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I just finished watching a Youtube video dealing with how batteries work. In the video, it said that when the battery was discharging, the direction of current flow was out the negative post and back through the positive post. During recharging, current flow reversed going into the battery through the negative post and out through the positive post. This just didn’t make sense to me. I always thought current flow during discharge was out through the positive post. Can someone set things straight for me. Thanks.
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Conventional Current:
Assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. They were wrong!Electron Flow:
Is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source.It comes down to the function of atoms.
For all intent, the proton and neutron (nucleus) are fixed and the electron is the only part of the atom that has the ability to move.It’s true that, in most cases it’s actually electrons that flow form negative to positive voltage (Some semiconductors such as PMOS transistors work on hole flow, not electron flow but that’s an exception. ) Because electrons are negatively charged, there is a negative charge flowing from lower to high voltage. Mathematically, it’s the same as defining the same current as a POSITIVE charge flowing from higher to lower voltage. When us engineers are trying to mathematically trying to model a circuit, it’s just easier to use the positive charge convention.
OK, so then if power leaves the battery from the negative post, then it must follow the chassis of the vehicle seeking a way back to the pos. terminal of the battery. That means that the whole chassis is energized so to speak with electrons and enter, say the blower motor, through its casing then back to the pos post via insulated wires. (Seems to me like a less efficient way for electrons to travel to the load than the other way around.) Thanks, for the quick lesson. It was a great revelation for me. Makes you really appreciate what’s going on under that hood.
[quote=”Gearwrench” post=178697]OK, so then if power leaves the battery from the negative post, then it must follow the chassis of the vehicle seeking a way back to the pos. terminal of the battery. That means that the whole chassis is energized so to speak with electrons and enter, say the blower motor, through its casing then back to the pos post via insulated wires. (Seems to me like a less efficient way for electrons to travel to the load than the other way around.) Thanks, for the quick lesson. It was a great revelation for me. Makes you really appreciate what’s going on under that hood.[/quote]
You are correct. Also, electrons are lazy and will take the path of least resistance back to the positive terminal of the battery.
Electrons don’t have a sense of direction, they simply are driven by a voltage (electric field). If the voltage changes direction, the current flow changes direction. Voltage is the electric force, and electrons are the carriers that react to the force and perform “electrical work”.
The electrons in the outer shell (valence) of a metal are promiscuous. They can move freely through the material, hopping from one atom to the next i with no overall change in the material. Incidentally, this is also why metals reflect light well.
In a circuit, the electrons that leave the battery from one terminal don’t necessarily flow straight through the circuit to the other terminal. The battery “pushes” some of its electrons into conductors in the circuit and “receives” some electrons that were in the metallic conductors initially. The net current flow is available to perform work – drive the blower motor or speaker, measure O2 content in the exhaust, compute fuel trim, etc.
The Brits tried to be technically correct for a few years and built cars with a “positive ground” electric system.
It was confusing for mechanics and DIY owners, so they decided to revert to the conventional negative ground system.
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