Why Does a Circa 1905 Solenoid Have Two Different Wires?

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Discussion Overview

The discussion revolves around a circa 1905 solenoid used as an electromagnet in a self-winding clock. Participants explore the characteristics of the solenoid, which features two different gauges of copper wire wound in layers, with only one wire connected to the circuit. The conversation delves into potential reasons for this design choice, including electrical effects and manufacturing practices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the solenoid may be a bifilar wound coil, with the second winding left unconnected intentionally.
  • Others propose that the unused winding could serve a purpose in production testing or be intended for another application, though this remains speculative.
  • A participant mentions the possibility of the second coil inhibiting hysteresis loss in the main coil, although it is not connected directly to the circuit.
  • One participant notes the resistance ratio between the two wire gauges, suggesting implications for current and voltage in the circuit.
  • Another participant raises a concern about the effect of adding a shorted turn to a coil, questioning whether there is any impedance present in the second coil.
  • Some participants discuss the historical context of the technology, referencing the era's limitations in electronic components.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the purpose of the second wire and the design of the solenoid. No consensus is reached on the exact reasoning behind its configuration.

Contextual Notes

Participants acknowledge that the solenoid's design may reflect manufacturing practices of the time, with some suggesting that the coils might have been sourced from different manufacturers. The discussion also highlights the lack of detailed documentation from that era, complicating definitive conclusions.

  • #31
In post #28 you show pair of back-to-back Zener diodes on an AC supply. You also show data for a MOV = metal oxide varistor.
Since you have a DC supply you only requires one power diode to suppress the flyback arc.

A single diode would keep the current flowing for longer after the contacts open because the reverse voltage across the coil would be less than with a MOV or the Zeners. Just make sure the diode and battery polarity are correct so it does not normally conduct.

The shorted coil would waste energy while turning on and extend the field while turning off. If you disconnected or removed the shorted coil, the single diode would go some way to compensating for the removal of the shorted coil.
 
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  • #32
Perhaps it is to get rid of DC flux when driven by a directly connected (non-capacitive) connection? One would use a serial capacitor now as a DC block, but I imagine wire was cheaper than capacitors in those days.
 

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