FYI, Pin 1,2,3,4,5,6,7,8,9,14,16 & 17 are output signals, Pin 10,11,12,13 & 15 are input signals, and Pin 18-25 are ground connections.
Pin 2,3,4,5,6,7,8,9 are output signals with slightly higher current than Pin 1,14,16, 17.
If you would like to buy your own solid state relay, I would suggest using Pin 8, since I would guess that you're using 3 Axis for your Plasma CNC, and A Axis is not used.
1. Wire up Pin 8 and Ground Pin to a AC Solid State Relay Input.
2. Connect output end of AC Solid State Relay to 120VAC Relay
(suggested relay: OMRON MY2 120VAC Relay or equivalent,
Pin 13 and Pin 14 of MY2 Relays are trigger pins).
3. Connect MY2 Relay's Common(COM) and Normally Open(NO) to Plasma start signal.
I'm not sure which Hypertherm you're using, however all Hypertherm manuals contain information about plasma start signal wiring so that shouldn't be of a problem.
Be very careful while connecting solid state relays, do not confuse input wirings over output wirings, else you will have AC striking your motherboard.
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