Those Miller taillights are really nicely made. I'm pretty sure it's made in England like the rest of the Miller gear. Beautiful chrome.

I set up one of those Miller sidewall dynamos a few years ago, running LEDs fore and aft. I took it out for a midnight ride and the light was amazing. About a mile out, the dynamo started screaming like a raccoon stuck in an air conditioner and after another hundred yards the lights quit. I don't know if the LEDs put too much draw on the dynamo, or if the 50+ year old bearings on the dynamo just weren't up to the job.

Rudi, do you think I should try to drop some oil in before I take it out for a test ride?

The generator says Made in Great Britain, but the light says Made in Germany. Ooh, and I just noticed the generator says it's rated at 6V and 3.3 watts! Fancy!

The greater convenience is that you can disengage them when you don't need the light. (I'm sure that's what you meant.) Disengaged = no drag at all, of course. Some people say then can feel the drag of a hub generator, but measurements also show that it is quite small.

LEDs require so much less power than incandescent bulb, so a lower-output generator of any sort should work. Also the drag difference between the light switched on or off is much smaller.

I don't know, Tom! I don't know exactly what's in those things. What kind of bearings are there, and where in the gizmo are they? If you can confidently get oil into the bearings and you are confident it will rejuvenate the cold war era grease it finds there, then yes, this sounds like a good idea. But that's a couple too many 'if's for my taste. Dripping oil in the general direction of a potential problem... well, I really don't know what effect it might have, whether to hasten or postpone the problem.[/QUOTE]

Interesting!

Ability to disengage a bottle generator is one convenience. The other is the ease with which you can install and uninstall them. It's easier than building a wheel and cheaper than buying a wheel.

My Raleigh Twenty is my project bike. It has a drum brake front hub. Changing that to a dynamo hub would be a big investment, especially a dynamo-and-brake hub. In this light, a bottle dynamo makes more sense for this bike. I can feel the drag, but I won't be running the dynamo on long rides on this bike.

I plan to give one of these bottle dynamos away to my young friend Al who was my housemate in NJ. He doesn't have much cash, and since I gave him that Super Course, he has switched from riding the bus to riding the bike a lot. He would like lights on it. I can give him some lights with filament bulbs, and perhaps he can buy himself some LED lights. Giving him the bottle dynamo will save him a big pile of money, and running either type of light -- filament or LED -- will be a lot convenienter than running battery lights.

Rudi, we cross-posted. Since these bottle generators were dirt cheap for me, I'll take the risk of dropping oil in them. I won't hold you responsible for the ensuing adventure.

[QUOTE=noglider;16261787]

So I gather (and dimly remember) that the bottle dynamos always put out 3W and the dynohubs had lower output and lower drag. Now they have higher output, so the big disadvantage with bottle dynamos is that they present more drag than hubs. Still, the higher drag is sometimes justified by the greater convenience.

[QUOTE]

If you mean "all bottle dynamos are rated at 3 watts at some speed," I can probably agree, but it's not true of all hub dynos. If you mean "bottle dynos put out 3 watts no matter how fast you're spinning it, it just isn't true. Just look in the hub dyno thread in Electronics, at the graph of power output for hub dynos at several different speeds. Electrical output increases as speed increases with constant resistance load - it's just how generators work. The same trend applies to bottle dynamos.

Good point. So they all put out at least 3 watts at some sort of realistic speed.

FWIW, I've used Tri-Flow on my Soubitez bottom bracket dynamo with good results.

http://www.os2.dhs.org/~john/soubitez.jpg

There are a lot of old dynos around. Chances are some were designed before the German spec was in force, so those may not comply. Some early hub dynos were designed for 2.4 w, I think, and some modern ones are designed for about 1.5 w, choosing to forego the German market. The physics of generators says that at some high speed those will probably output 3 watts if no design limits are violated. Whether that speed is "realistic" or design limits are or are not violated, I don't know.

I also can't say at what road speed most bottle generators actually satisfy the 3 watt output requirement. The only products you can nail down are the ones that have been certified as meeting the German specification. But despite the fact that the spec requires 3 watts at 6 volts at a specific speed, any of these generators will put out more than 3 at higher speeds. You'd need electronic limiting to prevent it, and there's no good reason to do that, beyond the protections that modern LED lights already have built in.