The ZVS induction board comes with a work coil that is too big for brass case annealing in my opinion. I wound a replacement using smaller 1/8” (3mm) copper tube to better concentrate the magnetic field on the case shoulder and neck. The inductance of the coil is important to keep the system operating at an efficient frequency. I suggest starting with the design I have below and tweak it if you need.
The 1/8” tube gets soldered into the supplied larger copper as shown below for easier connection to the ZVS board and water hoses.
28mm ID – wrap the 1/8” copper tube around a 28mm OD tube, socket, whatever you can find.
Wrap 7 ½ turns with an air gap in between each turn – if you can find some insulating sleeve like on the picture below, that’s even better. Some have enameled the tubing to give insulation between the windings.
Finished coil height is about 30mm
This is the coil used on my annealer.
Example of high temp insulation on a coil
To keep the ZVS unit running efficiently, it should be operated around 100kHz which means the coil needs to be around 1.25uH. There are online calculators that will tell you the coil inductance based of the dimensions you enter. If you want to change your coil size, try and keep the inductance around that 1.25uH number.
coil diameter = 28 + 3 = 31mm
Coil length = 30 - 3 = 27mm
Turns = 7.5