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Basic Electrical Concepts

by Chris - June 24th, 2011.
Filed under: Solar Education. Tagged as: , , , , .

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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.

Electrical Charge

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.

Electrical Current

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.
Mathematically:

$I = Q/t$
(Coulombs / seconds)

Amp-Hours

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.

Voltage

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.

Resistance

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.