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VS. |
 More efficient and quieter in most cases. |
NOISE
In my experience using a belt seems to be much quieter than the tire roller combination. Quietness is especially important when you are teaching kids in a class environment or trying to enjoy watching a movie when generating pedal power to your television.
EFFICIENCY
The belt / pulley method also seems to be more efficient than a roller at higher wattages. Think about it from the standpoint that you want to transfer a tremendous amount of energy from the wheel of your bicycle to your generator. When a belt is wrapped around a bike rim like the photo above on the right, it has much more surface area to grab and drive the generator. However the rubber tire / roller combination as shown in the photo on the left only offers you a small sliver of surface area for the mechanical energy to transfer from the wheel to the generator. It can get hot, which means you are loosing energy due to friction.
SAFETY
One last consideration is that the belt pulley or chain gear method is more dangerous for toddlers to get their fingers in to. Roller is the safest. Although the bike already has a chain and gear combination which is very dangerous for toddlers. So the point is probably mute.
When looking over fractional horse power DC permanent magnet (PM) motors, one will notice that there are many flavors of them. Voltages ratings vary from 12V to 180Volts DC. Current ratings also vary quite a bit. Here are some key points to consider when trying to select the best voltage / current / horsepower ratings for the DC PM to be used on your DIY pedal power bicycle generator.
OPERATING VOLTAGE
You must decide what the desired output voltage from your bike generator should be. Let's assume you are going to have it run in the region of 12Volts DC. You may ask why size the bike generator for 12 Volts DC? Because 12 Volts DC is common in the United States for powering TV, Computer, Laptop, LCD, through an inverter. 12 Volts DC is also in the range of where you will be able to charge a lead acid AGM Deep cycle battery for an alternative energy power backup system for your home.
MAX POWER OUTPUT LEVEL, NOMINAL POWER OUTPUT LEVEL
The next parameter to determine is the desired maximum sustainable power output from your pedal power bike generator. Typically an adult in great shape can peak at 300 to 400 Watts in short "Sprints" or bursts of speed. Also for a long 60 minute bike ride a person in great shape can average 100- 150 Watts of power. So in this case the max power would be 400 Watts, and the nominal operating power would be 150 Watts. (Always assume the worst case or higher rating to reduce risk to person or property).
CALCULATE MAX and NOMINAL CURRENT RATINGS
Once you have decided on the voltage and wattage of our bike generator system, you can now calculate the current requirements of your DC PM Motor / generator. Consider the formula for Watts:
Volts X Amps = Watts Taking this into account, you can solve for Amps:
Watts / Volts = Amps
So using the assumptions from above,
Max Current is 400W / 12 Volts = 33.3 Amps
Nominal operating current is 150 Watts / 12 Volts = 12.2 Amps
Now that you have your current ratings calculated you have established the most important parameter in selecting your DC PM magnet motor to be used as a generator. The danger of choosing a DC PM Motor that is rated for less current than you will have flowing through it is that it will over heat as explained in this section of the FAQ- click HERE.
THE VOLTAGE RATING
Assume you are choosing between two DC permanent magnet motors on eBay that you have determined will handle enough armature current to give you 150 Watts of pedal power energy with the following ratings:
| Voltage | Amps |
Horse Power |
Cost |
|
| Motor A | 180 DC | 4.5 | 1/5 | $90 |
| Motor B | 12 DC | 14 | 1/5 | $90 |
A common misconception is that you you have to buy a PM motor rated for the same voltage that you want to operate at. This is false. So which one is the best? The answer lies in knowing three things:
-
The operating voltage of your generator system
-
The average power you will be putting out of your bicycle generator
-
And how many revolutions per minute (RPMs) you can spin the PM motor generator at.
-
The resistance of the armature inside the motor.
The chart below shows theoretical data based on the bicycle generator being driven at a fixed speed of 2,000 RPMs. This is not real data from actual motors just theoretical data from a software program called LabVIEW. Real data will be posted once I have test results done in the next couple of months.
What this data shows you is the theoretical load line or voltage droop when you increase the Wattage output or "load" for your DI bicycle generator. Assume you do an experiment with two types of PM motors. The experiment consists of pedaling the generator at a constant velocity of 2,000 RPMs while wired to fifteen 10 Watt Car Head lights through individual switches.
The data below shows you the theoretical voltage output of the DC PM motor rated for 180 Volts (White Line), and the DC PM Motor Generator rated for 12 Volts (Red Line) as each of 15 theoretical car head lights is turned on. With no head lights turned on, the 180 Volt DC PM motor puts out 36 Volts, much more than the 12 Volt DC PM magnet motor's 14 Volts. However, after about the 10th head light is switched on and the Wattage load reaches about 100 Watts, you can see that the 12 Volt DC motor puts out more voltage than the 180 Volt PM Motor - Generator.
So in summary, using the PM motor rated for 180 volts at lighter Wattage loads will require you to put in less speed than the other motor, but at the same time will be some what harder to pedal. The opposite is true for higher Wattages where the 12 Volt DC permanent magnet motor is the better choice for loads over 100 Watts because you will pedal at a lower speed then 180 Volt PM motor.
Perhaps a better way to look at this is to look at a comparison plot of how fast you would have to pedal for each PM Motor to maintain a constant 12 Volt output while varying the Wattage Load from 0 to 150. The graph below shows this simulated data.
By looking at this graph, you can see that at little or no Wattage load, you will have to pedal much faster on the 12 Volt Rated PM Motor than on the 180 Volt PM rated Motor. But at ~ 30 Watts, the tables turn and both bicycle generator PM motors will have about the same output at 1,700 RPMs. Note that at loads higher than 30 Watts you will need to pedal faster with the 180 Volt PM motor.
So again, the conclusion is the PM Motor rated at 180 Volts DC is better for small loads, like a 5 Inch television that kids can power with a smaller bike using a voltage regulator / charge controller. But for Wattage Loads in the higher range, the PM motor rated for 12 Volts is better.
How Much Money Can I earn from pedal power kW-hours?
Assume your power company charges you $0.10 per kW-Hour. This means that it would cost you 10 Cents to run a 1000 Watt projector for one hour while watching a movie in your living room.
Now assume that you wanted to run that same movie projector by bike pedal power generator. You would need 10 adults in good shape. Each one would average about 100 Watts. So 10 People all at once pedaling for an hour would earn a total of $0.10 (Each of the ten bikers could split the money and walk away with a penny). So the bottom line in this example is you can earn about $0.01 U.S. Dollars per hour using a pedal power generator.
Now the other scenario is if you are in a 3rd world country where there is no infrastructure to deliver power to your town. Assume it would cost more than a Million Dollars to pay for power lines and power poles to be installed along a path to bring your town power. What would a kW-Hour be worth then? Much more than $0.10 per kW hour !! It would cost $50,000 to setup 1,000 bicycle generators which is much cheaper than paying over 1 Million Dollars to bring in power lines.
Continuing with this small village scenario, you would have to pay the inhabitants of the village to work in shifts pedaling the 1,000 bikes while hooked up to deep cycle batteries). This would provide people with many jobs in the village!
FYI- Solar panels would cost 40 times than bicycle generators to implement. Part of that reasoning is that solar panels do not work at night time, so you would have to setup twice the wattage capacity as you would need to setup when using bicycle generators.
What happens if I exceed the current rating of the permanent magnet DC motor - generator?
To understand this concept, you must first understand how a bread toaster works. Heat is created from wire coils from inside of your toaster when they are hooked up to the power outlet.
The wire heating element coils have a certain resistance, usually around 10 Ohms. When you push the button down on your toaster it connects the 120 Volts of electricity to your wire heating element coils as shown in the basic toaster schematic diagram above. So the amount of heat generated is calculated by Ohms law and the formula for power.
OHMS LAW: V=IR (Volts = Amps X Ohms), Watts = VI = I2R = V2/R
Dissipated toaster power is calculated by the formula:
Watts = Voltage X Voltage / Resistance = V2/R
In this case it would be (120 X 120 / 10) = 1,440 Watts
The amount of current going through the heater coil elements is calculated by the formula:
Amps = Volts / Ohms = V/R
In this toaster case it would be 120 / 10 = 12 Amps
The DC Permanent Magnet Motor has a component inside of it just like a toaster called an armature which is shown in the pictures below. The voltage rating of the DC PM motor tells you how many Amps the armature can handle before it burns up. For example, if you run your bike generator at 12V volts and you are using a DC permanent magnet motor with a current rating of 10 Amps, then your armature is dissipating 120 Watts of power (using Watts = Volts X Amps). If you pedal faster and make your DC permanent magnet motor put out more current and power, then your armature may be handling 12 Amps of power, which could over heat and permanently damage or fry your Armature / DC PM motor.
How do I measure power generated by a bicycle generator?
The formula for power is POWER = VOLTAGE X AMPs. Below are voltage and amperage charts / graphs of actual pedal power bike generators setup at a school science night. These graphs came from a LabVIEW power monitoring software program that I wrote. If you want to see a video clip of these great event, take a look at this Youtube video. (http://www.youtube.com/watch?v=QM8W76nGc0o)
If you want to measure DC power you may want to to use the
Astro Flight Digital Watt Volt Meter
 |
Price: $52.00 (Click here for order information).
Maximum Voltage 60 volts |
Can I charge deep cycle lead acid / car battery with a bike generator?
Yes, a permanent magnet DC motor used as a pedal power bicycle generator can charge lead acid deep cycle / car batteries through a charge controller as shown in the diagram below.
One
of the cheaper solutions you can try and use is the Xantrex C35 charge
controller. It costs about $107.00 (Click
HERE
The Xantrex C35 owner's manual is very explicit on how to setup your battery system. See page 47 of this manual. A wind turbine is shown in the diagram schematic on this page which is equivalent to a bicycle generator.
The C35 is also used as a LVD which is a "low voltage drop out". This is very important to a battery backup power system that uses lead acid batteries. The reason why is that you could be able to make your batteries last one to two years longer if you keep them from fully discharging. The LVD cuts the power to your inverter when it determines that the batteries are 50to 70% depleted. You decide how low you want the batteries to get before they are protected by the LVD. The C35 owner's manual explains how you can set you LVD limit.
So you would need two of these Xantrex C35s to implement the human powered energy / backup power system shown above. One as a charge controller and one as a LVD.
The diversion load is a set of water heater elements. They act as a safeguard against situations where the person pedaling on the bicycle generator is going to fast. They actually a braking system. If you are pedaling too fast and over charging your batteries, then the charge controller will start "braking" and slowing you down by diverting some of your energy to the water heater elements. You will actually feel your bike generator get harder to pedal! See Xantrex charge controller owner's manual for more information on the diversion load. Here are some parts that could work with this system.
Major parts to look at ordering for a 400Watt system.
| Description | Model | Manufacturer | QTY | Unit Price | Order Link |
| Charge Controller | C35 | Xantrex | 1 | $109 | Click
HERE |
| Heating Elements | #9000253 | Reliance | 5 | $12.00 | Click HERE |
| Deep cycle batteries | AGM 12V 55AH | Power Star | 1 | $82.00 | Click HERE |
| LVD | C35 | Xantrex | 1 | $109 | Click
HERE |
| 12VDC to 120V Ac Inverter | Xpower Plus 700 Watt | Xantrex | 1 | $43.47 | Click HERE |
How efficient is the human body at producing power on a bike generator?
Typically the average person is able to run about 25% efficiency. This means that for every Watt produced by a bike generator, the person doing the pedaling is putting out 4 Watts. So if you are pedaling to provide to your laptop computer at 80 Watts, you body is really running at 240 Watts.
How do I convert Watts to Calories burned?
First keep in mind that Watts and Calories are two different units of measurement that can't be directly converted back and forth. However if you use Watt- Hours instead of just "Watts" you then have a way to convert to calories. Here are the steps:
-
Convert Watt-Hours to Watt-Seconds (Joules)
-
Then convert Joules to Calories
-
Then adjust Calories with human body efficiency factor
So for this example let's assume that you provide pedal power to a 100 Watt television for one hour. Since one Joule is equal to one Watts X Seconds you perform dimensional analysis and get:
100Watt-hours X (3600 seconds / 1 Hour) = 360,000 J
Now use the conversion factor: 1 cal = 4.184 J to convert Joules to Calories
360,000 J / 4.184 = 86,042 Calories
When you look at the label of Oreo cookies or other food items at teh store, the term "Calories" is realy (kili-Calories). So you divide by 1000 to get 86 Calories.
Assuming that your body is about 25% efficient when cycling you divide by .25:
Calories burned running a 100 Watt Television for 1 hour = 86 / 0.25 = 344 which is about equivalent to one piece of PIZZA!
Here is the conversion graph showing Watt-Hours to Calories:
Why use a permanent magnet DC motor as a generator?
DC permanent magnet motors are
readily available on surplus web sites, thrift stores, garage sales, and old
cars. Here is a Leeson 14 AMP
DC Motor
which is very much suited to be a generator.
Click here to see more information about this DC motor/ generator. The interesting thing about using these motors is that most of them create DC power that can easily be fed into an AC inverter so you can power up your television or computer with it.
Ho many watts can a typical person put out?
There is no rock solid data for this answer, but from my experience, someone above 12 years old, and rarely exercises can generate power up to about 50 Watts for about 20 minutes. On the other hand, professional bike riders can put out 300 to 500 Watts for an hour. Results will vary with age and agility.
Why run your power through an AC inverter?
AC inverters have built in voltage input protection that allows for safe operation of your AC powered item. Let's say you are trying to run a 12Volt TV That comes with an AC adapter. You would have two ways you could power that TV with your DC pedal power bike generator.
First you could hook up your pedal power bicycle generator directly to your 12V Television TV. The problem is that your TV might blow up in smoke if you provide it with 10 Volts or 14 volts. So it would be very hard to give the 12VDC TV Exactly what it wants.
It would be much safer for you to supply bicycle generator power to your TV through the AC inverter as shown here because as soon as your bicycle generator is not providing 12V, the AC Inverter will alarm and you will know that you need to pedal faster or slow down because you are pedaling too fast.
How can I store the energy that I produce?
If you want to store the energy that you produce the easiest most efficient way is to use a car battery or even cheaper a yard vehicle battery which cost $17.00 at your local Walmart. This battery will store incredibly large amounts of energy. If you setup LED lighting for your house - you can run it from the 12V battery. Or if you want to power your computer with a 12V Car battery you can hook it up to an AC inverter which will convert 12Volts DC to 110 Volts AC.
How do I pick out the size of my fuses and wire for my generator elecrical system?
Let me first start by saying the standard disclaimer stuff that you are responsible for following electrical guidelines established in your part of the world. In the U.S. you must comply with the national electrical code (NEC). Attention should be given to Articles 310, 392, 400-5 (flexible cords), and 501-4 Class I, II and III, Divisions 1 and 2 hazardous locations. Remember to use the "Ampacity Correction Factors" when the Ambient Temperature is different than those indicated in the Tables. Also, derating is required when using more than three conductors in a Raceway or Cable. You need to have a certified electrician or automotive mechanic look at your wiring to make sure you didn't do something dangerous.
With that said, a typical person generating power at 12 volts will get a max current of about 10 Amps. This is calculated by assuming a case where a fit adult person can average 120 Watts over a 10 minute period. Using the formula Watts = Volts X amps you can solve for Amps = Watts / Volts = 10 Amps. Now double that value to make sure you have chosen a safe current limit. When you look up the wire size requirement for 20 Amps in free air at 60 Degrees C you will note that a size 12 AWG wire is well suited for this rating. Play it safe and pay $5.00 more in wire and get something that will not warm up when you supply current through it from your bicycle generator. Your fuse should be rated for the same rating as your wire. You can buy inline fuse holders from you local automotive pats store. They are cheap! Here are some more very conservative ampacity ratings, ones that are used for very confided spaces like when your wire is inside of a metal conduit pipe and there is no free air to cool the wire down. It's best to plan for the unexpected and select a wire size one or two sizes bigger than you really need, and select a fuse size as small as you can use without blowing it. It is a matter of life and death - fires can be started and burn down your home.
NOTE: The American Wire Gauge sizing system is counter intuitive! You may thing that a bigger size is better for carrying more current, but you are wrong! It is the opposite.
|
Gauge |
Amps |
| 6 | 65 |
| 8 | 40 |
| 10 | 30 |
| 12 | 20 |
| 14 | 15 |
|
What is an inrush / surge current spike? When you turn something on, there is often a large spike in current as shown in the waveform plot graph chart below.
If you are turning on a motor or something that has a lot of capacitance you will see this type of behavior of the current. A motor like a kitchen blender or electric weed eater takes a couple of seconds to spin up. During that time the resistance of the motor changes from being very low to high. When the resistance is low, the motor requires or "draws" more current then it's typical nominal operating current.
When there is a big surge in current, you may see a dip in the voltage being supplied by the voltage source. This is sometimes called voltage droop or "the IR drop".
Typically voltage droop is very bad in a system, it can cause problems in the case of supplying voltage to an AC inverter. The AC inverter has a built in protection circuit that turns the inverter off if it sees a voltage less then 11V DC. So if you have TV hooked up to the inverter that has a big inrush current spike, the voltage will droop and the inverter will turn itself off by going into protection mode.
You can minimize voltage droop by having large wires or cables and good solid connections with a lot of surface area. An example of a bad connection is aligator clips. These have only a tiny bit of surface area contact with a wire so the resistance of that connection is very high.
What does the power look like during a current spike? Since Power is calculated by multiplying current times the voltage or : P = IV
We can take the product of the red line and the blue line and get the current which is the green line. In this example, the power spike goes above 1000 Watts. Which is normal for a blender, or electric weed eater, or a table saw. After the 1 or two seconds the power settles down to the nominal operating power which is based on the nominal operating current (I) & (V)
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What should I know about pedaling speed when delivering
power to a 12 volt DC television running at 15 Watts?
Hello. My name is Rachel and I'm a sophomore in high school. For science fair my group and i are building a bicycle powered television. We are connecting an alternator to a 15 watt television. I'm confused on how exactly this works out. We wanted to change the gear ration between the bike wheel and the alternator and the mph that the person pedals. When we talked with my dad, he said that this wouldn't work because the wheel speed has to be constant. I thought that if we had a mph measuring device and roughly three different gear ratios we could determine how fast a person would have to pedal with each different gear ratio to generate the same voltage. My dad said something about how we need wattage, not voltage. I thought that if we just had to determine the voltage??? So, then my dad brought up the idea that we could measure RPM per watts for each different BIKE gear. (not the gear ratio between the bike and the generator.) This would give us a certain RPM for a person to maintain on each gear. I just would like to know your thoughts and advice. Thank you very much!
Rachel Rachel, You can power up your 15 Watt television but you have to watch a volt meter carefully and pedal at just the right speed so your voltage stays within the operating range of your DC powered television. You need to look at the owner's manual for your T.V. and look at the specifications to find out what the min and max voltages are for your T.V. Typically a D.C. voltage television will run in a range of 11 to 13 volts. If some one gets on your bike and peals too fast, or too slow, they could easily fry your t.v. or as some say in the industry "let the smoke out of it".
If you take a look at this video clip you will see a D.C direct current permanent magnet (PM) bike generator hooked up to a volt meter and to a television through an inverter. When you see the video clip, you will notice that the volt meter is jumping around between 10 volts and 13 volts. This is because it is difficult to pedal at a precise speed to keep the bicycle generator output constant at 12 Volts. But it can be done very carefully. The inverter in this video clip (the orange box in between the volt meter and the T.V. ) makes a beeping noise every time the voltage is not between 11 volts and 13.5 volts. It is giving a warning to let you know that your voltage is out of range.
If you wanted to help make the voltage coming from your D.C. bicycle generator, then you could add a capacitor to it, but it is expensive. Click here to look at a typical capacitor you could use.
To summarize, here are your options and considerations:
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