Home-Made Slip Ring Connector

October 16, 2008

I built a slip ring connector for a rotating fluorescent light fixture that I have been working on. I did a bunch of research on fluorescent tube lights for this project.

I was encouraged by this tutorial on MakeZine. Although there are some serious issues with this design, all seems to be working correctly at this point. It is a bit risky putting the ballast on the wall-side of the assembly because it means that the slip rings has to transfer a much higher voltage to the bulb. This increases the risk of sparks, shorts and other unfriendly occurrences.

Although there is already an amazing piece that utilizes this same mechanism, I am still intrigued by it and excited to see if I can make one. Lozano-Hemmer’s Piece

Fluorescent Tubes and Ballasts

In order to light up, a fluorescent light fixture needs a ballast. When the bulb first lights, a spark is generated through its center – from one end to the other. The conditions inside the bulb are such that there is almost no electrical resistance (unlike a phosphorescent bulb, which heats up a lot from the resistance). The ballast functions as an inductor, both moderating the free flow of electricity through the bulb, and also ramping up the voltage to start the bulb. In order to create the arc (or the long spark from end to end), the bulb is supplied with initial voltage spike of several hundred volts. The high voltage spark (much like a static shock), is able to bridge the air and conduct between the two poles. The arc excites the gaseous mercury in the tube, which then emits ultraviolet light, causing the phosphorescent coating on the inside of the bulb to flu0resce. The chain reaction lasts, even as the voltage drops back down to 120 again.

One more interesting tid-bit from Wikipedia:
“Electronic ballasts are often based on the SMPS topology, first rectifying the input power and then chopping it at a high frequency. Advanced electronic ballasts may allow dimming via pulse-width modulation and remote control and monitoring via networks such as LonWorks, DALI, DMX-512, DSI or simple analog control using a 0-10V DC brightness control signal.”

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