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Is there such a thing as an AC Battery?!
In the original page about batteries, I said that the AC battery was a mythical device... All batteries are DC. The notion of the "AC battery" was thought up some time ago by amateur radio enthusiasts just for fun. No-one has yet managed to build anything of the ilk of an AC Battery!
The point is of course that all batteries are DC. Literally, a "battery" is a "battery of cells" and each cell produces a small DC voltage.
I also added that the "Power Tube" was "a device, made by Zyra in the 1980's, not an AC battery but a 240volt battery. It's a copper tube 54 inches long with a 240volt UK 13A socket on one end. Contains 210 x 1.2volt NiCd batteries. Capable of powering AC/DC mains devices such as table lamps, electric drills, BBC Computers, etc in wild situations, this generates more normal-reality defying interest than electricity".
Note that whether it's mains voltage is not the same thing as whether it's AC or DC. Batteries are DC.
Although AC has a frequency, typically 50Hz (UK), 60Hz (USA), or 400Hz (on aircraft), DC has no frequency.
Mains can theoretically be AC or DC, but in practice it tends to be AC because of the fact that AC is easier to transform to high voltages, convey along power lines, and then transform back to reasonable voltages at the other end.
There is a device which I have seen some people describe as an "AC Battery", which is a battery voltage power supply powered from the mains. In effect it's a PSU, a battery eliminator. It's not an AC Battery!
The myth of the AC Battery has puzzled folks for a while as they've wondered how to create such a thing. It's a bit like the dream of perpetual motion, or the Unicorn.
There has been a slight development in the notion of AC Batteries in a curious scientific observation which seems to show that batteries sometimes produce some AC...
A large lead-acid accumulator battery was connected up to a resistive load, but with a loudspeaker as a ballast resistor in-line. The speaker cone deflected as expected because of the high amount of DC going through it, but there was also a strange sound coming out, a hiss like static noise on a radio.
The fact that this sound came from the battery itself shows that the battery did produce SOME AC! The experiment should be repeatable, but remember that you saw it first here at the Zyra website. (Zyra.org.uk)
The conclusion is that batteries such as lead-acid accumulators produce DC but also produce a small amount of AC. This can be manifested as white noise coming from a speaker.
Another way to think about the output of a battery is that it is, say, 12 volts DC, but not a perfectly smooth 12 volts DC. The variance is probably a few millivolts and at a surprisingly high rate of change, in the audio frequency band.
What causes the AC component of a battery? One good suggestion is that it's the bubbles on the lead plates in the acid. This would mean that batteries of different proportions would produce different frequency characteristics.
Also see battery shops