OK. So you can assess my comments, I want you to know that I am awaiting my BO'd LEDs and optics, otherwise, my first lights would be done. I thought a lot about going your route, but I could fund a more ambitious builds so I did. This will be your light. Only you need to be happy with your selections. That said, I hope my questions, comments help you make the choices that work best for you.
I was planning on building a
cheap and dirty bike head light.
I was planning on using the following parts. I have a few questions...
emitter =
http://dealextreme.com/details.dx/sku.2395
Instead? Your selection is a warmer white but about 30% less bright. Some people see sticks and things on the road better with warm white, so this may or may not be a good option.
One user calls this a wide spot, so if you are looking to flood the path/road just in front of you, that would seem to be its forte.
If you want a general light or a 'thrower' this is not your optic.
I have only used one driver so can't advise on this one. It is used in flashlights and a search using Google at the top of this page will likely give you some reviews. That said, if you move your cursor over the pictures they enlarge (you may need to scroll to get them all). Notice the large + and - labels for the solder pads on one side? They match the red and black wires in the other pic and go to the LED, the other side has a spring contact for the battery nipple and the rim is the - battery connection.
No idea. If the plastic isn't too brittle, you can always rewire it if the wiring is not the best or fails.
housing = 1 inch copper pipe
two part epoxy
thermal glue =
http://www.dealextreme.com/details.dx/sku.4579
heat shrink tubing
22 guage wire
1. did I leave anything out?
2. will I need a heat sink? if so can I just use some older pennies?
3. re: the driver - where do I solder the leads from the battery? where do I solder the leads to the LED?
thanks, sorry if these are dumb questions
-Davy
You almost always leave something out. I don't see a lens cover. Dirt and water inside the light are not good. The link was $AU, so depending where you on that vast island-continent, you have more or less dust, am I right?
Batteries I assume you left out because they are obvious or you have lots. If rechargeable, you may need a charger.
Connectors unless the battery case and light will be hard wired and not free to disconnect. On/off switch?
Heatsink is a misnomer. It is not like a heat sink to protect delicate parts from a temporary input of heat while soldering by simply being massive and storing the brief spike in heat.
An LED light heatsink is more a case of a good thermal path to the air because the heat just keeps on coming if the light is on. Fortunately heat wants to go from hotter to cooler. Being a bike light with air moving helps a lot to cool the outside of your light's case closer to air temperature depending on how much heat you are moving into it. The LED junction temp must be kept below certain limits or you greatly reduce the LED's life.
The junction to LED's back is part of the LED. The LED to star ace is a function of the soldering job done by the supplier to DX. Those are the most critical and are out of your hands. You need a way to move the heat from the star which spreads the heat over more surface, to the body of the light, then to the air, with as little resistance as possible, with as little weight as possible, and as simple to make as possible. Oh, and as cheaply as possible, in this case. These are not compatible, so you have to compromise.
Metal to metal is the best contact for heat transfer, metal to heat compound to metal is about 100 times worse per unit thickness and metal to air to metal another 100 times worse. The Heat compound is way better than air much poorer than metal, so you want a VERY thin layer between the star and the heatsink. You are just trying to fill any air gaps of the microscopic irregularities of the two flat surfaces. Some builders polish or lap the stars and heatsinks to use less compound. You can't lap the inside of a pipe cap so if you go that road, you save the time but the transfer may be 5-10% slower assuming good assembly and depending on thickness of the compound, in other words YMMV.
Experience has shown many, that the common copper pipe cap with its bottom and walls makes a good heatsink/body for a 3 watt LED, holds the optic, and provides a place to seal a cover lens. Some have soldered another back to back to house the driver. A plug in that end can hold an on/off switch and a port of the wire to come out. Copper is a lot heavier than aluminum but is 60% better at moving heat. Anodized aluminum is better at transfering it to the air tahn copper, but if you have enough copper to air contact it will do, saving extra parts.
Judging from lights that work, you need between 1 and 2 square inches of body air contact per watt of light output assuming you are moving the heat easily to the body and riding 15 mph and more. Maybe 3 if you ride slowly with little wind or sit at stop lights with the light full on a lot. The MagicShine has a bit more than 1 sq in per watt but a difficult narrow thermal path to get to it, yet no one is reporting the LED failing. You can guesstimate from other homebuilts to see whether the 1 sq inch/watt estimate is correct.
You can find out TONS of stuff on most of your ideas Googling in this forum. Good Luck!
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