Dan Thomas
Touchdown! Greaser!
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Dan Thomas
The term "electron flow" implies the movement of electrons. As I was taught, the electrons jump from atom to atom, but they'll travel at a rate of maybe inches per hour in a conductor. Their effect in the conductor is immediate (speed of light or something close to it) as shown by the balls-in-a-pipe analogy. A Coulomb is about 6.24 x 10*18th electrons past a given point in a conductor in one second and represents a flow of one ampere. Sounds like a lot of electrons, but there are a lot of atoms in a conductor.
A battery's weight doesn't rise with charge. The number of electrons within it doesn't change. Every electron leaving the negative pole requires another one entering at the positive. In the typical lead-acid battery, the plates consist of lead and lead peroxide. They're immersed in sulfuric acid, and as electrons are moved along they're pushed by the reaction of the acid with the plates, with the result that the acid mostly becomes water and the plates both become lead sulfate. With the battery made of dissimilar metals and an acid, it produces electron flow. With plates of the same material immersed in water, it makes nothing. The neat thing about secondary cells like this is their rechargability; forcing electrons backwards through it turns the water back into sulfuric acid and the lead sulfate into lead and lead peroxide again. The chemistry here: http://www.green-planet-solar-energy.com/how-batteries-work.html
Sure, the specific gravity of the acid is higher than the water, which makes it heavier, but as the acid turns to water the lead picks up the weight by turning to lead sulfate.
Old and clumsy and somewhat dangerous technology that should soon disappear.
The generator typically seen on old airplanes (and in old cars) was a heavy thing that produced much less power per pound than the alternator. It does produce AC but the action of the commutator and brushes rectify it to DC. The world had to wait for compact, efficient, low-forward-resistance diodes for the alternator to produce its DC output. The old generators could "bootstrap" themselves using residual magnetism in the field pole shoes, so that if the battery was totally dead the generator (if you got the engine started somehow) would produce a small current that was fed to the field poles via the regulator and the output would rise to a useable level real quick. The alternator is not inclined to do this, because the diodes still have a breakover cutoff (or whatever the EEs call it) of a volt or so, just enough to prevent that first little bit of flow from getting to the output. This is textbook stuff, but I also learned it the hard way by once killing a battery really dead by leaving the headlights on in my truck. My elders, having grown up with generators, said "we'll just tow it and it'll start." It did not. They were used to the old generators that would pony up enough juice to get themselves going and eventually (rather quickly, actually) making enough for spark. Had to find some jumper cables.
The magneto is an AC generator. No diodes, no commutators, no brushes. The coil in it gets an alternating flow so that the spark output is also alternating, which is why we rotate the spark plugs when we clean them. A spark erodes one electrode depending on its direction, and if we leave them in the same positions for a long time they won't last as long since one electrode will wear out really quickly. Like not rotating your tires periodically.
Dan
A battery's weight doesn't rise with charge. The number of electrons within it doesn't change. Every electron leaving the negative pole requires another one entering at the positive. In the typical lead-acid battery, the plates consist of lead and lead peroxide. They're immersed in sulfuric acid, and as electrons are moved along they're pushed by the reaction of the acid with the plates, with the result that the acid mostly becomes water and the plates both become lead sulfate. With the battery made of dissimilar metals and an acid, it produces electron flow. With plates of the same material immersed in water, it makes nothing. The neat thing about secondary cells like this is their rechargability; forcing electrons backwards through it turns the water back into sulfuric acid and the lead sulfate into lead and lead peroxide again. The chemistry here: http://www.green-planet-solar-energy.com/how-batteries-work.html
Sure, the specific gravity of the acid is higher than the water, which makes it heavier, but as the acid turns to water the lead picks up the weight by turning to lead sulfate.
Old and clumsy and somewhat dangerous technology that should soon disappear.
The generator typically seen on old airplanes (and in old cars) was a heavy thing that produced much less power per pound than the alternator. It does produce AC but the action of the commutator and brushes rectify it to DC. The world had to wait for compact, efficient, low-forward-resistance diodes for the alternator to produce its DC output. The old generators could "bootstrap" themselves using residual magnetism in the field pole shoes, so that if the battery was totally dead the generator (if you got the engine started somehow) would produce a small current that was fed to the field poles via the regulator and the output would rise to a useable level real quick. The alternator is not inclined to do this, because the diodes still have a breakover cutoff (or whatever the EEs call it) of a volt or so, just enough to prevent that first little bit of flow from getting to the output. This is textbook stuff, but I also learned it the hard way by once killing a battery really dead by leaving the headlights on in my truck. My elders, having grown up with generators, said "we'll just tow it and it'll start." It did not. They were used to the old generators that would pony up enough juice to get themselves going and eventually (rather quickly, actually) making enough for spark. Had to find some jumper cables.
The magneto is an AC generator. No diodes, no commutators, no brushes. The coil in it gets an alternating flow so that the spark output is also alternating, which is why we rotate the spark plugs when we clean them. A spark erodes one electrode depending on its direction, and if we leave them in the same positions for a long time they won't last as long since one electrode will wear out really quickly. Like not rotating your tires periodically.
Dan
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. no it comes from the chemical reaction of the electrolyte and the electrodes. The battery doen't really increase pressure, if it did, you'd get an increasing voltage from it.
Isn't that exactly what happens when you charge it?
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