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When trying to explain electricity and electrical concepts, many times we use water and plumbing as examples. They are not exactly the same, but similar enough that most people can pick up the basic principals. Even though we can’t literally “see” electricity flowing, we have all observed water pressure and flow so it can make it a little easier to understand the basic concepts of electrical flows.
In electrical terms, Voltage is the equivalent of water pressure in a pipe. It takes some amount of pressure to create any flow of water, no pressure (or voltage), no flow. The flow of water in the pipe would be the electrical equivalent of current (or Amps). Anything that would slow down or restrict the flow of water would be the electrical equivalent of Resistance.
Ohm’s Law is a simple formula that explains the relationship between Voltage, Resistance, and Current.
It states that V=I x R or Voltage = Amps x Ohms. The symbol for current is (I) for Current Intensity. The formula is usually shown in a circle or triangle figure
This also shows how the formula can be changed around to calculate for either Voltage, Amps, or Resistance. If I ever get confused about how it works, I will draw this little diagram and remember that if I cover up the one I am trying to find with my thumb, the other two symbols showing tells me what to do to calculate the answer.
This can still be a bit confusing, so I also like to think of them as separate functions –
1. If Resistance stays the same, Amps will be directly proportional to the Voltage.
Simply stated this means for any given Resistance when the Voltage increases the Amps
increase. Makes sense right – add more water pressure (Volts) and more water gallons (Amps)
will flow. It is a direct relationship, increase the Voltage and the Amps will show a matching
2. If Voltage stays the same, Amps will be inversely proportional to the Resistance.
Simply stated this means for any given Voltage when the Resistance increases the Amps will
decrease. This also makes sense, since Resistance is trying to restrict the flow, the more the
Resistance the less the flow (Amps).
That last rule is probably the most important rule for those of us that work on cars and trucks. In the systems we work on, the Voltages are usually fixed at either 12 or 24 Volt. So, for the most part, the voltage never changes making calculations for Amps or Resistance easier. The Resistance of the component being operated will be what determines how much current (Amps) the circuit will draw. You can not force more Amps into a circuit and a component will not draw more current than it’s Resistance allows. (Unless you applied more pressure/voltage.)
Also, the component or load ideally is the only resistance in the circuit and therefore the sole factor in determining circuit amperage. In reality, however, there are tiny resistances through every connector, switch, or even section of wire, but these are normally very small and have minimal effect on the circuit current. Any excessive resistance at those connectors and wires (due to corrosion or loose connections) will have an effect on the total current that the circuit can supply the Load item and adversely affect the performance of that component.