Measuring power cosumption of CC led drivers.

Scrogit

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Sep 3, 2017
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I built two separate led fixtures a few months apart; both with constant current drivers dimmable via built in potentiometers between 350mA and 700mA. I also purchased a plug in energy consumption moniter to set the lights to certain power outputs. To get to the point; after a few months I noticed that the energy consumption moniter had gone from 100W to 30W on one of he fixtures without me touching the driver so I turned the potentiometer up to maximum and it only went to 170W when it had previously been 250W and on the lowest setting it is now reading 7.5W which is crazy as the minimum forward voltage of the diodes is 280 odd volts and the minimum operating current is 200ma on some of the diodes and they are lit. I plugged the power meter into my other fixture and it also said the power consumption had gone down drastically; MUST be the energy meter right? Well I'm not sure as when I plug it into any other device it still gives what seems to be accurate and close to specification power readings. Is there anyway the circuitry of these drivers could be interfering with the power meter?

Thank you in advance for any help!

Drivers - meanwell HLG-240H-C700A
meanwell HVGC-240-700A
 

ssanasisredna

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Oct 19, 2016
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I built two separate led fixtures a few months apart; both with constant current drivers dimmable via built in potentiometers between 350mA and 700mA. I also purchased a plug in energy consumption moniter to set the lights to certain power outputs. To get to the point; after a few months I noticed that the energy consumption moniter had gone from 100W to 30W on one of he fixtures without me touching the driver so I turned the potentiometer up to maximum and it only went to 170W when it had previously been 250W and on the lowest setting it is now reading 7.5W which is crazy as the minimum forward voltage of the diodes is 280 odd volts and the minimum operating current is 200ma on some of the diodes and they are lit. I plugged the power meter into my other fixture and it also said the power consumption had gone down drastically; MUST be the energy meter right? Well I'm not sure as when I plug it into any other device it still gives what seems to be accurate and close to specification power readings. Is there anyway the circuitry of these drivers could be interfering with the power meter?

Thank you in advance for any help!

Drivers - meanwell HLG-240H-C700A
meanwell HVGC-240-700A

LEDs don't have minimum operating currents.

The minimum forward voltage is 280 (at what current?). What is the maximum voltage and at what current?

As a guess, and only a guess, the forward voltage of your LEDs has drifted upwards and the power supply is limiting the maximum voltage and hence that is limiting maximum current. That would not be the expected behaviour (Vf often drops a bit after break-in), but it's the only explanation other than the drivers are broken.

Do you have a voltage meter? Can you measure the voltage at the output of the LED driver?
 

Scrogit

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The fixtures consist of 8 modules with the following characteristics...


350mA ~28.0V 700mA ~32.0V maximum current for these modules is 1000mA at 35V


And 16 individual diodes with the following characteristics...


350mA ~2.8V 700mA ~2.9V maximum current for these is 1800mA at 3.2V


So at 350mA the voltage of the fixture should be roughly 270 and at 700mA it should be 300 giving power consumption of 95W and 210W respectively without adding the inefficiencies of the drivers (93% efficient apparently).


The driver says it provides constant current of 350-700mA between voltages of 178V-357V and is rated at 250W. I don't currently have a working multimeter; i will have tomorrow though.


Thanks












 

DIWdiver

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Yes, LEDs do have minimum operating currents. It's just typically low enough that it doesn't matter. An engineer at Luminus assured me that they were serious when they specified a minimum operating current of 1A (maximum operating current was 6A), and that they would not guarantee that the LEDs would produce ANY light below that value.

There are at least two reasons I can think of that many people think LEDs don't have a minimum operating current:
1. Very few manufacturers specify a minimum operating current (only one that I know of).
2. Most LEDs light up at such a low current and such low output that it's not easily seen.

You've probably heard it said that any sufficiently advanced technology is indistinguishable from magic. I claim that a sufficiently low light output is indistinguishable from zero.

Once, I was working on a lantern with 30 LEDs in ten strings of three. I was working on a problem where there was some leakage current in the array when it were supposed to be off. For some reason I put my eye right up to the LEDs (it was a long time ago, and I don't remember why) and I noticed that some of the LEDs were on and some were not. The ones that were on were all at about the same brightness. It was quite clear they were binary ON or OFF. As I pushed the leakage current around I could see that in many strings the three LEDs came on at slightly different currents.

So unless you are buying LEDs from Luminus, it's probably effectively true that LEDs don't have a minimum current, even though it's likely to be precisely true that they do.
 
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ssanasisredna

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Yes, LEDs do have minimum operating currents. It's just typically low enough that it doesn't matter. An engineer at Luminus assured me that they were serious when they specified a minimum operating current of 1A (maximum operating current was 6A), and that they would not guarantee that the LEDs would produce ANY light below that value.

They only specify minimum "guaranteed" current for their color devices and I believe right now, they just spec 200mA across the board, no matter the maximum current and no matter the color (which means the spec is technology agnostic). It is NOT the minimum current at which the LED will produce light. As these devices are typically mixed for color, it is the current at which they guarantee performance.

Well LEDs do have some parasitic conduction and hence there can be some current flow before the voltage gets close enough to the band-gap voltage to create light, that value is very very small and not relative to this thread and hence of little value other than confusing the original poster. Effectively, LEDs, being diodes, do not have a minimum operating current though they may have a minimum current where light is produced.

Scrogit, can you provide us the make and model of the LEDs you are using.
 
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