Make: Volume 90

That is a healthy amount to apply to a transistor

(Q1) to turn on the motor. A number of different

lower-voltage NPN transistors will work. I used

a 2N3904, but a 2N2222 or ZTX450 type would

also work.

TIMING CAPACITOR

The smaller capacitor (C1) controls the depth

of discharge. Pick something in the 1µF–47µF

range. The higher the capacity, the longer the

MCP112 and transistor will stay triggered and

the deeper the discharge will be. Because

the TT motor is not ideal for a solar engine, I

maximized how long it’s discharging and used

a 47µF capacitor. In my testing, this discharges

down to less than 0.5V. If you use a lower value, it

won’t discharge ...