Why Does a Circa 1905 Solenoid Have Two Different Wires?

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SUMMARY

The discussion centers on a circa 1905 solenoid used in a self-winding clock, featuring bifilar winding with two different wire gauges: 21 AWG and 26 AWG. The thicker wire is connected to the circuit, while the thinner wire forms a closed loop but is not connected to any circuit, likely serving to mitigate sparking due to self-inductance. This design choice may have been a cost-saving measure or a remnant of production testing. The solenoid operates mechanically, activating every two minutes to wind the clock.

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  • Understanding of bifilar winding techniques in electromagnet design
  • Familiarity with wire gauge specifications, specifically 21 AWG and 26 AWG
  • Knowledge of self-inductance and its effects on electrical circuits
  • Basic principles of electromagnetism and mechanical clock mechanisms
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  • Research the historical context of early 20th-century electromagnet designs
  • Explore the effects of self-inductance on circuit performance and sparking
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  • #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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