Basic Principle of "Power by you"
All modern equipment in gyms are equipped with an internal generator to power the control board that people watch and adjust when training. The different resistance levels are controlled by electronic regulators controlling the value of a resistor.
The energy spent by the machine user is simply converted into heat (P=RI*2). The idea is that instead of converting this energy into heat, we collect this energy to charge a rechargeable battery.
The energy collected can then be used to power the lighting system of the gym. Technically, there are no major obstacles.
The generator delivers a voltage between 15 to 70 volts depending on the rotation speed of the equipment.
By connecting it directly to a 24 volt battery (through an AC/DC converter), the voltage drops to 25 volts regardless of the generator output. Only the current changes. A user will produce from 20 to 100 watts depending on their physical capacity.
(a small person = 20 watts and a large, strong person = 100 watts).
We then have between 0.8 to 4 amperes produced. By collecting several machines to a unique battery, the energies are combined and added together, making a contribution to the electricity needs of the facility. Once the battery is charged (24 V 150 Amp/h), we use a DC/AC (24 volts DC / 230 volts AC 1.2 kW) inverter to power fluorescent tubes in parallel.
We have equipped 5 + 5 + 8 machines in Lan Kwai Fong California Fitness on the nights of Nov 3rd and Nov 7th, 2006, following a meeting in May 2006 with the California Fitness management. The machines selected for the first test are all stationary bikes (5).
Four machines are used to recharge a battery, and one has been set with a direct connection to a set of 3 light bulbs of 20 watts, 45 watts, and 100 watts.
The machine connected directly to light bulbs allows a direct visualization of transformation of energy produced. After testing with gym users, we concluded that the resistance produced by charging the battery was too high for some users and we decided to add a regulation system to ease the resistance.
Since we can not change the voltage and current produced, the regulator will control the connection time to the battery.
In December, we connected 5 elliptical machines and 8 steppers. We found that the elliptical machines are the most suitable for electricity production. The system uses the full body weight of the user and due to the high torque generated the output power and the output voltage. A strong user can quite easily produce 80 to 100 watts.
The steppers are different because in the design of the machine, the energy is converted into mechanical energy (through a powerful spring ). The generator delivers low voltage output in the range of 10 to 12 volts with a low current. To become efficient, the steppers have to be structurally modified.
We have calculated the different saving levels.
When the exercisers convert energy into heat, it takes the same amount of energy to offset the heat increase by using an air conditioner.
It can be interesting to produce heat in cold countries, but it is inconvenient in hot countries. Since machines are connected to a central battery, we can monitor the machines being used and we have connected the light above to a sensor. The ceiling lights will turn on only when there is a user exercising. In that way, when there is no user the lights are off.
Out of the 16 hours of gym opening hours, the machines are being used in average 6 to 8 hours a day. We therefore save approx 50% of the lighting cost and we save the other 50% by producing the electricity needed.
When we generate with one machine 70 watt h we save in fact 200 watt h .
The ratio energy saved / energy generated is approximately 3