LED SMD's on a string, overheat protection?

Discussion in 'General Electronics Chat' started by trader007, Dec 26, 2013.

  1. trader007

    Thread Starter Active Member

    Feb 27, 2010
    If you had a string of LED's, or really any LED for that matter, how would you protect them from overheating?

    In one of my projects, I am finding that if left on for days they can get very warm and the diodes start to lose intensity. What I also notice that even though they are not as bright as they were when new, they seem to dump the same amount of heat into the fixture.

    In my setup, the LED's are drawing about 1 amp of current total, at 12v. Is there a special type of thermal resistor I could use that would automatically pull back current when temperatures hit a certain point?

    If not, I think I might have to lower the overall voltage a bit...
  2. MrChips


    Oct 2, 2009
    LEDs will last a bit longer if you lower the power output if you can live with slightly lower light output. You can achieve this by any of the ways you have suggested, lower voltage, lower current, or adding some resistance in series with the LED circuit. You can even try one or two 1N4001-1N4007 series rectifiers in series with the LEDs.
  3. trader007

    Thread Starter Active Member

    Feb 27, 2010
    Yeah I just went to the garage and tested a lower voltage. Dropped it down to 11.1v. When I did that, it wasn't much dimmer at all, still very bright but I bet it makes a dramatic difference on the heat output.

    I will let them burn for a few hours and see how hot they get.

    What I find interesting is, that when a high output LED burns out a little, and its luminosity diminishes, the current seems to stay the same. It appears to produce less light but not less heat...

    The other issue(s) are I don't know the true specs for the SMD diodes- they are china made, and have a branding of '3650' on them, but that doesnt mean much since LED's can vary greatly depending on how they are made. China doesnt play by any rules, so to figure what the ideal voltage is for these is just a crapshoot really.

    That, and my power supply is voltage regulated, its not like a battery. If I hook these lights to a 12v battery, the voltage in the circuit drops a volt or so due to the voltage drop of the diodes. The power supply, on the other hand, pushes out 12v no matter what, so I am not sure how that effects the amount of current running through the diodes...
    Last edited: Dec 26, 2013