one of
>> the big power companies.
>
> I have one of these, an Eon meter, and it is basically misleading:
>
> 1) Switched everything off in the house (took a while as I forgot
> things like alarm system and security light).
>
> 2) The Eon meter read 13 watts in use, but the rotating disc in the
> real meter didn't move in 15 minutes.
>
> 3) Unclipped the cable current clamp, meter read zero, put it back -
> 13 watts
>
> 4) Switched the security light back on - it didn't light as it was
> daylight. The meter now read 0 watts!
>
> 5) Switched it off - back to 13 watts. Back on again = 0 watts.

I think you may have unrealistic expectations...

Most of the clip on "whole house" monitors will be using a current
transformer with a range of 0 to 100A. The CT will generate (say) up to
50mA of current into a burden resistor. You then use the voltage drop
across that to feed a ADC so you can read a value.

However before you can feed the ADC, that voltage will need to be biased
up so that the waveform never crosses zero on the negative part of the
wave, and scaled to fit into the typical 3.3V or 5V range acceptable to
the ADC. So to allow a bit of headroom you will probably scale the
waveform to be around 4V peak to peak (on an ADC with a 5V range). If
you are feeding a 10 bit ADC (fairly typical of many off the shelf
microcontrollers), you have 1024 possible values, of which you are using
4/5s of them due to the scaling. That is around 820 possible discrete
readings, to cover a reading range of 100A. Hence you have only ~8
possible readings per amp - a resolution of 125mA. That is 30W at 240V.
Even if you use a discrete 12 bit ADC you are still looking at a minimum
resolvable load of around 7W.

Then you need to consider that ADCs will typically get some jitter in
the least significant bits - that can vary with temperature and the
local electrical noise. You can assume that the bias and scaling
elements are not 100% accurate and stable either - especially as the
bias will typically be derived from the units own PSU.

So errors of only 10s of watts on a metering range that covers 24kW
seems "pretty good".

> 6) The gutter press states microwaves cost a fortune when in standby.
> So switched the Panasonic on, display illuminated - Eon meter now
> reads 18 watts. But the disc in the real meter didn't move in 10
> minutes.
>
> 7) Opened the microwave door, light came on and Eon reading increased
> by 16 watts. The disc is now rotating slowly as expected.
>
> Hmm!

So probably a movement of 1 least significant bit on the digitized
current reading. To look at small loads like that with any accuracy, you
will need to meeter with a much tighter range to get enough resolution.

(Imagine if you were using a DMM set to the 10A range while looking of
low mA changes in the readings).

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 20/11/2022 11:12, Jethro_uk wrote:

> Does anyone know of an energy monitor for the electricity that I could
> use without having to sign up for a smart meter ?

For entertainment, I built one:

http://wiki.diyfaq.org.uk/index.php/DIY_Real_time_mains_power_meter

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 25/11/2022 18:18, John Rumm wrote:
> On 20/11/2022 11:12, Jethro_uk wrote:
>
>> Does anyone know of an energy monitor for the electricity that I could
>> use without having to sign up for a smart meter ?
>
> For entertainment, I built one:
>
> http://wiki.diyfaq.org.uk/index.php/DIY_Real_time_mains_power_meter
>
>
>
Its nice but note it does not account for the power factor. Most modern
devices use switched mode PSUs and present a highly reactive load to
mains. This means this will over-read for many loads, especially for
devices in standby, LED lamps etc.

Dave

On 26/11/2022 11:06, David Wade wrote:
> On 25/11/2022 18:18, John Rumm wrote:
>> On 20/11/2022 11:12, Jethro_uk wrote:
>>
>>> Does anyone know of an energy monitor for the electricity that I could
>>> use without having to sign up for a smart meter ?
>>
>> For entertainment, I built one:
>>
>> http://wiki.diyfaq.org.uk/index.php/DIY_Real_time_mains_power_meter
>>
>>
>>
> Its nice but note it does not account for the power factor.

When you say does not account for the power factor, could you clarify
what you mean?

After all it does calculate the pf, display it on screen, and show you
both the VA and real power loads on the display...

> Most modern
> devices use switched mode PSUs and present a highly reactive load to
> mains. This means this will over-read for many loads, especially for
> devices in standby, LED lamps etc.

Indeed...

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 25/11/2022 18:18, John Rumm wrote:
> On 20/11/2022 11:12, Jethro_uk wrote:
>
>> Does anyone know of an energy monitor for the electricity that I could
>> use without having to sign up for a smart meter ?
>
> For entertainment, I built one:
>

One question - of purely academic interest to me as I've no ambitions to
build one. If (please read a BIG if) I u/s correctly "emon.calcVI( 20,
2000 )" means the readings are an average over 0.2 seconds, updated
every 2 seconds. Left me wondering about what - if any - differences
there are in practice* from that compared with - say - averaging over 2
seconds.

*I wouldn't count as "in practice" for this purpose edge cases such as
lights that flash every 2 seconds :)

--
Robin
reply-to address is (intended to be) valid

On 26/11/2022 13:09, John Rumm wrote:
> On 26/11/2022 11:06, David Wade wrote:
>> On 25/11/2022 18:18, John Rumm wrote:
>>> On 20/11/2022 11:12, Jethro_uk wrote:
>>>
>>>> Does anyone know of an energy monitor for the electricity that I could
>>>> use without having to sign up for a smart meter ?
>>>
>>> For entertainment, I built one:
>>>
>>> http://wiki.diyfaq.org.uk/index.php/DIY_Real_time_mains_power_meter
>>>
>>>
>>>
>> Its nice but note it does not account for the power factor.
>
> When you say does not account for the power factor, could you clarify
> what you mean?
>
> After all it does calculate the pf, display it on screen, and show you
> both the VA and real power loads on the display...
>
>> Most modern devices use switched mode PSUs and present a highly
>> reactive load to mains. This means this will over-read for many loads,
>> especially for devices in standby, LED lamps etc.
>
> Indeed...
>
>
you are right I mis-read the article. And current transformers are cheap
enough to build a multi-sense version....

On 26/11/2022 13:56, Robin wrote:
> On 25/11/2022 18:18, John Rumm wrote:
>> On 20/11/2022 11:12, Jethro_uk wrote:
>>
>>> Does anyone know of an energy monitor for the electricity that I could
>>> use without having to sign up for a smart meter ?
>>
>> For entertainment, I built one:
>>
>
> One question - of purely academic interest to me as I've no ambitions to
> build one.  If (please read a BIG if) I u/s correctly "emon.calcVI( 20,
> 2000 )" means the readings are an average over 0.2 seconds, updated
> every 2 seconds.

No, that is the instruction to take the reading over 20 mains cycles
(400 mSec), with a timeout of up to two seconds. The code starts by
waiting for a zero crossing in the voltage waveform before going any
further - hence there is the risk that if you made the call but the
hardware was not connected to a AC voltage source it would hang at that
point, waiting for a zero crossing that never comes. (it would not be an
issue in this particular application, but could be in some - it is a
general purpose library)

> Left me wondering about what - if any - differences
> there are in practice* from that compared with - say - averaging over 2
> seconds.

You could make the call and ask for a reading over 100 cycles... that
would amount to 2 secs worth of mains cycles. However the result would
still be computed on the cumulative effect summed from many
instantaneous voltage and current readings taken per cycle. So the
result would be an average of two seconds worth of consumption taking
into account the pf (both conventional and harmonic). Depending on the
nature of the load that may differ (with a lower real power reading)
from the simple multiple of average RMS voltage and average RMS current.

> *I wouldn't count as "in practice" for this purpose edge cases such as
> lights that flash every 2 seconds :)
Well if they are lit during the sample time, they will be counted! :-)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 26/11/2022 17:15, John Rumm wrote:
> On 26/11/2022 13:56, Robin wrote:
>> On 25/11/2022 18:18, John Rumm wrote:
>>> On 20/11/2022 11:12, Jethro_uk wrote:
>>>
>>>> Does anyone know of an energy monitor for the electricity that I could
>>>> use without having to sign up for a smart meter ?
>>>
>>> For entertainment, I built one:
>>>
>>
>> One question - of purely academic interest to me as I've no ambitions
>> to build one.  If (please read a BIG if) I u/s correctly "emon.calcVI(
>> 20, 2000 )" means the readings are an average over 0.2 seconds,
>> updated every 2 seconds.
>
> No, that is the instruction to take the reading over 20 mains cycles
> (400 mSec), with a timeout of up to two seconds. The code starts by
> waiting for a zero crossing in the voltage waveform before going any
> further - hence there is the risk that if you made the call but the
> hardware was not connected to a AC voltage source it would hang at that
> point, waiting for a zero crossing that never comes. (it would not be an
> issue in this particular application, but could be in some - it is a
> general purpose library)

>> Left me wondering about what - if any - differences there are in
>> practice* from that compared with - say - averaging over 2 seconds.
>
> You could make the call and ask for a reading over 100 cycles... that
> would amount to 2 secs worth of mains cycles. However the result would
> still be computed on the cumulative effect summed from many
> instantaneous voltage and current readings taken per cycle. So the
> result would be an average of two seconds worth of consumption taking
> into account the pf (both conventional and harmonic). Depending on the
> nature of the load that may differ (with a lower real power reading)
> from the simple multiple of average RMS voltage and average RMS current.
>
>> *I wouldn't count as "in practice" for this purpose edge cases such as
>> lights that flash every 2 seconds :)
> Well if they are lit during the sample time, they will be counted! :-)
>

Thanks for taking the time.

One tiny point: I arrived at 0.2 seconds from the comment in your code
"No.of half wavelengths (crossings)" assuming 20/(2 x 50).

--
Robin
reply-to address is (intended to be) valid

On 26/11/2022 17:39, Robin wrote:
> On 26/11/2022 17:15, John Rumm wrote:
>> On 26/11/2022 13:56, Robin wrote:
>>> On 25/11/2022 18:18, John Rumm wrote:
>>>> On 20/11/2022 11:12, Jethro_uk wrote:
>>>>
>>>>> Does anyone know of an energy monitor for the electricity that I could
>>>>> use without having to sign up for a smart meter ?
>>>>
>>>> For entertainment, I built one:
>>>>
>>>
>>> One question - of purely academic interest to me as I've no ambitions
>>> to build one.  If (please read a BIG if) I u/s correctly
>>> "emon.calcVI( 20, 2000 )" means the readings are an average over 0.2
>>> seconds, updated every 2 seconds.
>>
>> No, that is the instruction to take the reading over 20 mains cycles
>> (400 mSec), with a timeout of up to two seconds. The code starts by
>> waiting for a zero crossing in the voltage waveform before going any
>> further - hence there is the risk that if you made the call but the
>> hardware was not connected to a AC voltage source it would hang at
>> that point, waiting for a zero crossing that never comes. (it would
>> not be an issue in this particular application, but could be in some -
>> it is a general purpose library)
>
>>> Left me wondering about what - if any - differences there are in
>>> practice* from that compared with - say - averaging over 2 seconds.
>>
>> You could make the call and ask for a reading over 100 cycles... that
>> would amount to 2 secs worth of mains cycles. However the result would
>> still be computed on the cumulative effect summed from many
>> instantaneous voltage and current readings taken per cycle. So the
>> result would be an average of two seconds worth of consumption taking
>> into account the pf (both conventional and harmonic). Depending on the
>> nature of the load that may differ (with a lower real power reading)
>> from the simple multiple of average RMS voltage and average RMS current.
>>
>>> *I wouldn't count as "in practice" for this purpose edge cases such
>>> as lights that flash every 2 seconds :)
>> Well if they are lit during the sample time, they will be counted! :-)
>>
>
> Thanks for taking the time.
>
> One tiny point: I arrived at 0.2 seconds from the comment in your code
> "No.of half wavelengths (crossings)" assuming 20/(2 x 50).

Yes good point and well made :-)

You are right it counts crossings and not whole cycles.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/