Why didn't this become standard?


Ad in a 1921 radio trade journal. Note the 'self-polarizing' feature. It's easy enough to see how it would be done. Leave the main relay open at startup. Use a small rectifier in each direction to detect voltage coming from the battery. Energize a crossover relay from these small rectifiers, and energize main relay only after determining the polarity. (Solid-state rectifiers were already common in 1921, even though solid-state triodes were several decades away.)

I couldn't find a patent from that era, but this 1961 patent using transistors shows the probable technique. The jaws of each clamp are electrically separate. The top jaw of each goes via a separate coaxial wire to the sensing circuit, which is thus able to do its job of energizing the relays from the battery before power is available through the relays.

Why didn't this feature become standard, even mandatory, in auto battery chargers? It would have prevented a whole lot of fires and failures. Why isn't it part of jumper cables? You wouldn't need a separate power source, just a sort of snap-switch reversing relay similar to a circuit breaker. (Come to think of it, just a plain circuit breaker in each wire would do. If it snaps, you know you were backwards.)


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Part 2, so to speak. I got curious to see if this trick was standard in Nature. The nearest analogy seemed to be nerve axons seeking dendrites to 'charge'. Do axons have separate coaxial sensor circuits to find the right 'polarity' of dendrites? (Here the 'polarity' would be more like excitatory vs inhibitory, not pos vs neg.)

Quickly found the answer. See here for nice diagram and explanation.

Axonal growth is a key mechanisms of neural circuit formation. In the developing brain, neuronal axons (and dendrites) grow out along reproducible paths via growth cones at their tips.

How do growth cones advance and navigate? Single splayed microtubules (MTs) push from the axon into the actin-rich periphery of growth cones, essentially powered by polymerisation processes at MT plus ends. Upon stabilisation, such MTs guide bulk elongation of axonal MTs, thus elongating the axon. External guidance cues influence the directionality of these events.

From other sources: These growth processes are constant and fast. Axons change shape noticeably within a minute or so.

Well, didn't really need to ask, did I? Nature is always there first. Endlessly astonishing.

Labels: Grand Blueprint

  ¶ 4:42 AM