Following on from our earlier post, quite a while back now, I managed to get around to constructing a stator coil a month or so ago. This particular project has had a very low priority due to work commitments and the many other projects I'm also on with, especially in the garden.
Firstly, I made a mould to cast the coils from an old piece of timber, using the CNC machine to generate the internal disc profile. Using the CNC wasn't strictly necessary, a simpler but equally effective mould could have made up from plastic strips or similar.
|on the CNC machine....|
Pins were added to form the four stator mounting holes, and then the mould was coated with a few coats of liquid latex to make it easier to get the coil out after casting.
In the end I decided to make serpentine coils which would be much easier to wind than individual coils, so I printed-off a template of the magnet and coil leg locations and pasted it onto a piece of board. Using wire oval nails, a simple winding former was constructed. Twelve magnet pairs on the rotors, and hence twelve coil legs at the same radial spacing.
|the coil former....|
So then it was a case of winding the coils. I made three, one for each phase. After winding, the coils were tie-wrapped and then flattened between two pieces of wood in the vice.
|the three coils.....|
At this stage I replaced the tie-wraps with insulating tape, to make the coils thinner overall. The coils were checked with a meter for continuity and resistance, and each wire lead marked to its coil location and also indicating the direction of the wind. It's important that the three coils are all laid and connected with the winding in the same direction.
|now taped and marked.....|
The coils were then stacked, with each slightly offset circumferentially from the one below.
|the coil stack...|
Then the assembly was placed in the mould, ready for encapsulation with polyurethane resin. The mould was first sprayed with a dry PTFE lubricant, to aid demoulding. The M6 capscrews and nuts as seen in the photo below were also placed in the mould to assist with removal.
|in the mould....|
|after pouring - a couple of air bubbles, but no problem....|
Getting the solidified stator coil out of the mould was much more difficult than anticipated, and eventually required splitting of the timber mould using a chisel along the grain.
However, I was quite pleased with the overall appearance of the finished stator. Some of the wire enamel is slightly exposed in places around the periphery, but this is not a problem - in any event, it's intended to paint both the stator and rotors.
After a day to allow the polyurethane to fully cure, I dressed the casting with a file and countersunk the fixing holes.
Note that I cast the stator with all 6 coil leads available for external connection. This allows experimentation with either star or delta connections in the case of a three-phase arrangement, or even to connect all the coils in series to make a single-phase generator. If you know in advance exactly how you want to configure the windings, then some of these connections could be made earlier and encapsulated within the resin, resulting in fewer external wiring leads.
|finished stator coil trial-fitted to bearing housing.....|
Still to fully assemble & test - more in a future post....