I'm using a 5V boost regulator?

to charge a cell phone battery.  BUT maximum current is 200 mA.  That's not enough current I'm assuming, right?  I need a continuous output of 5V but my students are most likely not going to get 5V from a shake charger (neodymium magnets going in and out through a coil of wire) which is why I was going to use a LM7805 but that needs 3 volts more than the output voltage.  Any suggestions??  Thank you!

frollard5 years ago
What you need>

Coil >> rectifier >> Capacitor that doubles the peak voltage attainable from the shaker >> your boost converter.

That means you can draw a max of 200mA out of the chip. You need to read up on what that boost converter does when you undercurrent it - does it still provide 5v?

The reason I say is that it will keep outputting 5v at whatever mA is willing to flow at that 5v.
mckywer (author)  frollard5 years ago
Some of my students are already able to light four LED's in series with the shake charger, but I'm afraid if I use the boost regulator it won't provide enough amperage for the cell phone batter. Do you know if 200mA would be enough to charge it? Or is the voltage most important... Thank you!
The volts are the most important thing, 200mA sounds like its one heck of a charging current, from a source that you are managing to just about extract 20mA @9V from. That's 180mW. You aren't going to magic 2400mW from it !

essentially what you want...

except, they make a good point of:
"At first we considered using a design similar to one of those shake-up flashlights and converting it so that a runner could strap it on for a run and have energy to charge their iPod or whatever device they use. The shake-up flashlight gets its energy from the interaction of the moving magnetic field of the magnet in the flashlight and the coil of wire wrapped around the tube the magnet slides through. The moving magnetic field causes electrons in the coil to move along the wire, creating an electric current. This current is then stored in a battery, which is then available to use for the flashlight bulb/LED. However, when we calculated how much energy we would be able to get from a run, we determined that it would take a 50-mile run to get enough energy to charge one AA battery. This was unreasonable so we changed our project to the bike system."