Science Notes (Mad)
04Mar09 -- Dimmer/Motor Drive Schematics (Schematics updated 05Mar09)
Here is the schematic of the Cooper Wiring Devices Model #600 lamp dimmer I used in my prototypes and which unfortunately failed after 15-30 minutes of cumulative operation. Some checking showed that the potentiometer failed and the excessive resistance reading of 12K ohms with the pot at minimum indicated that the wiper was probably burned by inductive spikes from the coil.
The failure of the potentiometer also partially explains the erratic firing of the large coil -- each zap of current damaged the potentiometer internals further.
Simply, this unit was not designed for inductive loads and there's no filtering (snubber) to handle the inductive kickback of the coil or the phase reversals that sort of load applies to the circuit.
The following schematic is a motor drive found on the internet. The original source is unknown.
The big difference here is the addition of a snubber (1uF and 100 ohm resistor) to handle the tansients produced when the coil fires.
I'll be adding the snubber to the Cooper circuit (and replacing the pot( in the near future. Then I'll give the big coil another try.
15Feb09 -- Safety Note re: High Voltage Arcs and Chemistry
An arc in free air produces ozone and oxides of nitrogen. The ozone is an irritant but the nitrogen oxides when combined with moisture in the lungs and sinuses produces nitric acid -- much more than a mere irritant!
Assure adequate ventilation when operating Jacob's Ladders and similar devices.
15Feb09 -- Jacob's Ladder: Development Continues, Prototype #2
The acquisition of a larger automotive ignition coil has allowed me to begin experimentation with a second prototype.
The larger coil creates a larger (but very unstable!) spark but capable of jumping about twice the gap of the original motorcycle coil.
The spark from the new coil also appears much hotter than the other -- Thicker, blue-white and considerably louder -- all superb attributes!
Obviously, some fine tuning will be necessary.
14Feb09 -- Jacob's Ladder: Some Notes on the Use of Ignition Coils and Lamp Dimmers
In researching the use of ignition coils to provide high voltages in Jacob's Ladders it became quite apparent that the vast majority of experimenters don't comprehend the operational differences between transformers and ignition coils: thus the preponderance of transformer-based devices.
It is also apparent that there is little understanding of the role of the lamp dimmer used to adjust the input to the primary of the ignition coil.
A transformer is essentially a linear device providing a smooth transfer of power from the primary winding to the secondary winding. Thus, an audio (or other) signal may be reproduced from one side of the transformer to the other. Variations in turn ratios between primary and secondary will then produce either a step up or step down in either voltage or current.
An ignition coil is inherently non-linear and is designed to temporarily store energy and then release it in a burst of electricity. This is accomplished by applying a DC current through the primary winding which builds a large magnetic field in in the core of the coil. When the DC is switched off, the magnetic field collapses and induces a large voltage in the secondary winding of the ignition coil.
The characteristics of the DC pulse applied to the primary of the ignition coil are critical. It must be of sufficient power and duration to saturate the core with a magnetic field, of fairly short duration to minimize the resistive heating of the coil primary winding and have sufficient off-time to allow the complete discharge of the core's magnetic field.
Electronic lamp dimmers function by varying the conduction angle of the applied AC line voltage with a variable resistor-capacitor timing circuit firing a triac. The delay between the zero crossing of the of the line voltage and the firing point of the triac determines the conduction angle, so a zero-degree delay will allow full power and a 180-degree delay will allow no power to flow.
The function of the lamp dimmer in these circuits, then, is to provide short conduction angle voltage pulses to the coil primary rather than to vary the AC line voltage applied to the coil as it would seem at first glance.
13Feb09 -- Jacob's Ladder: Prototype Diagram
A full-size diagram of the prototype Jacob's Ladder I constructed can be copied from my PhotoBucket account:
http://i279.photobucket.com/albums/kk128/jimmyj900/Steam%20And%20Mad%20Science/Jacobs_Ladder_Gill_Coil.jpg
NOTE: This is a prototype device and no safety provisions were included for builders, operators or innocent bystanders.
Lethal voltages are present at every point in the circuit and I'm not responsible for any accidents or injuries due to your stupiditity or ignorance.