Electrical

Search Autoparts/Motorage/Electrical/

Ground circuits — Part 2

A look at battery electron current
Thursday, March 30, 2017 - 07:00
Print Article

Answering ground circuit questions
Following is a reader’s comment and two questions from readers. Some readers have considered similar questions and may benefit from the answers.

Motor Age Magazine Want more ? Enjoy a free subscription to Motor Age magazine to get the latest news in service repair. Click here to start you subscription today.

SAVE 20%

On Automotive Electric Training Videos , ASE study guides and more.

 

Comment: I understand there (are) two camps (describing electrical current in a circuit) - conventional flow and electron flow.

Reply: One version of electrical current has to be correct and the other is therefore incorrect. They both cannot be correct. “Electrical” current cannot flow both ways at the same time. The scientific community assures us that electrical current is the movement of negatively charged particles we call electrons. This is known as the “Electron Theory.” Electrons leave the negative terminal of the voltage source, travel through the circuit and return to the positive terminal of the same voltage source.

Think of the circuit as if it were a large diameter pipe several feet long and filled with ping-pong balls (representing electrons), all resting quietly in their place within the pipe. You have an extra ping-pong ball leftover and try to push it into the pipe to get rid of it. What happens at the other end of the pipe? All ping-pong balls become momentarily agitated and move a little so a ping-pong ball can be inserted but at the same time a ping-pong ball must pop out the opposite end to make room for the new one you just pushed into the pipe.

The pipe always contains the same number of ping-pong balls. Think of these ping-pong balls as electrons in the circuit. If an electron enters (is pushed into) the circuit at the negative terminal ("ground side") by the voltage source, all electrons in the circuit path become agitated and move so an electron leaves (is pulled out of) the circuit and enters the positive terminal of the voltage source ("voltage side"). This all happens at the same time.

Remember this very important fact of how electron current “flows.” Do not confuse electron flow with battery voltage present at the battery terminals.

If an electron leaves the negative terminal of the voltage source and enters a circuit, at the same time an electron must leave the circuit and enter the positive terminal of the same voltage source.

The number of electrons in a circuit will always remain constant.

If an electron cannot enter the circuit and an electron leave the circuit at the same time to make room for it, an electron will not leave the negative terminal and enter the circuit in the first place.

When electrons are “flowing” they move from atom to atom through the circuit. When electrons are “not flowing” they remain in orbit circling around the nucleus of an atom.

Voltage is the force (pressure) that causes electrons to “flow.”

The electron theory is essential to explain how solid-state components work, such as semiconductor (solid-state) diodes and transistors. Prior to the arrival of semiconductor components in the world of electronics beginning in the late 1950s, discussion about the direction of electrical current didn’t have to be so specific. Since semiconductor components have been introduced into the world of electronics the electron theory becomes essential to explain how solid-state components work. Solid-state theory is up for discussion somewhere down the road.

Electron flow is measured in units called "amps" and is measured with an ammeter or a current clamp. Measuring electron flow in amps has nothing to do with measuring voltage with a voltmeter. Voltage and electron current are two separate and distinct measurements taken in a circuit to evaluate circuit conditions.

Question: “….. in an electron flow circuit, why are the fuses after the load if they are intended to protect the load from excess current? In these diagrams the excess current would first have to travel through the load before the fuse would be able to do its job.”

Answer: For purposes of discussion let's say Lamp #1 draws 1.0 amp when switch S2 is CLOSED. One amp flows through all points in Lamp Circuit #1 at the same time because it is a series circuit. (The pipe is full of ping-pong balls throughout the pipe.) If we were to measure the electron current in the circuit (we will do that next in Part 3) we would find there is 1.0 amp in the ground side of the circuit, 1.0 amp is flowing through the lamp and 1.0 amp is flowing through the voltage side of the circuit at the same time.

In this circuit the fuse is placed on the voltage side of the Lamp. It could just as easily be placed on the ground side of the lamp and still protect the circuit from excessive electron current through the load. Since current is constant at all points in a series circuit (1.0 amp in this circuit) wherever the fuse is placed will monitor the circuit electron current and blow if the circuit electron current gets too high.

Most of the time the fuse is placed on the voltage side as close to the B+ source as possible. The reason for doing this is the voltage side of the circuit could become shorted to ground somewhere in the harness if a wire is pinched to ground. This would create excessive current that would burn up wiring. If the fuse were placed on the ground side of the load the high current would not flow through the fuse to blow it. So for safety reasons, the circuit fuse is high up in the voltage side of the circuit to protect the voltage side of the circuit should it become shorted to ground.

Question: In the first installment of this series you mentioned that Bat+ (+Batt ed.) was the "supply" and in this second one you mention the "battery voltage is available through fuse #2.” Why (does) this series seem to indicate that Bat + is the voltage supply but the electrons are flowing from the negative post to the positive post?

Answer: Don't confuse measuring voltage (in volts) and measuring electron current (in amps). That is easy to confuse and one of the reasons I am writing this series on ground electron current. Voltage and electron current are two distinct different values in an electrical circuit. Voltage, provided by the voltage source - the battery in Figure 2 - is stationary but electron current moves through the circuit as explained. In this series, we are focusing on the electron current produced by the voltage source, not the voltage of the voltage source. Electrons leave the negative terminal of the voltage source, flow through the circuit and return to the positive terminal of the same voltage source.

We can discuss a circuit in terms of how the circuit is connected to the voltage source. We can also discuss a circuit in terms of the path of electron flow through the circuit. Those are two separate discussions. Our discussion in this series is focusing on electron current, not the voltage. Earlier we discussed how circuits of the electrical system are connected to hot-at-all-times B+ and switched ignition B+ voltage simply for purposes of explanation. Let’s keep our attention focused on electron flow, negative to positive through the circuit. You will see a reason for this as this series of articles continues.

Article Categorization
Article Details

< Previous
Next >
blog comments powered by Disqus