Tuesday, November 17, 2009

Fahrradsport Wednesday - Dynamos

Berlin is way far North, which means it gets very dark very early in the winter. Thus, anyone riding a bike must have lights for his/her bike. A nice old lady made this perfectly clear to me a few weeks ago when she screamed at me "Mann muss Lichter haben!!!" Ach so, alles klar...

The thing is, I had a light on my bike. It just happened that at the time it decided to stop working. This is because my bike has a dynamo on it. For those of you not in the know, a dynamo is a little generator that is powered by running along your tire. The idea seems nice; with a dynamo, you are self sufficient and not dependent upon batteries that will run out, so you should have a light that always works. But guess what? Dynamos are a pain in the ass. Let me explain.

Dynamos essentially require degrees in mechanical engineering and electrical engineering in order to be properly maintained. Mechanically they must be in exactly the right position against the tire so that it is optimally turning as the tire turns. Otherwise it doesn't turn and instead rubs a hole in the side of your tire. Also, your tire pressure has to be exactly right. And then the dynamo can't be too dirty, otherwise it won't turn properly. Which is so easy to do on the ultra-clean streets of Berlin.

Then these things require a wire from the dynamo to the back and front lights. To complete the circuit, electricity then runs through the frame of the bike itself! So, here you have an electrical circuit running over the whole of your bike through a flimsy wire and the bike frame exposed to the elements. Sure, nothing could go wrong there!

If it's working, great! You get a nice bright light (except only when you're peddling). But if it's not, then how do you figure out what's wrong? Is it the light bulb? Is the wire broken someplace? Is the dynamo working properly and making good contact with the tire? Has the rain shorted out the bike? At the time when the nice old lady was informing me that my light wasn't working, it would work (temporarily) if I bounced up and down on my bike. So what the heck could be wrong to explain that?

Guess what? I don't want to find out. A light with a battery is just much easier to figure out, and it's not distributed over the whole bike. And LED technology has made batteries go for much, much longer without compromising brightness. I've noticed that nearly all the old bikes in Berlin have dynamos, but that many of the newer bikes have battery-powered lights. So even the slow-to-adopt-new-technology Germans are catching on.

Do yourself a favor: ditch the dynamo!

8 comments:

Mandi said...

I also have a dynamo on my bike and it has given me a lot of grief. My biggest problem is that it doesn't like to work when the tires are wet -- which, of course, is pretty much all winter long in Hamburg. Luckily my German has been fixing dynamos and bikes since he could walk, but still. Today we have an appointment at the bike repair shop to give the entire bike an overhaul, including the dynamo. BUT, if this doesn't work, I'm switching to battery operated...

C N Heidelberg said...

I have one of those too. Surprisingly it hasn't given me any problems, except that it in heavy rain it doesn't power the front light very well. It just makes me feel like a hamster running in his little wheel to light up a bulb. ;)
Damon's gives him grief, though, and it's hard to know where to start to identify the problem!
I like it because if I had a battery light I know I would never remember to turn it off.

lettershometoyou said...

Couldn't agree more - junk the generator! I like my battery-powered LED lights because you can set them to blink fast for maximum visibility. You can't see much of what lies ahead, but unless you're riding down lonely dark paths, you should be OK.
One dynamo that actually works is the in-hub variety. No drag, works all the time in all weather, but I think they're heavier and more expensive.

cliff1976 said...

Do they even sell the tire-side dynamos anymore? Sarah got a new bike in March or so and I got one at the beginning of October. I don't recall seeing any new bikes for sale equipped with tire-side dynamos -- they were all the in-hub kind.

Sometimes I have to jostle my bike a bit while enroute if the connection between the wires and the front lamp peters out (and I can definitely tell when that's happened, even without old lady screamers). Seems like despite the improvement of the Nabendynamo the wiring into/out of the lamp hasn't gotten any better.

Afferent Input said...

Oh yeah, forgot about how they slip in heavy rain. Add that to the mechanical engineering category.

Cliff- they do sell the tire-side dynamos, but just as replacements for anyone insane enough to actually buy a new one to replace their old broken one. I was in Stadler a few weeks ago, and I can't recall any of the new bike having tire-side dynamos, so maybe the transition is complete.

I'm not familiar with the in-hub dynamos, but it sounds like a much better idea than the tire version.

Snooker said...

The first time I ever saw a Dynamo was when I moved to Berlin. Funny, I looked at that questionable piece of machinery, judged that when it worked it would be like a gift from the gods, but at the same time knew that there were a LOT of "if's" in the equation about it working all the time.
When I bought my bike I asked for options and was shown the in-hub variety. Then the sales guy went one further and showed me an in-hub that stored enough energy to keep the back light on for a few minutes after the pedaling had stopped. SOLD!

cliff1976 said...

Regarding the weight of an in-hub dynamo (Nabendynamo auf Deutsch, right?) — it is so much heavier that someone who wants a light on her bike would notice?

I mean, those who are concerned about the extra weight of an in-hub dynamo vs. a side-of-the-tire dynamo probably aren't the types commuting 20 minutes to work one way on pavement. You gotta be a long-haul trekker or racer or something for the weight factor to be worthy of discussion, and then you probably have already switched out the standard saddle for a carbon-fiber one which weighs 12 grams and removed your chain guard and fenders as well.

My route takes me along some streets where I have to share the road with cars at stoplights, so I to appreciate the kind of setup that Snooker mentioned, with the charge built up to power the rear light for a bit even after I stop moving.

Babu said...

Hey there,
A friend sent me this link, presumably because he knows I work with bike dynos. So, don't hate me for talking about my stuff, but my company has a cool bike dyno that is rack mounted and is driven by the rear wheel. It actually puts out 30W, so it's an insane amount of power for lighting. You can check it out at www.rollergen.com. Thanks for listening.