Odd power usage by freezer.

[ericmark]

New toy an energy meter plug in type, plugged in chest freezer in garage detached to test how the new toy works, however some odd readings.

The freezer normally reports using 63 watt however these spikes show varying wattage up to 111 watt and not even, this time of morning I have not opened lid.

Although I can see how some hours the motor will run 4 times and other times 3 times that chart seems to have more variation than expected, yesterday the average watts were 14 today average watts are 11, at 200 kWh/annum the average watts should be 22.8 at 14 watt that's 122.6 kWh/annum which is not far out but at 11 watt it's 96.36 kWh/annum which seems rather low.

So question is the freezer super economic or is the energy meter missing data transmissions? every so often I get this.

does it store info then send again, or if it loses internet or local connection does it mess up the reading, it would seem my info is sent to a server then back to me, so the local hub may still be getting info but not sending it to server so I can read, or it could be the local hub missing chunks of info. Main reason for device is so when I remote switch it, there is a report saying on or off, although I can switch other sockets they don't report their state. So the power measuring was not really why it was bought. Idea is to use it in my house so if I get the green light I know power is still on so I can see if my RCD has tripped, a report as above would mean a visit to check house. Normally it shows like this.

So I know freezer is running and using 66W the Unknown is not that often seen and when it is watch for a minute or so and back to green light. However I expected the chest freezer to show a regular on/off patten except when door has been opened, but the patten is not regular, freezer only 2 months old so should be A1.

I think nothing to worry about and it's the power meter which is out, but other power meter will show what it uses but not how often motor runs and for how long. And it's not the power used but non regular patten which is worrying. What do you think?

 

[mfarrow]

Voltage could play a factor too. Does the meter record that?

 

[Jackrae]

It's maybe German built and we know your opinion of their equipment

 

[ericmark]

It's maybe German built and we know your opinion of their equipment

Good point, I was rather disappointed write up says it does monitor voltage, but I have failed to find out how.

 

[SimonH2]

The power taken by the compressor will vary with temperature - both internal and external to the freezer. In very simple terms, the larger the temperature difference, the more power it'll take. That's assuming a standard "on off" compressor control.
Is it a "frost free" version by any chance ? We have an upright frost free freezer, cooling is by blowing air round the cabinet and through an evaporator coil. There's an electric heater in the expansion coil so it can be warmed up to melt any frost from the coil and allow it to drain away. IIRC it takes something like 80W when cooling, but the heater takes about 120W when defrosting.

 

[JohnW2]

Although I can see how some hours the motor will run 4 times and other times 3 times that chart seems to have more variation than expected .....

I think you are probably expecting too much - I would not have said the the hourly averages show more variability that I personally would have expected. For a start, in terms of those hourly averages, it's obviosuly not only the number of times the compressor comes on in an hour that matters, but how long it comes on for on each of the occasions. There are some difficulties with the plot of 'recent usage' (see * below), but, IF (see ** below) each data point represents the instantaneous power at 1 minute intervals, it looks as if the first 'on period' could have been anything between 1 and 3 minutes (present at two 1-minute readings), the second between 2-4 minutes and the third between 0 and 2 minutes.

Why this variability? Well, few things in life are constant or perfect, and there are many factors involved. For example, the differing durations of the on-periods suggests that the hysteresis of the thermostat is not consistent/constant, even if ambient temp remains unchanged (and the freezer is not opened!). Also, we are talking about pretty small currents. 65W at 230V is only about 280mA, and it would not surprise me if there was an appreciable (variable) measurement error. I would also expect that the amount of current used by the compressor probably varies a little according to the compressor temperature - which will depend on the duration of the ('cooling') intervals between 'on' periods. In the plot, the third 'on' period appears to have used a higher power than the first two, but the interval between second and third is much longer than the interval between the first two.

* As I said, that plot of 'recent usage' is a little odd. If each of the data points is at 1-minute intervals, for some reason they are not evenly spaced on the x-axis. Also, the fact that the points have been joined with a 'smooth curve' is potentially misleading, particularly for a load which (presumably) is either 'on' or 'off'.

** As I said, I initially assumed (since the axis label is silent about details) that the data represents the instantaneous power consumption at 1-minute intervals. An alternative would be that they are 1-minute averages. That would not alter the generality of what I've said above, but it would explain why there are a range of figures, rather than just 'on' and 'off' ones.

However I expected the chest freezer to show a regular on/off patten except when door has been opened, but the patten is not regular, freezer only 2 months old so should be A1.

As above, I suspect that is partially due to a less-than-perfect thermostat (varying hysteresis). Indeed, even if the ambient temp were constant (and not opened) you might well find that a corresponding plot of the temp inside the freezer did not show the perfect horizontal line which you 'expected'.

And it's not the power used but non regular patten which is worrying. What do you think?

As above, I would personally not 'worry'!

Kind Regards, John

 

[big-all]

ok i havent got a clue lol
is this a freezer in a house or in a say shed where outside temperature will effect the consumption hour by hour or indeed on a long run where the volt drop or cable temperature may make a difference
another thought is moisture ingress casing power leakage or inballance effecting readings

 

[JohnD]

If it is a frost-free freezer, the heating element will be coming on at intervals, less often than the compressor.

I use a different type of energy monitor, which is quite inaccurate at low currents below about a kW

I don't know about your house, but in mine the voltage has always been 240v give or take two or three every time I'm checked it. This is known as "230v nominal."

 

[ericmark]

I am unaware of any chest freezers with auto defrost, I see no panel to have the fans to work auto defrost. As far as I know auto defrost or frost free is only used with upright freezers, I would not have an upright freezer without auto defrost as not only does it defrost but the fan ensures whole freezer at same temperature. Not really tested here, I know at home for years after the voltage dropped from 240 to 230 we still had over 240 volt, then a row of houses had solar panels fitted and our voltage dropped to 230 volt, seems unless dropped the solar panels lock them selves out on over voltage.

I read the spec on the unit and it should report voltage however it may report voltage but it does not display voltage on the web page used to show what is going on. I did not get it as an energy meter, idea was it shows if on or off, the simple remote controlled sockets don't report their state. However before using I thought it would be good to test how it works first.

 

[SimonH2]

Not really tested here, I know at home for years after the voltage dropped from 240 to 230 we still had over 240 volt, then a row of houses had solar panels fitted and our voltage dropped to 230 volt, seems unless dropped the solar panels lock them selves out on over voltage.

What's happening is that historically the substation taps would be set to give as close to 240V as possible under typical loadings. It's in the DNOs interest to keep the voltage as high as possible as that minimises the current and hence their I²R losses. Of course, if a few houses then get 4kW each of Solar PV panels, that reverses the power flows at times, and hence the cable & transformer losses reduce or even change direction - adding to the voltage instead of subtracting from it.
So when you've seen your voltage change, it's because they've changed the tap at the local substation to lower the voltage to compensate and avoid the over-voltage when all the PV is at high output. I could see that as the amount of embedded generation increases, they might have to start putting in remotely controllable/automatic tap changers in some substations - another of those hidden costs the renewables brigade seldom talk about when crowing about how cheap their power is

 

[winston1]

It's in the DNOs interest to keep the voltage as high as possible as that minimises the current and hence their I²R losses.

Not according to Mr Ohm.

The heavy loads in a house are generally heating appliances which certainly obey Ohms law. Smaller electronic items will generally take less current as voltage increases. I would think overall as voltage increases, current increases.

 

[Jackrae]

Not according to Mr Ohm.

The heavy loads in a house are generally heating appliances which certainly obey Ohms law. Smaller electronic items will generally take less current as voltage increases. I would think overall as voltage increases, current increases.

Those 'small electronic items' are generally capacitive with an extremely high value of leading power factor so their actual W is way less than their rated VA. This potentially (excuse the pun) causes further headaches for the supply system.

 

[JohnD]

The heavy loads in a house are generally heating appliances which certainly obey Ohms law.

Electricity distributors have no objection to that. A 240v supply just means your room, hot water cylinder or oven heats up a bit faster than on 230v, and the thermostat ticks off sooner. Averaged over all the county's houses. there is no difference. But the load on their cables is less.

This is why nobody is pushing for low-powered kettles. They'd just run for longer.

 

[JohnW2]

The heavy loads in a house are generally heating appliances which certainly obey Ohms law.

In terms of instantaneous current that's true. However, what matters to a DNO is the current in their network averaged over many consumers (and time). If those heating loads have thermostatic control, then that average current will be lower if the voltage is higher.

Kind Regards, John
Edit: Whoops - I somehow missed JohnD's post - but at least we agree!

 

[EFLImpudence]

but at least we agree!

Do you?

then that average current will be lower if the voltage is higher.

Averaged over all the county's houses. there is no difference.

Won't the average be the same?
Surely the same amount of energy has been used in, say, a day - or even an hour.