# Is a 12V car battery more powerful than a 12V power adapter?

1. Feb 13, 2013

### Minhtran1092

I'm confused about the relationship between the voltages of different power sources. Since a car battery is more powerful than an adapter and both are known to have output of 12 Volts, what can be said about how much power is consumed by the devices running on 12V?

Will the same amount of current flow through a simple circuit which comprises a 5kΩ Resistor if you supply 12V from a car battery and if you supply 12V from the power adapter?

2. Feb 13, 2013

### Staff: Mentor

For everyday purposes we can say that yes, the same current will flow through the circuit. If we look a little deeper into it we would see that it depends on the internal resistance of the battery and how much current your power adapter could provide at 12 volts. For example, a 12 volt power adapter plugged into a circuit with only 1 ohm of resistance would be expected to put out 12 amps of current. The power adapter may or may not be able to supply 12 amps of current, as it may be current limited.

http://en.wikipedia.org/wiki/Internal_resistance
http://en.wikipedia.org/wiki/Current_source
http://en.wikipedia.org/wiki/Current_limiting
http://data.energizer.com/PDFs/BatteryIR.pdf

3. Feb 13, 2013

### davenn

and following on from that..

whereas a car battery can supply 800A or so for brief periods when the engine is cranking over ( starting)

Dave