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Old 14th Jul 2022, 11:44 am   #8
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 4,961
Default Re: Old coil switch thing

Yes, definitely a Ruhmkorff induction coil.

I think they may have been used in school science lessons, perhaps in the 1930s.

I went to an inner city secondary school in Nottingham from 1950 - '54.

All of the text books and equipment were pre-war cast-offs from the Grammar School. I recall the science teacher demonstrating a Ruhmkorff induction coil, in part, to to explain how an induction coil is used to create a spark to ignite compressed gases in the 'Otto cycle' of a four stroke internal combustion engine. The underside of the coil was stamped 'Mundella Grammar School', so I guess it dated from the 1930s.

I picked a Ruhmkorff coil up from the NVCF in 2015 for a couple of pounds.

It needs re-wiring and a new base, which I've never got round to making.

It does work, and boy does it tingle if you're minded to hold the output terminals!

Some pics attached, and a diagram showing how - when the trembler vibrates and induces a stream of low voltage pulses in the iron cored primary coil - that in turn induces a much higher spiky voltage in the induction coil, which appears at terminal marked 'G'. (Fully explained in the Wiki article linked in the previous post).

It would have had two metal tubes about 15mm diameter, and 7.5cms long connected by wires to the terminals. A party trick was for several people in a circle to hold hands and the end two to hold the tubes, causing the current to flow through the group. Didn't take long before someone let go!
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