The Shocking Truth, Part 4: Dynohubs

If you check around bicycle message boards, you will see that, prior to ten years or so ago, most cyclists in the US relied on lighting systems powered by batteries, whether these were comparatively small systems, operated by AA or AAA batteries, or more sophisticated systems, running on sealed lead-acid or Nickel-based rechargeable batteries. Generally, such lights used halogen-based incandescent bulbs or—in the case of the smaller lights—some used small white LEDs, as that technology began to grow.

In the rest of the world, many cyclists continued to use dynamo-based systems. These were much lower-power, but had the advantage of not needing batteries (and so not being subject to batteries running out and/or the need to recharge. German law required lights on virtually all bicycles, and so it was there that lighting systems grew most sophisticated.

Then, and it’s not clear to me which came first, at some point 10 to 15 years ago, some American cyclists started to use European dynamo systems, and Peter White (of Peter White Cycles) began to import dynamo lighting gear that met the German standards.

This is my impression; it may have happened earlier, but that’s when I started to see more chatter about dynamo systems. I’m guessing the internet had something to do with this.

In any event, Randonneurs or Audax cyclists—folks who ride time-competitive events ranging from Paris-Brest-Paris on down—were among the adopters of dynamo systems. Their popularity in the USA might be traceable to the establishment of Randonneurs USA in the late 1990s. Randonneuring events often required equipment like fenders, as well as lights capable of running all night long, that were not part of the ordinary “racing” bicycles of the times.

Around ten years ago, a new (or rather, vastly improved) type of dynamo became popular among randonneurs. This was the hub dynamo, or dynohub, and it has probably supplanted all but batteries in the American bicycle power pantheon. Battery lights continue to be popular for their very high power output, useful in MTB night riding. With the advent of LED headlights, which are far superior to halogen or other conventional bulbs in turning power into light, dynohub popularity exploded.

This is because the dynohub has the highest efficiency of any dynamo system, and this is because it does not require any mechanical coupling to the wheel. Instead, the dynohub replaces the front hub of a bicycle, eliminating the need for any kind of roller, and the only coupling is electromagnetic, inside the hub itself. There, a set of magnets on the inside of the hub rotate around coils of wire which are fixed to the axle. The rotation generates alternating current in the coils, and this is brought outside to connectors on the hub.

The very sophisticated and popular SON dynamos, produced in Germany by Schmidt, are the best-known. However, Shimano also produces a wide range of hub dynamos at a significantly lower price, and these are held by most writers to be nearly as good as, quite a few just as good as, or (by a few) superior to the Schmidt units. My sense from reading over the material in this area and my own experience is that the Schmidt models are Dura-Ace to the Shimano’s Ultegra status. In other words, that the aesthetic and operational differences are marginal, while the price differential is not (Schmidt units cost two to three times as much as Shimano dynohubs). There are a number of other companies that produce dynohubs, but where they fall in the scheme of things is unclear, as none are as popular as these two. Generally, most dynohubs meet the StVZO standard, putting out (at least) 6 volts at 3 watts.

My primary experience has been with the Shimano DH-3N70, purchased and first built into a wheel in 2005. This is the unit I will discuss here, but it is reasonably representative of the class of dynohubs.

Cost Associated with Hub Dynamos

Time

At the time I bought my hub dynamo, it was comparatively difficult to locate one, but that was probably because, being low on funds, I was looking for the Shimano rather than Schmidt units. Schmidt dynohubs have been available via web/mail order for some time, the most famous source being Peter White Cycles, who is also (unless I am mistaken) the North American importer for those hubs.

Pretty much any shop in the USA that deals with Shimano parts can order one of the Shimano dynohubs and build a wheel with it. Prebuilt dynohub wheels using Shimano parts are available through Quality Bicycle Products and often via eBay.

Money

A good Shimano dynohub will cost around $100-150, depending on the model (the more costly units are somewhat lighter). There are lower cost units, but these often run at lower (sub StVZO) power levels or have have lesser bearings, solid axles, etc. A Schmidt hub will run in the $275-325 range.

Remember that this is the cost only of the hub. In addition, you will need a rim, spokes, and (unless you DIY) a builder. These items can add up, which is why dynohubs tend to be seen by maby as a high-priced spread. A wheel equipped with a Shimano dynohub will cost more than a good many low-end bicycles cost.

Weight

An ordinary Shimano 105 front hub (5500 series) weighs about 150g. The lighter and more costly of the Shimano dynohubs, the DH-3N80, runs 490g. (measured weights, Source here). The claimed weight for the SONdelux, Schmidt’s lightweight unit, is 390g. This means that going from a Shimano conventional hub to a Shimano dynamo hub costs you about 12 ounces.

Installation

Mechanical

Once it has been built into a wheel, installation of the hub dynamo is exactly the same (with one exception, see below) as installing any quick-release front wheel. The only exception is orientation:

Electrical

Orientation is a factor because you will need to connect the hub to your lighting system any time you change a tire or tube, so you’ll need to make sure that the electrical connector is where you can get at it. Shimano uses a small plastic plug to connect wires to the hub; Schmidt uses tiny “spade” connectors. Both are easy to use, and take perhaps five seconds’ work to connect/disconnect (if, say, you need to patch a tube).

Performance

Overall performance

Overall, performance of the dynohub is outstanding. Its relatively high mass, large size, and robust construction mean that a dynohub can be extremely responsive.   As an example of this, when I walk the bike across the basement floor, both the headlight and the taillight flash brightly as the wheel turns. This is indicative of excellent low-speed performance. Indeed, although hub dynamos appear to be current-limited, in the sense that they will not put out more than 0.5 Amps (thus achieving the StVZO standard at 6v), they are capable of putting out a great deal more voltage. Indeed, this is one of the reasons that standlights work so well with hub dynamos; the extra power is stored in the light’s electronics and released to power the LED itself while the bike is stopped.

Wet performance

Because the dynamo does not require any mechanical coupling to the wheel’s rotation, there is no possibility of slippage in wet weather. Indeed, I have in the past ridden my bike through streets flooded by the Mississippi to the level of 10 inches or more, and while my feet got wet (and I moved plenty slowly!) the dynamo never failed me.

Charging performance

Dynohubs put out plenty of power for charging devices (like smart phones) while you travel. A number of companies make devices that turn the hub’s AC into USB-level output more suited for the diet of small electronics. This is nothing to sneeze at; a cell phone provides multiple functions that can be useful on tour(though my preferred approach is to charge an external battery, and use that to charge the phone later—belt and suspenders!).

Operation

One important difference between the dynohub and all other forms of dynamo is that with a dynohub, which is always rotating, turning your lights on and off is done with an electrical switch rather than by removing the dynamo’s contact with the wheel. (At least one company produces a dynohub that can be physically disengaged, but I have neither seen nor tested one). This means that the control for dynohub lights can be located anywhere you want it to be—e.g., in a small box on your handlebars, on the light itself, etc. This is not a huge deal, but it’s nice to have the option.

Noise

Hub dynamos are essentially silent. This is because the source of noise and vibration in dynamos is almost entirely the wheel/roller interface—and here, there isn’t one. Consequently, any nois from a hub dynamo is indicative of a defect in the product (I once bought a wheel with a Shimano hub dynamo that made a “wiping” sound as it rotated, and I returned it.

Vibration

While noise should be a non-issue, I have experienced (as have others) a small amount of vibration when the hub is powering a light at certain speeds. The amount is fairly trivial, and seems to have to do with some electromagnetic resonance. Different hubs appear to generate this resonance at different speeds, and I experienced it at around 28 MPH with my particular unit. In general, the more power drawn by the load, the greater the vibration (hence, a halogen bulb connected to a dynohub is more likely to cause vibration than an LED headlight). This is not a major issue for all riders, but could be disconcerting if it happened unexpectedly during a high-speed descent. This is a good reason to get familiar with the operation of your lighting system, whatever it may be, during daylight hours.

Subjective Resistance

There are two questions here, really. Does the dynohub cause resistance, and can you feel it?

The first question is objective, and the answer is that yes, it does. This can be seen easily by spinning the wheel off the bike next to a wheel with no hub installed, or by holding the axle and turning the wheel. You’ll feel a definite “notchy” quality. As the wheel turns, one magnet is leaving and another engaging with a particular coil (actually, this is happening in several places in the hub at any given point). Thus, magnetic resistance will tail off as you turn the axle away from one magnet, and increase as you turn it closer to the next. The wheel will want to remain in a “stable” configuration. It is important to emphasize that this is not mechanical resistance, but an artifact of the generator. However, it is easily overcome on the bicycle. Note also that this resistance is greater when the dynamo is connected to a light.

But can you feel it? This is a subjective matter. Prior to undertaking this project, I would have said no. However, at that point I had been riding with a dynohub for almost ten years. I tended to leave it on at all times, so as to make myself conspicuous in traffic. I’ve done centuries this way, and did not notice any resistance. However, the first step in this project was to replace the front wheel with one using a conventional hub, and the bike did feel slightly livelier than it had before. It is possible that this was due to the twelve ounces or so that were gone from the front wheel. I do not appear to be any faster! But I would say that subjectively, you can sense a small amount of resistance.

Concerns

Serviceability

In theory, dynohubs cannot be serviced, and places that sell them will warn you not to try. In fact, you can find videos on the internet that show you how to service dynohub. I have not tried this, and don’t plan to. Mine has served for 10 years, and I expect modern dynohubs are better built than when mine was produced. Once concern has been raised by Schmidt about moisture, because a typical hub dynamo contains a great deal more air and ferrous metal than a normal front hub. Consequently, sudden temperature shifts can cause air to move into and out of the hub through the bearings and seals, and that air can bring moisture into the hub, which can in turn cause internal rusting. Schmidt claims that its hubs have a system for equalizing pressure so that this does not become an issue. I have lived in places like the American Midwest and Northeast that have significant temperature and humidity swings, and have not experienced problems like this with my Shimano hub, but if it is a concern, the Schmidt units might be worth a look.

Fragility

Dynohubs are as strong as any normal front hub. They are unlikely to be damaged by potholes, and no more likely to lose a chunk of flange than any other front hub. They are directional, and electrical connections are generally made on the hub’s drive side (in theory, running the hub backwards can cause the generator to “unthread,” but I have never heard of this in practice. (Schmidt now produces a hub that doesn’t need to be plugged into the bike’s electrical system; instead, custom faces are placed on the dropouts that connect when the hub is inserted—this does, however, require a custom fork at a minimum.)

Attractive Nuisance?

Your hub will probably not attract thieves. It is significantly larger than most front hubs, but it’s just a hub. At first, because in my younger days I had had a front wheel stolen, I was extremely nervous about leaving the bike locked up. However, other things on the bike are more likely to be stolen (a Brooks saddle, a nice headlight, a pump) and so I gradually lost my paranoia. Correct locking procedure will protect your front wheel in any event.

So, what’s not to like?

Some people think that dynohubs are ugly. Here’s a regular front hub (a current 105):

 105

And here’s a dynohub (the model I use):

 DH-3N70 001

(The grey and black object obscuring the drive-side end of the skewer is the connector for the dynamo’s electrical output.)

The dynohub is clearly fatter, with much larger flanges (on the other hand, shorter spokes!).

Dynohubs are also significantly heavier than standard front hubs, as discussed above. Because the weight is at the hub rather than the rim, it shouldn’t have much impact. However, it’s clearly there when you pick up the bike.

You’re limited in terms of wheels. If you’re the kind of person who likes to switch wheels a lot, having your dynamo built into one of them can be an issue. Alternatively, if you’re happy with the wheelset you have, converting the front wheel to a dynohub may be costly—or impossible. Low spoke count wheels in particular will have problems with dynohubs, which typically come as 32- or 36-hole units.

Over time, however, a typical commuter will probably save money by running a dynohub instead of batteries. It cost me roughly $130 to have the hub and spokes of a wheel replaced with a dynohub; ten years later, it still works, which means it has cost me around $13 each year to have instant, no-charge, no-battery power.

That’s a lot to like.

I’m going to wait a few days before posting my next shocking truth, so if anyone has any questions—or wants to point out an inaccuracy J–feel free. Next up, we take a walk into the past, and spend some time battling the bottle.

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5 Responses to The Shocking Truth, Part 4: Dynohubs

  1. InvisibleHand says:

    10 years is a long time for a hub on a commuter. Are you surprised by it’s longevity?

    • Well, the stresses on a front hub are not all that great, and since there are no real additional stresses imposed by adding a dynamo…I guess I’m not surprised by its lifespan so far. Pleased, but not terribly surprised.

  2. Steve Kurt says:

    regarding standlights….most bike lights are designed to work with any standard dynamo, so the standlights are more of a testimony to the efficiency of LEDs than any factor of the dynamo. If you are into designing your own lights, it is possible to design them to extract more power from a hub dynamo than can be extracted from a bottle dynamo.

    regarding vibration…. I’ve noticed the vibration on my upright commuting bike, but not on my recumbent commuter. The ‘bent has a much stiffer fork (it is designed for disc brakes). I would attribute the vibrations to mechanical resonance and not electromagnetic resonance.

    regarding serviceability…. Peter White does service Schmidt hubs. I’ve had my first generation returned to him for pre-emptive bearing replacement. The second generation is designed for easier bearing replacement and doesn’t require the hub flanges be pulled apart to gain access to the bearings.

    • Steve:

      1. Yes, hub dynos put out a lot of juice. For several years, I rode with a pair of 3W Luxeons that ran very brightly on a single “3 watt” Shimano hub. With some of the other dynamos in this “test,” I have noticed substantially shorter run times for stand lights (it’s worth noting, however, that even the ‘weakest’ unit in the test got the standlights working for a time–though clearly not as well as the hub).

      The efficiency of LED headlights really has changed the dynamic of bicycle lighting for the better.

      2. The reason I don’t think it’s as likely to be mechanical as electrical resonance is that I can change or kill the vibration by changing the electrical–but not mechanical–characteristics of the system. That is, by switching the lights on or off. That changes only the electromagnetic interactions in the hub (and of course, the photons streaming from the headlight).

      3. With respect to serviceability, I meant service that could be performed by the user, but I take your point. I believe that Shimano dynamos can also be serviced (the Youtube videos show the possibility) but Shimano is not as good at making parts available as is Schmidt, and unlike Schmidt (which has single point of distribution and thus node of expert knowledge in Peter White), Shimano dynamo hubs are widely but shallowly distributed, and no shop that I’ve run into knows how to service them. The shops just don’t get enough call to learn how to do it, which is a pity. When my current hub goes bad on me, I may have to try the Youtube video method for home-brew repairs!

      Even though dynohubs are very long-lived, in my experience, it’s likely worth noting that service can extend their lives considerably, further lowering their effective cost.

  3. Pingback: The Shocking Truth: Dynohub Progress | Law School is So Over

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