On Mon, Mar 30, 2009 at 10:43 AM, Jeff Deutschle <oaronshoulder at gmail.com>wrote: > 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. > > Please note that I prefaced my tutorial on how to build a zapper with the words "We used to". The point of this little device is to remove moisture, primarily from the felt, by running DC current through the center pin, thereby heating it and voila moisture removed. Of course if the flange/bushing/pin happened to be in a humid environment it didn't last very long. As we discovered, the removal of said moisture is temporary(no one asked if it was successful, just how to build one) and when the moisture returns the initial problem is still there. Proving, as with most "quick fixes" it looked better on the drawing board than in actual practice. Mike -- I intend to live forever. So far, so good. Steven Wright Michael Magness Magness Piano Service 608-786-4404 www.IFixPianos.com email mike at ifixpianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090330/d81580bd/attachment.html>
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