Tuesday, November 15, 2011

Specific aim 1: making an LED light bulb

I need to mount a single LED with sufficient heat sinking into the base of an E10 Edison screw thread bulb.

I've collected some lovely French lamps. Historically, these would be powered by a bottle dynamo.  My intention is to power them using one of the... um... 10 or so hub dynamos that I own.  Old incandescent bulbs don't light up much so a LED upgrade is in order.  Experience has taught me that commercially available LED E10 Edison bulb upgrades are OK, but I think I can do better, especially with the selection of high power LEDs now available.  Power LEDs get hot, so whatever retrofit I come up with will need to be able to deal sufficiently with the heat.

Late night scrawlings

Thus far, I think I have an idea involving a turned copper pillar of some sort that can be pressed/epoxied into an E10 bulb base.  Something like this:

Copper pillar LED heat sink
Pressed into something like this:
MES/E10 lamp base

This way, any cycle lamp that takes an E10 threaded bulb can be retrofitted without modification.  Getting the heat out of such a small package will be a challenge, though; something that my previously proposed solution might not be up to.  The best solution would be to mount the LED directly to the copper heat sink, which eliminates any of the thermal resistance encountered in an FR-4 board perforated with plated vias or in a metal core PCB that is then attached to a heat sink with thermal epoxy.

There are several elaborate methods described for doing this. Lambda Lights seem to have mounting LEDs directly to a large copper heat sink down to a science, so I might contact them before attempting to reinvent the wheel.  From what I can tell, they turn a copper pillar and then machine a square nub on the top where a PCB is mounted with a slot milled in it so the nub can poke through and be soldered directly to the thermal pad of the LED.  Something like this:

While ideal, this solution may be cost prohibitive...


Bike Santa said...

I've been looking into this concept for retrofitting Sturmey-Archer lamps, driven by S-A DynoHubs. I have found a company that makes e10 based bulbs that might be suitable: http://www.dosoe.net/skin/deshun/images/pdf/1.pdf. If the LED has good thermal connection to the base, a metal lamp should be able to conduct enough heat away. Of course, S-A DynoHubs put out AC, which needs to be rectified to produce DC required for the LED lamp.

minisystem said...

Yeah, I've tried a few of those E10 based LEDs and they don't put out enough light for my purposes, which is the whole point of developing a custom solution. They also have built in drivers which complicate standlight design. I am, however, intrigued by the E10 bulbs described here. They have a built in standlight. The format seems impossible to allow for a very bright standlight and no measure of output is given, but it is an impressive technical feat to fit all of that into such a small package.

Bike Santa said...

I like the taillight bulb design. The standlight feature is probably a supercap, which is another idea I've been playing with. I know what you mean about the headlight LED output requirement. I will try to get a sample from DOSOE of their 1 W bulb and test it. They are in China an are on holiday until early February. I'll post a message with the results if I can get one. The nice thing about the S-A headlamps is the size, which has lots of space for prototype electronics.