Bicycle USB Charging Efficiency

People started to use bicycle generators to power lights. Today, the concept has evolved to charging USB devices. However, the power conversion from pedaling to USB output can be quite inefficient. To avoid these pitfalls with PedalCell, our team looked at each step of this process to understand where power was getting lost.

Rider Power

The mechanical power input by a cyclist to move forward is expressed in watts (W). The speed, elevation, weight, and aerodynamics of the environment, a person, and the bicycle affect how many watts a rider must exert to maintain a set speed or accelerate. Cyclist athletes use wattage power meters while riding to measure how efficiently their energy transfers into a bike’s motion. This measurement is also prominently displayed on indoor trainers used by companies such as SoulCycle and Peloton. On average, riders must produce about 120W to maintain a 16mph coasting speed on their bicycle (source).

Watts the problem? Pros give their views on proposed power meter ban -  Cycling Weekly
Bicycle Power Meter

Spinning the Generator

Bicycle generators (also known as dynamos) use a series of magnets and coils to convert a bicycle’s mechanical “input” into electrical “output” via harnessing a wheel’s rotational energy. The efficiency of this process is known as mechanical-to-electrical efficiency. The efficiencies of such generators vary depending on the composition of their internal components and rider speed.

Bicycle Dynamo Efficiency (Source:

Electronic Loss

Riders must use electronics to convert raw generator power for modern USB devices. The efficiency of this electrical-to-electrical conversion measures the loss in power (watts) from the generator output to the electronic’s USB port. Electronics in this category typically have efficiencies ranging from 30%-60% (source).

Kemo 172N USB Dynamo Charger | Battery usb charger, Usb, Usb chargers
Kemo 172N USB Dynamo Charger

An Efficient System?

After all of these conversions, a great deal of power can be lost from a rider’s pedal to their USB port. The efficiencies of average bicycle generator + USB electronic combinations are presented below.

Data Captured from Cycling About here and here.

A rider that tries to charge their phone with a common bicycle dynamo system can lose over 60% of their power. Poor efficiencies result in little charge and exhausted riders. You could be putting in 10W of power to charge your phone, but only get ~4W of output! The primary reason for lower efficiencies results from no company designing both the generator and electronics together. This siloed development process promotes poor optimization and excess power to be left on the table.

Efficiently Generating a Lead

PedalCell prototype efficiency. Data imported from Fahrrad Zukunft. Full data can be viewed here. Products shipping now have improved performance.

PedalCell maximizes efficiency by focusing on the whole system of the rider, generator, and electronics. We reach a 70%+ peak mechanical-to-USB output efficiency – the most efficient pedal-to-USB port bicycle power system ever made by a large margin. Moreover, CadenceX performs this feat while producing up to 4X more power than competitors.

PedalCell CadenceX is the most end-to-end efficient bicycle power source

We achieved this performance after years of research and development to integrate our patented electronic, generator, software, and mechanical systems. We use a clean-sheet design that shares zero components with any dynamo generator or USB electronics. This process is commonly used by others in various industries, such as Apple’s integrated hardware and software. Now, PedalCell has brought this same process to bicycle power for the first time.

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