QUESTION: Will a using a bigger generator or adding multiple small generators together or making a generator go much faster translate to more power output?
ANSWER: Only up to a certain point. The fact is that the human body is limited by the laws of physics to only so much power output. I have countless people bring up the idea that a really big generator could put out much more power than a small generator. Consider that a person consumes about 2,000 calories a day. This equates to about 8 million energy units called “JOULES” . A Watt is defined as a Joule per Second. So if you burn 500 food calories on a human power generator for 1 hour that equates to about 2 million Joules in one our. To convert Joules per hour to Joules per second we divide 2 million by 3600 which is about 555 Watts of power.
The disappointiong thing is that when your body burns this 555 Watts during the hour up to 75% of this power gets lost in conversion from one state to another. So it first starts as fuel that your muscles burn, The muscles then use this energy to push on the pedals of the bike, The pedals then transfer their energy to the cranks of the sprocket. The sprocket then transfers its energy to the chain, the chain then transfers its energy to the wheel, the wheel then transfers its energy to the rubber roller of the generator (Which has losses to due friction), Then the rubber roller transfers it’s energy to the shaft and rotor of the generator, the rotor then transfers its energy to push electric winding coils through a strong magnetic field created by permanent magnets, the winding coils capture flux from the magnet fields and drive current through the windings, the current flows into your battery or light bulb.
In every one of the state changes mentioned above, some energy is lost. So if your body is putting out 555 Watts during that one hour then the actual amount of electrical energy it is generating is around 145 Watts of power. It doesn’t matter how big the generator is or how fast it is, you will always have the limitation of the human body. The more power you try to generate with your body, the more your body feels drag and you slow down and get tired. Another way of looking at it is if I tell you to ride your bike up a hill that is too steep. You tell me no , and I say “why” and you say , because it is too hard to ride up that hill. Let me know if you have any more questions, Bradley – Electrical Engineer – http://PedalPowerGenerator.com
How do I remove the tire from my bicycle? Watch video instructions shown Here
What is a Watt? A Watt can be compared to Velocity which is a measurement of how fast you are going. When a Watt is combined with a time value such as second, minute, hour, then it becomes a measurement of work done. The formula for Watts is Volts x Amps.
Below is actual data collected from a bike generator during a one hour session. The white line in the graph below shows actual Voltage of a lead acid battery being charged by the bike generator. The red line represents the Amps measured.
At one point in the chart the Amps reach a value of 21. At that same point, the Voltage reaches about 14. When we multiply 21 x 14 we get 294 Watts. The second graph below in green is the Watts graph.
How much energy can I generate with a Pedal Power bike generator system?
Typically an adult who exercises on a regular basis and can generate about 100 Watts of power over a one hour period. A competitive rider can average 200 to 300 Watts during a one hour period. To put this into perspective, that much energy would power a cell phone for over a month. But would run a 500 Watt blender for only a few minutes. The calculations for energy produced are in “Watt Hours” which is calculated by multiplying Watts x Hours. The energy unit used to charge you for power being delivered to your home is “KiloWatt Hours” Which is simply Watt Hours divided by 1,000 .
What kind of things can I do with energy generated from my body?
- Charge a deep cycle 12V DC battery (Using a blocking diode)
- Charge cell phones (Using a blocking diode and Voltage regulator)
- Light a room with an LED light bulb (Using a blocking diode, Voltage regulator, and AC inverter).
- Charge a laptop computer (Using a blocking diode, Voltage regulator, and AC inverter).
- Power a 12V blender to make drinks or smoothies at a party
- Power a leaf blower pointed in the up direction with a pin pong ball floating in the air.
- Power a wheat grinder to make bread (Using a blocking diode, Voltage regulator, and AC inverter and portable powerpack)
- Power a 50 Watt flat screen TV and DVD player (Using a blocking diode, Voltage regulator, and AC inverter).
- Power a PA sound system (Using a blocking diode, Voltage regulator, and AC inverter).
How do implement an adjustable dumpload circuit for over Voltage protection?
This schematic and bill of materials in the PDF file below shows a simple solution to suppressing too much Voltage from a human power generator. This happens when an over excited rider decides to go crazy on the generator system at a speed that is excessive. When using pedal power bike generator it is often necessary to use this type of circuit to protect a 12V light bulb from being blown. The 300 Watt 12 ohm power resistor in the bill of materials is adjustable and can be kept from over heating by installing a fan next to it.
What are the calculations regarding charging a 12V battery?
Some people like to store their energy into a potable battery powerpack. A typical battery size for a powerpack is something near the 25 Amp Hour range. Amp hours is different than “Watt Hours” because the unit of measurement is in “Current” or “Amp” instead of “Watts” . Amp hours can be converted to Watt Hours if you use the Voltage rating on the battery which is typically 12V DC. Amps X Volts = Watts so in an ideal world you could say that a battery with a 25 Amp hour rating can put out 25A x 12V = 300 Watts during a one hour period.
Below is a graph showing Watt hours. The green line on the chart below shows you the output of the belt drive pedal power generator system. The red line represents the Amps of current flowing into a battery and is associated with right axis on the chart in red font. The data was captured by the WattsVIEW power monitor. In this demonstration the person riding the MNS Power generator system started pedaling at about 3:07 PM and stopped at around 4:30 PM. The peak current during the time period shown was about 12.5 Amps. You can see that the average current during this time was about 5.5 Amps. So if you had a 25 Amp hour battery then the time required to fully charge it from being completely dead would be calculated by dividing 25 AH / 5.5 Amps = 4.5 hours.
Can I get more energy out of my system by using two generators instead of one, or by using a flywheel, or using a bigger generator or higher gears?
The human body is limited too how much energy it can put out, no matter how you setup your generator system, the human body can only put out an average of 100 to 150 Watts during a one hour period. Putting a bigger generator on your system does not give you the ability to generate more energy. It may make your system a few percentage points more efficient like from 94% efficiency to 95% efficiency (Where efficiency is calculated by power out of the system divided by power into the system.)
We were recently asked to analyze a a pedal power system that an inventor had claimed would allow a person to generate well over 1,000 Watts of power. He had a fly wheel on the system and TWO generators. Dozens of investors had dumped in hundreds of thousands of dollars into this invention. The results of testing the system out by measuring current to the battery bank showed that this inventor had made a huge mistake in his claims. He had made two mistakes:
- He had assumed that because his generator was rated for 1,000 Watts output that meant that a person could automatically put out 1,000 Watts on a bike generator
- He had assumed that putting two of these on a pedal power system would automatically double his output to 2,000 Watts .
The rating on a generator or PMA (Permanent magnet alternator) simply states the max rated power output of the unit. There is no free lunch.
Some people have tried adding a fly wheel to the system to store the energy. This does nothing to increase power output. It simply stores your energy represented by the formula for kinetic energy stored in a rotating body which is
Note: The inertia is calculated by taking the mass of the flywheel in kg and multiplying it by the square of the radius of the flywheel. And angular velocity is in radians per second. But you don’t need to be a scientist to understand all this. Just know that a fly wheel stores energy. IT DOES NOT INCREASE IT. So when you see the many misleading web pages on the internet claiming that fly wheels will increase energy output beware.
How can I build a DIY light bulb display that turns on while being powered by a bike generator system?