I’m about to start publishing an impressionistic comparison of various dynamos. It seemed like a good idea to write a technical introduction, so…
A few days ago, I drafted two single-spaced pages of electrical theory. Then I realized just how unnecessary that was. So here’s a quick overview of what you need to know before I dive into the dynamos. Ready?
- All of these dynamos work the same way. They use magnets and coils of wire to turn a fraction of the rotating motion of a bicycle wheel into electricity.
- All of these dynamos meet the same standard, defined—for reasons beyond the scope of this introduction—by German standards known as StVZO. Each must generate enough power to run a 2.4-watt, 6-volt headlight. Here’s a useful side-bit: almost all modern headlights intended for use with dynamos fit this definition. Why 2.4 watts? Because traditional taillights used 0.6 watt bulbs. So: all of these dynamos are designed to put out 3 watts (at 6 volts).
- But they aren’t really dynamos. A dynamo puts out pulsating direct current (DC). These are actually generators, because they put out alternating current (AC). But I’m going to call them dynamos anyway, since most of the world does.
- But (2) is what a dynamo puts out. No dynamo is 100% efficient. The less efficient a dynamo is, in general, (a) the nosier it will be; and (b) the warmer it will run. Noise and heat are evidence of wasted energy. If a dynamo makes a lot of noise and runs warm, it may be putting out 3 watts—but it may be using 15 watts of your power to do that. A silent dynamo that runs cool might be using only 6 watts of input to create 3 watts of output. Consequently, a nosier and hotter dynamo will usually be a draggier dynamo (see: Bart Simpson).
All of that being said, I’m going to be looking at four different ways of building a dynamo:
- Hub dynamos (as represented by the Shimano DH-3N70—since replaced with newer versions that seem to be functionally equivalent);
- Bottom-bracket dynamos (as represented by the Sanyo NH-T6—no longer manufactured; replaced with the NH-T10, which was sold until a few years ago. There is a photo and brief discussion of the NH-T10 here—scroll down a bit;
- Traditional bottle (sidewall) dynamo technology (represented by the Dymotec 6, widely acknowledged as one of the best bottles ever produced); and finally,
- Updated sidewall dynamo technology in the form of the Velogical Trekking Model.
I have developed a set of categories within which I will rate each dynamo as Excellent, Satisfactory, or Poor (you may remember this system from elementary school). I will also have some miscellaneous comments on each unit. Each will be covered in a single post, and I will end this series with a discussion of the pros and cons of each.
Now, wasn’t that better than two pages of electrical theory?