Auto Battery Output

The existence of internal resistance in an auto battery limits the output power. The effect can be very drastic on a low resistance load like a starter. Its effect on an intermediate resistance load like the headlights is less pronounced, and you may not even detect a problem in the operation of high resistance loads like a radio. Change resistances or battery voltage to explore their effects.

The values for battery voltage, load resistance, and internal resistance may be changed in the exploratory calculation below. Default values will be entered for any one of those values left unspecified, typical of the battery example, but any of those values may be changed.

For a battery voltage of VB = volts and a load resistance of Rload =Ω
the power delivered to the load by an ideal battery would be Pload = watts.
However, in the real world, a battery always has some internal resistance.
If the internal resistance is Rinternal = Ω ,
the total current is I = A
and the total power produced by the battery is P = watts.
But the situation for the load is even worse than that,
because Pinternal heat = watts is wasted in internal heat in the battery.
So the final power which gets delivered to the load is Pload = watts,
down to just % of what you would get with an ideal battery.

DC Circuits

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