I have built a 1987 Chevy S10 now called a Chevy E10. WAVE stands for wind assisted electric vehicle. An 8 inch squirrel cage fan is driven by the forward motion of the vehicle. The resistance is less than the radiator or blocked front end would produce. I am currently trying to monitor the RPMS of the fan. I need a minimum of 180 rpms under load to produce enough power to charge my 12 volt system. Currently the voltage only reaches 10.5 volts, not enough to do the job. I have a 12 volt input proximity sensor. I need a 12 volt single pulse tachometer, driven by a 12 volt battery to read the pulses from the fan. At 180 rpms it will produce 14.5 volts. Monitoring the RPMS will allow me to calculate the gearing necessary to overcome the torque necessary to step up the RPMS.