heat of led board!

[Navid]

Hi friends
I use hundreds of leds in a board for lighting, there are 7 of 3volts leds and 330 ohm resistor in series and those are parallel together(3v and 9ma on each led) when led pitch is high, temprature goes up but current and voltage is still fix. im worry about this heat, may it hurts leds or its ok because of my standard voltage and current?
Regards

 

[ronsimpson]

There is some information missing.
How hot? Can you hold your hand on the back of the PCB? Is it too hot to hold. It is hard to know if the die (the silicon part) of the LED is too hot. Do you have a way to measure the LED lead temperature?
What part number for the LED?
White LEDs will not last as long when hot.

I have made LED advertising signs and camera light sources. I made the PCB traces as wide as possible. With both side of the PCB 90% copper the heat from the LED is pulled away better.

 

[Navid]

thanks for your attention
yes i can hold my hand on pcb but it's hot anyway, leds are 15-20ma and 3.2-3.4 volt. led are HG -CM5W2SCXY1012
about 210 led on 12x12 pcb board. but i use 10ma and 3v instead of 15-20ma and 3.2-3.4v

 

[ronsimpson]

My suppliers can't find that part number. HG -CM5W2SCXY1012

My guess is that if you had only one LED it can handle 15 to 20mA.
With 210 LEDs 10mA is probably the max current.
I think your board is not "hot" but very warm.
If you want to make 1000s of boards then you need to put a temperature probe on one of the center LEDs and see what reis happening.
If this is a hobby then probably you are OK.

It is hard to know what temperature the inside of the LED is at. A warm board probably indicates the LEDs are hot.

about 210 led on 12x12 pcb board

Many people think metric. I can't see where you are.
12x12 meters....probably not. Feet.....no. Inches? cm?

 

[Navid]

these are chines led!!
oh sorry i forget to write units. 12x12 cm.
10 ma is in each line of 7led. there are 30 line of 7 leds, and max current is 0.29 amper!

 

[MrAl]

Hi,

The packing density will affect temperature also. One LED standing three feet away from another LED in free air will not affect that second LED very much. But one LED mounted 0.5mm next to another LED will raise the temperature of that second LED by some amount.
Furthermore, six LEDs mounted around a single center LED will raise the temperature of that center LED more because it has air that could be heated now than when it stands alone.

You could try mounting an LED by itself, driving it with a constant current, and measure the rise or fall in voltage over time starting the instant it is turned on. You could then mount the same LED where it is supposed to go in the board, drive it with the same current, turn it on, measure the voltage again over time, then compare the final temperature (rise or fall) to the first test to see how much difference it makes with the different the mounting patterns.

 

[NorthGuy]

210 Led 0.01Ax3v = 0.03W = 6.3W

if each has a 330 Ohm series resistor, it's 0.01 x 330 = 3.3V on the resistor, 3.3V x 0.01A = 0.033W x 210 = 6.9W

6.3W + 6.9W = 13.2W

This is enough to make the 12x2cm board very hot, but not burning hot.

 

[Navid]

210 Led 0.01Ax3v = 0.03W = 6.3W

if each has a 330 Ohm series resistor, it's 0.01 x 330 = 3.3V on the resistor, 3.3V x 0.01A = 0.033W x 210 = 6.9W

6.3W + 6.9W = 13.2W

This is enough to make the 12x2cm board very hot, but not burning hot.

there are only 30 resistors not 210! ( 1resistor for 7leds ) so 0.033 x 15 = 0.495w for resistors

 

[Navid]

i cant make bigger pcb and i cant use fan or heatsink too because of my pack, maybe i can use small bag of oil or water in back of my pcb to get temprature!!

 

[MrAl]

Hi,

Is the temperature really bothering anything or is it just annoying?
If it does not bother anything really then maybe it isnt that much of a problem after all.
LED's produce some heat, they are not perfect light producers, so some thermal management always has to be part of the overall design plan. Once the board is produced however it's more difficult to fix. You may be able to lower the current to get less heat but of course that will also reduce the total light output.