Wireless Power Transmitter Coil Winder

Split Bobbin For Large Area Coils

Ever need a coil for remote power transmission over a short distance. You can buy these online to light LEDs randomly arranged inside the coil and not too far away. This is useful to brighten up your Lego transformer or your mini Christmas tree.

Unfortunately the options available online are limited and if you want a bigger or smaller coil you have to make your own. Easily wound around a pipe or tin but not as easy to remove and keep together when you do get it off. 

This bobbin is used to hold your coils and with all the files available as F360, STP and STL you can change the design.

This bobbin can be split in two to remove the hand wound coil. It has gaps to bind the coil before you remove it. I made the centre hex 6.45mm to fit a standard power tool hex bit, I uses a screwdriver bit but turned it around so that the hex sticks out of the drill and turns the bobbin. Could easily be done by hand too.

The gaps are also used to bring the wire ends and taps out, I just wrap them around the centre pin.

I use a piece of masking tape to hold the start and to count turns.

If you want to count the turns using your mobile phone there are apps for counting a magnet passing, iOS has has “Turns Counter” by Dmitriy Kharutskiy. Android has similar apps like “Magnet Counter  RPM meter”. I have only used the iOS version.

When removing the coil, I find these methods helpful:

• Use short pieces of wire to wrap around the coils to keep them together as you take it off.
• A spot of CA glue or nail varnish also works.
• Alternatively, to keep the coil tight for removal. use a generous length for the last turn and instead of winding it, stop one turn short, cut a long length for the last turn, then tie 2 half hitches in each of the gaps as you complete the last turn. 
• Add nail varnish in the gaps to permanently hold the ties.
• You could use string, waxed dental floss is ideal for tieing the coil together, again, us half hitches, the wax stops it slipping.

If you are planning to add sparkle to your toy gift, here are some thing you may find useful .
 

• LED's are easy to find. I suggest you buy your LEDs online, they have a coil, a LED and maybe a capacitor - all soldered together in a tiny bundle in many colours. Very hard to beat that for the price. 
• I found they need to be operated at 180khz - I have a suggested circuit in one of the pictures, you can easily run it from a USB type charger.  The capacitor will have to be adjusted for best performance in this very simple circuit.
• You will recognize the circuit as a very common but simple "Joule Thief" configuration. Super easy to build without even a PCB, many tutorials online.
• Larger diameter coils work at a greater distance but the frequency will be affected -  adjust the capacitor to suit
• If you buy a coil and driver, I believe the frequency is fixed and will remain tuned if you increase the diameter - I may be wrong here. Feel free to add your experience to the comments

Printing:
No supports needed but the parts should be printed with the inside face on a smooth build plate so there's no gap when assembled. I have a flexible, textured PEI buildplate so I had to lightly sand the texture down to remove the gap. If you don't want the wire to go into the gap then you have to use a smooth surface or sand it lighltly on a flat surface like I did.

I used PLA, takes 4 hours (according to cura) to print the two haves.

Use a 0.2mm or less layer thickness else the wire will slip into the centre gap when winding.