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This section describes the general concepts of power we apply to power the Smart Parks Infrastructure. Many concepts we describe here will be presented in simplified form. For our users this section is more used as a quick reference. We encourage to find more extensive resources and documentation on this topic that suits your level of understanding.
We have found that a very helpful source of information is this wiki from The Stanford Center for Computer Research in Music and Acoustics (CCRMA) → https://ccrma.stanford.edu/wiki/Introduction_to_Electronics
To power any of the elements in the Smart Parks infrastructure we make use of electrical circuits and all concepts that come with it. An interconnection of electrical elements that contains a closed loop is an electrical circuit. The closed loop allows electrons to flow through the electrical elements.
We now explain how to analyze simple electrical circuits in terms of voltage, current, and resistance.
A common analogy may be used to relate these three quantities to water flow in pipes in place of electrons in wires. Imagine you have two water tanks connected from the bottoms by a pipe (such as the drain of a double sink). If one tank is full of water and the other one nearly empty we know intuitively that the water in the full tank will flow through the pipe into the nearly empty tank. Current (I) is analogous to the quantity of water flowing through a pipe at a given moment in time.
When we are working with electric power within the Smart Parks Infrastructure we often use the Ohm's law.
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
To use this law in practice, we need to take a look at the main equation:
Consider the following circuit:
The voltage in the circuit is given as 10V from the battery and the resistance is also given as the 100 ohm resistor is the only resistive element in the circuit. So now we can compute the current in the circuit as:
Calculating the power dissipated by a circuit element is simple. Often much of this power is converted into heat, so by thinking about the power dissipated by circuit elements, you can make sure that they don't burn up or catch on fire!
Combining with Ohm's law we get two other useful forms:
Power is a measurement of the amount of work that can be done with the circuit, such as lighting a light bulb or powering a LoRaWAN gateway.
Consider a 100 Watt light bulb in your home. We know the voltage applied to the bulb is normally 110V or 220V, so we can calculate the current consumed as follows:
So you can see why using a 60 Watt light bulb is more economical. Your electric company normally charges you for your usage in Killo-Watt Hours (kWh). One kWh is the amount of energy necessary to do 1000 Watts of energy for one hour - in other words to keep 10 100W light bulbs shining for one hour.
Now consider a LoRaWAN Gateway that uses 5 Watt, that needs to be powered by a battery. For simplicity we take a 12V and a 24V battery, so we can calculated the current consumed as follows:
So you can see why using a higher voltage battery system in this circuit reduces the Current. An important difference between the example with the light bulb and the LoRaWAN gateway, is the type of current used. The light bulb example uses power from the main grid and if the type Alternating Current (AC). The LoRaWAN gateway example is using a battery to power the gateway and therefore uses Direct Current (DC). You can see that the difference does not have an impact on calculating the power and using Ohm;s law. However, the difference is very important in building circuits. Therefore, these concepts are explained in more detail below.
Explain difference in AC and DC:
Conversion between AC and DC:
We have to understand that the conversion between AC and DC always comes with the loss of power. Therefore it is wise to prevent this conversion. Especially in situations of extreme power scarcity.
If you like this topic we strongly advice you to read about the “War of the Currents”.
Working with DC electrical circuits, we often connect batteries and solar panels in different configurations called Series and Parallel. In order to understand how these configurations impact our circuit, need to look at Kirchhoff's Voltage and Kirchhoff's Current Law.
Kirchhoff's Voltage Law: The sum of the voltages around any closed circuit must be zero." An important consequence is that the voltage across each branch in a circuit is the same. This explains why the voltages across the battery and across the resistor in the above circuit are the same. Here are important consequences of Kirchhoff's Voltage Law. See if you can derive them:
Kirchhoff's Current Law: the sum of the currents entering a node must equal the sum of the currents leaving a node. This law is a consequence of the conservation of charge (electrons) in electrical networks. Here are some important consequences of Kirchhoff's Current Law. See if you can derive them:
The best way to show the impact of these laws onto our installations is to consider the following two examples:
To estimate the power consumption for parts of the Smart Parks Infrastructure, one need to look at the individual elements. We will provide a list of known power consumption per device for the purpose of helping to design an adequate power setup. The given numbers are not very precise and are more based on our own experience, but should be enough to serve the purpose.
Example total power consumption:
For this example we will try to estimate the total power consumption of a remote and solar powered LoRaWAN site with two Point-to-Point links.
The total power consumption for this LoRaWAN site is estimated at 27W → @24hours = 648 Wh per day
Lithium-Ion battery packs:
Portable Battery packs:
Example 1 : Europe - The Netherlands
Example 2 : Africa - Botswana