Slip Rings and Domed Observatory -- Continuing

Based on this one post of yours, I can see absolutely no reason why a slip-ring system would require a change from 110 to 220. (unless, of course, you also changed to "stuff" that needs 220 instead of 110)

If I were doing what you seem to be describing, I'd set things up like so:

On the skirt side, I'd install a slip-ring for each power line (I'm assuming you're talking about the standard "hot, neutral, ground" trio) plus one ring each for any control signals or feedback lines that might be involved.

On the dome side, I'd install one brush for each power, control, and feedback line. Obviously, they have to be placed so that they make contact with the correct slip-ring on the skirt.

From there, it's a simple matter to run a wire from each of the brushes to someplace convenient - *ON THE INSIDE OF THE DOME* - and terminate them all in a junction box mounted there.

Once you've got the junction box wired to the brushes and attached to the inside of the dome, you run cabling (Also secured to the inner surface of the dome, of course) from the junction box to wherever the power, signal, or feedback wires need to be, totally ignoring the fact that the brushes and slip-rings exist - As far as the dome-mounted stuff is concerned, everything comes from/goes to the junction box - where it comes from or goes beyond the junction box is unimportant - Maybe gnomes with buckets put it there and take it away. Maybe it's a solid wire. Maybe it's carrier pigeons - The stuff mounted on the dome just plain doesn't care.

Presto! The dome can now spin as much as you like without ever needing to worry about tangling any of the wires.

--
If the door is baroque don't be Haydn. Come around Bach and jiggle the Handel.

I am trying to envision why this would be a problem?

In any case, you can have multiple slip rings to get around obstacles like gears and bearings on the mass the rings maybe mounted to. The idea is to put a channel (slot) under the gear/bearings and pass the wires under to the upper set of rings. from there, you can extra power with out any problems? Another set of brushes are then used.

But still, I thought the whole obs turns on the post and why should the shutter not be turning with it? In which case, the slip rings on the skirt as you say, will be stationary and the brush assemblies will be mounted on the base of the obs that turns.

Jamie

Nor do I. It came up in a talk with the installer, but was probably unrelated to slip rings. I'll stick with 110.

I'll leave these details to the installer.

Ah, so brushes are involved. I have no idea how this would be done to cross from the skirt to the dome. This comes close to showing them and the rings in a professional obs. . See the photo on the right about 1/2 way down. One can see the rings under the shelf. I don't see any brushes.

This shows a use of rings in a photo a little big dowt on the right. Those are big brushes! See the legend under the photo.

Presumably the power would go to a control box on the side of the done for the shutter electronics (circuit board, relays, limit switches, motor), and another like it on the skirt for rotation. Gnomes are not allowed, but I've had a bird or two try to get through the open shutter.

The of the obs as a silo. There is no post. The dome rolls on a track sitting on the skirt driven by a motor.

Sounds like an easy job then.

I've seen induction power coupling that works very nice for that, it's nothing more than a transformer primary at the fixed base and the rotating part has the secondary of the transformer sitting inside the primary section. There are no slip rings and things are done wireless from a remote point.

Jamie

Overkill much?

There's an old saying - an elephant is a mouse built to a committee's specifications. Your idea is a prime case of that. You're trying to "over-tech" it beyond ridiculous for no significant gain. I suppose you'd advocate using a sledgehammer to swat a mosquito that just landed on your forehead, too?

A simple, reliable, purely mechanical solution in the form of slip rings and brushes will do the job more than adequately, be ultra-low maintenance, cost *A LOT* less, both to install and to operate, be orders of magnitude lighter, will be reasonably weatherproof without the need for expensive enclosures, won't generate anywhere near the amount of heat (which equals lower operating cost due to not having the waste of electricity being turned into heat instead of motion) that a magnetic coupling would, and have too many other benefits compared to inductive coupling for me to even try listing them all here - the ones I already listed practically wrote themselves - if I were to actually sit down and ponder the idea, I'd probably come up with dozens more.

--
If the door is baroque don't be Haydn. Come around Bach and jiggle the Handel.

My best guess from the picture is that the brushes are hidden by the motor.

And now I think I know where the 220 versus 110 question comes up - The page you're looking at *SEEMS* to be written specifically for a 220 (240, actually, but lets not quibble) volt system. Exactly the same concepts apply for both voltages - You've got 3 rings on the tower, each isolated from everything else, and all 3 stationary. For a 110 system, one rai gets connected to "hot" (110 volts relative to "ground"), one to "neutral" (theoretically zero volts relative to ground, in practice, not ALWAYS true), and the third to "ground" (which, for 110, is the so-called "safety ground") For a 220 system, instead of "hot, neutral, ground", the labeling is usually "L1, L2 and ground" (Each of "L1" and "L2" are +110 volts relative to "ground", giving you a total working voltage of 220 volts)

On the dome side, you've got three brushes - each one will be a piece of spring metal (perhaps something like a strip of phosphor bronze) pressing a block of graphite down against one of the three rails. for a

110 system, one brush will be riding on the "hot" rail, another on the "neutral" rail, and the third on the "ground" rail. Same thing for a 220 system, but the brushes are called "L1", "L2", and "ground" respectively.

Put it all together, and the whole mess gets power - either 110 or 220 - across the gap between the tower and the dome, with no solid wires connecting the two pieces, leaving the dome able to rotate freely. A wire from each brush then goes to a junction box mounted on the dome, where anything on the dome that needs power can be connected - Notice I said *ANYTHING* - the rotation motor, the shutter motor, electronics to control both, a fluorescent light fixture, a socket to plug in a blow-dryer to unfog the 'scope mirror - ANYTHING you can imagine that might need to both have power, and rotate with the dome can be powered out of that junction box. (up to the limits of the wiring supplying the juice, of course - if you've only got a 50 amp circuit powering it, it should be obvious that you're not going to be able to run 100 amps worth of gear)

Yep, exactly.

--
If the door is baroque don't be Haydn. Come around Bach and jiggle the Handel.

It's not clear what you have, what you're buying, and what you're building.

John Nagle