Energy consumption meters' accuracy

[KAZANI]

I have been using a VOLTCRAFT Energy Check 3000 meter which is rated at 3000W max load with a resolution of 0.1W. Metering various electronic and electrical devices with it I have noticed that the readings are almost always below what is the particular device's nominal power. Some examples:
-20W CFL light bulb ⇨ 18W
-105 incadescent light bulb ⇨ 102W
-1800W hair dryer ⇨ ~1500W
-3000W room heater ⇨ ~2600W

So, you think this is normal?

 

[magomago]

Voltage and Current aren't in phase, so you have reactive power to deal with? Maybe the device automatically measures the phase angle between both and simply gives you the actual power consumed?

That said I am most definitely not a power engineer at all, so I don't know if that is simply too much reactive power to deal with.

However, looking at your link, and seeing that it just costs about 33 USD, I'd say its inaccurate.

Edit:

Resolution of 0.1W doesn't necessarily imply. Resolution just means how many digits they will show you.

edit2:

'Nominal' or whatever is listed might be listed as the maximum power.

 

[velis]

This is also what I have observed with a different device measuring my appliances. I think it's because the measured appliances really do consume that much less. I once had a water heater that was nominal 3KW and it really consumed that much. Turns out I had to replace its switch (rated 16A = 3KW) every six months or so because it would simply burn out.
That heater of yours doesn't burn 3KW for probably that same reason, but marketing sure likes to say it is THAT powerful.

 

[JackMDS]

The general variation in your measures are about 10%.

The Meter and each of the appliances have some tolerance to begin with. I.e., a 3000W appliance might leave the factory a little bellow or above the number that is stated on the box. Each device can also vary in its performance according to the temperature/humidity and the timing of its usage.

So given the price of your meter and the nature of the measures, it is a Good outcome.

 

[piasabird]

From an engineering perspective most electronic devices like a FAN or a power supply are over-engineered. When a PC Starts up it purposely make all the drives spin up to test them so starting a computer puts a lot of stress on the computer. However, normal running conditions are a lot lower. This even applies to processors. Intel takes a group of processors and says they are rated say for low power with a rating of 35w. However, they may be able to run at a lot less power when idle like 18w. However, the total computer may use 100 watts when playing a Blu Ray Movie because you have the Optical drive, the Hard Drive and the Graphics all working hard to get the job done.

 

[mfenn]

I have been using a VOLTCRAFT Energy Check 3000 meter which is rated at 3000W max load with a resolution of 0.1W. Metering various electronic and electrical devices with it I have noticed that the readings are almost always below what is the particular device's nominal power. Some examples:
-20W CFL light bulb ⇨ 18W
-105 incadescent light bulb ⇨ 102W
-1800W hair dryer ⇨ ~1500W
-3000W room heater ⇨ ~2600W

So, you think this is normal?

If your house's voltage sags below nominal, than any simple resistive devices like incandescent bulbs will draw less current, and thus use less power.

As for more complex devices, especially ones with powerful fans, they don't apply a purely resistive load, but instead have some sort of inductive components. This results in a power factor of less than one. Your meter may report real power because that is how most residences are billed, but the device is going to be rated in terms of apparent power.

 

[KAZANI]

If your house's voltage sags below nominal, than any simple resistive devices like incandescent bulbs will draw less current, and thus use less power.

I haven't noticed any correlation to fluctuations of voltage. Another incadescent bulb (same make with the 105W above) rated at 70w gave me a reading of 71.5w.

As for more complex devices, especially ones with powerful fans, they don't apply a purely resistive load, but instead have some sort of inductive components.

Hmmm...The hair first time I started wondering about the accuracy of this meter is when, some time ago, I had measured the hair dryer and, in its lowest heat output setting, it registered as absolutely zero watts. It gives a normal reading now, though...odd!

Right, thanks for everyone's replies and, unless somebody submits data from his metering device that suggests otherwise, I conclude that the verdict is: normal