UNIVERSITY OF MASSACHUSETTS DARTMOUTH
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
ECE 201
CIRCUIT THEORY I
PRACTICE PROBLEM – ALTERNATOR
An automobile alternator with an internal resistance of 0.2 Ω develops an open circuit
voltage of 16.0 Volts. The storage battery has an internal resistance of 0.1 Ω and an
open circuit voltage of 12.8 Volts. Both sources are connected in parallel to a 1.0 Ω
load. Determine the alternator current, the battery current, and the current in the load.
The circuit diagram is shown below.
Is the battery supplying current to the load, or is the battery being charged? Give your
reasoning.
Use the Node – Voltage Method
V1
v1  16 v1  12.8 v1

 0
0.2
0.1
1
v1  16  2v1  25.6  0.2v1  0
3.2v1  41.6
v1  13V
V1 =13V
Ialternator
Ibattery
I alternator 
Iload
16  13V
0.2
 15 A
13V
 13 A
1
13  12.8V  2 A
I battery 
0.1
I load 
The current in the battery is in the direction to charge the battery.