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retailer 16th Feb 2021 2:21 am

DIY Transformer Bobbin
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I believe there are forum members that diy their own transformers from time to time, finding the lams can be an issue, one source is to reuse lams from a scrap transformer and if you do find a suitable sized lams then the lack of a bobbin can be another issue. Winding without a bobbin is do-able, I've done quite a few myself just for the experience but you do really need a coil winder with auto traverse. An acquaintance came to me the other day and wanted 2 matching PP output transformers - he had 2 sets of lams and bell ends but no bobbins, feeling lazy and not wanting to wind without a bobbin I thought of my 3D printer and came up with a bobbin fabricated from 3 pieces - a central square tube and two identical end cheeks. Design time was around 2-3 hrs and print time is around 4.5 hrs, once cleaned up some epoxy glue was used to fit the bits together, a perfect fit, once the glue had set I just needed to file away 2 sections of the central tube to allow the laminations to seat against the bobbin end cheek. I could have designed the central tube so eliminate this step but I wasn't sure how well the part would stick to the printer bed with only 2 small strips 1.5mm wide contacting the bed.
I used PLA which all I have at present it is not great as far as temp goes, around 55-60C being the limit, but we figured an output transformer shouldn't get that hot, the output transformers in my my workshop SE stereo amp get barely warm to the touch, I'll get some ABS which a better as far as temperature goes for any future transformer projects.

Diabolical Artificer 16th Feb 2021 7:07 am

Re: DIY Transformer Bobbin
Tasty! Would that you lived round the corner on even in Blighty, a decent bobbin makes tfmr winding so much easier.


Ed_Dinning 16th Feb 2021 9:13 am

Re: DIY Transformer Bobbin
Hi Retailer, a neat solution.
At one time it was possible to get paxolin square/ rectangular section tube in the UK in the popular core sizes as most transformers were "stick wound"; as most now use moulded bobbins this supply has dried up.
Pax sheet is still readily available and it may be quicker to print the tube and fabricate the cheeks.

In your design were the slots and steps for stiffening or simply to make it look like a commercial unit?


retailer 16th Feb 2021 1:50 pm

Re: DIY Transformer Bobbin
Slots are for the connections to the windings and the ribs between slots are for stiffening most of it is only around 1.75 - 2.0mm thick so I assumed it would need stiffening, the rib running across the width is for stiffening and also to increase surface contact area for the adhesive. Winding a transformer the old way with just a tube and margins you need to take a lot more care, I was making bobbins cut from fibreglass sheet I had left over from making turret boards, 6 pieces are needed 4 for the tube and the two end cheeks - they all lock together like a child's toy, it works quite well, but you need to be quite precise with the cuts - within 0.5mm or so otherwise the bobbin won't hold itself together, so it can be time consuming, marking it out cutting it and finally file a bit and trial fit - too tight? file some more etc.

I held off buying a 3D printer for a long time - I didn't think it would get much use but since buying I've found many things I can make/fabricate. Mounting the bobbin on the winder has always been a PIA, they are all different sized rectangles, I have always used a piece of wood cut to just the right size for a tight fit into the bobbin and drilled a hole through the middle, once again you need to be reasonably precise, if you get the hole slightly off, the bobbin may wobble - makes it hard to wind right up to the edge of the bobbin cheek. It is not real clear but if you look at the first photo top right, next to the bell end is a small square 3D printed piece with a hole through the middle, I printed two they fit precisely into the bobbin tube - hole is perfectly central, a groove across the hole takes a driving dog that is fitted on the spindle.

ChristianFletcher 22nd Feb 2021 7:31 pm

Re: DIY Transformer Bobbin
I thought I would mention that I have made a few 3D printed bobbin for audio and small mains transformer. I was initially worried about the internal temperature melting the bobbin but it’s been ok so far. A better option may be the UV cured resin printers as the resin won’t melt but I don’t yet trust the reliability of these style of printers

retailer 25th Feb 2021 5:56 am

Re: DIY Transformer Bobbin
It it's ok on mains transformers then it should be output transformers - thanks for the info.

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