Measured cfl wattage

[Bkaufman]

First post here. Please forgive any noon errors.

I am not a conspiracy-oriented person, but my recent measurements of wattage has me looking for answers.

I bought an reliance amwatt to measure wattage on household items and decided to checks it accuracy on some knowns, namely light bulbs. I used a 40w standard bulb and a 45 watt r30 bulb, which were both within 1 watt accuracy. I then tested a 13 watt cfl (twist) and a 15 w r30. I got 38-40 watt and 47 watts, respectively! Someone tell me why I bought these? I hate to over-react, but my bs meter just went off. Insights from this learned group?

Thanks,
Brett

 

[brickbat]

... I hate to over-react, but my bs meter just went off...

The BS meter isn't the problem, your wattmeter is!

I couldn't find the manufacturer's specs for the Reliance AmWatt, but my best guess it that it is inaccurate for small non-linear loads, such as CFLs. There are several recent posts about CLF energy usage. Trust me, the use the wattage they claim, and they do save energy.

The Kill-A-Watt meter (similar to your AmWatt) is pretty accurate for CFLs.

So, before you charge off calling in to Rush Limbaugh about the big CFL scam, get your facts straight

 

[ddawg16]

As Brick said, I would not put a lot of faith into what the Amwatt says.....

An incandescent bulb is a resistive load....in other words, the current is linear with the voltage across the load.

However, a CFL presents a capacitive/inductive load....in other words, the current does NOT stay linear with voltage....

Watts is Voltage x Current.......so, if a cheap meter measures 1A with an applied voltage of 120 Volts, it's going to say that is 120W. But that is only accurate if the 1A of current happens at the moment the voltage is at it's peak of 120V (RMS). In the case of a light buld, it will be.

Now, when you look at the current/voltage phase relationship into an electronic ballast as you would have with a CFL, I bet that the full current is going to lead the voltage by about 90 deg. So, while the current may look to be high...it's actually at a lower voltage...hence, the true wattage (power) is going to be more in line with what the bulb is rated.

Look at this way....cheap stereos use the convers idea to brag about their power output...."200W Peak (total all 4 channels)" ...hence, you get guys saying "Yea, I have 200W of power".....so, divide that by 4 chan/speakers, now your down to 50W....and since they are saying peak, its really .707 of that value which is more like 35W RMS per chan....big difference between 200W (peak) and 35W true RMS.

So....no conspiracy.......just a cheap meter....