The relay output

The Seletek's relay is a dry-contact switch capable of switching loads up to the relay's rated current and voltage. It can be used to control any accessory that runs from a DC supply — cooling fans, dew heater strips, indicator lights, or any other switched load.

The relay is controlled by the Seletek software and can be toggled manually, triggered by a temperature threshold from an attached temperature sensor, or scripted as part of an automated focus or cooling routine.

Wiring

Seletek relay output wiring diagram for cooling fan connection
Relay output wiring — connecting a telescope cooling fan to the Seletek relay terminals.

Connect the cooling fan in series with the relay contacts and the fan's DC supply:

  1. Connect the positive supply rail to the relay's COM terminal.
  2. Connect the relay's NO (Normally Open) terminal to the positive wire of the fan.
  3. Connect the fan's negative wire directly to the supply negative / ground.

When the Seletek activates the relay, the COM and NO terminals close, completing the circuit and powering the fan. When the relay is off, the circuit is open and the fan is off.

Current rating: Do not exceed the relay's rated current. For high-current fans (over 1 A), interpose an external relay or MOSFET driver — use the Seletek relay to trigger the external switch, not to carry the full fan current.

Software control

In the Seletek software, the relay can be controlled in several ways:

  • Manual toggle: A button in the main panel switches the relay on and off directly.
  • Temperature-driven: Set a temperature threshold — when the attached sensor reads above the threshold, the relay switches on automatically. This is useful for starting cooling fans when the primary mirror temperature is above ambient.
  • Pre-focus cooling: Configure the software to turn the fan on for a set period before focusing begins and turn it off automatically when the mirror has stabilised.