Simple 1 Resistor Battery Charger9V Battery Charge Rate
Actual Power Supply Used
Fixed Resistor CalculationThe difference between the power supply voltage of 20 and the battery voltage of 9 is 11.Divide 11 mA by 1000 to convert to amps. This is enough information to use Ohm's Law. ; LEGEND R = Resistance E = Voltage I = Amperage P = Power I = E / R E = I * R R = E / I ; RESISTOR VALUE R = E / I R = (20  9) / ( 11 / 1000) R = 11 / 0.011 R = 1000 Ohms ; SHORT CIRCUIT CURRENT I = E / R I = 20 / 1000 I = 0.020 ; SHORT CIRCUIT POWER DISSIPATION OF RESISTOR P = (E*E) / R P = 20 * 20 / 1000 P = 0.400

9 Volt Battery Charger Charge Rate Wall Warts Simple 1 Resistor Battery Charger Constant Current Battery Charger from 2 LED's and a NPN Transistor 9V Battery Charger from 2 NPN Transistors Adjustable Charge Rate Battery Charger from Op Amp 0  160 mA Adjustable Charge Rate Battery Charger Test Results 741C Cheat Sheet 

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