My first light - dynamo powered

[nicknoxx]

Well after considerable reading on here and elsewhere I've almost completed my first light. It's based on Martin's circuit 2 as I didn't physically have room to include anything else and includes help from Trout, Bobblehat, Ktronic, Acme-fixer and others so thanks are due to them.

The light uses 2 XPGs and Reginas with a smoothing cap and 4 schottky diodes as a rectifier

First I bought a 1oz stainless steel flask from a car-boot sale for £1, identical to this one:

It measures about 40mm x 45mm excluding the cap. I cut the bottom off with a dremel:

I had to file the LED stars considerably to get them to fit into the case. The edges were later painted with liquid insulation tape to prevent shorting on the case:

A heatsink was made from some aluminium angle and a switch fitted to the back of the flask:

The smoothing cap, rectifier and switch before painting with more liquid insulation:

The insulated stars ready to be stuck onto the heatsink with artic adhesive:

The completed light just waiting for some 1mm polycarbonate to arrive. I had 2mm but ended up without enough room:

Whole thing including this bracket weighs 106g

Mark 2 light already planned will have boost caps, a standlight and 4 LEDs and may also have daylight detection:

 

[Bobblehat]

OMG ...that is so neat! I raise my bobblehat to you!

Love the Mk II casing too! After the components are fitted will there be any room left for storing a little bladder and fill it with a drop of malt for emergency purposes? :naughty: You could claim you have liquid cooling.

I'd be interested to hear what your impressions are of how the circuit #2 performs with the double xpg/regina ..... like at what speed it produces light, when the flickering becomes unnoticeable and an estimate of when you think it peaks. There should be no problem using stainless for this application.

 

[nicknoxx]

I'll let you know when it's on the bike. The stainless is very thin and AAA'd to aluminium plates either side, (the heatsink and the bracket) so I'm confident it won't get too hot.
I've got an even larger 'Singletrack' flask for Mk 3 . . .

Oh and I forgot to say, I used a waterproof switch from RS and an O ring to seal the case. Mk3 should have room for a bladder as well but I'll need to re-route the cable.

 

[Firework]

Nice light, similar in principle to my first, built with 2 x Cree XRE R2s with Hammond housing, a simple circuit from Martin's site with socket and switch to rear. The optics were 10 degree reflector cheapies from Dealextreme which were 5 for about £4 and have next to no artifacts. I had to file a little off the stars and the optics to get them to fit in the case.

Currently mounted on my fork it lights up the road well and I find that cars now dip their headlights from about 200m away. Very satisfying to put together your own light, powered your own energy while producing very decent output. I'm now putting together a Cree XP-G triple. Your Glenfiddich special should be quite a sight.

What size cap did you use, seems very compact?

 

[nicknoxx]

It's a 4700uF but I spent quite a long time looking for a small one
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=708-3608

 

[nicknoxx]

Here it is with polycarbonate sheet and fitted to the bike.

 

[bbaker22]

Very nice! I like the simplicity, originality, and size.

 

[pe2er]

Very nice stainless steel housing!

 

[BrianMc]

The lower current and power of a dynamo means thermal load isn't too much for the stainless case to handle. Spreading the heat around inside with Al helps. But it is a beautiful adaptation. I wonder if someone makes Al flasks?

Stainless can be hard on saws. How tough was it to cut the bottom off?

 

[nicknoxx]

I used a very fine cutting disc on a dremel, it was surprisingly easy.
There's no booster caps so I'd be surprised if the maximum current ever reached 700mA which means that is will be using less than 5 watts and that will be at full speed when airflow is also maximum.
Unfortunately I've hurt my back and can't get out on the bike to test it.

 

[BrianMc]

Bummer about the back! The rig's ready,weather's cooperating, and you can hardly move. Wishing you well.

That IS good news on the cutting. Quick nice looking, rugged light.

It will be interesting to know if the light warms any when you feel good enough to ride again.

It looks like an Al flange to adapt to a steel mount. If that is directly below the Al heat sink, it will be a very effective added heat sink.

Stainless steel makes a nice nearly bulletproof body. I wish it was a better heat conductor. The thick walls of the flask will help move heat through the body and offset the lower conductivity of SS vs Al some (SS is 5-24% of Al depending on the alloy). That means it takes 4-20 times the temperature to drive the same rate of flow of heat through the same thickness of metal from the LED to the air. The thickness likely halves that difference to 2-10 times more resistant than thin Al. If I estimate the area of air interface at about 5 sq inches correctly (not counting the bracket or mount), and the light is giving 4 watts of heat for the 5 watts of input, it has something like 1.3 sq inches per watt of heat. In the breezes the outside should be air temp or close. The LED's will be a bit warmer than if the flask was Al, and so slightly lower output, but ease of construction and the nice looking solid case, offset that.

It is hard to estimate the area of the bracket from the photo, but it looks like it might be another square inch, maybe 1.5, and if under the heat sink, at 1/2 to 1/10 the thermal resistance, it may radiate nearly as much heat as the rest of the light body. Aluminum bolts through the bracket, flask and into threaded holes in the heat sink, flask, would help thermal flow into the bracket and furher reduce LED temps and gain a few lumen, especially if the flask gets warm at all. It would make the bracket the primary heat sink and the flask, secondary, but add some complexity to a build.

 

[nicknoxx]

Interesting stuff. The flask is REALLY thin, maybe .1mm, there's a lip at the front which makes it look thicker. There IS one bolt through the bracket and flask and into the heatsink inside but there wasn't room for two because the caps is in the way.

 

[BrianMc]

I am having interesting thermal issues with a revision of another light (battery powered). I will post when complete and beamshots are available as Version 1 has been reported before. The Taskled drivers with thermal monitoring help this issue a lot. With dyno lights like ours, with no temperature montioring, we risk overheating them, cooking the LEDs and shortening the light's life.

You won't need a lot of strength in the bolt through the mount, so an Al one would be good for thermal path and a bit of weight too! It's good for weight that the flask is thin but not so good for thermal resistance.

I tested my dyno light today (60 * F outside), with more attention than the brief touch, and a 'Yeah it's good!' Will post in my thread. The problem is that cool on the outside can mean no heat transference and hot inside OR very effective thermal path to the air keeping it cool inside. In the case of that light, the sinking is proven and works great. Had better with that much copper in it. The problem light had the thermal activation kick in, so though cool, it was not moving heat as it should. Dang. May have a handle on it now, and a test ride is next.

Back to your light. Is the cap pinched for space in it's diameter? If you have a bit of clearance that way, a piece of copper sheet shaped as a lining inside might move enough heat away from the heat sink and into the SS to do the trick with minimal extra weight. SS saucepans with copper bottoms use the same trick. It is close to what I have done with the "too small surface area" lights.

Google thermal conductivity on AL, Cu, SS, Ag. Silver is about 10% better than Cu, which is about 60% better than Al depending on alloy, eveything else (except carbon) is outclassed. Brass, is further down , steel and stainless further again. Al is so much lighter and cheaper, it is the clear winner, with copper having some usefulness to move heat fast.

The stainless case makes a great looking light. Many have fried LEDs with poor cooling. Sounds like you aim not to be another.