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PVC pipes and winding Tesla coils.... Answered

There are still people out there playing with high voltage.
And one big problem when it comes to Tesla coils is winding the secondary coil.

Now, I won't go into the details and options of the actual winding part, instead I would like to share some tricks that might make things easier for your project.

Whether you wind fully by hand or make use of some mechanical winder, magnet wire is a very slippery thing on PVC.
For that reason and some others we usually wind as tight and close as possible.
Any leftover spaces that you find after the winding is finnished will severly compromise the overall tension of the wire in this region if fixed.
Next problem is what many call aging.
No matter how good you coat your coil with varnish or paint it will start to degrade over time.
I found a simple fix for these problems :)

Well, not really that simple but I am too lazy today to make a full Instructable for just an addition that everyone can make in a few minutes....
Let me start with idea behind it all:
I noticed that no matter how thick the pipe or wire is that there is little to no chance at all to get any of the coating material through the wire and all the way down to the PVC.
One coil failed after I abused it so I did some cuts and had a close look with a magnifying glass.
The coil itself was really good covered but it was like a sleeve that sits on the PVC with nothing on the underside of the wire except for a few single spots.
Some people will now say to just a much thinner mix for the coating to allow the stuff to sweep through but that does not always work.
One big issue I noticed is that not all paints or varnishes actually stick to PVC.
Especially those non smelling eco friendly ones most places now sell.
This means when the coil expands due to the vibrations and heat the wire can simply rattle off the varnish or the coating itself can crack under the stress.
So I thought there must be a way to fix this right at the winding stage....

PVC is a good insulator too!
So why not use PVC instead of messing with other things?
My first attempt here works quite well with thin wire and goes like this:
Go outside with your winding rig and have a bottle of PVC primer and a little brush or sponge ready as well as some gloves.
If you have use a friend, if you have none make a small rig to hold the sponge right in front of your winding area.
The key is to keep the sponge wet with the primer so it will wet the pipe properly.
Best is to have the speed and distance set so the surface just starts to dry off under the wire.
The primer will cause the PVC to soften, so the wire slightly sinks into the surface.
An automatic winding rig is best here as it allows for consistency.
There is no too much or too little here is nothing drips terribly and your wire sticks without fully sinking in.
Once done you can cover the winding with your prefered coating.

For thicker wire, lets say 0.3mm or thicker, I now use a similar way but with more preperations:
Using some very rough sandpaper on a belt or vibrating sander I create a small pile of PVC dust.
If you prefer some fancy color you can use ABS plasic here too and it dissolves in a similar way.
The resulting mix should be free of lumps and of even color, if in doubt use more primer.
Consistency should be a bit thinner than honey, if yours is too thin you can add more ABS/PVC or let the primer evaporate off while stirring it every now and then.
To get a good start I do a few turns dry first with quite a big spacing.
When approaching the actual start of the winding area I use some stick tape to make the last alignment and start to apply the mix onto the first bit of the winding area.
Some lint free cloth with a bit of primer is used to wipe off any excess towards the still uncovered part of the pipe.
Every time the mix on the pipe dries out too fast a brush with some primer is use to wet it.
Every time the excess runs out a bit more mix is applied onto the wound area.
The key is to only have a small area in front of the winding covered with mix with the most is on the winding and "cleaned" off towards the empty area.
This way the entire wire is covered by PVC all around.
To finnish off you simply use a brush and paint the mix onto the rotating coil until you have an even finnish.


What are the downsides?
The primer stinks and is certainly not healthy to breathe in.
So good ventilation is a must have and it works better in colder temeratures as it gives you more time.
It might require some test runs with braided fishing line or similar to get a feeling for how much mix or primer you need to apply and how much max tesion you can use to preven the wire from sinking in.

Any benefits?
IMHO using this method makes it possible to get a proper bond between the PVC pipe and the wire.
And by using PVC or ABS as the coating there is little to no change material properties.
This in return gives far less chances for vibrations or wire expansions that result in failing insulations.
The whole thing just is one piece of PVC with the wire embedded in it instead of having a wire on top of the PVC with some coating above. ;)

Are there alternatives to the PVC primer?
If Acetone is much cheaper than you can use it but the same safety measures apply and the mix might dry a bit quicker.

What if I need a break or stop the winding for one reason or another?
Simply wipe off all access and stop with just enough tension on the wire so you can star again with no problems.
Then start by wetting and applying the mix and continue winding as before.

Discussions

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petercd

3 months ago

Thats an excellent tip right there.

Not that I'll ever be messing with tesla coils, but well worth a read through.

Another option is an ABS/acetone slurry that some users use in the 3D printing scene.

Might even be a good use to put all the failed prints to.

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Downunder35mpetercd

Reply 3 months ago

From my experience this only works well if you add a little bit of PVC dust or shavings as well and mix it really well.
Using some PVC in the mix (about 30%) for the first few coats allows for a proper bonding.
ABS has slightly different properties and in a direct mix it can cause a brittle layer between the PVC and ABS.
Once the wire is fully coated a pure ABS slurry can be used for coloring in and getting a thick enough insulation layer on top.