[Question] LED strips over heating

[skatingsparks]

Anyone else had trouble with LED strip lights running hot (3 x 2 meter runs of 14.4 watt per meters running from a 12.5 amp 12 volt dc power supply). Even one strip at a time they still get hot. I have used loads of this stuff before but I have one batch (bought 11 packs) there are "hot spots". The strip is straight of the roll, so no kinks and bends and as of yet I haven't fixed it to anything, just laying on my desk. I have tried 3 different power supplies and same happens. Tried resoldering, still the same. Is it just a bad batch? I mean they are hot to the point where you can't put your hand on them for much more than 5 seconds before you have to let go. I have cut them into 2 meter lengths for the job and was was just showing the client the colour for approval and I noticed then how hot they were. I have never had LED's run this hot before and will have to take them back (which is going to be pain because they have been cut). Just wondering....

[Justloadit]

The heat that you are experiencing is normal, people tend to forget that when the LED is rated at a certain wattage, it stands for the heat they generate. You probably never noticed the heat before, it has always been there. The brighter the LED the higher the wattage and the heat created.

14.4 watts per meter is quite a substantial amount of heat that must be dissipated into the air over the thin strip. Usually when you stick it to any surface, the heat is transferred to the surface, and you probably would note a remarked drop in temperature. Just in free air, there is nothing to draw the heat out of the strip, but for the air surrounding the strip.

If you can just hold it for 5 seconds, and then the pain is unbearable, usually turns out to be just below 50 Degrees centigrade. LEDs can run up to 70degrees at the point where they are soldered on the strip before long term damage occurs. Usually the point which emits light runs around 150 degrees.

I would not worry, unless there is a high rate of failure over a short period of time.

[adrianh]

Wouldn't this depend on the type of led though. Those 350mA leds run terribly hot and require fat heatsinks but I am sure that normal 30mA leds shouldn't.

Why don't you post a pic of the led strip then I'm sure it would be easier to judge what the issue is.

[skatingsparks]

I have LED strips(from the same supplier come to think of it) which are very very mildly warm, 14.4 watts per meter, the same. The ones I'm having trouble with are hot in places, not throughout the whole length. They are warmer than usual though out the strip but just some points are are really hot, like I said, I can hold them for a few seconds. I put the ones I had before next to the new batch I have now from the same power supply and the heat from the new ones is much higher, like I said in places untouchable where as the other is fine. LED's life is shortened by heat. Why would they be hot in places not though out the entire length?

I had a problem a couple of years ago with LED down lights popping before because of power quality in the area and I ended up driving up and down for weeks on end changing lamps and was a VERY expensive experience. I just don't want a repeat of that experience, going back and forth fixing lights, just because they are kak product or something.

By the way they are 5050 chips.

[adrianh]

There is no reason for 5050 to run hot. Depends how they are wired up in the strip. Lets say they are 60mA 3.2V driven at 12V. You would expect to find 3 in series with a 46 ohm resistor. Each series set would draw 60mA so lets say they are spaced 5cm apart then you would expect a 60mA draw per 15cm which is of course 40mA /10cm and ends up being 400mA/m

You should be able to work out how it is set up counting the number of resistors and leds in one meter length. Lok very closely at the resistors around the hot spots and see if they are are an odd value

My personal opinion is that the manufacturer probably used the wrong resistors here and there during manufacture. Possibly even substandard leds got into the batch.

[AndyD]

Regardless of what temperature they run at, if the LED's are evenly spaced then the heat dissipation should also be even. I'd return it under warranty or highlight the issue to the supplier and if they say it's not an issue get a reassurance from them that they're willing to cover the cost of your time as well as the product if it fails under warranty.

[adrianh]

...but he cut it up into lengths already!

[Justloadit]

The strips that are getting hot, do they seem brighter than the ones that run cool?
If so then the current limiting resistors may be the incorrect value, or there may be shorts on the board, bypassing the resistors, and connecting the LEDs straight to the supply.

Also is it possible to check the current of the ones that run cool, versus the strips that are hot. There should be a noted difference indicating incorrect components.

[skatingsparks]

End result. Took them back to supplier. They refunded immediately and apologized for inconvenience. Manufacturing fault. Sorted.