Pedal power is a great, inter-active demonstration of power generation and consumption. Building your own pedal generator is also an amazing learning experience. There are a number of plans and designs around for the generator and stand (check out our own here), but information about the electrical systems is usually lacking.
Here is a full design for a shunt regulator for pedal power systems. A PCB, kit of parts and a fully built circuit will be available.
The main problem with using pedal power to provide electricity is the fact that the output voltage of the device depends totally upon the speed at which the cyclist is pedalling. If they are pedalling too slowly, there will not be enough voltage to drive the device. If they pedal too fast, there will be too high a voltage and the output device will very probably be damaged.
In order to stop this happening, some form of voltage regulation is required.
A number of techniques can be used:
- Direct connection (such as to a battery) – NOT a good idea unless the speed of the pedal generator is regulated some other way, such as mechanically. You might be able to get away with it using a discharged battery, but when the battery becomes full you could damage the battery by over charging.
- Series regulation (such as a PV charge controller) – this is NOT a good idea as it will apply a series of high voltage spikes to the powered device, which could cause problems. Also you will get high input voltages to the controller, which may cause some damage.
- DC/DC conversion (such as the Magnificent Revolution design) – this works well, but is a relatively expensive option. If the cyclist goes VERY fast, then there is the potential to go over the input voltage of the converter and damage the DC/DC converter. Also complex electronics is not a great idea at a muddy festival…
- Shunt regulation (such as a small wind turbine charge controller) – this also works quite well, but requires some feedback to the cyclist that they are going too fast. This works by pushing any excess power (above a certain voltage) to a dump load (such as a heater). Hence if the cyclist is going too fast then they are wasting energy as heat. Commercial units are good, but expensive and usually over the top for this situation.
I wanted to build a relatively simple shunt regulator which will divert any excess power to a dump load. This will ensure the output devices are supplied at the correct voltage, even if the cyclist really tries to go fast. The design brief was to build a cheap but robust unit which could be built by someone with basic soldering skills.
Overview of the circuit
This is a shunt regulator which is wired up as shown below, in-between the pedal generator and the storage component (this could be a capacitor or a battery).
This design is based upon a hysteresis comparator. This means when the voltage goes above a set value the dump load will turn on and it will stay on until the voltage has dropped to another, slightly lower voltage. The difference between these values is called the hysteresis voltage.
This circuit has been designed to be inexpensive but also robust and reliable and configurable for different situations.
Kits and Parts
re-innovation are working to produce this design as a printed circuit board, a kit of parts, including the main components, and a complete built and tested unit. Approximate prices will be £5 for the PCB, £15 for the kit of parts (including a 50W dump load but excluding CPU heatsink/fan), £25 for the constructed and tested circuit board (excluding CPU heatsink/fan) and £40 for the constructed and tested circuit board including CPU heatsink/fan. Please contact us to register your interest in obtaining one. Note: 22/6/12 – We are working on a new design.
Other uses for the shunt regulator
- Wind turbine regulator
As this is a shunt regulator, this can be used as a very simple regulator for a small DC wind turbine. In this case I would suggest using a better dedicated dump load which can cope with dissipating the power for a length of time (with pedal power people get tired pretty quickly and hence the regulator is only at a high power for a relatively short period of time). You can add more MOSFETs to control a larger load. In this case use the gate signal and source (negative) for all the MOSFETs, but use a single dump load for each MOSFET. Please email for more information.
Warning: Ensure all connections are really well made, as if the wind turbine is not controlled then the turbine could over-speed and be destroyed.
- Micro-hydro regulator
Similar to the wind turbine regulator.
- Solar photovoltaic regulator
This is not recommended – there are other commercial and DIY units to do this. This circuit could, potentially, be used as a solar PV regulator on a DC system, but it is probably a bit over the top – you can use series regulation for solar PV, which is easier on the MOSFET and does not require a dump load.For more information on charge controllers click here.
We are also in the process of writing a more detailed guide to the electrical systems for pedal generators. Please check back soon or contact us.
Note: While every effort is taken to ensure this information is correct, no responsibility is taken for any damage to equipment or people that may occur.