Author Topic: CFL power rating appears wrong.  (Read 3961 times)

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clpc

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CFL power rating appears wrong.
« on: September 25, 2011, 08:46:23 AM »
I am new to this forum so hi to all.

I am also new to saving energy but now I have started I am looking into anything and everything.
I have reduced the daily kWh from 15kWh down to 7kWh and I am looking to do much better if I can.
I have also started work on a VAWT.

I have a power meter on the mains that show me power consumption to an accuracy of about 10watts.
With all equipment unplugged the reading is now zero. If I power up a 100watt incandescent light the meter reads 100watts just as it should.
If I do the same test with a 20watt and a 40watt I get exactly what is expected.

BUT.... if I connect an 11watt CFL it reads 60 watts. if I connect a 23watt CFL it reads 100watts. I have over 30 various CFL bulbs here and not a single one uses the amount of watts they claim they will, they seem to use just slightly less than the old incandescent bulbs.

Am I doing something wrong here or are all these figures stamped on the bulbs a load of rubbish ?

Thanks
Clive

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Rover

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Re: CFL power rating appears wrong.
« Reply #1 on: September 25, 2011, 09:08:18 AM »
The wattage figures I've seen are not rubbish, however my testing methodology is different I was measuring the DC current and Voltage before an inverter. CFL plugged into the inverter.

Subtracting out the inverter losses, the wattage being used was roughly the same as the claimed ratings of the bulbs.

Might be your testing methodology or some strange CFL.

Rover
<Where did I bury that microcontroller?>

clpc

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Re: CFL power rating appears wrong.
« Reply #2 on: September 25, 2011, 09:19:11 AM »
Hi Rover thanks for the reply.

I am not testing on an inverter, I am using the main grid supply, everything off except one single table lamp and I am testing using that lamp.

I see very little difference  in the power drain between incandescent and CFL bulbs.

I find this hard to believe but a 11Watt CFL shows 60Watt power drain and a 60Watt incandescent shows the same.
I have tested this meter with various items from freezers to computers and the meter is always accurate to about 10watts.

Has anyone else out there actually measured the power drain of a CFL?

BTW... UK here so main grid is 240VAC. (not that that makes any difference).
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clpc

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Re: CFL power rating appears wrong.
« Reply #3 on: September 25, 2011, 09:58:00 AM »
Okay, so the power meter on our mains supply is a bunch of crap.

Decided to take some current readings using a professional AVO 8 multimeter. (I worked in electronics all my working life, got lots of meters and oscilloscopes.)

A 11watt CFL draws 0.044Amp (44mA)

A 100watt incandescent light draws 0.450Amp (450mA)

So the CFL's are fine and the meter supplied by our electricity supplier is rubbish (probably why it was free).

Problem solved.

Thanks for reading.

Clive
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DamonHD

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Re: CFL power rating appears wrong.
« Reply #4 on: September 25, 2011, 09:59:24 AM »
The 'power factor' of electronics such as CFLs is often nowhere near 1 (though is getting better for newer kit on the whole), and that can make simple clamp-on meters give very misleading (high) numbers.

Eg see here: http://www.earth.org.uk/note-on-clip-on-power-meters-for-the-UK-REVIEW.html

and here: http://www.theregister.co.uk/2011/08/24/alertme_energy_monitoring_system_review/

and the comment thread of the second one.

In general, if you have a reading that seems way off for something like CFL, put it in a plug-in (eg standard) lamp, and measure its consumption with a plug-in meter such as the Killawatt, which is much less put off by the strange power factor.

(A power factor of one means a purely resistive load with the current being drawn strictly in proportion to voltage, which is what a simple/clamp-on meter assumes.)

Rgds

Damon

PS. This doesn't make a clamp-on meter useless; you just have to understand its limitations.  And it will still generally give you an indication of when you have too much stuff on.

Rover

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Re: CFL power rating appears wrong.
« Reply #5 on: September 25, 2011, 10:01:19 AM »
No problem, glad you worked it out.

As an aside imagine the lawsuits if the CFL wattage ratings were bogus :)
Rover
<Where did I bury that microcontroller?>