Transformer Winder for SMPS Flyback Power Supplies

This 3D printed model can assist you in winding the very small RM6, EFD20, and EF25 transformers used in flyback switch-mode power supplies (SMPS) for off-line (mains) applications.

The parts assemble together with M3 hex cap screws and M3 heat-set inserts.  The enameled wire spool goes in front, and the shafts hold the transformer bobbin in place where it can be spun with the hand crank.

Refer to the following Reddit thread for pictures of the unit, this will guide you on assembly and where to put the heat-set inserts and screws.

https://www.reddit.com/r/electronics/comments/18milin/handwound_a_flyback_smps_transformer_with_a/

I do not have detailed instructions on the assembly and use of this unit, as I did not intend to publish it, but some users in the Reddit thread requested the 3D print files.  The FreeCAD design file is included as well should you wish to use it, modify it, or create new shafts for other transformer sizes.

Recommended print settings:

• 0.2mm layer height
• 0.4mm nozzle
• Perimeters: 3
• Solid Horizontal Layers Top/Bottom: 4
• 20% infill, Gyroid pattern
• PLA material
• Recommended to use a lower-than-normal bed temperature when printing the main base, this will minimize any warping of the base.

If I remember correctly, the heat-set inserts used for this model are a specific brand/size from Initeq, available here:

https://www.amazon.com/dp/B077CL322T?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_6

Standard/common M3 heat-set inserts may be too small for the holes in the parts, so if you want to use standard M3 heat-set inserts, you probably will need to edit the model in the FreeCAD file and shrink down the hole sizes.