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Why is this LED not 20 Watts?

Al Slitter

Nov 4, 2016
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I ordered off of E-Bay a combo 20 Watt LED and a 20 Watt driver for an application that I have.
When I received it I tested it with a meter that I made up which shows the voltage, Amperage, Watts and Power.
The combination of the driver together with the LED showed as 9.1 Watts and not the 20 Watts that I wanted.
I suspected the driver was the cause so I tested the driver by wiring an existing 30 Watt LED ( 3-series of 10 ) and it showed when tested to be again only 9.1 Watts.
What do I do now, the driver cannot be used with 10 Watt LED's due to the voltage and under drives all of my LED's on hand.
I would appreciate your thoughts on this driver I have linked an image of the LED and driver for viewing.

LED problem.jpg

Thank you in advance.
 

Bluejets

Oct 5, 2014
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Just at a guess I'd say the supplier is doing some sort of comparison between tungsten, fluro and led. Led consumption may not be their favourite as this way you seem to get more than what you pay for. The old saying buyer beware comes tomind.
 

Al Slitter

Nov 4, 2016
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The issue is not how they tried to decive me I can work around that on E-Bay.
The question is; is it possible to modify the driver so that is will run at 20 Watts +/- .
 

(*steve*)

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The issue might be that the LED is indeed a 20W LED, the driver is indeed a 20W driver, but the driver does not match the LED.

That driver is a 600mA constant current driver. For a power of 20W, the LED voltage must be about 33V.

If the Vf of the LED module is around 15V at 600mA, that would perfectly account for the 9W you measured.
 

Al Slitter

Nov 4, 2016
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The issue might be that the LED is indeed a 20W LED, the driver is indeed a 20W driver, but the driver does not match the LED.

That driver is a 600mA constant current driver. For a power of 20W, the LED voltage must be about 33V.

If the Vf of the LED module is around 15V at 600mA, that would perfectly account for the 9W you measured.
Thank you that makes sense, now is there any way to fix the driver to yield 32 - 35 volts?
 

(*steve*)

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Thank you that makes sense, now is there any way to fix the driver to yield 32 - 35 volts?

Yes, you ensure your load requires at least 32 volts to draw 600mA

Can you measure the current drawn by your LED when connected to this driver and the voltage across it?
 

BobK

Jan 5, 2010
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What are the specs of the LED you are using? Voltage and current?

You could probably get close to 20W of output by putting 2 of them in series and driving them with the driver you have.

Bob
 

Al Slitter

Nov 4, 2016
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What are the specs of the LED you are using? Voltage and current?

You could probably get close to 20W of output by putting 2 of them in series and driving them with the driver you have.

Bob
The AC voltage here in Thailand is 220 Volts the same as China!
 

Alec_t

Jul 7, 2015
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They are not deceiving you with the 20W rating. For a LED rated at 38V (the driver maximum) drawing the rated 600mA the power would be 22.8W.
 

Bluejets

Oct 5, 2014
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What is the "measured" input and output voltage and current in your test? I am aware the standard voltage in Thailand is 220 just as I know how much it can vary.
 

(*steve*)

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What is the "measured" input and output voltage and current in your test? I am aware the standard voltage in Thailand is 220 just as I know how much it can vary.

The input voltage is not an issue.

Measuring the LED voltage and current will tell us the story.

Even if the input voltage causes the output current to vary, the measurements of the load will tell us.
 

Bluejets

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Well, I will quote it once again directly from the specs ......

Changes in constant output current depend on supply voltage
 

(*steve*)

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Well, I will quote it once again directly from the specs ......

Changes in constant output current depend on supply voltage


Yes, but unless you measure the load voltage and current to determine what they are, a measurement of the mains is moot (assuming it's in spec -- 85 to 265V).

If the change in mains voltage from 220 to 185 results in a change in the current from 600mA to 550mA, we know more by measuring the load current than we do measuring the input voltage.

I'm pretty sure the current will vary with temperature too, but wouldn't you want to see the size of the effect first?

There are multiple possibilities ranging from the driver actually being a 10W device to a mismatch in driver and load, to... well some other option. I would try to find out what is happening first, then try to determine why.
 

Al Slitter

Nov 4, 2016
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They are not deceiving you with the 20W rating. For a LED rated at 38V (the driver maximum) drawing the rated 600mA the power would be 22.8W.

The issue is not and has not been the 20 Watt rating but rather the combination of the driver and LED only consuming 9.1 Watts. This is less than 1/2 of the Wattage needed to effectively drive the LED.
Thank you for your input!
 

Bluejets

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Steve,
As the specs showed the change in output relative to input voltage I was assuming the output voltage would be changing also. ( output 21v-38v)Trying to get at how the op came to his conclusions rather than just a quoted 9.1w but doesn't seem as though that info will be forthcoming.
 

(*steve*)

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The issue is not and has not been the 20 Watt rating but rather the combination of the driver and LED only consuming 9.1 Watts. This is less than 1/2 of the Wattage needed to effectively drive the LED.
Thank you for your input!

Please measure the voltage across the LED while it is operating and the current through it (placing the meter in series with the LED). With this information we will most likely be able to identify WHY this is happening and possibly suggest a course of action.

If you can post links to the actual ebay auction(s) then we may be able to ascertain the reason without you making the measurements.
 

Al Slitter

Nov 4, 2016
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You are correct the driver is just supplying a low voltage to the LED, if the driver was providing the needed 32 Volts to 35 Volts as specified the Wattage would be in the 20 Watt range.
The seller on E-Bay is willing to make things right but needs to talk to the manufacture.
As is now stands the driver is nearly useless as with 9 Watts of power being used the LED is running below 50% of it rating. This driver cannot be used to even drive a 10 Watt LED as the voltage is to high given that a 10 Watt LED only requires 12 Volts DC.
One thing I will try today or tomorrow is adding a boost converter to the driver and try and get the forward voltage to around the specified 32 - 35 volts DC.
I do not expect any sort of technical reply to the issue from the E-Bay seller as they are for the most part product movers.
 
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