Electric Vehicle Basics
Assume in the following circuit we have a 12V battery and the resistance across the motor when running without a load is 40 ohms.
- How much current, in mA, will flow through the motor?
- What is the power, in watts, dissipated by the motor?
- If the motor ran for 10 minutes under the above conditions, what is the minimum battery capacity in mAh?
Hint
$$$Power=voltage \times current$$$
Hint 2
Ohm's Law
$$$V=iR$$$
where
$$V$$
is the voltage,
$$i$$
is the current, and
$$R$$
is the resistance.
To solve for the current, use Ohm's law:
$$$V=IR$$$
where
$$V$$
is the voltage,
$$I$$
is the current, and
$$R$$
is the resistance.
$$$I=\frac{V}{R}=\frac{12V}{40\Omega }=0.3A=300\:mA$$$
Power absorbed by a resistive element:
$$$P=VI$$$
where
$$P$$
is power,
$$V$$
is the voltage, and
$$I$$
is the current.
Solving for power dissipated by the motor:
$$$P=12V\times 0.3A=3.6\:W$$$
To solve for capacity:
$$$300mA \times 10min \times\frac{1h}{60min}=50\:mAh$$$
Current = 300 mA
Power = 3.6 W
Capacity = 50 mAh