23-10-2015, 01:18 PM
A couple of years ago at the NVCF, a stallholder gave me an incomplete Induction Coil, though all the important bits are there, apart from a capacitor. I'd forgotten about it but have just 'unearthed it' in the workshop. At some point I'll strip it and restore it, and make a new base for it. As far as I can tell, the coils aren't open circuit. Some experimentation called for in choosing a suitable cap. I think they draw quite a lot of current, so I don't think a PP3 will be up to the task. I think it's the sort of thing that might have been used in school science classes in yesteryear. (No maker's name on it).
It looks identical to the one on offer here:
http://www.ebay.com/itm/221917946715?ssP...EBIDX%3AIT&fromMakeTrack=true
The references in this explanation refer to the diagram below:
Induction coil (Ruhmkorff coil) circuit to generate high voltages. The induction coil consists of a "primary winding" P of relatively few turns of coarse insulated wire, and a "secondary winding" S of many turns of fine wire, wrapped around an iron core M. The battery B sends a DC current through the primary winding. The interrupter A is pair of vibrating switch contacts which repeatedly breaks the primary current, creating flux changes in the coil needed to induce a high voltage in the secondary coil. The interrupter has an iron armature piece on a springy arm next to the coil's core. When the current is switched on, it creates a magnetic field in the iron core. The iron interrupter arm is attracted to the core, opening the contacts. The primary current to the core is cut off, the magnetic field collapses, and the interrupter arm springs back, closing the contacts again. The primary current turns on again, and the magnetic field attracts the arm again. This cycle repeats rapidly 20 - 40 times per second. Each time the primary current "breaks" and the magnetic field collapses, it induces a voltage in the secondary winding. Since the secondary winding has many turns, the voltage is large, large enough to cause a spark to jump across the spark gap G. Small induction coils can create a 1 - 2 inch spark (40 to 80 thousand volts), while large coils can create sparks up to 40 inches (about 1 million volts).
Capacitor:
An arc forms at the interrupter contacts at 'break' which consumes energy stored in the coil, slowing the rate of change of primary current, reducing the output voltage. To prevent this a capacitor of 0.5 to 15 μF is connected across the contacts to increase the speed of switching on 'break', producing much higher voltages. It also prevents damage to the contacts by the arc. The capacitor and primary winding together form a tuned circuit, so on break an oscillating decaying sinusoidal current flows in the primary. This induces a sinusoidal voltage in the secondary. So the high voltage output pulse at each break actually consists of a rapidly alternating series of positive and negative pulses (left) which decay rapidly to zero, each pulse causing a separate spark between the output electrodes.
https://www.youtube.com/watch?v=1C4lOAPBu7A
Interesting old book (published 1901) entitled “Induction coils : how to make, use, and repair them”, including Ruhmkorff, Tesla, and medical coils, Roentgen radiography, wireless telegraphy, and practical information on primary and secondary battery:
https://ia700707.us.archive.org/12/items...00schn.pdf
Hope that might be of interest to someone.
It looks identical to the one on offer here:
http://www.ebay.com/itm/221917946715?ssP...EBIDX%3AIT&fromMakeTrack=true
The references in this explanation refer to the diagram below:
Induction coil (Ruhmkorff coil) circuit to generate high voltages. The induction coil consists of a "primary winding" P of relatively few turns of coarse insulated wire, and a "secondary winding" S of many turns of fine wire, wrapped around an iron core M. The battery B sends a DC current through the primary winding. The interrupter A is pair of vibrating switch contacts which repeatedly breaks the primary current, creating flux changes in the coil needed to induce a high voltage in the secondary coil. The interrupter has an iron armature piece on a springy arm next to the coil's core. When the current is switched on, it creates a magnetic field in the iron core. The iron interrupter arm is attracted to the core, opening the contacts. The primary current to the core is cut off, the magnetic field collapses, and the interrupter arm springs back, closing the contacts again. The primary current turns on again, and the magnetic field attracts the arm again. This cycle repeats rapidly 20 - 40 times per second. Each time the primary current "breaks" and the magnetic field collapses, it induces a voltage in the secondary winding. Since the secondary winding has many turns, the voltage is large, large enough to cause a spark to jump across the spark gap G. Small induction coils can create a 1 - 2 inch spark (40 to 80 thousand volts), while large coils can create sparks up to 40 inches (about 1 million volts).
Capacitor:
An arc forms at the interrupter contacts at 'break' which consumes energy stored in the coil, slowing the rate of change of primary current, reducing the output voltage. To prevent this a capacitor of 0.5 to 15 μF is connected across the contacts to increase the speed of switching on 'break', producing much higher voltages. It also prevents damage to the contacts by the arc. The capacitor and primary winding together form a tuned circuit, so on break an oscillating decaying sinusoidal current flows in the primary. This induces a sinusoidal voltage in the secondary. So the high voltage output pulse at each break actually consists of a rapidly alternating series of positive and negative pulses (left) which decay rapidly to zero, each pulse causing a separate spark between the output electrodes.
https://www.youtube.com/watch?v=1C4lOAPBu7A
Interesting old book (published 1901) entitled “Induction coils : how to make, use, and repair them”, including Ruhmkorff, Tesla, and medical coils, Roentgen radiography, wireless telegraphy, and practical information on primary and secondary battery:
https://ia700707.us.archive.org/12/items...00schn.pdf
Hope that might be of interest to someone.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
