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Home made sliprings. Page 1 | 2

We use sliprings to transfer power between a rotating and a fixed object. When it comes to wind turbines, the sliprings transfer the power from the nacelle ( the bit at the top ) to the mast. But do we really need sliprings?

Most who have built a few wind turbines would say no. I don't have slip rings on any of my turbines, instead I use a drop wire down the centre of the mast.

Because I live near my turbine, I can go out to my turbine mast, unplug the drop cable at the bottom, and unwind any twist in the cable before plugging it back in. The drop wire is anchored to the nacelle, and dangles down the centre of the tower, as shown to the right.

You can see this in more detail here.

How often do I need to unplug and untwist the cable? Well that depends on the season, it could be once a week or once a month. So in my situation, I wouldn't consider adding slip rings to my set up. Slip rings can be unreliable, susceptible to corrosion, bugs and dust, so by not having them I don't have to worry about the problems they can cause.

However, if your in a location that could see your nacelle rotate around the mast several times a day, or could be left unattended for weeks and months, then slip rings are a necessary evil.

 

Home made slip rings.

When I put this article together, I had two rules, the slip rings would be built from parts available from a hardware store, and you could have any number or rings depending on your alternator set up. With that in mind, I came up 2 designs. Both use the same slipring, but different brush assemblies. And because the rings are mounted one above the other, there is no limit on the number of rings used, within reason.

Note I've used very few dimensions in this design, its up to you to work out the part sizes based on what materials you can dig up.

First up, the slip ring itself. I chose to make my slip rings from zinc coated steel plate. Its a easy material to find and work with. Copper is the preferred material for slip rings, if you can find some copper sheet or copper tube that would suit, go ahead and use it.

My rectifiers are at the alternator, so I only need 2 slip rings to transfer my power down the mast, but you could use this same design for 3 or more slip rings.

The slip rings are fixed to the windmill mast, and spaced apart with timber insulators. Timber is easy to work with and wont melt. Timber can burn, but the rings will never get hot enough, our slip rings are well ventilated and will act like heat sinks.

 

 

To the right is the top view of our slip rings, minus all the nuts and bolts. 3 timber spacers are used, but you could use more if you like, especially if using a softer slipring material like copper. Its important to make sure there is a air gap behind the slip rings to improve cooling.

Below is sectioned side view of the timber insulator. As you can see, its a pretty simple affair. The sliprings are held to the timber insulators with screws and nuts, and you can see how the screw heads are in a countersunk hole to insulate them from the windmill mast, this is important.

 


The timber insulators. the harder the timber the better. I've used pine, not the best material but its all I had at the time. I've radiused the top face to suit the slipring.

 

The timber insulators are taped to the mast ( this is a dummy mast I use for building my windmills, its very handy ). I'll use this setup to get the rolled diameter of my slip rings right. When making the rolled slip rings, its better to go slightly undersize. Then just plane a shaving or two off the timber insulators to get a nice fit..

Rolling the steel sliprings. I used a length of scrap pipe to roll my slip rings.

Instead of rolling your slip rings, you could use large diameter exhaust pipe ( or any steep/copper pipe ) that is large enough to fit over your mast with the insulators in place.

Once I worked out the correct diameter using the insulators taped to the mast, I cut the ends square and butted together for welding.

Butt welds can be difficult if you don't have a good welder ( Mig, Tig or gas wire welding will work fine ), so another option is to use a plate behind the slipring and pop-rivet the ring together. Make sure the pop rivets are not in the path of the brushes, stick to the outside edge. This is also the best option if you use copper plate for your sliprings.

Bottom left is a plan of the backing plate. Bottom right is a overlapping joint, and not recommended because the grove it leaves for the brush to slide over is too large, the brush could jam in the grove.

Once the ends are welded or joined together, clean up any sharp edges.

Next drill the mounting and connection points. The mounting holes are evenly spaced around the slip ring, to suit the number of timber insulators. Drill the holes about 10mm in from one side. This will give a wide area for the brush to slide without the risk of hitting the mounting screws.

You also need to drill a hole for the power take off point.

Next grab the timber insulators and drill to suit the sliprings. You want to keep about 10mm between rings, and allow 30m or more at the ends so you can secure the insulators to the mast. Don't forget to countersink the screws holding the slip rings. Its also an idea to put a drop of filler on top of the countersunk screw, just in case it ever comes loose in the future.

 

The assembled slip rings and insulators..

And slide onto the ( test ) mast. I've attached the power leads and secured the cables to the mast.

The insulators can be screwed into the mast, or you could just use a couple of hose clamps, probably a better option, just as secure and it means you can easily remove the slip rings or adjust their position.

© TheBackShed 2011