One suggestion that is not meant as criticism - is there an EE program at school? See if you can get them involved. I realize that may be easier said than done. Once you get done with school you'll likely be part of a team that will include all sorts of people with many different skills. No better time than the present to learn how to collaborate.
What you might do is read up on the charging requirements for batteries. You will find that by controlling voltage, limiting current, monitoring temperature, etc etc that battery life and efficiency can be optimized - all of that is kind of at one end of the spectrum. You'll also come to learn - and others have suggested it here - that many batteries or cells are quite tolerant of abuse. They might not last quite as long as if treated perfectly but they still last long enough.
Now - you will need to apply at least slightly more voltage to the battery terminals than exists at the terminals for a given state of charge - in order for the current to flow into the battery. Kind of like putting air in a tire (tyre) - unless the pressure from the filling hose is higher than what's in the tire - no air will flow in.
The really great thing about your situation is that you can model or predict many things that will aid you in the design of your system. You may come to learn that a complex switching power supply is useful - or an exotic embellishment that's more trouble than it's worth.
What you can do right off is determine what the generator will do at various RPMs. There will be points where the output is sufficient to charge the battery and other times when it is not. Those "points" might be in terms of voltage or power.
In terms of voltage - lets say you have a generator capable of 13 volts maximum under some light load - and your system battery is 12 volts. A very crude look tells us that you'll only be able to charge the battery when the generator or dynamo is at or near maximum RPM. Clearly unless you are going fast you'll not charge the battery. If you switched to a 6 volt battery you can run at a lower RPM and still charge the battery with a simple system. The generator/battery combination may be such that the battery voltage will not rise to harmful levels - those little generators can only do so much.
We haven't touched power - volts times amps - watts. With switching circuits we can take a 6 volt generator output and boost it to 13 volts quite easily to charge a 12 volt battery - in fact your circuit could convert a fairly low voltage to 13 volts so the generator could be turning slowly and you'd still get something out of it. The problem - the power available at any given moment, at lower RPMs may be measurable but may not be sufficient to be useful in your situation.
If I were given this assignment I'd put the generator on a fixture that would allow you to measure the output at various conditions. That is relatively easy to do though you could get quite involved with it by varying the load. You might start with the simple rectifier and put it across a battery - monitor the battery voltage and current to see where it begins to charge, how high the voltage rises - etc. You'll have a good sense of what the dynamo can do.
Then - apply an estimate of RPMs and time to what you know about the generator - so you understand the potential power available to charge the battery. If much of the time your model of speed is such that the battery will be charging you may decide that the power available when it is not charging - is just not worth going after with exotic charging systems - or maybe it is.
I think I've given you a start - there is much more but well within your grasp in my opinion.
What you might do is read up on the charging requirements for batteries. You will find that by controlling voltage, limiting current, monitoring temperature, etc etc that battery life and efficiency can be optimized - all of that is kind of at one end of the spectrum. You'll also come to learn - and others have suggested it here - that many batteries or cells are quite tolerant of abuse. They might not last quite as long as if treated perfectly but they still last long enough.
Now - you will need to apply at least slightly more voltage to the battery terminals than exists at the terminals for a given state of charge - in order for the current to flow into the battery. Kind of like putting air in a tire (tyre) - unless the pressure from the filling hose is higher than what's in the tire - no air will flow in.
The really great thing about your situation is that you can model or predict many things that will aid you in the design of your system. You may come to learn that a complex switching power supply is useful - or an exotic embellishment that's more trouble than it's worth.
What you can do right off is determine what the generator will do at various RPMs. There will be points where the output is sufficient to charge the battery and other times when it is not. Those "points" might be in terms of voltage or power.
In terms of voltage - lets say you have a generator capable of 13 volts maximum under some light load - and your system battery is 12 volts. A very crude look tells us that you'll only be able to charge the battery when the generator or dynamo is at or near maximum RPM. Clearly unless you are going fast you'll not charge the battery. If you switched to a 6 volt battery you can run at a lower RPM and still charge the battery with a simple system. The generator/battery combination may be such that the battery voltage will not rise to harmful levels - those little generators can only do so much.
We haven't touched power - volts times amps - watts. With switching circuits we can take a 6 volt generator output and boost it to 13 volts quite easily to charge a 12 volt battery - in fact your circuit could convert a fairly low voltage to 13 volts so the generator could be turning slowly and you'd still get something out of it. The problem - the power available at any given moment, at lower RPMs may be measurable but may not be sufficient to be useful in your situation.
If I were given this assignment I'd put the generator on a fixture that would allow you to measure the output at various conditions. That is relatively easy to do though you could get quite involved with it by varying the load. You might start with the simple rectifier and put it across a battery - monitor the battery voltage and current to see where it begins to charge, how high the voltage rises - etc. You'll have a good sense of what the dynamo can do.
Then - apply an estimate of RPMs and time to what you know about the generator - so you understand the potential power available to charge the battery. If much of the time your model of speed is such that the battery will be charging you may decide that the power available when it is not charging - is just not worth going after with exotic charging systems - or maybe it is.
I think I've given you a start - there is much more but well within your grasp in my opinion.
Or are you going to use the dynamo with some machines?? Maybe adding an LM317 won't increase the cost so much?
