# Confused about a Millman's theorem problem

#### cranberrysky

Joined Feb 15, 2022
33

Calculate the voltage across the starter motor terminals of the “dead” car, and the current through the starter motor, while a second car is giving it a jump-start:

Regard the starter motor itself as a 0.15 Ω resistor, and disregard any resistance of the jumper cables connecting the two cars’ electrical systems together.
It's a little hard to make out the numbers, but I found another site with a clearer picture. The left battery is 10.2V, the right battery is 13.0V and the motor is 15V.

I don't understand the 15V on the starter motor. Is it even possible for it to have a greater voltage drop than either of the parallel batteries? And if it is, how do I use Millman's theorem on a component where I know the voltage, but not the resistance?

I tried just making both motors 0.15 ohms and ignoring the 15V, but I don't get the right answer.

#### MrSalts

Joined Apr 2, 2020
1,818
I think the motor on the right is supposed to be the alternator that is continuously charging the right battery at 15v.