Just doublechecking: Raleigh dynamo lighting question
 

I did search the forum and I think I have the best answer, but I want to make sure.

I bought a 1953 Raleigh Sports over the weekend with a lovely, working generator light. It is, however, too dim to depend upon. I was thinking of getting a new hub-powered light, but the mechanic suggested I just look for an LED bulb that would fit the housing (it is all in really good order). From the archives, I found this site:

http://www.home.earthlink.net/~steinborn/gentlemancyclistmerchandise.htm

And I am planning to order an LED bulb from them. Is this the best plan if I want to keep the light as is? It seems the technology has changed so much in the last few years...

A few months ago, the bulbs were out of stock with no supplier in sight

I ended up getting replacements at www.reflectalite.com

The site says they are back in stock now (although I am still waiting on a reply). But just getting a bulb will work? That is my basic question - I don't need to do anything besides screw it in, and everything will be okay?

If it is designed for it, which appears to be the case, then you don't need to do anything else. LEDs do need additional circuitry to limit the current, as well as a heat sink. One would suppose an LED bulb with a standard screw-in base already has all that stuff.

The downside, of course, is that while the screw-in replacement LED will be much brighter than the original bulb, it still won't stay illuminated while the bike is stopped. I've heard a rumor that a screw-in white LED with a standlight capacitor might be under development; Sixty-Fiver, have you got anything more to say about that?

The bigger problem with just putting LED bulbs in a dynamo headlight is that the reverse voltage can kill the LED. It's a question of how much reverse voltage the LED in the bulb can handle; and this doesn't appear to be listed on the Gentleman Cyclist page linked above.

You can alleviate the problem somewhat by making sure the headlight and taillight are wired on opposing circuits, so the flash alternately. But I don't think this will solve the problem entirely. Different diodes have different properties. The ones you would use to rectify the current (that is, convert AC to DC) are specifically designed to allow the current one way and not allow it the other way, while the ones they use in LEDs are designed to give off light when the current goes through them the right way.

All that said, I have not been impressed with the screw-base LED "bulbs" I have used. They don't give out as much light as better LEDs in the same price range, and they are really finicky. They stop working for nor reason I can understand.

For best results I think you should put a bridge rectifier into the circuit. You can buy one cheap at Radio Shack; it is inconveniently shaped and requires four soldered connections. Alternately you can build a more efficient one in any shape you like, which is equally cheap and also requires four soldered connections. I prefer the latter; here's a diagram for how you can hide the whole thing inside a piece of heat-shrink tubing; I usually put this near the dynamo, where the wire runs on the inner side of the fork blade from the hub to the light. Then you wire the headlights in series.

http://bikeforums.net/attachment.php...hmentid=224814

Need a rectifier for a standlight capacitor. Thus a complete new wiring of the lighting system rather than just a bulb replacement.

On the good side, there are lots of retrofit ideas in the electronics and lighting forum if you're kinda DIY handy...

Oops- RHM beat me to it... But there are a lot of good ideas in the lighting forum. I'm going to put together a 3-watt LED dynamo system with a standby battery and a regulated supply using a CREE bulb- it should be wicked bright, and it will fit into a vintage housing... but I gotta finish building the wheels first...

Cycle Maven, when you finish that system, please do share!

Correct me if I'm wrong, but doesn't a bike generator put out AC? One would suppose that someone marketing a plug-in LED bulb must have provided the circuitry for rectification as well as a heat sink. Of course it all depends on the execution, doesn't it? Someone could have used a single inline diode, in which case you'd get a duty cycle of only 50% (like a PWM control of only 50%), which is to say not as bright as it could be. On the other hand, that's one way to control the heat if that's all the fitting can handle. And of course a tiny screw-in bulb is unlikely to have a supercap to provide a stand-light capability.

For what it's worth, the B&M lights are marvelous and do provide a stand-light feature. They are expensive (but my own scarce time to build the circuitry is worth more than that). If you want a C&V-looking light it might be simpler to mount a new B&M light in an old housing.