Bike dynamo bushings became popular in the 1940s. Standard bottle generators working from contact with the tread or rim of the tyre suffer significant energy losses due to friction between the dynamo machine and the wheel. They are also unreliable in wet weather, as the bottle dynamo constantly slips off the wheel. The hub dynamo offers a simple and reliable way to generate energy for the bike lanterns.
SON-XS front hub dynamo
But it is only in recent years that effective dynamo sleeves have become available. Currently, the most popular dynamo sleeves are manufactured in Germany by Schmidt Maschinenbau and in Singapore by Shimano. At the same time, together with the improvement of the dynamo sleeves, the loss of bottle dynamo machines has been reduced thanks to modern technology. It was reported that the Lightspin bottle dynamo machine is more efficient per dynamo sleeve, also considering that there is no resistance when the bottle dynamo is turned off. However, there is still the problem of wet tire rollers slipping off.
Bike dynamo sleeve testing technique
We chose the most popular models of dynamo bushings and bottle generator Lightspin, which were tested in Tuebingen in Germany on test equipment by Schmidt Maschinenbau.
Three completely new generators from the standard production cycle were taken for testing and tested within 15 minutes. Then their resistance was measured without load and with a Schmidt E6 headlight (Philips HPR64 3W 6V lamp). After these preliminary tests, the lamps of the same model with higher efficiency/losses were not taken into account as not suitable, and the “average lamps” were tested in more detail.
Tested models of bike dynamo sleeves and bottle dynamo machines
Dynosys Lightspin (2004 model, discontinued): bottle dynamo machine; cost $120.7; weight 280 g.
Shimano HB-NX32 (2004): dynamo sleeve; cost $50; weight 729 g
Shimano DH-3N30 (2004): dynamo sleeve; cost approximately $60; weight 872 g.
Shimano DH-3N70 (2004): dynamo sleeve; cost $100; weight 667 g (replaced by model DH-3N71).
Shimano DH-3N71 (2005): hub dynamo, cost $90; weight 675 g.
Schmidt Maschinenbau SON28 (2005): dynamo sleeve; cost $209; weight 575 g.
Schmidt Maschinenbau SON20 (2005): hub dynamo, designed for small bicycles with small wheels, but used in the test with 700C wheels; cost $209; weight 575 g.
Capacity of bike dynamo sleeves and bottle dynamo machine
All the generators tested, except for the SON20, provided almost full power of light at a speed of 10 km/h. At low speed, the Shimano DH3N71 dynamo sleeve model was the winner because it produced more power and therefore brighter light. The SON20, which was used with the 700C wheel for which it was not designed, produced the least amount of energy at low speed. At 20 km/h, all the generators tested produced at least 6 volts of voltage, which is required for a standard bike headlight at its full brightness.
Power loss on the hub bike dynamo with the headlamp on
At the switched on light resistance of the majority of generators increases – except for model Shimano HB-NX32 which resistance becomes less at high speed at the switched on light.
Model Shimano DH-3N30 has better indicators in comparison with model HBNX32/ Resistance is less at any speed – actually it is even less, than at more expensive model DH-3N71. Model DH-3N71 did not live up to its advertising, as the company Shimano has announced an increase in efficiency by 30% and more (and a decrease in resistance by 70%, when the light is off) compared to its predecessor, which could with this bushing to come off far ahead of the model SON. In contrast, the new DH-3N71 dynamo sleeve model has a slightly higher resistance at any speed than its predecessor, the DH-3N70.
As a whole model SON28 still is the most effective dynamo sleeve, but the model of dynamo sleeve Shimano DH-3N30 not much behind it. At very high speed it requires less energy. The greatest advantage of model SON20 over model SON28 is shown on average and big speed.
Resistance of bike dynamo-bushings at idling speed
When the light is off, the Lightspin model has shown minimal loss: when the generator is not in contact with the wheel, only the front bushing creates resistance. The Shimano HB-NX32 model creates significant resistance, especially at high speed, and is really not suitable for racing bikes. On the other hand, the DH-3N30 has a significantly improved resistance and can compete with the more expensive DH-3N30 dynamo sleeves.
The new Shimano DH-3N71 has a slightly higher resistance than its predecessor, the DH-3N70. At idling speed, the SON28 model still generates much less resistance than other hub dynamos. As expected, the losses of the SON20 model with the wheel 700C even lower, but the price of weaker light at night at low speed.
Connect one or two headlights to the hub bike dynamo?
At speeds above 25 km, any hub dynamo can be used to power the two headlamps in series. Many long-distance cyclists use two headlamps. If two headlights can provide good lighting, additional weight and resistance are not as important. The single E6 headlamp provided sufficient lighting even on a tandem during the Paris-Brest-Paris bike marathon at 70 km/h on unfamiliar, challenging roads. Those who do decide to install two headlamps can benefit slightly from the lower resistance SON20 hub dynamo.
The use of small wheel hub bike dynamo sleeves with large wheels
Most of the bike headlamps are designed in accordance with German laws, which require a power of 0.75 watts at a speed of 5 km / h and 2.7 watts at a speed of 15 km / h. These laws are designed for German cyclists travelling short distances at low speeds, rather than for avid riders. Many cyclists rarely travel at speeds below 15 km/h, so they may decide that they do not need full lighting at speeds below 15 km/h.
Using the SON20 with 700C or 650B wheels instead of the 20″ wheels it was designed for reduces power output but also reduces resistance. The large wheel rotates more slowly than the 20″ wheel for which the generator was designed.
Test results have shown that precious energy can be saved in this way. For four years I used the SON20 hub dynamo model with 700C and 650B wheels. On very steep hills, the light started to shake. But at low speed, I didn’t need that much light to see the road. For those who ride in the city on busy roads, the SON28 may be preferable because even at low speed the bike remains visible to other vehicles.
Since the end of 2005, the specialized model SON-XS (for folding bikes with narrow forks) has been available for a standard 100 mm dropout. Although the efficiency of this model is about 2% lower than that of the SON20, it weighs 179 grams less per SON20, which weighs 398 grams. However, the narrower flange spacing (40mm instead of 58mm for a standard SON) and the aluminum alloy axle (instead of stainless steel) eventually weaken the front wheel and make it unsuitable for hard riding.
Test results for bike dynamo sleeves and bottle dynamo machine
The light generated by the dynamo sleeves is a reliable source of energy in most cases. Additional resistance has been measured and is undoubtedly overrated. It is most important (as a percentage of output power) at low speed. At high speeds and on uphill gradients, there is little additional resistance compared to the total power required for cycling.
If you are not limited in money, the SON28 hub dynamo is the best choice for most cyclists. It combines high efficiency and quality construction. Since 2002, the SON dynamo sleeve models have included a pressure compensation seal that prevents problems with the bike in rainy cold weather. Without a special seal, the relatively large internal air volume of the dynamo sleeve is compressed and thus contributes to the penetration of moisture.
Dynamic bushing Shimano DH-3N71 is a good choice, but in comparison with its predecessor DH-3N70 it has slightly worse performance. Both models are much heavier and less efficient than the SON dynamo sleeves. The cheaper model DH-3N30 offers better performance, but weighs 200 grams more, because it has lower quality bearings and seals, so that a higher price for the Shimano dynamo sleeve is justified. The expected service life of bearing cones in inexpensive Shimano dynamo sleeves (HB-NX32, DH-3N30) is about 5000 km. It says that the model DH-3N30 offers surprisingly good performance at its price.
If it weren’t for the slippage problems in wet weather, the Lightspin could be a good alternative to the hub dynamo. Its low weight (even including the weight of the front hub mount) and lack of resistance during the day attract cyclists who rarely ride in the dark. When the lights on the bike turn on, the resistance of the Lightspin increases to a value greater than that of the SON28 and modern Shimano hub dynamo. It is difficult to achieve and maintain the correct attachment of bottle generators, so that the resistance can vary greatly during its operation.
For cyclists participating in various competitions, the use of the SON20 model or the surprisingly light SON-XS with a large rim reduces resistance both during the day and at night. Especially at speeds between 25 and 35 km/h. Their drawbacks include reduced luminous flux at low speeds.
|Speed||Full power developed by the cyclist||Standard sealed front bushing||SON28 (light off)||Decrease in speed (light off)||SON28 (lights on)||Decrease in speed (light on)|
|10 km/h||15 watts.||0.1 Watts||+0.2 W (+1.3%)||-0.1 km/hour||+3.3 W (+22%)||-1.6 km/hour|
|20 km/h||50 watts.||0.2 W||+0.7 W (+1.4%)||-0.1 km/hour||+5.3 W (+12%)||-1.1 km/hour|
|30 km/h||130 watts.||0.3 W||+1.3 W (+1.0%)||-0.1 km/hour||+6.7 W (+5.2%)||-0.7 km/hour|
|50 km/h||500 watts.||0.5 Watts||+2.7 W (+0.5%)||-0.1 km/h||+9.0 W (+1.8%)||-0.36 km/h|
How harder is it to pedal on a bicycle with a dynamo sleeve? Compared to a bike without a hub dynamo, the table shows the additional power required to maintain the same speed, as well as the reduction of speed at the same speed on a flat road. Only turning on the night resistance (light on) at low and medium speeds will slow down the rider significantly. At high speeds, the added resistance (light on) is less significant. On ascents, the resistance of the hub dynamo as a percentage of the total resistance is even lower. For example, a 5% slope of 10 km/hour requires about 140 W. In this case, the 3.3 watts consumed by SON28 (light on) slows down the cyclist by only 0.2 km/h.