Fail-safe Chamber Heater SSR for Qidi Plus 4

This project enhances the safety and reliability of a the Qidi Plus4 chamber heater by upgrading critical components and adding multiple layers of protection. The modifications include replacing the original 5A Solid State Relay (SSR) with a higher-rated 40A SSR, incorporating a secondary failsafe relay, and adding a thermal switch for over-temperature protection.

The original 5A SSR was technically sufficient for controlling a 600W heater, but only in ideal circumstances. On the US power grid, where voltage is 120V, the heater draws 5A, pushing the SSR to its maximum rating and leading to increased heat and potential reliability issues. The manufacturer's firmware update, which limits the duty cycle to 40%, is an inadequate fix as it does not address the root issue of switching high current loads with insufficient headroom. To properly address this, the SSR was upgraded to a 40A model, providing additional headroom and reducing the risk of overheating, particularly considering potential inconsistencies in component ratings.

In addition to upgrading the SSR, a secondary failsafe relay was introduced. The relay is controlled by the Heater Fan, ensuring that it remains closed only when the fan is actively cooling the chamber. This configuration ensures that the heater can only operate when proper ventilation is provided, preventing the heater from staying on in unsafe conditions, such as when the fan or printer shuts down.

This project also includes a thermal switch, which serves as an additional safeguard by disconnecting power to the heater if the chamber temperature exceeds a specified threshold. This protects against overheating and ensures a safe operating environment even if other components fail.

Components used:
https://www.amazon.com/dp/B0BLL9M59C
https://www.amazon.com/dp/B0CFY5CB2V

Assorted bits you probably already have:
https://www.amazon.com/dp/B08W3QXN9B/
https://www.amazon.com/dp/B09X48S35Z/
https://www.amazon.com/dp/B095NZVRBY/
 

A detailed wiring guide is forthcoming, depending on interest.