DX Recommendations - cheap and cheerful dynamo build.

Hi Folks,

Haven't been on CPF for a while but it does feel great to come back and read what people are up to.

A while ago I built my brother a great dynamo outfit using one of Martin's simple circuits with a bit of the CPF Standlight thread thrown in. After 2 or 3 years it still works fine and is a testament to hot glue and alu angle!

My brother has asked me to build him one for another bike and this time I'd like to use generic MR-16 type bulbs from DX. I already have a nice single red led bulb for the rear.

So I now want to find 2 X single white led spot bulbs for the front. Rather than go searching DX for hours I wonder if I might borrow some wisdom from the hive mind & those dedicated DX explorers who have gone before me? What do cpf dynamo geeks recommend as a decent MR-16 spot bulb from DX. I'd prefer single led bulbs, around 48mm diameter, maybe with convex lenses rather than triples or quads.

I know this is the easy/lazy route but time marches on and I don't have time to file away at alloy strip for hours these days.

Any help much appreciated.

Sam.

Just grab one of the XML lightheads and retrofit with a 6V or 12V XML (depending on use). Throw a rectifier and smoothing cap inline.

Yes - probably the most sensible thing to do. I wonder if DX is the best source these days. I have read comments on another thread (now mislaid) that there are some better sources. Can anyone advise please on alternatives?
ta,
Savvas.

Fasttech.
XML light heads for 11$

Jeez - things are quiet on CPF bikes these days eh bro?

Savvas

It's not just CPF bikes that has cobwebs growing on it.

It's a bit of a shame, but I suppose that the improvement in commercial bike lights has diminished the urge to go out and make your own.

I'm still tinkering with a few things. I've had the idea of just making a little buck converter that would provide a higher impedance to the dynamo, making it easier to get 6 or more watts out of it. The converter would also produce a lower output voltage and higher output current, making it possible to drive a single LED at 1 amp, or two LEDs in series at 1 amp.

I did a few simulations, and had some troubles making it work. Fellow CPF'er Bandgap recently suggested that a Cuk converter might be better suited to this task than a plain buck converter. The reason is that the Cuk has a fairly steady current draw, as opposed to the surges drawn by a regular buck converter. It seems like a good idea, and a good excuse to get familiar with Cuk converters. Now I just need to find time to run some more simulations!

Steve K said:

It's not just CPF bikes that has cobwebs growing on it.

It's a bit of a shame, but I suppose that the improvement in commercial bike lights has diminished the urge to go out and make your own.

I'm still tinkering with a few things. I've had the idea of just making a little buck converter that would provide a higher impedance to the dynamo, making it easier to get 6 or more watts out of it. The converter would also produce a lower output voltage and higher output current, making it possible to drive a single LED at 1 amp, or two LEDs in series at 1 amp.

I did a few simulations, and had some troubles making it work. Fellow CPF'er Bandgap recently suggested that a Cuk converter might be better suited to this task than a plain buck converter. The reason is that the Cuk has a fairly steady current draw, as opposed to the surges drawn by a regular buck converter. It seems like a good idea, and a good excuse to get familiar with Cuk converters. Now I just need to find time to run some more simulations!

Click to expand...

Well of course most of that went straight over my cranium but I do get the general idea (I think)! And I await further education about how electrons behave! I know I should have studied harder in Physics instead of spending all that escapist time in the library readin'! I guess it's spring in Preoria. Extraordinarily mild autumn here in Southern Australia. Bodes poorly for the summer months I fear!

I suspect that there's still likely to be a lot of latent interest in homegrown dynamo lights. People are probably just a bit time poor these days and maybe distracted by f/book and all that stuff. I note that lots of the circuit diagrams seem to have disappeared from CPF discussions over the past 7-8 years or so. I've actually collected a lot of them along with some of the written discussions and post links. I thought I might try editing them into a sort of 'best of' document - as a sort of 'left field' complement to Martin's resource pages as many of the experiments sort of carry on where he chose to (sensibly) stop. Maybe something for winter evenings!

The current limited hub dynamo is a wondrous thing! I reckon that sooner or later we'll see most ordinary bikes coming with them. So it good to learn a few of these practical aspects about electricity and useful things like leds. Most of the commercial dynamo lights out there are still expensive and more than many can afford. I think we'll see resurgent interest in DIY sooner or later!

Savvas.

Physics class did explain the underlying phenomena of electronics, so you do get learn about storing energy in capacitors in the form of an electric field, and in an inductor in the form of a magnetic field. Beyond that... I think it almost made it harder to understand electronics.

Switching power supplies are interesting in the way that energy is transfered between capacitors and inductors, and the way that they can convert a high voltage, low current power source to a low voltage, high current power output. It can also convert low voltage to high voltage, etc. They are a bit tricky to design and implement though, partly for the challenges of getting the control loop stable, partly for the challenge of not making too much electrical noise, and also for the usual challenge of not over-designing it and keeping costs down.

The benefit of converters like I discussed would be the ability to modify an existing light with good optics to produce more light (potentially). It's a better option, I think, than schemes where a number of LEDs are run at 0.5A with symmetric optics that don't make the best use of the light. That would include the light that's on my bike now.

Yep, it's spring in Peoria, with all of the wind and rain that comes with it. Still, temperatures are pleasant and the memories of a harsh winter are being supressed. I think that means that it's time for folks in your half of the world to start working on their 'tronics projects, doesn't it?

My own modest forays into DIY/adapting have been a bit of a learning curve. For DIY, other than learning lots of cool new things, I think people will be drawn into it if either the process is simple (i.e. a simple use of rectifier and smoothing cap), or it's something they can only get from niche (expensive) products (i.e. lots of lumens).

As LEDs get better, even the simplest lights trump some complex lights from a few years back. Everything else is a bit of a game.

My view is that the next useful challenge is to have a powerful DIY standlight. The basic cap-across-two-LEDs light is great for being seen, and a well matched use of the average memory backup capacitor. But, especially for MTB'ers, there's a demand for an (additional) short-lived, yet powerful, standlight.