Energy monitor - plug in your kettle

and see what it costs to make a cup of tea.

I've always considered these things to be a waste of money, why the need to know what it costs to boil a kettle?
It's obvious to only fill it as much as required but what's the interest in the cost?
It costs what it costs.

Well, after starting to use a food dehydrator I thought it would be interesting to plot the energy use over time to see if economies could be made such as:

• initial operation using the fan only
• fan only with the door open or closed
• benefit of thermal insulation.

So I invested £15.99 +£2 p&p in an Eco Eye Plug In 2
 from eco-eye down by the coast in Lancing. It arrived very quickly and I was off.
First task is to check the numbers.

Battery check

Both read 1.478V which is pretty close to 1.5.

Boiling a kettle

Meter accuracy
Volts - 700V range ±1.2%
Ampères - 20A range ±3%

			meter accuracy
	monitor	meter	-	+
A	10.135	9.77	9.4769	10.0631
V	246	244	241.072	246.928
calc W	2493.21	2383.88
max W	2542
kettle rating	2300

but since we're not launching rockets it's pretty good.
I have no way of checking power factor but it's 1 for a kettle so I'll believe the monitor for stuff with motors.

Next task is to enter the settings.

• Set the clock
• Electric cost per kWh - tariff 1
• Time when tariff 1 starts
• Electric cost per kWh - tariff 2
• Time when tariff 2 starts
• Greenhouse gas emission kg/kWh
• Overload Watts
• Overload Amps

or ignore all of that and just plug it in.

I didn't, and still don't, know a lot of that data but I did set the clock and just as well...

Anyway, this is a plot of kWh v h for Biltong in the dehydrator

The first hour was using only the fan then I switched on the heat and went to bed. The plot doesn't make sense; the red line is an extension of the blue actual vales but it doesn't join up with the first bit.

Next project was to monitor the power of an iced up freezer and look at how it, hopefully improved, after defrosting.
The kWh reading in the morning was less than the night before.🔔
The kWh reading is reset to zero at midnight.🔔²
Now, is this some muck down the mains doing it?
After a bit more head scratching it appears to be a 'feature' of the monitor and can be easily reproduced by resetting the clock to just before midnight and watching the kWh value.
Here's a video which demonstrates the problem, the monitor dances around a bit as I kept pressing the History button to keep the backlight on.

I've tried

• 12h clock settings
• 24h clock settings
• plugged in with a load
• plugged in without a load
• unplugged
• reset button

and the kWh setting is zeroed at midnight everytime.

But the Greenhouse gas emission value doesn't reset so the workaround is to set this to 1kg/kWh and use that instead.🔔³

Current cost (pun intended) of electricity is ~3.35p/kWh including vat @5% excluding standing charge of 26p/day

Finale

It takes 0.104 kWh to boil a full kettle ≡ 0.35p

but only 0.057 kWh to boil enough water for two cups ≡ 0.19p and you'll get to drink it quicker.

A bit more

This shows the overhead of heating up the element but other than that it's pretty useless

Full kettle 1290ml so that's 0.27p/l

Two cups 500ml which is 0.38p/l.

Just another soupçon

Clear the stored values like this, it won't affect the settings or the clock

Here's a plot of the freezer using approximated values after I realised about the 12pm reset

Zone 1 shows the energy used by the iced up freezer for a day prior to defrosting
Zone 2 shows the increased energy usage as it chills back down after defrosting
Zone 3 show the reduced energy consumption after defrosting, this is estimated. The savings start when the blue line crosses the red projection.
Actually it's flawed because it doesn't include the energy used by the steam gun during the defrost so I need to do it again.

Click to download an Excel spreadsheet (pc) to plot kWh v hours as above

To be continued