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Old 09-06-2011, 01:01 PM   #1
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Cree CR6 Efficiency


Cree lists the CR6 as a 10.5 Watt unit, but when I plug it in through a Kill-A-Watt I'm seeing 6.5 Watts at full bore. Is my Kill-A-Watt crazy, or have the LEDs in the CR6 been silently upgraded?

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Old 09-06-2011, 02:06 PM   #2
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Cree CR6 Efficiency


Maybe leave it on (wait for it to heat up) and see if that makes any difference?

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Old 09-06-2011, 02:33 PM   #3
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Cree CR6 Efficiency


You can't trust a kill-a-watt at such a low power level, especially with such a complex load. You're measuring a current of around 0.054A on a device with a full scale reading of 15A. That's 0.36% of full scale. The kill-a-watt has a rated accuracy of "0.2%", which probably means +/-0.2% of full scale. +/-0.2% of full scale is +/-0.030A. Thus, the actual range of currents that you may be measuring is 0.024A to 0.084A. That's approximately 2.9W at the lower end to 10W at the upper end, assuming perfect power factor and exactly 120V. The results are probably even less accurate than this, because an LED driver is a very complex load. It not only has an odd power factor, but is highly nonlinear. This makes it harder to accurately measure the power consumption because the phase relationship of the current and voltage waveforms is more complex, requiring shorter sampling intervals to accurately integrate.

Bottom line: you need a much more sensitive meter to measure power consumption of such a low current device.
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Old 09-06-2011, 02:50 PM   #4
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Cree CR6 Efficiency


But would it always read under? I would expect to see separate measurements read some high, some low. It does read 12VA, but 6.5W. I'll put a Fluke meter on it one of these days.

It just seems like Cree wouldn't keep manufacturing old emitters just for the purpose of putting them in the CR6. It makes more sense that as they upgraded their production lines to XP-G and XM-L emitters that they naturally use these in their light fixtures.
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Old 09-06-2011, 11:25 PM   #5
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Cree CR6 Efficiency


With any electronique load I have ran into I will grab a diffrent ampmeter which it have true RMS { Root Mean Square } to dealt with electronic harmoinic loads while most common ampmeters are average reading and some of the electronic loads you read thur the average ampmeters { common types } will result a lower reading than what it really draw.

Kill-a-Watts is average reading wattmeter not the true RMS I have check it myself and it show a bit of differnce on electronique loads.

For reading very low loads I use the splitter or pigtail and coil up the ampmeter to get the correct reading.

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Old 09-07-2011, 02:54 AM   #6
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Cree CR6 Efficiency


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Originally Posted by BobSmitt View Post
But would it always read under? I would expect to see separate measurements read some high, some low. It does read 12VA, but 6.5W. I'll put a Fluke meter on it one of these days.

It just seems like Cree wouldn't keep manufacturing old emitters just for the purpose of putting them in the CR6. It makes more sense that as they upgraded their production lines to XP-G and XM-L emitters that they naturally use these in their light fixtures.
It could always read under. The total error percentage includes both random and systematic errors. Meters are very prone to systematic errors, even more so than randomness. I would expect that the primary source of error in any meter's measurement will always be a systematic one, so it will always read high or low by some fixed amount or percentage.

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