Filed under: Solar Education. Tagged as: basic electrical concepts, basic solar, current, resistance, voltage.
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In previous posts, such as my solar powered pond pump pages, I’ve tried to pass on hands-on knowledge of how to build solar circuits. However, I rely on a common foundation of electrical concepts such as voltage, current, resistance, etc. I assume that my readers are familiar with these concepts, but this is not always a valid assumption. This post covers some basic electrical concepts that need to be understood by anyone wanting to work with electrical solar circuits. Each definition below includes links you can follow to get more information on that topic.
Charge, abbreviated ‘Q’ is a specific quantity of electrons. Specifically, Q = 6.25 x 10^18 electrons, which is one Coulomb. This measurement does not rely on time. For instance, one cubic centimeter of copper contains 13,622 Coulombs or 13,622 Q of free electrons.
Current is a measure of the flow of electrons. It does depend on time and is expressed as Amps, abbreviated as ‘I’. Specifically, one amp is equal to a flow of one Coulomb of electrons per second.
(Coulombs / seconds)
Closely related to the concept of Charge and Current is Amp-Hours, which is a common way of rating batteries.
If you’re good with math, you might note an interesting detail. If you multiply amps (Q/t) by time (t), the ‘t’s cancel and you left with Q, or Charge. So, mathematically, amp-hour and charge are the same thing. Why use two different terms to describe the same thing?
Theoretically Charge and Amp-Hours work out to be the same quantity, but in reality, a batteries ability to deliver charge is time dependent. You get many more Coulombs of charge out of a battery over a long period than then you’ll be able to get over a short period. This is because the battery needs time for it to change potential chemical energy to electrical energy. This is why amp-hours are used to describe battery capacity rather than charge.
The simplest analogy to describe voltage is water pressure. If you imagine that the electrons are like water, then voltage is the analogous to water pressure. If there is no pressure, then there is no flow, and hence no current. Charge may still exist, but no amperage exists because those electrons aren’t moving.
Extending the water analogy, resistance would be similar to the size of the hose. More water can flow through a large hose than a small one. Similarly, current can flow more easily through a bigger wire than a smaller one. Small hoses and small wires both have more resistance.
Measuring Voltage, Resistance, and Current
In a nutshell, electricity comes down to three things: Voltage, Current, and Resistance. Things like ‘charge’ and ‘amp-hours’ are different ways of expressing these three basic concepts. In real world practice, you can measure all three of these elements of an electrical circuit with a digital multimeter (DMM). These devices go by other names such as multifunction meters, volt meters, amp-meters, ohm-meters, etc. The last three are actually different meters, but a multimeter can perform all three functions.
A multimeter is a bit like a swiss army knife for electronics. It’s the first tool anyone should turn to when trying to troubleshoot an electrical circuit. The good news is that they are widely available and easy to obtain.