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continuing my PhotoBioReactor project.

Need some assistance determining not only what kind of rotary slip ring I need to use but where to get it as well.

Basic overview: I plan on oscillating a vertical shaft 360 degrees over a varied timeframe. This shaft has some aquarium lights vertically mounted to it. I need to power these lights without the cords getting tangled up, hence the idea to use a rotary slip ring to pass the electricity needed through the rotating shaft's axle housing and have a stationary cord to the base unit and an automagical electrified light pole. Of doom.

Needless to say, finding a slip ring supplier (or even someone who knows WTF I'm talking about) has been... challenging. Help?

I need the rotating joint to be able to attach to 1/2" thick transparent lexan, support at least 30 pounds of weight on it (likely need ball bearings), pass enough electric-juice through to power (at full peak power) four fluorescent 24" T8 light fixtures that suck down 120v~277v 50/60Hz each, allow a geared servo or stepper motor to effortlessly rotate the shaft, and preferably not be a pain in the arse or wallet. :P

A work-in-progress Google Sketchup shot of the light-shaft:

http://goo.gl/kVBAi

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3 Answers 3

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You didn't say how large the shaft is, but...

Thrust bearing or lazy susans can support the load. Search for those at AS&S: www.sciplus.com

Slip rings are expen$$ive. If you're oscillating, can you just use flexible cable that can wrap and unwrap around the shaft?

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  • \$\begingroup\$ Oh sorry, knew I'd forgotten something from that first post. :P The shaft dimensions are split into 3 parts due to materials and placement mounts: wooden shaft = 29" (tall) x 3 5/64" (width & depth as equilateral triangle); aluminium tube central shaft (embedded through center of wooden shaft) is currently sized for 3/8" in diameter and extends to 37" tall (2" above the top of the wooden shaft and 6" past the bottom of the wooden shaft); the light mounts are 8" at their widest diameter (including wooden shaft measurement) and 24" tall. \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 1:08
  • \$\begingroup\$ Concerning the flexible cable, I'm sure I can use this in the interim, however future plans include continuous motion in a single direction which would mean that one of the bearings needs to be able to pass the electricity through like a slip ring. I guess I could effectively build a "victorian" slip ring by use of a copper disc and copper brush, but I'd much rather use something off-the-shelf. :) Actually, the original plan was modified to an oscillating movement due to this cabling issue with the idea to allow cable movement until this issue is able to be resolved. \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 2:13
  • \$\begingroup\$ This, is awesome. \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 2:41
  • \$\begingroup\$ Found some thrust bearings that look like they'll do the job, however now I need to figure out how to build the support to fit the application... it looks like I'll need to use bushings to connect it. Any suggestions for the parts/method to connect these bits? \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 6:00
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Can you arrange a stationary vertical lights and rotate mirrors / slits around them?

If you absolutely must use a slip ring, look at the brushes and commutator of a DC motor for ideas. Or just save up a little money and buy a Mercotac connector (mercury inside, not RoHS). Or save up a big pile of money and buy a slip ring connector.

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  • \$\begingroup\$ Unfortunately rotating mirrors wouldn't work for the reactor. Yeah I would prefer not to have to part with a tonne of money for this one function... I've considered using Revolving Christmas Tree stands, oscillating tower fans, etc. So far haven't found a way to do this (revolving christmas tree stands don't push enough power their their slip ring). \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 1:00
  • \$\begingroup\$ I like these Mercotac connectors, however because this bioreactor is growing microalgae (spirulina and chlorella) to be within regulations for human consumption I'll need to check if these mercury filled connectors are an option. If not, I'll built my own slip ring using bearings as per the above posted link. :) \$\endgroup\$
    – Daerk
    Commented Apr 8, 2011 at 5:58
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A couple of thoughts.

  1. Do you absolutely need to use fluorescent lamps? At about 20W each that's a lot of current to pass through slip rings (not to mention being at line voltage.) Can you use LED instead, maybe 12V strips? That would be safer.

  2. Rather than use a slip ring, would it be feasible to have a single contact at each end of your shaft?

  3. If your light column oscillates, could you use a coiled wire like a steering wheel does? Then you don't need a slip ring.

That said, slip rings generally aren't designed to take a lot of thrust or side loading (at least, not the inexpensive ones.) You'll need to deal with that in the fixture separately.

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