An availability of spare electronic components at my home and a project that is due next week has led me to wonder about making a Ruhmkorff coil that can produce good sparks. However, the traditional design demands a mechanical breaker circuit which I think can be easily replaced by a circuit as shown in following figure :

My Design

Is the design sufficient or do I need some adjustments to make it work with the available parts ?

These are the parts I currently have:

  1. TIP31C Transistors
  2. Diodes (UF4007)
  3. 48k Resistances

I have already wound a ~900 turn coil for the primary coil made of thin enameled copper wire. The classical design states that a capacitor is good for better performance. I don't seem to have one. Is it really necessary? If yes, what rating would you recommend.


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  • 1
    \$\begingroup\$ The TIP31C has a max. emitter-collector voltage of 100V and is completely unsuitable for what you are trying to do. For one thing you need a high voltage switching transistor, for another the coil would have to go into the collector branch, not at the emitter. Building such a coil is not easy, either. Your best bet would be a flyback transformer like they were used in old tv sets. Whatever you do, use your brain! This circuit hurts and it can severely burn you, if you are not careful. \$\endgroup\$ – CuriousOne Jun 24 '15 at 4:38
  • \$\begingroup\$ To get a good spark, you want to push a lot of current through the primary (use fewer turns of bigger wire) and many many turns on the secondary of the transformer. Voltage output is the ratio of turns from primary to secondary. So if you put a 12v pulse into a primary of 10 turns, then a secondary of 1000 turns would produce about 100x the input. (It will also produce 1/100th the input current.) Read up on the inductive kickback of transformers... without careful consideration, many driving circuits could be damaged due to this. \$\endgroup\$ – rdtsc Jun 24 '15 at 12:20
  • \$\begingroup\$ How does that circuit replace a mechanical breaker. To me it just looks like a transistor that is biased on all the time. \$\endgroup\$ – Andy aka Jun 24 '15 at 12:28
  • \$\begingroup\$ This will help instructables.com/id/super-simple-ignition-coil-drivers \$\endgroup\$ – Dirk Bruere Jun 24 '15 at 14:47

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