Hot LED COB Panel - What can we do?

[sotal]

I installed the COB panels as a few others have on here.

I used a 24 chip panel for the rear light - this one doesn't get hot.
I used a 36 chip panel in the AFT - this one doesn't get hot.

I used a 48 chip panel in each of the cab lights - these get very hot when left on but are OK for normal use.

I used a 112 chip panel for the main light - this gets very hot quite quickly.


The heat seems to get worse when the engine is running or when on hookup (battery charging) - but this makes sense as they are given a higher voltage. The small panels still don't seem to get hot even with the engine running.

So the only one that bothers me is the main light as that one gets the hottest and is the one we often want to use the most.

Originally I stuck it in place using double sided foam tape but this fell down on the first use when it got hot.

Whilst we have been away it has been sitting against the inside of the plastic cover and the plastic gets very hot to the touch, so we have been careful with how long it has been left on.

So my thoughts were...

Get three of the 36 LED panels and wire them up together - stick all 3 in the light housing and fingers crossed they won't get hot but will give out a similar amount of light. (Even better if I could rig up a switch to allow me to switch between 1, 2 or 3 panels - for brightness control)

Create a heatsink to dissipate the heat better.

Put a voltage regulator in place to keep the voltage at 12v and no more.


I decided to try the heatsink first and see what happens. I took the opportunity to fix the panel in properly as well so it can't drop down. I went for a very basic heatsink to start with - I cut a piece of alloy and bolted the COB panel to it. I had to drill the holes in the panel out to fit some little bolts through but it seemed OK with that!

I then bolted the alloy plate into the housing using some nuts as legs to give good air flow around the heatsink.

Put it all back together and the alloy plate certainly does its job as it gets very hot too! Not sure if that really helps though?

I'm not sure if the heat matters now either - the panel is held away from the lens so won't melt it and hopefully the plate behind will spread the heat a bit?

I'm sure I've got some old heatsinks from old computers somewhere (might have chucked them) but that was going to be my next try - could mount a few on the back of the alloy plate to give more surface area.

What are your thoughts?

In my box of wires I did find an old adapter which was used for powering a 9v CD player in the car, but it is switchable on the front to 12v. I'm wondering if it is worth putting that on the main light too, to regulate the power to 12v.

[g8dhe]

Other than spreading the heat, adding any more heat sinking won't reduce the temperature, you need to provide a path thru the rear plastic into the metal work of the internal roof, then the heat will be able to escape the box. I am planning to check out the four bolts that hold the light in position and see if they actually screw into metal or plastic clips, if the latter then it won't help much! If into the metal work then bolting the alu. plate you've added down via the bolts will help as it will conduct the heat out of the light itself and away.

[sotal]

The 4 screws that hold the light up screw into the metal above, directly into metal (no plastic clips etc)

So I have 2 screws taking some heat away to the panel above.

I'm happier knowing that the panel isn't going to just fall on the plastic now, so will monitor how hot it gets (only by touch).

I know that regular bulbs can get very hot anyway so hopefully it will all be OK as it is now.


Only other thing I can think is to cut a section out of the plastic at the back and sandwich a block of alloy between the sheet I have put in and the metal that it screws into - this would hopefully give more heat transfer into the metal above. Could be like an electric blanket for the roof tent!

[windywatson]

Hi, are you using LED's to reduce load on the battery or to improve lighting quality in general? The reason I ask is that heat just like light is a form of energy and as the unit is getting hot it suggest that there is a reasonable amount of current being drawn. I would be intrested to know the differance between the current consumption of the fluorescent tube & the LED unit. May turn out that the fluorescent unit may have been more efficeint than the LED's.

Cheers

[g8dhe]

The measured current for the Fluorescent light is 1 Amp and for the 10 Watt COB panel is 0.4 Amps.
In general we have found the LED light to be brighter and a slightly higher colour temperature than the warm white tube we had in place.

[sotal]

Hi, are you using LED's to reduce load on the battery or to improve lighting quality in general? The reason I ask is that heat just like light is a form of energy and as the unit is getting hot it suggest that there is a reasonable amount of current being drawn. I would be intrested to know the differance between the current consumption of the fluorescent tube & the LED unit. May turn out that the fluorescent unit may have been more efficeint than the LED's.

Cheers

As Geoff says the current consumption is less than half. The light output is much higher than the tube it replaced, maybe a little too high - you could possibly go slightly smaller. I do wonder if the tube was the original though as they do fade over time. Mine wasn't great.

I'm still tempted to try 3 x 36 LED panels to give approx the same number of LEDs and see if that runs as hot. The 36 LED panels I have seem to stay cool - only warm to the touch. They do look significantly dimmer though - perhaps not as 'good' light output from them.

[mikeonb4c]

Hi, are you using LED's to reduce load on the battery or to improve lighting quality in general? The reason I ask is that heat just like light is a form of energy and as the unit is getting hot it suggest that there is a reasonable amount of current being drawn. I would be intrested to know the differance between the current consumption of the fluorescent tube & the LED unit. May turn out that the fluorescent unit may have been more efficeint than the LED's.

Cheers

As Geoff says the current consumption is less than half. The light output is much higher than the tube it replaced, maybe a little too high - you could possibly go slightly smaller. I do wonder if the tube was the original though as they do fade over time. Mine wasn't great.

I'm still tempted to try 3 x 36 LED panels to give approx the same number of LEDs and see if that runs as hot. The 36 LED panels I have seem to stay cool - only warm to the touch. They do look significantly dimmer though - perhaps not as 'good' light output from them.

My tube was dim when I bought the Bongo 9 years ago. So I bought a new tube. But then I found it was the contacts that were the problem. Cleaned those up and the original tube (now possibly 20 years old?) has given out a nice bright light ever since. I did consider trying LED etc alternatives but given the way some I've bought have failed in 'flicker' mode, I decided it against it. For the time it spends on the higher current draw didn't seem too big an issue. The new tube sits in the glovebox still waiting to be called into service

Your aluminium plate heatsink principle would work at its best if the ali plate could have an air space beneath it and the cover of the light had airflow entry and exit holes that allowed heat convection to get going so as to pull ambient air in over the ali plate before being exhausted / expelled into the car interior (or roof void as long as there are no issues with venting into a hidden space).

[helen&tony]

Hi
I haven't had any problem with mine in 11 years of ownership................................(I never use it)
Cheers
Helen

[sotal]

It seems to have done the job in making me feel happy enough with it! With it on the plate I left it on for 2 hours with no problems. It got hot but now the surrounding plastic is only very warm rather than hot. I'm sure regular halogen bulbs get the plastic as hot if not hotter. I think the plate helps a little but more than anything it does the job of keeping the panel away from the plastic lens.

[sotal]

To confirm further - my modification using the aluminum plate and screws seems to be working fine.

We went away for a few days - on EHU so the voltage was slightly higher and the panel therefore runs a bit hotter, on one night the light was on from about 5.30pm until midnight. So over 6 hours of continuous use. It got warm but not worryingly so.

Very happy with it as it is - would recommend this mod to anyone who decides to fit one of these larger COB panels.

[Tony x]

You could try putting a resistor in the power feed to the leds.
I'd start as a guess with something around the 200 ohm mark and work from there. Buy a bag of five and you have a range you can try from 40 ohm if wired all in parallel to 1000 ohm if all in series

As a bit of background, leds get brighter and hotter as you reduce any resistance in the power feed but they reach a point when they wont get any brighter. Reduce the resistor value further and they just get hotter and don't last so long.

I usually find that even the leds that come with a resistor built in can handle a bit more resistance without any dimming.

In case you're not electrically minded, adding a resistor to the power feed will reduce the power consumed, not increase it

[cmm303]

Resistor power rating? It's going to vary on the optimum current consumption of the LED but is there a general safe rule of thumb?

[sotal]

I'm happy enough as it is without the need for the resistor. It gives nice bright light.

The issue was that the heat generated from the panel made any adhesive that was used to hold it in place melt. It would then drop down and rest against the plastic lens (I was worried about the heat damaging this). This was always worst when running the lights when the battery charger was on or if the alternator was running.

I was attempting to disperse some of the heat and at the same time keep it mounted securely. The picture above shows the mount in place - I mounted the COB panel onto an aluminum plate using two small bolts. I then mounted the plate itself to the casing and to the metal roof panel above.

This all seems to do the job.

[Tony x]

Resistor power rating? It's going to vary on the optimum current consumption of the LED but is there a general safe rule of thumb?

If you want to be really safe, then 12 watts which can be done with the commonly available 3 watt resistors, using 4 in parallel of the same value resistance.