Power to the Pedal

Power to the Pedal

How to Power Domestic Appliances with your Ebike Hub Motor

Forget “clean coal” it’s a myth, North Sea gas is cleaner than coal but it is still a greenhouse gas emitting fossil fuel, nuclear works but has serous safety issues, solar is great if you have a roof and sunshine, tidal might be OK if you can dam up an estuary, wind is the answer when it is windy.

But what are you supposed to do when you’re out on your ebike and you;

  • fancy watching a film on a large screen LED TV that you happen to have brought with you on a bike ride?
  • want to power a local band giving an outdoor performance?

The ChiCycle team imagine a green, pedal powered future so we looked into these ideas as fun ways to illustrate how we use electrical energy in every day life.

Feasibility: it is obviously possible on a small scale:

Science Fiction: These ideas feature in the Black Mirror episode Fifteen-Million-Merits


What follows is an indication only of what ChiCycle has tried and tested. We give no guarantee these ideas are safe for  individuals using the equipment nor safe for the equipment being powered. If you choose to replicate any of the setups that ChiCycle has employed, be certain to consider the mechanical risks and risks of mains voltage electricity if stepping up the output to power mains appliances. If a sensible approach is taken there should be little risk but  reasonable precautions are necessary.

What Hub Do I Need?

ChiCycle have been experimenting with a rear EBike hub with built in dérailleur gear sprockets. Some EBike hubs won’t easily work as generators as they have freewheels to stop the motor turning unless it is powering the bike. However most other EBike hubs without motor freewheels will make very efficient generators as well as drive motors.  You will probably want to find a way to hold the rear wheel off the ground so the E-motor can generate electricity without the bike having to move forward. We have been testing a wheel very similar to the one shown below.

26" Rear Wheel 36V 500W Electric Bicycle Ebike Conversion Kit Hub Motor
26″ Rear Wheel 36V 500W Electric Bicycle Ebike Conversion Kit Hub Motor

An alternative idea stolen from Barreg Cycles, Fishbourne, is to drill out a single rear sprocket and bolt it onto a front motor hub where the brake disk should normally go. A front hub with brake disk is shown below.

Barreg solution
Barreg Cycles just drill and bolt on a rear chain sprocket where the front disk should be!

ChiCycle assume the hub is going to work most efficiently as a generator in top gear. However this is just an educated guess.

Most hubs have fine wires for their hall sensors. These are of no significance if the hub is to be used as a crude simple generator.

There are usually three thick wires that connect directly to the three phase motor windings.

At a sustainable but energetic peddling rate in top gear we measure approximately 18 volts AC at 100 Hz with no load, across one phase winding.

Spinning the peddles a little faster gives 24 Volts between each phase. Three 24 volt 21 Watt indicator bulbs can be connected between each phase and fully illuminated by pedalling quite quickly.

Powering TVs, computers and other consumer electronics.

Most TV’s, computers, smart phone chargers and even Christmas tree lights operate using internal ultrasonic frequency switch mode transformers. Most UK and European consumer equipment appears to have an extremely wide range of input voltages over which the devices will power up and operate without issue. Most specifications cover a range of 100V to 240V mains AC in the equipments documentation but since these devices internally rectify the incoming AC supply the AC frequency is not critical. In fact most devices seem happy to operate on a DC supply! Ideal rectification of 240 V mains would give 240 V (ac) × √2 = 339 (dc). Assuming the device internal power supply is designed to cope with 20% variation in the mains supply, its storage capacitor and chopper circuit should be able to cope with up to 240 V (ac) × √2 × 1.2 = 407 V (dc). It is likely most UK/EU devices will tolerate higher DC input voltages but finding the upper limit will probably damage the devices internal power supply so this is not an advised activity. Most consumer equipment we have tested, begins working reliably with approximately 100 V dc input. Aiming for a supply voltage under load (at a sustainable pedalling rate) of between 150 and 170 Volts seems a safe option. To achieve this we used a circuit similar to the one shown below.

Ebike Hub motor wiring to power TV
Ebike Hub motor wiring to power TV or similar appliance  

Stopping People Pedalling Too Fast

We have discovered that if general members of the public pedal, they can go much too fast while there is little load and produce undesirably high voltages. This is a particular issue with over enthusiastic youths. If powering expensive pieces of equipment such as TVs, excess supply voltages could lead to damage that might be expensive/difficult to repair ! 

We have solved this issue by creating a voltage activated switch. The switch uses power MOSFET transistors to connect a 1 Ohm 280 Watt resistor across the low voltage (A & B) outputs (referred to in the diagram above). The resistor is switched in when the low voltage output reaches 35 Volts and switches out again when the voltage falls to approximately 25 Volts. From the cyclists perspective this produces a defined resistance opposing pedalling effort but only when the cadence becomes too fast. Even extremely athletic cyclists are unable to to pedal fast and hard enough to overcome this speed limiter. However, the excess energy mostly goes into the 1 Ohm resistor which can become warm! The switch circuit is designed to turn the MOSFET on and off relatively fast. This prevents the transistors being destroyed through overheating. 

The components of the brake system are shown below. The smaller golden 68 Ohm 25 Watt coloured resistor can be connected in series with a 3 Watt red LED. These can then be connected in parallel to the large red 1 Ohm 270 Watt resistor to give a bright red warning light that comes on when the electronic brake activates.

Components of Speed Brake. This avoids the ebike providing excessive voltages.

The original electronic brake circuit design (available here) used only one STP55nf06 Power MOSFET transistor but the circuit board design (available here) allows two identical power transistors to be connected in parallel to ensure reliability in handling the heavy switching current.  The speed when the brake activates can be adjusted by altering the value of the 27kOhm resistor shown in the circuit diagram. Reducing this resistance slightly will lower the voltage when the brake activates.

Amplifying Sound

These devices are available from E bay. The low voltage rectified output supply (terminals A & B) can power this very adequately.

WONDOM 2 X 100 Watt 6 Ohm Class D Audio Amplifier Board – TDA7498 Module Stereo

Business seller information
Sure Electronics
Zhang Cheng
3F, Building F6, No.9 Weidi Rd., Xianlin
210000 Qixia Dist., Nanjing, China, 江苏省

Our unit does deliver 100 Watts RMS per channel into 6 Ohm loads with a 36 Volt power supply input but in normal use the ebike supply voltage will be lower and there will be a reduction in output power. However it still sounds loud even used outdoors! A laptop or phone can supply a signal directly to the amplifiers phono connectors. For use with a microphone a preamplifier is needed and we will publish details of something suitable when we have arrived at a satisfactory design for this.

Our current Bike Powered Equipment risk assessment for events is available on the following link.