Homemade LED too hot?

This is my first mod - so be gentle... After reading a few mod posts, I tried to mod a bicycle halogen light to LED for trail riding at night.

I used the DX sku 26111 3v-8.4v buck/boost with a Cree 14mm Q5 led and a DX collimating lens.

The converter spec says 1.2A with the Q5, but I measure 1.4A with 4xAA NIMH.

It ran really hot, so I ditched the old housing and mounted the works in 3 3/4" copper pipe end caps (soldered together) with lots of heatsink compound. Around the LED housing, I put a #280 helicopter motor heatsink.

Now it's brighter than I ever imagined - the brightest light I've ever held (maybe mediocre by CPF standards), but the whole housing heats up (on my workbench - not riding) to untouchable in ~10 minutes (my guess is it's ~120 F).

My question to you who have been here before: Will this thing burn out the LED if I continue to run it like that, or is this just par for the course?

neveready said:

It ran really hot, so I ditched the old housing and mounted the works in 3 3/4" copper pipe end caps (soldered together) with lots of heatsink compound. Around the LED housing, I put a #280 helicopter motor heatsink.

Now it's brighter than I ever imagined - the brightest light I've ever held (maybe mediocre by CPF standards), but the whole housing heats up (on my workbench - not riding) to untouchable in ~10 minutes (my guess is it's ~120 F).

My question to you who have been here before: Will this thing burn out the LED if I continue to run it like that, or is this just par for the course?

Click to expand...

Try it when riding, or put a fan on it... then see what kind of temperature it stabilizes at. It sounds like there won't be enough mass to prevent it from heating up a lot when stationary, but as soon as you get some airflow over the heatsink then it should help a lot. My guess is that it will be fine for riding. If you want to run it more efficiently and thus generate a lot less heat, try a driver that will run the LED at ~800mA. Runtime will be a lot better and I don't think you should lose too much output.

As the previous poster stated, there might not be enough material to heatsink the LED in a stationary area. Try using a fan and see if that keeps things cooler.

Also, can you post pictures of the setup? (remember the rules, no pics above 800x600 pix)

:welcome:

lets see it, post up a pic of that bad boy

You may be interested in suggestions here: Particularly his advice on cooling... though I've yet to make my own custom light

BikeLED.org: Copperhead

Yes, too hot is bad. How hot is a question of how long you want that emiter to last, but in your case the hotter it gets the more current it looks like your board will feed it, and the hotter it will get. At some point things get way too hot, deform, emiter turns angry blue and dies.

Options:

• Get another board (800ma, 1amp is great for you)
• Switch the power supply to 2s2p
• Add a 2nd emitter in parrallel (solder led + 's leads together to driver +'ve, then -'ve leads to driver -'ve)
• Do with-out the board (2s, 3s and direct drive. doesn't sound like it could be any harder then your driver is being)
• Go riding, touch the light every so often and check it. (You may even ride it while waiting for parts> I don't recommend this long-term b/c inevitably you'll have a situation where you've left the light on, (fixing gear, checking trail, talking) and then things get way too hot, deform, emiter turns angry blue and dies: you won't be impressing anyone when that happens, least of all yourself.)

You should put that feedback on Dx. so many people go nuts wanting high amp drivers.

Emiter inside the bottom of a 3/4 copper cap is great - then put the cap on a heatsink. I'm not sure how you've done it with "three soldered together..."
(too much compound can be a bad thing - look at dark-zero's mods, you'll never see a drop, and you'll get the idea. compound doesn't add thermal mass, just improves transfer between surfaces)

I tried it outside in some wind and it was fine - never hot to the touch,but I can imagine wiping out and my light turning to toast while I'm sitting around figuring out which end is up. I think I'll try to back down the amps a bit. ... I was driving it with 4xAA NIMH - I just tried it with 3XAA and it seems to have nearly the same light output, but much less heat.:thumbsup:

Can't get in to measure the amps anymore - guess I'll just use it and see.

I'll post pics, but didn't take any while I was building it.

Thanks for the advice.

max safe current: 800 mA
... and it will get warm with that current, too

You are running it with too much of current, improve heatsinking additionally.


PS: You can still measure the current from the battery, even when the light is no longer to be opened, or the led soldered in. Thats a rought but also good way to calculate current to the led