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Re: an interesting mechanical engineering problem

Original poster: Tom Perigrin <tip@xxxxxxxxxxxxxx>

At 08:56 PM 1/9/2007, you wrote:
Original poster: Mike <megavolts61@xxxxxxxxx>

 You can't get cheaper and simpler than some saw cuts and
electrical tape.

-Phil LaBudde
(save your time and money for the IGBT's)

Although I'm a big advocate of going cheaply as possible, I'd have a problem with the visual asthetics of this idea when spending thousands on what is a showpiece.

More than that... consider the power going through the coil. Consider what happens if those saw fingers only contact the next section of pipe at a few places, with a little copper oxide in between the two layers of copper metal, giving a resistance of 1 ohm for each joint. The current flub through a joint of 1 ohm and 10 square mm is going to be "fun". Also, as the copper heats it will oxidize even faster, giving us the sort of problem we see with a poorly fitting terminal on a car battery. Heck, I've seen that sort of problem with the poorly made plug on my Chinese Air Conditioner... after 1 year of use I unplugged it and was scared to death by the amount of carbonization evidenced around the prongs.

I'd suggest getting a plug and socket made for each joint. The plug and socket would consist of a 4" OD taper by about 12" long. These should be accurately turned to be +/- 0.001 (or better). Then, get them gold plated with at least 0.005 of 24K gold. Also, there should be a mechanism like a pipe union that snugs the joint together. Clean the joints with warm soapy water before each use, and make a protective covering for transport. That's not going to be a lot of gold..

Sound like MIL-SPEC ? Yeah, probably... but when you are working with something like this, it's better not to screw it all up by trying to save a few bucks on such a critical part.

Failing that, I liked the previous suggestion of Stainless Steel inserts... those can be wire brushed with a brass brush before assembly to assure there is no oxidized layer contributing resistance. I don't think you should use copper on copper, unless you implement a strict protocol of having each joint thoroughly cleaned and degreased before each assembly.