Paul: I have never used a zapper, so what I have written and am writing should be viewed as possibilities and not necessarily practical. You are right, a scientific constant current source would be overkill. You mention using a resistor to limit the current. Since we are dealing with AC there is a better way. It is called a “ballast” and is in a very common hosehold device with a transformer already attached. A fluorescent light ballast (which is really a transformer and ballast in one package) may be just the thing. Not sure what the required amps for zapping might be, but a transformer and ballast for a metallic vapor light may work if a fluorescent does not. Or two florescent ballasts in parallel might work, too. On Mon, Mar 30, 2009 at 11:03 AM, pmc033 at earthlink.net <pmc033 at earthlink.net> wrote: > My question is, what are we trying to accomplish with the Zapper? Are we > trying to "iron" the felt, remove moisture, "singe" the felt (smoke the > bushing), or drive out the vertigris? Even if you use two soldering irons, > that pin conducts heat very well, and you're going to heat the wood in the > birds-eye anyway. Whatever the idea, you don't want to ruin the bushing in > the process. This discussion is probably in the archives somewhere. It is > not something that should be done on a quality instrument, as the result is > usually a very loose flange pin fit. It is a down-and-dirty fix when you > don't want to, customer can't afford to, or otherwise aren't going to fix > it the right way. Do I have one? Yup. Do I use it? Yup, but I don't > expect to get 4-6 swings consistently. > Having said that, I have thought of ways to regulate the heat produced, as > suggested by Jeff. The trick is to have the timer begin when the probe and > pin are a complete circuit. It's not always easy to make the probe contact > the center pin to complete the circuit because the pin is often buried in > the bushing. A foot switch would work, with a separate circuit for the > power source and a continuity checker. You would connect the probe, and > verify the circuit was closed by using the continuity checker (a buzzer > perhaps), then press the switch. The continuity checker would then > disconnect and send power to the probe. > I've built several of these, and one problem I had using a doorbell > transformer was that the transformer has a built-in safeguard that prevents > a fire in case there's a short circuit. Guess what? The Zapper is a short > circuit device! After a few uses, the transformer gives up. What is > needed is a current limiter (resistor) in the circuit. The formula is > E=IR. If you have constant voltage (E), your current (I) will vary > inversely with the resistance (R). Another formula is for power: P=IE. > Power (P) is current times voltage. If your transformer is 12 volts, and > you have a resistor of 120 ohms, you will get 0.1 amp of current (divide 12 > by 120). Then, multiply 0.1amp times 12 volts, and you get 1.2 watts of > power. Your resistor must be able to carry 1.2 watts (most common > resistors are 1/2 watt). A potentiometer (variable resistor) in the > circuit will work to vary the power output. If you had a 12 ohm resistor, > you'd have 1 amp of current (careful here- can your transformer handle 1 > amp?), and you would have 12 watts of power (12 volts times 1 amp) and > you'd need a large resistor capable of 12 watts of power. Constructing an > electronic device with enough complexity to survive constant use is a > little more complicated than it may appear. A Zapper made of a doorbell > transformer is extremely crude. There may be some potential in a more > carefully designed circuit to accomplish one's desired purpose. Purchasing > a constant current device (such as is suggested) seems a little overboard, > but there is certainly room for further investigation and experimentation. > Now, where is my pin extractor... > > Paul McCloud KQ6FL > San Diego > -- Regards, Jeff Deutschle Please address replies to the List. Do not E-mail me privately. Thank You.
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