LED replacement bulbs burning light fittings?

[laika]

Last year I replaced all the festoon bulbs in my cabin aquasignal dome lights with LED festoon bulbs. I took the lights down as part of my refit but have just been putting them back and notice that the plastic underneath the bulb holders is melted and mis-shapen underneath the LEDs. The only light that isn't melted is the one that I haven't replaced the old 10w incandescents in. The burning seems worst underneath a sticky outy cylindrical component which I'm guessing is an inductor.

Is this common? I thought LEDs weren't supposed to get that hot. If it is a common problem, perhaps anyone else who's done the same replacement should check their fittings in case there's a fire hazard there.

 

[lenseman]

Re-fit the LED fittings and bulbs.

Turn them on and hold the assembly with your bare hands for two or three minutes.

If it gets hot (+50°C) then something is wrong or the LED lighting assembly is using a chopper circuit which is generating the heat.

Plastic fittings will not 'normally' melt if you replace incandescent filament bulbs with LED lighting.

You might be noticing scorch marks from a previous incandescent filament bulb?



.

 

[nigelmercier]

Unregulated LEDs can get hot, and as they heat up they pass more current so they get hotter...

Solution is to de-rate them from their maximum current by 50%, drop the voltage, or regulate them.

I bought some LED festoon bulbs via this forum which I plan to use in this way. I need to do some thermal tests at a sustained 14.4V first, but will probably add a couple of diodes in series.

 

[laika]

So it seems it's not the inductor which gets hot (although several light fittings seem melted especially under that component). There's an IC on the underside of the board which the LEDs are attached to which is getting very hot after about 10 mins or so. I can only imagine it's that. I have 10 of these dome lights. 9 have had the original bulbs replaced by LEDs. The only one which hasn't is the only one without the plastic melted under the bulbs. I mailed the supplier earlier today and am waiting to hear their opinion.

 

[nigelmercier]

So it seems it's not the inductor which gets hot (although several light fittings seem melted especially under that component). There's an IC on the underside of the board...

If it's got an inductor and an IC, they have a regulator. When you say very hot, how long can you hold your finger on it?

 

[claudio]

If it's got an inductor and an IC, they have a regulator. When you say very hot, how long can you hold your finger on it?

I would guess at less than 3 seconds. If it melts plastic it must be getting well over 100 degC, more likely over 150 degC.
Its either a bad design or faulty, in any case a possible fire hazard as cable insulation will melt at similar temperatures.

 

[nimbusgb]

Sounds like a linear regulator, the heat is the poor thing dumping energy. The LED's are efficient but the regulation is probably using as much energy as the original bulb.

 

[nigelmercier]

I would guess at less than 3 seconds...

I was attempting to gauge how hot they were getting under "normal" conditions, rather than when in plastic-melt mode. They can't be like that all the time, the IC would pop.

 

[noelex]

LEDs do get very hot. The regulator itself if well designed should not generate significant heat, but the LEDs themselves do. The maximum permitted junction temperature is often around 150 C and it is cheaper to skip on heat sinking and operate them at close to (or over) their limit.

The most common reason for led failure is getting them too hot. High powerd LEDs need large heatsinks. Cheap led "bulbs" often have poor heat sinking and this is exacerbated when placed in a small enclosure.

They can start fires, or melt fittings. You need to consider if this is possibility and change them if it is.

The all aluminium body and extensive fins on this torch are not just for show. They are to get rid of heat. Nearly all the heat comes from the LED itself not the driver or other components. Even with this massive heatsinking torches like this have temperature sensors and will reduce the current when the LED becomes too hot. Often the maximum output is limited by heat to a short duration.
Yacht led "bulbs" don't have the temperature sensors and they are often using poor quality emitters which generate more heat. Consumers want brightness so there is a natural tendency to push the limits.