Too many volts from a bike generator
I took a treadmill motor and hooked it up to an excersize bike in order to charge a 12v battery and power an audio system. Unfortunately, it worked far better than I ever hoped and is pumping out 75v at a max pedal, 45v on an easy ride. I've looked into various charge controllers, but they only charge batteries close to the input voltage, and step-down voltage changers take it directly down to 12v, too low to charge a 12v battery. Any suggestions? Thanks.