Hello,

I've got a 100 W LED from Aliexpress. (Better read the description)
If powering up with V = 32 V, the current amouts only to 1.06 A although the actual current shall be 1700 mA.
Is it safe to increase the voltage until the 1700 mA current draw?

Thanks

 

The specification says 32-34V with 1.7A (57W), the led will take it's own current depending on the voltage supplied , ideally with a constant current led driver.

 

The specification says 32-34V with 1.7A (57W), the led will take it's own current depending on the voltage supplied.

Yeah, but isn't it supposed to draw the rated current if the rated voltage is connected?

 

You need a constant current driver for that LED, you cannot drive it with a voltage. Even if you adjusted the voltage to get the desired current, if the temperature rises, so will the current, possibly destroying it.

Bob

 

You need a constant current driver for that LED, you cannot drive it with a voltage. Even if you adjusted the voltage to get the desired current, if the temperature rises, so will the current, possibly destroying it.

Bob

The LED is well cooled so it doesn't overheat.
But just a question: How does the constant current driver work except adjusting the voltage? How should it work if you don't ignore Ohm's law?

 

The LED is well cooled so it doesn't overheat.

Until you experience a situation where some unforeseen circumstance arises - and poof - up in smoke goes your money.

How does the constant current driver work except adjusting the voltage? How should it work if you don't ignore Ohm's law?

It maintains a specific current by modulating the voltage.

An LED isn't voltage driven. It's current driven. And every LED has a forward voltage. That Vf changes with temperature. So if the temperature goes up and the Vf goes down then the amount of current running through the LED will climb. Unless there's a constant current supply. If the Vf changes so will the output voltage in order to maintain a constant current. This follows specifically along with Ohm's Law.

Oh, and welcome to AAC.

 

From Alie Express, they have many LED drivers like this one. In this case the input voltage is 100 to 265VAC. The output is for 20 to 38V LEDs. The current is set at 0.9A. The current is fixed at 900mA the voltage is whatever it takes in the 20 to 38 range.

Some drivers have an adjustment for current.

 

Until you experience a situation where some unforeseen circumstance arises - and poof - up in smoke goes your money.
It maintains a specific current by modulating the voltage.

An LED isn't voltage driven. It's current driven. And every LED has a forward voltage. That Vf changes with temperature. So if the temperature goes up and the Vf goes down then the amount of current running through the LED will climb. Unless there's a constant current supply. If the Vf changes so will the output voltage in order to maintain a constant current. This follows specifically along with Ohm's Law.

Oh, and welcome to AAC.

Alright, thanks.

 

They lie about its power. They say 33V at 1.7A but that calculates to only 56.1W.
You are getting a power of only (32V x 1.06A=) 33.9W.
Reviews on Amazon say that some of the 100W LEDs draw only 15W or 50W.

 

They lie about its power. They say 33V at 1.7A but that calculates to only 56.1W.
You are getting a power of only (32V x 1.06A=) 33.9W.
Reviews on Amazon say that some of the 100W LEDs draw only 15W or 50W.

And where am I getting lied?
100 W is - I think - for teh power of the light equivilant to incandescent lamps.

 

As long as you understand that the 100W is marketing-speak, then that's all good.

But on this forum, 100W = V x A.

 

Do the simple math from their description:
10W LED= 10.5V x 850mA= 8.93W, 950LM.
20W LED= 33V x 600mA= 19.8W, 1700LM.
30W LED= 33V x 900mA= 29.7W, 2550LM.
50W LED= 33V x 1500mA= 49.5W, 4250LM.
100W LED= 33V x 1700mA= 56.1W, 9000LM.

 

Reviews on Amazon say that some of the 100W LEDs draw only 15W or 50W.

100 W is - I think - for the power of the light equivilant to incandescent lamps.

I was going to say that. And that's what I think. I just bought four 100W (EQUIVALENT) LED's. They draw about 20W I think. I'd have to check the box, but typically the power consumption on an LED lamp is 80% less than its equivalent incandescent lamp.

 

The power LEDs are No-Name-Brand and sold online from China. Then they might be rejects from a Name-Brand company.
They might be so bad that they produce as much heat as an incandescent light bulb.

 

If it is a 100W equivalent when driven by 56.W it is an extremely inefficient LED. Typically. they would use 13 or 14W.

Bob

 

Figure that today the best white LEDs give about 20x the lumens/watt compare to incandescent lamps.

You didn't ask but I would not spend time on a high powered LED unless I knew the manufacturer and had the datasheet showing the needed specifications and curves.

 

You need something like this: https://www.indiamart.com/proddetail/100w-constant-current-led-driver-19341039462.html

 

You CAN adjust the voltage to get the desired current BUT you MUST ALWAYS INCLUDE A SERIES RESISTOR to allow for the LED forward voltage to change a bit with temperature. And an LED will certainly heat up a bit as it operates. The resistor only needs to drop two or three volts during operation, so while it is a less efficient scheme it works very well.
And as for getting any information from Amazon, the only accurate data they can provide is the selling price, although they are also usually close on the shipping weight. I recall them selling a "100 Watt Stereo Amplifier" that delivered full power when supplied by a 12 volt 100 Milliamp wall wart. On evaluation it appeared to be a 100 MILLIWATT amplifier. Typical Amazon error. And only $24.95.