I’d like to get a little house cleaning out of way concerning a couple of formulas in the May 2000 issue. As you may remember the article concerned the balance of energies in the front spring. The formulas got messed up in the translation; they should have looked like this:

Ut = Ufs + Urs + Uor
or Ut = _kfsyfs + _krsyrs + _koryor

That’s out of the way, I feel better now.

Are your trays still stowed and your seats in their upright position? I sure as hell hope so…and by the way, this may be a good time to grab the little white bag from the seatback in front of you, just in case.

In the last issue I talked about looking at the coils in a tattoo machine as components in an electronic circuit. This issue we’re going to look at the circuit as a whole.

Here a tattoo machine is represented as a schematic diagram and it looks something like this:



This schematic illustrates a standard form of a parallel inductor/capacitor tuned circuit. The current flow through this circuit is inversely related to the impedance (Z) of the circuit:
I = E/Z

Where I is the current, E is the voltage and Z is the impedance. Some of you might recognize this as a variation of Ohm’s Law (E = IR) and it is. The difference in the two equations is; where R (resistance) is not frequency dependant, Z (impedance) is, meaning the resistance changes with frequency. We need to see if our tattoo machines respond to the opening and closing of the contact point.

Since we are dealing with a tuned circuit we need to make sure our frequency operating range doesn’t trigger additional resistance. We can find the range where we might find trouble like this:



Where L is measured in microhenrys, C measured in picofarads and f is the frequency in kHz. The numbers associated with tattoo machines are: L equals about 4 microhenrys and C equals 2.2 x 107 picofarads (22mf). That gives us a frequency of about 17 kHz. Our machines run at about 60 Hz

What does this mean? It means we only need to consider the coils in terms of DC resistance, but what an important thing it is! The coil resistance determines current flow and current flow determines how strong the magnetic field of the coils is. The other thing resistance affects is heat. Have you ever seen machines run so hot that they melt a barrier bag, or worse yet, scorch blisters on your knuckles? I have. The hotter your coils run the more energy you waste, and wasted energy is no longer available to pull the armature bar down.

Remember Ohm’s Law E=I/R? If you like your machine to run at 11 volts you can increase your coil field strength by lowering your coil resistance (which increases the current). There’s an added side effect: lowering resistance also reduces heat. You can lower resistance by reducing the number of turns or by increasing the thickness of your wire. Keeping in mind that the industry wire standard is 24 gauge, you can wrap your coils with, oh let’s say 22 or 20 gauge wire to reduce the resistance due to thickness. Since you’ve increased the thickness (increasing the current flow) try using 8 layers instead of 10. If you’re really adventurous, try 6! Winter’s right around the corner boys and girls, so there’s plenty of time to play. Experiment; find the combination that works best for you.

Another added benefit of looking at the coils as resistors is the ability to look at the effects of resistor/capacitor relationships. That discussion will move us into more familiar territory. I’ll give you a hint: How do older ignition systems work?

All of this is important because of, and you’ll always hear me say this…efficiency. A tattoo machine running at maximum efficiency is going to reduce the amount of work, not only for the machine, but also for you, and remember, the less connection we have to machine problems, the smoother our artistic delivery…reason without restraint.

Provided you haven’t used your airsickness bag, please place it in the seatback in front of you. You are now free to wander aimlessly through the confines of your mind, or the cabin, depending on what you’ve been consuming while reading this in-flight magazine. Thank you for flying Air Fowler.