It's a safety light for your bike that doesn't need batteries. Ever. It also has smart on/off function. Light turns on when you start moving and turns of about 5 seconds after you stop moving.
Oprimal slic3r settings:
perimeter width 0,6mm
layer height 0.24mm
pla print temp. 190 degrees C
magnet_housing_v3 (repaired) needs to be printed with 3 lower layers, 0 upper layers, infill 0%, wall thickness 0.6mm, 2 perimeters or any other combinations that will lead to wall thickness of 1.2mm. (for example 3 perimeters with wall thickness 0.4mm).
You have 3 different coil housing options to use depending on your coil size.
Simplest to use is coil_housing_square with coil_housing_square_cover. This two files house a standard 24V, 10A relay coil such as: SRD-24VDC-SL-C. You don't have to "operate" the relay to get the coil out, you simply sand of one part of the relay and insert the whole relay.
coil_housing_square has a support modeled on the internal side which you simply snap off or drill out after printing. Its the only model that has or needs any kind of support.
Detailed parts list and build instructions: