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DIY flyback transformer

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boylesg

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Made myself a bobbin out of a piece of copper pipe and two PVC disks that fit over the end. This then fits into a ferrite core of a tv flyback transfomer.

I have seen some examples of these where people put a layer of transparency sheet in between each layer of wire, however I have found this ends up taking up a lot of space with multiple layers in the limited space I have available on the bobbin.

And unless you include insulation layers OR emerse the whole thing in oil after you wind it then you get corona problems.

But the problem with emersing the transformer in oil is that you are unlikely to get rid of ALL the air between the wire strands, unless perhaps you put the transformer under oil in a vacuum.

Others use araldite or some other epoxy as they are winding, but that is painful.

So I came up with another idea and am trying it.

I am not bothering to wind methodically since I am using quite fine gauge magnet wire (not sure what it is) and I will probably get more than enough turns even without methodical winding.

But what I am doing is smearing petroleum jelly over the windings every now and then and excluding the air while I am winding.

What do you experts think?
 

BradtheRad

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The petroleum jelly may be all right but there's something about using a metal pipe that is unsound. It creates a single winding.

The single winding will conduct a lot of current. It will rob energy and make the transformer unusable.

According to an article I just read, even one shorted turn in the windings will make the transformer unusable.

Link:

https://sound.westhost.com/xfmr2.htm
 

boylesg

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The petroleum jelly may be all right but there's something about using a metal pipe that is unsound. It creates a single winding.

The single winding will conduct a lot of current. It will rob energy and make the transformer unusable.

According to an article I just read, even one shorted turn in the windings will make the transformer unusable.

Link:

https://sound.westhost.com/xfmr2.htm

Bugger! Oh well you live and learn - that did not even occur to me.

I put a layer of overhead tranparency over the copper pipe so I might be able to slip it out and replace it with something else. Otherwise I could just wind the wire onto another all plastic bobbin - another adantage of using petroleum jelly rather than epoxy or silcone.

I salvaged the magnet wire from tv sets so there are perhaps a dozen long lengths soldered together. I placed the solder joints in a small piece of overhead tranparency folded in half and filled with petroleum jelly.

Does that sound like reasonablre way to insulate them? Or do you think it would better to cover them with a smear of araldite?

- - - Updated - - -

Just visited Bunnings and found some PVC pipe with the same internal diameter as my copper pipe.

I also found a 25mm poplypipe nut and tail, that to connect 25mm polypipe irrigation tube to a standard tap, fits nicely over the top of the PVC pipe.

So I have cut off the barb, removed the part that screw on to the tap and I am left with a small circular flange that I can glue onto the ends of a short section of the PVC pipe.

I can then cut out two larger disks of PVC and glue these onto the flange yielding a make shift bobbin.
 

betwixt

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As you are into plumbing parts, the best simple insulation over each layer of wire is PTFE tape. The stuff you wrap around pipe threads to seal and adjust tightness. Costs pennies for a 10m reel and it's thin enough to stretch around the wire and keep it nice and tight. It is also a very good electrical insulator and can withstand high temperature.

Incidentally, there is no reason to fill in the gaps between the wires with any substance, in fact the air gaps can help to keep it cool. I would be particularly cautious about petroleum products, even if it's safe to use on hands because it has solvent properties and a very low melting point. There is some sense in using insulating layers such as the PTFE because it keeps wires with high voltage differences away from each other. It also provides a degree of stability to stop the wires 'singing' if they can move in the magnetic field.

The golden tule of transformers is NEVER put a conductive loop around the core, it looks t the transformer to be a single turn short circuit and at best will just get hot.

Brian.
 

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