DIY LED Question.

[lpsouth1978]

I am just curious and hoping someone can answer my question for me. If I have LED's that have a max current of 600mA and I use a 700mA driver on them, what will the result be?

Will it blow the LED's, just not power them, is it a fire risk, etc...? Your thoughts would be greatly appreciated!

 

[theatrus]

You will stress the LEDs, leading to too much heat, lower efficiency, and have premature failure.

 

[Webmanny]

You have no problem here. The only thing that can hurt your LEDs is higher voltage not current.

I'll give you an example. Any outlet in your home runs at 120v 20 amps, but your TV only consumes maybe 5 amps. It doesn't care that is being fed 20 amps.

I have been building LED lights for years now and I always go a bit higher than the required amperage.

 

[yukimika]

amps are drawn not pushed- it'll consume what it needs. check the voltage rating like ^ said.

 

[Wolfex]

Yes do check the voltage. Also check if you are using a constant current driver. A constant current driver will adjust voltage to deliver the same current and could blow your LED. Measure the resistance of your string then calculate the voltage using V=IR. I and R would be fixed. If V is greater than your LED rating you will blow the string. Fire hazard is low since its low voltage and the LED blowing would create an open circuit. .

 

[theatrus]

You have no problem here. The only thing that can hurt your LEDs is higher voltage not current.



I'll give you an example. Any outlet in your home runs at 120v 20 amps, but your TV only consumes maybe 5 amps. It doesn't care that is being fed 20 amps.



I have been building LED lights for years now and I always go a bit higher than the required amperage.

LEDs are not ohmic devices (their I/V curve has a flat region, a knee, and an exponential climb - decidedly non linear), and do not "take what they need", which is why constant current drivers are required.

 

[theatrus]

Yes do check the voltage. Also check if you are using a constant current driver. A constant current driver will adjust voltage to deliver the same current and could blow your LED. Measure the resistance of your string then calculate the voltage using V=IR. I and R would be fixed. If V is greater than your LED rating you will blow the string. Fire hazard is low since its low voltage and the LED blowing would create an open circuit. .

Close - you can't measure the resistance of a string of diodes and make much sense of it. It's easier to add the Vf (forward voltage drop) from the data sheet and make sure your constant current driver is in range.

This still won't help the fact that the op will be driving the LEDs with 100ma more than rated current.

 

[yukimika]

just cause they don't obey ohms law doesn't mean they don't consume what they need. Just means that it's more sensitive to Vin swings. But if OP is using a constant amp driver that can't adjust then they need to match, so I agree there. A good driver would adjustable and have pwm to dim.

 

[colorful1180]

what is the output voltage on your driver?Series LEDs or parallel LEDs?

 

[theatrus]

just cause they don't obey ohms law doesn't mean they don't consume what they need.

Yes, they follow physics, which means they "need" (or at least will happily try to conduct) 500Amps when in the exponential region of the curve

 

[lpsouth1978]

I am using the Meanwell LDD drivers, so yes, I am using constant current drivers. The drivers I currently have are 700mA, but the Violet LED's are only rated at a max of 600mA. I have already ordered 500mA drivers to replace them with. Each LDD driver is powering a single string of 15 LED's.

 

[Webmanny]

LEDs are not ohmic devices (their I/V curve has a flat region, a knee, and an exponential climb - decidedly non linear), and do not "take what they need", which is why constant current drivers are required.

I respectfully disagree. I have been building LED lights for personal use and for friends for years using 3W, 1W and multi chip LEDS and I always use a higher amperage on all my builds.

LEDs are like every other light producing source, they respect the laws of electricity. As long as you add a resistor at the end pointy of the circuit, there is no need to bother with feeding the precise amperage.

This is an interesting read that may help you understand this a bit better.

https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law

Please note that I am done arguing this point with you or anyone else. I am just trying to educate you and remove some of the LEDs misconceptions found in many posts in this forum.

 

[theatrus]

Sorry, LEDs are diodes. They follow the laws of electricity, being a semiconductor PN junction. They however cannot be modeled as resistors, even as a first order approximation.

Your added resistor will linearize the circuit, yet will just be a large heater for any useful range of values.

If you'd like to discuss switch mode topologies, thermal stresses, diode behavior or any further EE topics I'm happy to oblige.