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LED star base heat sinking?

Folks,

To make a decent bright bicycle rear light I'd have to ideally remove a

1W LED from it's aluminum star base. If they are heatsinked like in this video it looks like some thermal grease is used:

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Not sure if that's the normal method with these small LEDs. I am concerned that such thermal grease will work itself out of there. This is for my mountain bike which is used on rough turf. Is there any other glue that can be used?

I'd like to glue or somehow otherwise mount the LED to a home-made copper carrier which much better fits the innards of a retrofitted old style bike light (one where the bulb is removed). "Modern" lights that already have LEDs are mechanically too flimsy, too dim, or both.

The LED is going to be operated at about 50% of rated power but then often for 4-5h.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
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The usual alternative to heat transfer paste is; some grey silicon rubber, its most often found in TO220 form, but is presumably cut from sheet.

Its turned up from time to time in other sizes, and can be had thicker for high voltages like horizontal transistors.

If you have 12V ready to hand - you could bolt your LED to an old left over CPU cooler.

Reply to
Ian Field

The Cree white T 1-3/4 LEDs are blindingly bright at 10 mA. Maybe use a few of them?

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Why remove? Just buy some loose ones...

Probably not a big worry, the grease is particle-loaded and doesn't flow freely after being compressed. Any old replacement (hot-melt glue, RTV, silicone pads) will work fine with a 1W or 3W LED if you're running a fraction of a watt.

Reply to
whit3rd

The PC overclockers use thermally conductive epoxy.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

Corn lamps are dirt cheap and can be disassembled to provide a bunch of aluminum-PCB LED panels.

formatting link 

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

I need red ones and they must at least rival the tail light of a motorcycle, preferably better. I found that 300mA with a nice lens is plenty bright.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I think I have some of those. I could probably cinch down the LED body with wire so it presses against the rubber. IME anything that's glued, semi-liquid or in any other form not rock solid will fail on a mountain bike.

My bike has an 8.4V bus.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Yes, silicone rubber is what Ian also suggested. I'll give that a try.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Good idea. I am just afraid it may crack on a mountain bike. The shaking and vibration can be incredible. One some streches everything in the panniers turns upside down over less than a mile no matter how I pack. Almost all electrical gear that I didn't build myself or mod has disintegrated. Even battery packs. So now it looks like this:

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Just came home from a meeting. It looked kind of clean this morning and now ...

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Can you solder to it? With "aluminum flux" I've tinned Al with 40/60 and then soldered that to what I wanted...

George H.

Reply to
George Herold

Just looked that up.

Mikek

Reply to
amdx

We used that type of epoxy building transducers vibrating a 660kHz,

1000 Watts, on a 2" disc. They sometimes burned up, but they didn't delaminate. The transducer builder did lap the pieces and clean with alcohol and acetone and bonded them under some pressure.

I figured out today my mind is acclimating to bike riding. I was pushing a shopping cart out to the car at Lowes, a glanced down to the left at the mirror, checking traffic behind me. Of course there was no mirror on the shopping cart. Mikek

Reply to
amdx

Why remove the LED from the star? It's already nicely thermally connected to the aluminum substrate.

It would be easy to clamp or screw the star to your copper heat sink. Trim the star to fit if you want, it's not critical.

An alternative would be to buy an SMD LED with a thermal pad on the back for soldering, like the Luxeon Rebel series. (now Philips?)

Cheers, James Arthur

Reply to
dagmargoodboat

silicones are not all the same, google for ACC silicones

AS1802 it has 2.3W/mK

as a comparisson:

Thermal epoxy Bonding compound from Electrolube TBS20S

1.1 W/mK

but nothing can beat PGS Graphite Sheets 700-1950W/mK

However if you keep 1cm^2 of the the star carrier plate you will be IMHO fine with any sil glue.

A little softness may keeps the contact over time. Other glues may lose the contact at some areas. The less glue the better.

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Reply to
Joerg Niggemeyer

Then I would have to keep the whole star carrier :-)

Which I may end up doing if I have to.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Yes, the good old backing materials. I remember those from my med-tech days.

That's what my bikes are still missing. But on the mountain bike only a stainless mirror would work, anything with glass will break very soon and then the shards create a hazard for animals on the trail. Even rear lights need to be of impact-proof material which I learned the hard way. Rear tire exploded, shredded the rear light, tore out and broke the battery controller board, and some other stuff. I was unable to find all the pieces back because they were scattered too far.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I probably could and I'd use a copper base anyhow but afraid that would kill the LED. Has anyone done this before, soldering the heat sink of an LED to copper?

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

The star is a smidgen too small. If I screwd it onto copper the screws would prevent me from getting the LED far eough into the reflector hole of an classic Spanniga 15 tail light (made for bulbs). Or I'd have to use really flimsy screws which won't hold on a mountain bike. Those Spanninga lights have great lenses and seem to be almost indestructible. But the reflector can't be ground back.

I'll have to try that, see if the metal pad would catch solder. Good idea.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
[about a 1W LED]

Yeah, I've done it. The LED survived, but that little button on the back is NOT the LED (it isn't electrically connected), merely a heat spreader. It is nickel plated, takes acid flux to get solder to stick.

Tinning both parts beforehand, the final join was made with a torch. It's a copper HEATSINK, remember...

Since the heat spreader is only glued in place, you're still just using glue to hold the pieces together.

Reply to
whit3rd

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