Failure to Work.
The following are the commonest causes of coils not working to their best limit: Contact breaker contacts dirty, burned, stuck, too small, not in good parallel relation face to face of platinum.
Secondary wires crossed outside coil, often happens that the secondary is quietly sparking away into or through some object touching it, particularly when long wire connections are run from secondary to place of desired sparking.
Condenser too small, burned out, badly insulated (see other pages on this subject).
Battery too small—too high internal resistance or wires leading from battery to coil too small—for ordinary coil work, distance of, perhaps, ten feet, use No. 10 to 12 B & S flexible lamp cord or solid wire. Ruhmkorff coils require plenty of current to produce large sparks.
| Dimensions for Different Spark Lengths. | |||||
|---|---|---|---|---|---|
| ½ inch | 1 inch | 2 inches | 6 inches | 12 inches | |
| Foil sheets | 5½ × 4 | 6 × 4 | 6 × 6 | 10 × 5 | 12 × 8 |
| Number | 40 | 40 | 60 | 60 | 60 |
| Paper sheets | 6½ × 5 | 9 × 5 | 8½ × 7 | 12 × 7 | 14 × 10 |
| Number | 60 | 60 | 80 | 80 | 80 |
| Core length | 5 | 7 | 9 | 12 | 19 |
| Core diameter | ⅝ | ¾ | 1″ | 1⅛ | 1½ |
| Primary size B & S | 16 | 14 | 14 | 12 | 10 |
| Secondary size B & S. | 36 | 36 | 36 | 36 | 38 |
| Core wire size B W G. | 22 | 22 | 22 | 22 | 22 |
| Quantity in pounds of secondary wire | ¾ | 1¼ | 2½ | 7 | 12 |
| Layers of primary | 3 | 3 | 2 | 2 | 2 |
| Area of paper, sq. in. | 2,000 | 2,700 | 4,800 | 6,600 | 11,000 |
| Area of foil, sq. in. | 880 | 960 | 2,100 | 3,000 | 5,760 |
As it is not always convenient to procure paper and foil in set sizes, the area of material needed for condensers is also given. The above table is approximate. It represents data collected from the best modern practice. The gauge above given for copper wire is that of Brown & Sharpe, and is used throughout these pages.