# How to charge two AA with hydroelectric generator?

For my Sophomore engineering class project I am making a hydroelectric generator that will need to charge two AA or smaller if not enough voltage is possible. The plan is to have my magnets spinning over the wrapped copper coils, but here's where I am stuck. I will have my two leads of the copper wire that are sanded down, but how do I go about charging the AAs form the wires? Do I have the positive copper wire go through some sort of diode then a container for the AAs that go back to the negative copper wire? Thanks in advance for the help. My engineering teacher is frustrating and says that I can go straight into the batteries which I know can't work.

5 years ago
If the magnet is spinning near a coil of wire, you will get AC from the copper wires, not DC.

You need to look at:
1. Total energy input to the water stream -- minus losses will be the resultant charge power.
2. Rectifier and DC smoothing - convert AC to DC and potentially use a capacitor to smooth out the pulsed DC if the voltage is too high for the battery
3. Regulating the voltage that goes to the batteries.  If the stream goes faster, the voltage will go up, and if its too high the batteries may be damaged.
4. Shutting off the charge current when the batteries are charged.
If you want to be clever, use an off the shelf AA charger that takes variable input - it probably does steps 2 3 and 4 all in one.  If that's beyond the scope of your assignment, maybe get one and figure out how it works.
Charles Sparkley (author)  frollard5 years ago
Alright this is exactly what I needed. My teacher also had argued with me that Ac to DC wasn't necessary but now I know what needs to be done, thanks!