Chapter 2: The Basics of DC Electricity

DC or “Direct Current” Electricity is the continuous flow of electrons from an area of negative charges to an area of positive charges. If you were to consider powering a 12v DC lightbulb with a car battery and jumper cables, the “power” would flow out of the negative battery terminal, through the the lightbulb, and finally back into the positive terminal.

What is a “DC Circuit”?
The most simple requirements of a DC circuit are a “power supply” and a “load”. We actually just described the most basic of DC circuits when we talked about lighting a lightbulb with a battery. A DC circuit simply requires a closed loop of wire, from the negative terminal of the power source, to the negative terminal of the load; and, from the positive terminal of the load, back to the positive terminal of the power supply. This is known as a “closed circuit”.

If one of the wires between any of the terminals in the circuit were removed, the flow of electrons would stop and the circuit would be considered an “open circuit”. Congratulations, you now know how a “switch” works! Switches simply open or close The contact terminals, controlling whether or not the load is powered.

What is a “Power Supply”?
In a DC circuit, the most commonly known power supplies are the 12v Car Battery, and the AA, AAA, C, D, 18650, etc. cell batteries. For the purposes of this blog, most of our examples will use 12v Deep-Cycle Batteries, but the concepts remain the same.

Additionally, wall power supplies are often used to convert 110v AC home-based electricity down to 12v/5v DC in order to power computers, phone chargers, etc. All of these are examples of suitable DC power supplies, as long as the supplied voltage matches the requirements of the components. In Chapter X we will dive deeper into batteries for off-grid purposes!

What is a “load”?
The “load” is any electronically powered device or component that consumes power from the power source. Examples include: LEDs, fans (electric motor), a USB charger, etc.,  are all considered to be loads. The loads are powered by the electrons flowing from the negative terminal to the positive terminal of the power supply.

Calculating Watts, Amps, & Volts
In upcoming chapters, we will be designing various aspects of solar powered electrical systems and will therefor need to understand a few simple concepts. Calculating Watts, Amps, and Voltage is very simple. Generally, when you are trying to calculate one of these values, you already know the other two. To calculate, we look to “PIE”

P = Power = Watts = Volts x Amps
I = Current = Amps = Watts / Volts
E = Voltage = Volts = Watts / Amps

Ohm’s Law
To calculate the amount of electricity moving through a wire, or other conductor, depends on the voltage (V), current (I) and resistance (R) of the circuit. Voltage is potential energy, current is the amount of electrons flowing through the wire, and resistance is the friction force on the electron flow. Ohm’s law explains the relationship between these 3 variables and how they effect each other.

“The Garden Hose”
A good way to understand Ohm’s Law and to understand the relationship between voltage, current and resistance is to think of the flow of water through a hose…Bear with me, this is the best method I’ve seen. I’ll be referencing the image above in the following paragraphs.

The hose is like our wire from the battery to the load. Instead of water flowing through the hose, we have electrons flowing through our wires. We can think of our power supply’s voltage in terms of a garden hose’s water pressure as psi. The higher the voltage, the stronger the attraction of negatively charged electrons to the positive terminal of the power supply. As you can see in the image above, this correlates to “Volt” trying to push “Amp” through the wire. Higher voltage is easier to transmit over long distances.

The same way we think of the flow of water in terms of gallons per minute, we imagine the flow of electrons through our wire. The amount of electrons flowing through the wire at a given time is known as the amperage, or Amps.

Finally, we have resistance, or Ohms. Ohms are easy to understand, its “friction” in the hose, or some kind of restricted path, or kink in the line. In the image above, we can see that “Ohm” has tied a rope around the hose and is making it difficult for “Amp” to pass through. ”Volt” will push as hard as he can do get “Amp” through, but “Ohm” is making it dif. Electrons will always attempt to take “the path of least resistance”.

On to Chapter 2!
With these foundations I feel we’re ready to take the next step and take a look at our next topic, Chapter 2: The Basics of AC Electricity

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