**Understanding a Basic Electric Circuit**

In an electric circuit there are a few important terms to learn about. These are voltage, current, power, Work and Resistance.

**Voltage:**measured in Volts and is the potential or pressure in a electric circuit that pushes the electrons around the circuit.**Current:**measured in Amps and is the rate of flow of electric charge through a wire or circuit component.**Resistance:**measured in Ohms and is the opposition to the flow of electric current.**Power:**measured in Watts and is a measure of the amount of work that can be performed in a given amount of time.**Work:**described in terms of lifting a weight against gravity. the higher the weight is lifter the more work has been done.

**The Water Analogy**

An electric circuit can be understood using a simple analogy to compare electricity to water flowing through a pipe.

Voltage can be compared to water pressure a pipe. The amount of water flowing through this pipe is comparable to the flow of electric current. Just like water if there is no pressure then there won't be any flow.

Resistance can be compared to the diameter of the pipe. The larger the pipe the more water can flow. This is the same for electrical wires the larger the wire the more current can flow.

#### Putting It All Together

Electric circuits always have voltage, 120V or 240V for households and 12v or 24v for DC circuits. This voltage normally doesn't change much unless large electric loads are connected. The resistance of the device you connect to your circuit determines the amount of current that will flow. When you have both voltage and current flowing in your circuit you will use power to perform work.

If nothing is plugged in the resistance will be infinite and no current will flow through a circuit. If no current flows no work is performed and thus no power is used. When a short circuit occurs the opposite situation happens, a very low resistance is present and this causes a large current to flow through a circuit. This can overload wires and cause insulation to melt or burn out complete circuits. This is why fuses and circuit breakers are used as they can protect people and property in the event of a short circuit.

High current circuits will need thick copper wiring. The electrons flow in the copper so the thicker the copper the more electrons can flow.

For high voltage circuits you will need thicker plastic insulation around the copper. Just like you need a thick walled pipe to keep lots of pressure from bursting out.

**Making Basic Calculations Using Ohms Law**

With some simple math's we can calculate all the values we usually need for simple circuits.

For example say we had a 12 volt (V) circuit and the power (P) draw of some led headlights was 140 watts we can use these values to calculate the current flowing through the wires allowing us to select an appropriate wire gauge. Current (I) = Power (P) / Voltage (V) so in this case current is equal to 140 watts divided by 12 volts which gives a current of 11.66 Amps.

It's important to keep your units consistent. eg if you use Volts, Also use Amps, Watts & Ohms. If you use Millivolts, Also Use Milliamps, Milliwatts & Milliohms.

This graphic shows all the formulas you can use to calculate Power, Resistance, Current & Voltage in simple circuits. If you have any two variables you can calculate the others. We have created automatic calculators you can use at the links below.

How many days should I charge a 20 watts solar panel to a 100 amps battery

Hi Benedict

It depends on many factors. And requires extra details for accurate calculation. However below is a proposed estimation based on making some assumptions about your set-up.

Assuming a 100 amp hour battery at 12 volts that is 1200 watt hours of total charge.

Assuming a efficiency of 75٪ for the solar panel given the various solar conditions and charging losses. That gives you 15 watts per hour of sunlight.

That results in 1200/15 = 80hrs to charge the battery or approx 10 days with 8 hours of good sunlight each day.