Household Power Usage Readings

Electric Energy Usage Meter

Measure Standby and Active Power

Including line charges and Tax; our power is costing over 24 cents per unit.

Info- Connections- Prices

Energy Meter

The new meter is an improvement on the original because it has local NZ / Australian power connectors built in; no need for the lead and adaptor.

It's an intelligent power meter that plugs into a normal power point or for convenience an extension lead can be used to bring it out from the wall. You can enter your electricity unit price and the meter will show you exactly how much the appliance is costing to run over a period of time. The power meter tracks the power used and can display the instantaneous voltage or current being drawn as well as the peak levels that have been drawn. The meter has backup batteries so it will not lose data during power outages or when being moved. Simple and very usefull for tracking down where the power is going.

How and Why

I purchased a couple of Energy meters some time ago because I was interrested in the standby and active loading of many common household appliances. This comes from an interrest in alternative energy sources and thoughts of developing a modular power inverter for domestic and general use.

The original energy meter operates at 230V AC, 50Hz and was rated up to 16 Amps although the lead and adapter are rated to 10 Amps. The LCD display shows voltage, amps, watts, KWh, accumulated hours and cost. You just plug the appliance to test (the load) into the meter and plug the meter lead into the mains.

The lead and adapter were needed because the meter is produced with Eurpoean style mains power connectors. We supply the meters with the adapter and lead permanently attached for safety reasons. The European plugs can easily be reversed which although it does not affect normal operation can produce a slightly higher than normal safety risk with some older appliances.

As of May 2007 electricity was costing us about 25 cents per unit when you include unit cost, line charges and tax.

With 8760 hours per year and one unit 1000 watt/hour, this relates to:

a 10 watt load costs about $18.40 per year (small compact fluorescent lamp)
a 50 watt load costs about $91.98 per year (large fluorescent lamp)
a 100 watt load costs about $183.96 per year (TV or good sized computer monitor)
a 200 watt load costs about $367.92 per year

Appliance

Standby Watts

Running Watts

Notes

75 watt incandescent lamp

n.a.

76

.

8 watt compact fluorescent lamp

n.a.

9

.

Pedestal fan,14 inch, 3 speed

n.a.

30 to 45

low to high

Stereo system

25

35

normal listening

TV,Goldstar, 24 inch

16

90

.

Cable TV decoder

21

21

.

Cable modem

n.a.

18

always on

TV masthead amplifier

n.a.

4

always on

DVD player

4

18

no disk in

VCR

14

28

play

Telephone,Uniden, dect1811

n.a.

7

always on

Answerphone,Uniden

n.a.

4

always on

Water bed

n.a.

320

on thermostat

Various plug-packs,wound transformers

n.a.

4 to 7

size varies

Security system,extensive system

n.a.

18

.

Washing Machine,F&P GW52

Heavy duty cold wash takes 40 min.
using 0.13 KWh of electricity.

See the note below.

15

21
38
150-300
133
415

doing nothing
filling
washing
draining
spinning

Refridgerator,standard family size fridge/freezer

5

150

compressor

.

.

.

.

PC,atx, 2100+ AMD
1GB, 80g hdd, ps2 mouse and keyboard, monitor

12

200

activity varies

PC,atx, 950mhz Duron
512mb, 60g hdd, 2x nic, ps2 mouse and keyboard

11

80 to 90

activity varies

Monitor,old 14 inch Phillips

18

61

.

Modem

n.a.

7

waiting for call

Network Switch

n.a.

7 to 14

activity varies

PC,mini-itx, 800mhz
512mb, 60gb hdd, wireless mouse and keyboard

7

45 to 55

activity varies

LCD monitor,MAG brand, runs off PC power supply

?

35

.

.

.

.

.

.

.

.

.

.

.

.

.

• Power factor (PF) is the timing relationship between voltage waveform and current waveform. If they are in sync the PF 1.00. Generally, only heaters and many common light bulbs have a perfect PF of 1.00. For a refridgerator, a PF of 0.30 (30) is not very good. It will be due to the inductive compressor motor. A poor power factor (less than 1) can mean that you pay for more power than you actually use because the the current draw is higher to achieve the same apparent power. Things like computers and monitors (switchmode power supplies) cause a distorted current waveform which complicates the power reading. Some equipment is power factor corrected, but not much of it yet here in NZ.

• If the power reading is unstable you could try measuring the load of each item and all together as a total. One thing you could try would be to run a fan heater on low (about 1000W). Measure the power draw of the heater on its own and then plug in the computer and monitors etc. so that you are reading the total power draw including the heater. Subtract the heater load. This may give a more stable result. I haven't tried this yet so I don't know if it will work.

• I noticed that many wire-wound plug-pack power supplies (the heavier ones) are not very good. In many cases the losses in the plug-pack seemed to be equal to or greater than the loading of the appliance they were powering. Some light-weight swichmode plug-packs that I've tested are much better. The power consumption with no load applied was almost zero or too low to measure easily. I did find one brand of switchmode plug-pack that was less efficient than most older wire-wound plug-packs. It runs very warm even with little or no load connected.

• The washing machine uses more power when it's plugged in and sitting on standby (off) than it does washing. 15 watts on standby is about 1/3 of a unit per day; almost $20 per year while it's turned off. If it does 5 loads of washing per week, it uses about 35 units of electricity per year; $5 to $6 per year. This doesn't include water heating if you use hot water for cloths washing.

• In this house we have a standing load of about 250 watts. This's about 2280 units per year costing over $450 per year. That's $450 wasted each year by clocks, plug-packs and appliances on standby.

last updated: 07 Feb 2010