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Electrical/Electronics Basics

 

Capacity (Capacitors and batteries)

So, while section 1 is all as clear as water, lets get into a couple more items. If we know the city is going to shut off our water for a couple of hours to do repairs, we can fill up a bucket with water to use during the outage. That's exactly what we can do with batteries and capacitors when it comes to electricity. Those two devices store electricity for us to use later when we need it.

So, what's with the two devices that do the same thing and have different ways of measuring their size? Well, they may do the same thing, but they do it in a very different way.

Lets start with a capacitor (also called a condenser in some circles). It quite literally stores electrons on a metal plate just as a bucket would actually hold liquid water. With a bucket of water, we would measure its size in gallons; with a capacitor we measure its size in units called Farads. You will usually see these stated as micro-farads or even pico-farads; because a Farad is very large - more like a swimming pool than a bucket.

So, why do batteries have a different name and different measuring units? We could say its more of those engineers wanting to remain magical; but there is actually a decent explanation.

Batteries do not really store electrons like capacitors do. Think in terms of turning our water into ice; charging a battery actually makes a chemical inside it (different chemical with different types of batteries - see related page here). Then, when we use electricity from our battery, the chemical it created while charging chemically breaks back down to the original chemical; actually re-making the electricity in the process.

Because batteries are not really storing electricity directly, we don't use Farads to measure them. Instead, we rate them in terms of how much electricity they can produce before they are drained. For that, we go back to one of the three building blocks we started out with - amperage. We state it in terms of how fast electricity can flow and for how long; resulting in the term Ah or Amp-Hours. For example, a battery that could supply 1 amp of current flow for one hour would be rated 1 Ah. If it could supply 2 amps for an hour, it would be rated 2 Ah.

Resistance (Resistors and kinks)

The concept of resistance was pretty well covered in section 1; but lets revisit it in respect to where you will find resistance in real life circuits. As I said in section 1, sometimes a kink in the hose helps us change the nozzle and sometimes it stops us from filling a bucket.

The truth is, in real world circuits, there is some degree of resistance everywhere. By nature, every part of a circuit has resistance. Just as putting several hoses together lengthwise will give you a bit less water flow(adds resistance in the form of friction to the water), adding length to wiring will reduce electrical flow thru it. You may have encountered this when using a long or undersized extension cord and noticed something didn't work as well as it does plugged directly to the wall. So, that's one place we find resistance but we really don't find it helpful.

Another place we might find quite a bit of resistance is in a bad connection. This can come from corroded contacts, loose fitting contacts, and bad(referred to as cold) solder joints just to name a few. Sometimes these can cause resistance that is so high, our device ceases to work. This extreme is commonly called an open circuit, because there isn't a continuous, unobstructed pathway for the electricity.

By design, we may add a specific amount of resistance to slow down current flow or reduce a voltage level. Usually, we do that with a device aptly called a resistor. As was stated in section 1, we measure resistance in ohms; and that will be the primary specification for a resistor. To properly select a resistor, we would also need to make sure it can handle the amount of power we will be asking it to - and that is determined by its wattage rating. Typical board level resistors are 1/4 watt and 1/2 watt; but there are many options. In most cases, we only need to make sure it can handle at least as much as our circuit requires - using a higher watt rating will not usually matter.

Another common use for resistance is to generate heat. A device made for that purpose is called a heating element; and common examples include electric stove burners and the glowing wires in electric space heaters. While ohms law does still apply to these, the resistance changes with temperature so you can't apply it directly. For now, I'm going to say that math is beyond the intended scope of this article. Also, because of the more complex math, you will commonly find these devices specified by their wattage (how much heat they produce) at some intended use voltage level.

Short Circuits

A commonly used (and misused!) term is the ubiquitous 'short circuit'. Yep, it kind of bugs me when I hear it misused; so let me explain what one really is.

A true short circuit is a conductive pathway that bypasses our resistance - in other words the electricity is taking a short cut. In the water analogy, it would be a leak. Typical cases might be worn insulation allowing two wires to touch each other or perhaps water or a foreign object making a bridge between two parts of a circuit. Normally, a short circuit will allow an excessive amount of current to flow.

Some failures that are not considered short circuits are broken wires or bad connections. As was said above, these are really open circuits(think clogged up or kinked hose). An open circuit is actually the opposite of a short circuit, because the electricity has no pathway at all rather than a shorter, easier pathway to the other wire.

In the next section, I will take much of what was covered thus far and explain some safety implications of what we just learned .. so I strongly encourage everyone to read it as well.

Back to Section 1

Continue to Section 3