Slip Ring location

[Boerman]

I put up a Selsam SuperTwin on a 35' tilt-up made from 4" steel pipe. I was originally told that it probably wouldn't need a slip ring, especially if my wire was flexable enough. Well, after just over a month of operation, it has gotten too stiff to unwind itself....twice. So I am going to have to break down and get a slip ring. I have been a little concerned about having the weight of the wire pulling down on the connections. So, is there any reason to not put the slip ring near the bottom of the tower?

[rossw]

A long story - but I'll try to make it brief. Those on IRC heard about it as it happened...

Early this year we had a terrible wind that blew a great chunk of tree some 200m and into my turbine - causing a lot of damage. Most immediately obvious was one shredded blade and two missing blades (found 600 metres away downwind). The next most obvious was the yaw shaft badly bent. Not so obvious was the 12.5 thou bend in the 40mm main rotor shaft. (This will all become relevant in a second!)

[img width= height=]http://house.albury.net.au/29apr2009/thumb.100_3314.JPG[/img] Bent yaw shaft (with sliprings)

I turned up a new shaft from a chunk of 70mm round stock, leaving a lot more metal than the original had, and was able to extract the sliprings off the original shaft, bored the centre and fit it to the new shaft.

[img width= height=]http://house.albury.net.au/20may2009/thumb.100_3383.JPG[/img] New shaft.

In order to secure the cable, without "pulling" on the sliprings I made a tapered collar that went over the wire:

[img width= height=]http://house.albury.net.au/10jul2009/thumb.100_3518.JPG[/img] Collar.

[img width= height=]http://house.albury.net.au/10jul2009/thumb.100_3519.JPG[/img] Slit both sides with a hacksaw.

[img width= height=]http://house.albury.net.au/10jul2009/thumb.100_3520.JPG[/img] which just slides over the cable.

[img width= height=]http://house.albury.net.au/10jul2009/thumb.100_3521.JPG[/img] Which fits into the end of the yaw shaft

[img width= height=]http://house.albury.net.au/10jul2009/thumb.100_3522.JPG[/img] All re-assembled. The harder the cable pulls down, the tighter the collar grips. All the weight is carried on the shaft itself, none on the sliprings.

[img width= height=]http://house.albury.net.au/11jul2009/thumb.100_3526.JPG[/img] Shaft back in the turbine (brush-holders not yet reinstalled)

[img width= height=]http://house.albury.net.au/24jan2009/thumb.100_3210.JPG[/img] I appear to have forgotten to take a pic once the brushes were re-attached, but here's one that shows them before I disassembled the whole thing.

Hope this might help.

[rossw]

I failed to explain why I made the collar!

In the original version, the shaft was quite thin-walled, and they used two bolts and nuts with a strip of metal to "squash" the cable to the inside of the shaft right at the bottom. It damaged the cable and wasn't very suitable in my view - but my new shaft was MUCH thicker walls and couldn't be done that way.

[img width= height=]http://house.albury.net.au/13may2009/thumb.100_3371.JPG[/img] You can see how big the internal diameter of the old shaft was (and therefore how thin the walls were!)

[img width= height=]http://house.albury.net.au/20may2009/thumb.100_3389.JPG[/img] compared to the new one. (This is looking at the end of the shaft at the top of the previous photo, which slips inside the base...)

[Ungrounded Lightning Rod]

I note that if you put the slip rings at the top of the tower you can clamp the cable to the tower below them as a strain relief rather than letting it hang.