If I need x Watts of Power what capacity battery in AH should i use?

Answer 1

There is no direct answer for this question, as voltage and wattage measure different quantities. It's kind of like asking "how many gallons are in a foot?" Volts are a unit used to measure the electric potential between points, while watts are a measure of power consumed by a circuit.

They are related, though, as expressed by the power equation: P = V x I

where: * P is power in watts * V is the voltage across a circuit, in volts * I is the current flowing through the circuit, in amperes (amps) Thus, if a circuit has 1 volt across it, and one ampere flows through the circuit, then 1 watt of power is being used. The amount of current depends on how resistant the circuit is to the flow of electricity, and the voltage applied, according to Ohms Law: I = E / R

where R is the resistance of a circuit in Ohms A useful analogy is to compare a circuit to a Plumbing system. Let's say we apply water pressure to one end of a pipe, with a closed valve in the middle. The difference in pressure accross the valve is equivalent to voltage accross a circuit. However, with the valve closed, no water is flowing - just as no current would flow through a switch if it is turned off, and thus no wattage would be used. Opening the valve would cause water to flow through a pipe, just as turning the switch on (closing the circuit) would allow current to flow through the circuit. The current flowing through the circuit (or speed of water through the pipe) would depend on the resistance of the circuit (or the diameter of the pipe) and the voltage accross the circuit (the water pressure). The wattage used by the circuit would then be roughly equivalent to the amount of water passing through the pipe per second.