Human/Bike Powered Electric Generator
- Thread starter loki7714
- Start date
loki7714
10 W
- Joined
- May 9, 2010
- Messages
- 70
Here's the info. Or the important stuff on resistors anyway.
Some kind of resistance (not necessarily a light) must be placed in between the field coil and the battery. If the field coil is shorted directly to the battery, a very large current will flow through the field coil. With the alternator we used – the alternator from a Suzuki Maruti 800 – shorting the field coil to the battery drew over 3A. This kind of current is too high for several reasons. For one, it can damage the field coil, which may not be rated to handle such a high current. (We destroyed the field coil of one of our alternators this way.)
The second problem with a high initial current in the field coil is that it makes the rotor extremely difficult to turn. An electromotive force (emf) will oppose any change in current in the stator coil. The larger the change in current, the larger the opposing emf. If a large current is initially flowing through the field coil, even a low rotor speed will result in a large change of current in the stator coil. The opposing emf will make the alternator very difficult to turn. Once the alternator is turning, this emf will disappear; it is generated only by large changes in current, not large currents in and of themselves. However, the initial emf may be too large a force to overcome, and the alternator may never become self-sustaining.
The key is to choose the appropriate resistance to limit the initial current through the field coil. In the Maruti 800, the warning light limits the initial current to the field to 0.15A. The initial change of current in the stator coil is not large, and the emf is easily overcome. The alternator becomes self-sustaining, and the regulator then controls the current flowing to the field coil.
When the Maruti 800 starts, it initially idles at 700 rpm. The pulley ratio between the crankshaft and the alternator is 3:1. Thus, the alternator rotates at a minimum of 2100 rpm. The current in the field coil – 0.15 A – is enough to start the alternator at this particular rotational speed. If the alternator is operated at a lower rotational speed, however, a higher initial current is needed to produce enough electricity in the stator coil to start the alternator.
This, then, is the important trade-off when choosing the resistance to place in series with the field coil. Too high a resistance will limit the initial current and require a high initial rotor speed. Too low a resistance will create a very large initial emf, and require a low initial rotor speed with a great deal of torque.
Ideally, the alternator will be run at the speeds for which it was engineered (2000-10000 rpm). In our case, however, we decided we could only run the alternator at half its minimum speed. We used three 22 Ohm resistors (each rated for 10W) in parallel, and this proved enough current to get the alternator running at lower speeds. We tried running it without any resistors, but found that the emf opposing the rotor motion was too great; the whole system ground to a halt under the load. We also tried connecting the original light from the Maruti 800. The resistance in this case was too high, and the system was unable turn the alternator pulley fast enough to turn the alternator "on."
If circumstances do not allow the alternator to be operated at its minimum intended speed, take time to carefully determine what resistance should be placed in series with the field coil. Make sure the resistors are rated for the amps being drawn from the battery. Use several higher resistance resistors in parallel if the amperage exceeds the rating. Once the alternator is self-sustaining, the resistors are no longer a factor in alternator operation; no current is being drawn through this connection.
Some kind of resistance (not necessarily a light) must be placed in between the field coil and the battery. If the field coil is shorted directly to the battery, a very large current will flow through the field coil. With the alternator we used – the alternator from a Suzuki Maruti 800 – shorting the field coil to the battery drew over 3A. This kind of current is too high for several reasons. For one, it can damage the field coil, which may not be rated to handle such a high current. (We destroyed the field coil of one of our alternators this way.)
The second problem with a high initial current in the field coil is that it makes the rotor extremely difficult to turn. An electromotive force (emf) will oppose any change in current in the stator coil. The larger the change in current, the larger the opposing emf. If a large current is initially flowing through the field coil, even a low rotor speed will result in a large change of current in the stator coil. The opposing emf will make the alternator very difficult to turn. Once the alternator is turning, this emf will disappear; it is generated only by large changes in current, not large currents in and of themselves. However, the initial emf may be too large a force to overcome, and the alternator may never become self-sustaining.
The key is to choose the appropriate resistance to limit the initial current through the field coil. In the Maruti 800, the warning light limits the initial current to the field to 0.15A. The initial change of current in the stator coil is not large, and the emf is easily overcome. The alternator becomes self-sustaining, and the regulator then controls the current flowing to the field coil.
When the Maruti 800 starts, it initially idles at 700 rpm. The pulley ratio between the crankshaft and the alternator is 3:1. Thus, the alternator rotates at a minimum of 2100 rpm. The current in the field coil – 0.15 A – is enough to start the alternator at this particular rotational speed. If the alternator is operated at a lower rotational speed, however, a higher initial current is needed to produce enough electricity in the stator coil to start the alternator.
This, then, is the important trade-off when choosing the resistance to place in series with the field coil. Too high a resistance will limit the initial current and require a high initial rotor speed. Too low a resistance will create a very large initial emf, and require a low initial rotor speed with a great deal of torque.
Ideally, the alternator will be run at the speeds for which it was engineered (2000-10000 rpm). In our case, however, we decided we could only run the alternator at half its minimum speed. We used three 22 Ohm resistors (each rated for 10W) in parallel, and this proved enough current to get the alternator running at lower speeds. We tried running it without any resistors, but found that the emf opposing the rotor motion was too great; the whole system ground to a halt under the load. We also tried connecting the original light from the Maruti 800. The resistance in this case was too high, and the system was unable turn the alternator pulley fast enough to turn the alternator "on."
If circumstances do not allow the alternator to be operated at its minimum intended speed, take time to carefully determine what resistance should be placed in series with the field coil. Make sure the resistors are rated for the amps being drawn from the battery. Use several higher resistance resistors in parallel if the amperage exceeds the rating. Once the alternator is self-sustaining, the resistors are no longer a factor in alternator operation; no current is being drawn through this connection.
zap
100 W
Ahhh... I see.
I also see another problem...
Your circuit shows the resistors in series.
I also see another problem...
Your circuit shows the resistors in series.
zap
100 W
lol I'm waiting for the day when you announce that your reply is being powered by you pedaling... or making your brother pedal!?!loki7714 said:
zap
100 W
Yes. Something like this.loki7714 said:
Code:
______Ω_______
____________/______Ω________\__________
\_______Ω_______/Have a look here.
http://www.electronics-tutorials.ws/resistor/res_4.html
yopappamon
10 kW
zap said:
22 ohm resistors in parallel like this will have a circuit equiv. resistance of 7.33 ohms.
Thud
1 MW
Food for thought:
http://www.gulland.ca/homenergy/lindabike.htm
Neet project.
http://www.gulland.ca/homenergy/lindabike.htm
Neet project.
zap
100 W
Nice... now that's parallel!
Looks like you're close now.
Looks like you're close now.
loki7714
10 W
- Joined
- May 9, 2010
- Messages
- 70
yopappamon
10 kW
I see a possible problem with some of your connections. You need to bolt the case wire on, just holding it against the case with a tie wrap isn't good enough, especially at higher amps, same with the battery posts.
Also, the case wire needs to be the same size as the large battery wire.
Also, the case wire needs to be the same size as the large battery wire.
yopappamon
10 kW
Either crimp on a ring lug and bolt it down or (less desirable) wrap the wire around the bolt and tighten the nut.
Wires touching each other is fine if they are the same connection.
Wires touching each other is fine if they are the same connection.
