What is a Bicycle Dynamo (and How Does it Work)?

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There are many ways in which you can decipher someone’s age without asking them. Any trip down memory lane that comes with a musical reference. Or how it was to watch a football match.

Perhaps one of the most telling is the hazy memories of playing out in the street. How far you could go without your parents knowing or minding where you’d gone. And the freedom that came with that.

I borrowed my dad’s fixed wheel bike for one such adventure as mine had recently been stolen. He used it for work. It wasn’t glamorous, a heavy steel machine that was sprayed black and had heavy wheels. I struggled to reach those bear-trap pedals that made me grateful for the fixed wheel rotation so that they could not slam into my shins.

As well as the novelty of going up and down like being on a carousel whilst pedalling, I remember the dynamo that I popped on when the skies started to darken and the world around me turned a very special orange, like a stained-glass window made by Quality Street.

If you remember those tombstone Ever-Ready front and back lights that each required two D batteries then you’ll appreciate the simplicity and sleek design of a dynamo.

Audax riders and endurance riders are turning back to the dynamo as a source of light that relies on our own effort to illuminate the road. In a sustainable world, one less purchase of a consumer product like a battery is no bad thing too. Let’s have a look at how we create electricity and light up our world on the roads and lanes.

What is a Bicycle Dynamo?

It is a method by which propulsion of the wheel generates an electrical current. This is transferred to provide energy. The traditional dynamo is referred to as a sidewall or bottle dynamo. Modern versions are powered from the wheel hub. You can also get a bottom bracket dynamo.

How Does a Bicycle Dynamo Produce Electricity?

The motion of the bicycle wheel in the most common forms of dynamo turns a magnet inside a coil of wire. This creates a flow of energy between the two ends of the coil. The energy difference between these ends is expressed as volts. The ‘work’ done causes an electrical current to flow.

How dynamo works

Is a Bicycle Dynamo AC or DC?

Dynamo comes from the Greek word dynamis (power). Chances are that your dynamo is actually a magneto. A standard dynamo creates a direct current (DC) – a one-directional flow of electrical charge. A bicycle dynamo creates an alternating current (AC), which reverses direction occasionally.  

Who Invented the Bicycle Dynamo? 

A German, Robert Bosch, founder of the eponymous company, introduced a front light in 1923 which was powered from a dynamo generating electricity from a small roller placed just behind the forks on the front wheel. The higher the speed, the more electricity was generated and the brighter the light.

In 1923, Robert Bosch Introduced a front light that was powered by a dynamo.

How Much Electricity Does a Bicycle Dynamo Produce?

The typical electrical output produced from a bicycle dynamo is six volts. It is a low-power outcome derived from your pedalling. Hub dynamos can sometimes be regulated to produce 12 volts. The electricity is generated immediately and ceases to be produced when you stop pedalling.

Lights can run on AC power and that has been the traditional use for dynamos. As we have moved into a world of communication and become more efficient, there have been sufficient advancements in battery technology, LED light technology and charging technology.

Along with the USB cable, this has given rise to the opportunity for the AC current to be converted to a DC current, which is required to power electronics. This means that modern dynamos (which usually run from the front wheel hub) are able to provide power to LED lights, or a battery pack or GPS device or phone. 

The sustainability and delight, nay achievement, that comes from powering your own electronic existence is a powerful force in its own right.

Are Bike Dynamos Good?

Your lights will always function. Most bicycle lights rely on batteries and whilst they can now be charged at home or the office via a USB, this relies on you remembering cables and collecting them when needed. You’ll never get stuck in the dark with a dynamo nor have to push your bicycle home.

If you are a bike-packer or cyclo-tourist, you will enjoy the electricity generated by the hub dynamo in particular and not be perturbed by the increase in energy required by you to power it.

Pros of bike dynamo

The power which you generate should be sufficient to charge most of the devices you take with you on such a trip. Apart from your laptop. 

Whilst a bottle dynamo powered from the front wheel relies on a physical connection to the tyre, or sometimes, the rim, to produce electricity, it may not be the most reliable and certainly would be of reduced benefit if you went off-road or somewhere that created a sufficiently bumpy ride to cause the connection to fail intermittently. Hub dynamos on the other hand offer a more stable, consistent production of power.

Dynamos have the side effect of producing some form of resistance to power them. In most cases, this is not too noticeable. A bottle dynamo will create a small amount of noise and rub. You might lose one minute off your personal best over a twenty kilometre ride. Overall, the maintenance and upkeep of a dynamo is not significant.

Cons of bike dynamo

Bicycle Dynamo: Pros and Cons

Dependable, especially if you ride at nightWeight and drag will slow you down
Usually bolted or fixed to the bicycle – less hassle and harder to stealHub dynamos should require a new front wheel to be built
Certain dynamos can be used to charge devices on the go when lighting not neededLight will work less reliably if you ride off road which will be off putting
Light emitted can be dispersed over a wider area than with battery powered lightsNo light when stopped which might concern you at junctions – also worth checking local laws about lighting

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