Nuts and Volts - September 2013

September 2013 17

QUESTIONS and ANSWERS

■ FIGURE 2.

Re: Beginner’s Question, July 2013:

Someone who was completely new to electronics asked you what you would recommend to start learning. Coming from a professional, your first answer was Algebra and to continue on with Calculus. Russell, I hate math. Almost just like you, at age 13 my father bought me a "cat whisker" crystal radio kit; it worked and I was hooked. How could this tiny radio play into the night every day with no power? What were those little resistors with the pretty colored stripes? Then, for Christmas I received a RadioShack 300-in-1 Electronics Kit, and my world changed. I made myself an electronic siren, a timer, a metronome, an amplifier, and even a radio transmitter! Almost everything I know and love about electronics was self taught. It is my No. 1 hobby; today, I even design and build my own projects using integrated circuit technology. Plus, of course, Nuts & Volts is my favorite magazine!

You know what, Russell? I still hate math!

Frank Alberts III

Math is not a requisite, although lack of it may be a limitation. SPICE is a good tool to learn because it will allow you to fiddle and tweak much faster and easier than with a breadboard. I once designed a circuit that worked but which I was not competent to analyze. I designed and built an oscilloscope with scrounged parts before I went to college, so you can do a lot with common sense and high school math.

Re: Jacob's Ladder Circuit, July 2013:

You were right on in identifying the diode on the primary as a problem. However, recommending higher frequencies is probably off the mark. The problem is the turns ratio of these coils requires about 200 volts to generate adequate spark voltage. In order to get a 200 volt inductive kick, we have to interrupt a sizable current in the primary. Since the inductance of the primary limits the rise time of the current, the 12V must be connected for a reasonable time to let the current build up.

In ignition systems, this was called the dwell time which was set by the angle of rotation of the distributer during which the points made contact. These units tended to have problems at high RPM in any case, which is why capacitive discharge — or solid-state — systems became popular. These units usually incorporated a DC-DC converter to generate about 200 VDC which was then switched onto the primary instead of the 12V in the circuit in question. This provided a faster rise time and thus sufficient current to generate a hotter spark. I would thus recommend the questioner to use a LOWER frequency or use a DC-DC converter to get strong sparks. At 2,000 RPM, an eight-cylinder engine only fires a spark about 133 times per second, so 200-400 Hz would be close to what the coil is designed for.