Our last few blog posts have dealt with the importance of good grounding in the electrical system. Now let's talk about some commonly used and misunderstood terminology (or should I be punny and say terminal-ology?).
#8. What is meant by the circuit “load”?
The term “load” is used in two ways. First it can refer to the specific component(s) in a circuit that are drawing the electricity. Such as; in the dome light circuit, the dome light bulb would be the load. It is the component that has the main resistance and that does the work in the circuit. Load can also refer to the specific amount of amperage which that component draws.
#9. You use the word “draw”. What do you mean by that?
The battery and alternator don’t send electricity anywhere. The electricity is there, available for use whenever a circuit is completed (the switch is closed) and a load component in that circuit calls for, or draws the electric current. And every load draws a different current (amperage) based upon its own internal resistance.
For example, let’s imagine having a fresh, charged car battery on our work bench. First let’s connect a high beam headlight to the battery...we get light! Lots of light! And it draws amperage. Not too much, not too little, but exactly what the headlight needs to do its job. We disconnect the headlight and instead connect a tiny little 12 volt LED dash indicator light to the battery. Guess what...we get light! Less light, of course, and drawing a lot less amperage, too. Not too much, not too little, but exactly what the LED light needs to do its job. Now, some people scratch their heads about now wondering why, if the battery has enough power to make the headlight shine that bright, why didn’t it burn out that little LED?
The reason is that the battery only sends (or can only send) the amount of current that the component draws based upon its internal resistance. The headlight calls for 8 amps and the battery is glad to oblige. The LED calls for just 2/100th’s of an amp and the battery is equally happy to meet that need. No more, no less. The internal resistance of the LED is much higher than that of the headlight. In my example the effective resistance of the LED would be about 600 Ohms compared to 1.5 Ohms for the headlight.
#10. O.K. They draw different amperage because they have different internal resistance, but why is that true?
Because they were designed that way based upon the job that they need to do on your cars 12 volt dc system. It’s important to realize that electrical parts; lamps, motors, switches, even the wire, have been designed to do a specific job with a specific result on their own circuit. That headlight, for instance, has a lot more light to put out - more work to be done - than the little dash LED, so it needs more amperage to do its job. If you start changing that circuit in any way, you need to consider the impact upon everything else in that circuit, and even the whole car.
#11. Can you give me an example for what you mean by that?
Gladly. We all want to be able to see, and be seen as well at night as possible. So lots of people are changing their headlights to a higher wattage bulb that puts out more light. More light means more work, more amperage being drawn by the bulbs. The new bulbs are designed for that, but what about the old headlight switch, dimmer switch, connections and wire that were designed for the old bulbs? Are they able to handle the extra amperage without being damaged, getting hot or even “burning up”. Whenever we make one change to an existing electrical circuit, we need to consider the effect upon everything else in that circuit.
Steve Watson, Watson's StreetWorks, http://www.watsons-streetworks.com
man i lovethis blog and electrical issues. some may remember the "electronics specialist" that used to work on our police car radio systems that i wrote about before. he once sent a car down to me because the alternator was causing his fuses to blow on the police equipment. he said there was too much output. when i explained that couldnt happen as amperage is pulled not pushed he had to proven wrong. we ended up fixing the problem when we found one of his 50 amp circuit wires pinched under the rear seat. because of this when things were tuned on there was so much resistance(not dead short) that it caused the breaker to blow. the explanation of voltage drop from the from to rear of the car because of the pinch(and too small of wire) went way over his head. of course this is the guy that also said adding a second 100 watt speaker to the 100 watt siren amp made it a 200 watt output. but thats a whole nother topic.
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