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still trying to get my head around electron flow as opposed to conventional current regarding automotive electrical circuits. There seems to be a ton of conflicting information/advice out there so I'm hoping to seek some clarity.

Basically I'm just wondering because electrons flow from the negative side of the battery to the positive, is the vehicle's entire electrical system essentially powered from the negative (earth) side then the current returns to the battery into the positive during the battery discharge cycle?

Would this then mean during battery recharge (alternator running) that the vehicle's electrical system is essentially powered by the alternator through its earth?

I made a picture to try and demonstrate this better: enter image description here

Where I'm getting confused particularly is that I measured current flow with an amp clamp during discharge and recharge of the battery and it gave me a positive reading when the arrow was pointing in the direction of conventional current as opposed to electron flow.

There's that and the fact that a lot of people are saying electron flow goes from negative to positive but the energy goes from positive to negative, like, what energy? How is that "energy" measured?

EDIT: also regarding spark plug operation, do electrons supposedly flow backwards to the ignition coil? Very confusing.

I appreciate any help, thanks

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  • \$\begingroup\$ Conventional current flow is opposite to electrons. It is universal thing and automotive electronics are nothing special in that regard. It is difficult to understand what is the actual question? Current flows in a loop so same current flows out of battery as in, and there is no earth on alternators. \$\endgroup\$
    – Justme
    Apr 28 at 13:05
  • \$\begingroup\$ Thanks for the comment, I understand the concept of conventional current, what I'm trying to understand is how actual current flows (electron flow) in an automotive circuit. Alternators do have earths as well, they are earth by the chassis bolt. They have to have an earth, they are part of a circuit. \$\endgroup\$
    – TMax
    Apr 28 at 13:10
  • \$\begingroup\$ But electron current flow is exactly identical to conventional current flow, except for the direction. And chassis is not earth, it's just the metal frame, and metal frame can be used as a conductor for currents. Sorry but the question is still unclear, as we can't see what is your misconception so it is hard to rectify. \$\endgroup\$
    – Justme
    Apr 28 at 13:18
  • \$\begingroup\$ It's more about the mention of energy going positive to negative which I've seen mention but that doesn't seem true. I was also confused about a spark plug, I always thought the coil had a large voltage and would push electrons but if they flow the other way it doesn't seem that this is the case so I wondered how they would flow into a coil backwards? For the alternator, what I'm trying to say is that it has an input and an output for current, I just had a different way of explaining it \$\endgroup\$
    – TMax
    Apr 28 at 13:32
  • \$\begingroup\$ Energy does not go from positive to negative. Current does. And electrons flow based on voltage difference. Spark voltage can be positive or negative, as long as it sparks. Thus nothing can flow backwards, only into intended direction. \$\endgroup\$
    – Justme
    Apr 28 at 13:38

2 Answers 2

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Where I'm getting confused particularly is that I measured current flow with an amp clamp during discharge and recharge of the battery and it gave me a positive reading when the arrow was pointing in the direction of conventional current as opposed to electron flow.

That's because the clamp meter is designed to show you the direction of conventional current flow.

There's that and the fact that a lot of people are saying electron flow goes from negative to positive ...

It does

... but the energy goes from positive to negative ...

No. Positive charges, if they were mobile, would flow from positive to negative. There are no mobile positive charges in copper wires, but in electrolyte solutions and plasmas, there are plenty of positively charged mobile species that move in that direction.

... like, what energy? How is that "energy" measured?

There are several ways to measure the energy. One is to measure the voltage across a load, and the current through it. The product is the power in watts, which when multiplied by the time of a period in seconds will give you the total energy in joules transferred in that period.

You'll note the voltage is between the two wires to the load, and the current is the same in each load wire. The energy is not 'flowing' in either the positive or the negative wire, it takes both to transfer the energy.

A more general treatment of energy flow uses the Poynting Vector, which at every point in space is at right angles to the voltage difference between the wires and the magnetic field caused by the current. You can interpret this as meaning the energy flows in free space around the wires, or that it's a fiction merely to calculate the energy flow in the wires. It needs both wires however.

During battery charge or discharge, energy flows into or out of it mediated by the current in both the positive and negative wires, and the voltage difference between them. There is no special role for just one of the wires, from a physics point of view.

From an automotive and commercial point of view, the two wires are very different, as one is bolted to the chassis.

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  • \$\begingroup\$ Thanks for the detail in your answer. So the diagram I've put up there, would the be the correct path for electron flow in such a circuit under discharge and recharge? \$\endgroup\$
    – TMax
    Apr 28 at 13:13
  • \$\begingroup\$ @TMax yes except I'm not sure whether any electrons flow at all inside a battery \$\endgroup\$
    – user253751
    Apr 28 at 13:17
  • \$\begingroup\$ @TMax Yes, electrons would take the path followed by the arrows. However, very few people worry about electrons, not even engineers most of the time. The only time I worried about electrons, and I'm now retired, was during solid state physics courses. Then you have to worry about electrons, holes, Fermi levels, yada yada if you want to design semiconductors materials or the devices that use them. If you want to use electronics, or automobiles, all you need is conventional current. Electrons complicate things and add absolutely nothing, not understanding, not predictive power, totally useless. \$\endgroup\$
    – Neil_UK
    Apr 28 at 14:15
  • \$\begingroup\$ Thanks for the clarification I appreciate it \$\endgroup\$
    – TMax
    Apr 28 at 14:58
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Are vehicle electrical components powered from the negative side?

  • Power is voltage multiplied by current
  • Current leaves one side of the power source, travels through the load and, returns to the other side of the power source

In other words, both positive and negative sides of the power source are needed for current to flow.

  • Voltage is the potential difference between one side of the power source and the other side of the power source.

In other words, both positive and negative sides of the power source are needed to produce a voltage.

Hence, from the standpoint of current or voltage, both sides of the power supply power the load.

Would this then mean during battery recharge (alternator running) that the vehicle's electrical system is essentially powered by the alternator through its earth?

I prefer the term "chassis" here because a vehicle is insulated from earth by its tyres. So, chassis is just a convenient electrical conductor and that's all. The fact that it is attached to battery negative in modern cars doesn't mean it wouldn't work on a "positive chassis" system (such as early VW beetles and probably a whole lot more).

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