Winding 30W Amp Transformers

[katopan]

Tom, it's a reed switch glued to the winder frame/base and I've got a magnet just taped to the side of the plates which go around with the bobbin. Idea of that was from someone else's site.

[katopan]

OK, this thread just turned warts and all-ish. If the calcs say the copper won't fit in the window, even though the 'real' PT uses an undersized core and seems to fit everything in still, trust the calcs.

PT_5: First layer of the secondary.
PT_6: First layer and next tap.
PT_7: HT secondary finished, but the alarm bells were going off way before I got to this point.
Uh_oh: Self explainatory.

I'm going to go back to my calcs to double check I've actually wound what I should've. I had a fair bit of tension and have trouble believing my winding is that bad that the coil takes up twice the room it should. Measuring the space left on the primary side equates to allowing 80% of the available window in the calcs. But no clamping in a vice is going to squish that enough to fit. But yeah, a quick look as I'm typing this and I've wound double the number of turns I allowed enough height for in the calc. Must go and get some lunch and then look it over.

Options are: working out where I stuffed up making the winding chart and re-do it properly; working out if a winding made for a bridge recto (half the turns, but needs bigger wire diameter) will fit; or go for a bigger core, which means making a new bobbin and starting from scratch;

[katopan]

Can anyone say d**ckhead? OK, having a winding chart that you can tick off as you go is a really good idea. It's also a really good idea if that chart actually corresponds to the number of turns in your calcs. For some reason I had padded out each side of the HT secondary to be 26 layers instead of just the 13 layers they each should be.

Now I've triple checked, ruled out a few lines of tick boxes on my winding chart, and I'm ready to go back out and do some unwinding. I'm not going to go back and correct the winding chart, but this note is here for someone silly enough to refer to it - it's wrong!

[xtian]

Wow, man. Thanks for doing this, just so I don't have to!

Love the photos. Stay strong!

[katopan]

Back on track! Gee I hope the counter got the turns right that I un-wound before re-winding the second half of the HT secondary. Suppose we'll find that out right at the end when I power it up and measure voltages. Taps are hopefully balanced and the 300-275-225-0-225-275-300V I designed for.

Actually, thinking about it I might assemble the core with the winding as is and hook it up to test the voltages next. If I've stuffed up the counts and need to re-do the HT secondary, now is a good time to find out instead of after I've put the heater secondary on top.

And winding height is spot on for what I calculated. I've easily got the bit over 2mm I need for the two layers of heater secondary.

Phew!

[JazzGuitarGimp]

Nice! And good to be back on track. The older I get, the more I psych myself out like that. The old grey matter just ain't what she used to be - at least, in my case!

[katopan]

Man it's good that I'm a very patient person. But gee this hobby tests it sometimes though! When I was near the end of unwinding back to where the CT should've been, I noticed a couple of times that counting in my head didn't match my counter. Although I had tested it before starting this whole thing, I do remember reattaching the magnet with a new piece of tape at one point. I wasn't so careful about where it went back on. After I finished up (for the second time) yesterday I did a bit of a test and noticed that the play in the shaft backwards and forwards and the bad positioning of the magnet meant that when the bobbin was pulled away from the base (less than 1mm) the counter stopped. I found that getting the right spot for the magnet fixed that and it didn't miss at all. But that was after I'd finished.

Sure enough this morning's test revealled that my turns on one side of the CT compared to the other are uneven. Looks like I'm going to be unwinding the whole secondary and doing it again. I has to be right. Nothing like a bit more practice, but at the moment I'm feeling a bit bummed about it.

[sagitt]

dont give up man!!!

[katopan]

No givin' up around here! Already repsyched myself and just glad there's spare wire on the spool.

[katopan]

Yesterday I did a total rewind of the HT secondary. Then I was suspicious of possible lost turns on the primary, so I also unwound and then rewound that (it turned out to be spot on ). In the evening I wound the bifilar heater secondary which is shown in these photos. It all fit (just). PT winding is officially finished. I think I'm going to just tape over the windings with the yellow insulation tape rather than a final layer of mylar. It's thinner but more importantly I'm worried that I didn't leave any winding margin in the end. Using the tape the winding will be completely encased which will make this ok again. If I used mylar it would have a small gap at the sides which means I won't make the 3kV insulation breakdown requirement. The yellow tape has a strength of around 3.5kV per layer. I'll wrap two layers just to make sure and also ensure that it sticks up against the sides of the bobbin cheeks. I'll still put a small piece of mylar under where I'll wrap over the wires and solder on the flying leads. This will make sure that no small wire ends pierce through or scratch into the winding turns insulation and create a short circuit in the future.

Interesting note about the reed switch. I had assumed these things worked the best with the magnet passing beside the long side of the glass switch case. That's the way I think they're mounted in door security alarm switches, etc. With more testing I found that the switching distance was really picky and had to be a very definite distance. A fraction closer I got double counts and further away it dropped counts. Funnily enough with the switch mounted so the end faces the passing magnet, the sensitive distance was quite wide and anywhere in that area gave a reliable single count every time. Don't know if that's the way they work or if it's because of the magnet shape I'm using (just a flat square one). I just superglued the reed switch into this orientation instead of how I originally had it. While re-winding everything the counter matched the counts in my head every time.

[JazzGuitarGimp]

If you ever rework your winding jig, you might consider using a hall effect sensor instead of the reed switch. I believe they are more repeatable, and have no moving parts inside.

Transformer looks beautiful, man!

CHeers,
Lou

[katopan]

Good call Lou. The reed switch is working now I've spent the time getting it right, but it it ever plays up I'll turf it and look at a hall effect.

Here's the primary (left side) and heater (right side) flying leads after soldering. After the photo I taped them in place. And after getting about 15 years out of my roll of solder I just ran out before getting all the HT secondary leads done. So it's out to the shop, but I'll hopefully finish the leads when I get back.

Then I need to print an external label, varnish the label (which will have to dry overnight) and put it on. Then I can assemble the PT and it's done and ready for testing.

[katopan]

And here's the windings all taped up and the HT secondary flying leads done. In between each wire you can see the silicon sleeved winding wires bent up and over to the solder connection to the flying lead wires.

[JazzGuitarGimp]

Purrrrrdy!

[Chad]

And here's the windings all taped up and the HT secondary flying leads done. In between each wire you can see the silicon sleeved winding wires bent up and over to the solder connection to the flying lead wires.

What a fantastic project to try and achieve and achieve I hope you do. I would love to have enough confidence in my self to try something close to that.I have been wanting to try my hand at pick-up winding in the future so maybe one day at a time. Good luck Kato and thanks for the info and pics of your progress. Chad