5 A pulse oximeter is powered by two batteries in parallel E

5) A pulse oximeter is powered by two batteries in parallel. Each battery has a nominal voltage of 1.5 V, an internal resistance of 12, and a capacity of 1.2 A-h. The pulse oximeter can be modeled as a load resistor of 19O. Estimate how many hours will last the batteries connected in parallel to the pulse oximeter powered on. (20 pts)

Solution

Ans)

Equivalent of two batteries i.e single battery with Voltage V and internal resistance Ri from 2 batteries in parallel gives

V=1.5 V and Ri=1||1=(1*1/(1+1))=0.5 ohms and total A-h now is 2*1.2=2.4 A-h

Now the circuit is Voltage source V=1.5 V in series with two resistances Ri=0.5 ohms and RL=19 ohms

Now Load current I_L=V/(Ri+RL)=1.5/(0.5+19)=1.5/19.5=0.0769 A

I_L=0.0769 A

No of Hours batteries will last is =A-H/I_L=2.4/0.0769=31.2 hours

time it will last =31.2 hours