Shifting Grounds in Electronic Circuits: Understanding Relay Power Supplies and DC Outputs

When working with electronic circuits, especially those involving DC power supplies, the concept of grounding can sometimes be tricky. In this article, we will explore the complexities of sharing grounds between different components, specifically focusing on the situation with relay power supplies connected to 110V main power and 12V DC power supplies. We will also discuss the implications of using a single ground path for both sides of the system.

Introduction to the Scenario

In a typical setup, the main power is 110V, feeding into two 12V 15W DC power supplies. One of these power supplies powers a series of relays, while the second triggers these relays and provides power to other components. The question at hand is whether it is possible to use a single ground (GND) path for both the 12V DC power supplies, or if there are potential issues that need to be considered.

Is a Common Ground a Good Thing?

As a rule of thumb, sharing a common ground (GND) between two circuits is generally acceptable as long as there is no risk of polarity issues. This setup can simplify wiring and make the circuit easier to manage. However, if the system includes sensitive electronics, it is crucial to ensure that the ground path impedance is kept as low as possible.

The Role of Relays and High Currents

The scenario described involves relays switching large currents. This can introduce several issues, especially if the ground path is not properly managed. In such cases, the ground path impedance can become a significant problem. If any high-current relay paths are involved, and the downstream electronics are sensitive to ground shifts, the ground path must be low-impedance to avoid potential issues.

Best Practices for Grounding in Relay Systems

Given the complexities involved, here are some best practices to follow:

Low Impedance Ground Path: Ensure that the ground path impedance is as low as possible. This can sometimes be achieved by using a ground plane on a printed circuit board (PCB). Proximity to Power Supply: If the system does not include a PCB, it is recommended to connect the ground as close as possible to the DC output of the power supply. This minimizes the risk of ground shifts and ensures that any potential ground noise is contained within the circuit. Isolation and Cautions: For highly sensitive electronics, it is generally better to isolate the relay ground from the electronics ground. This can be done by maintaining a separate ground path for the relay, with only the GND path shared. Solid State Relays (SSRs): Solid-state relays (SSRs) can be a different matter, both with AC and DC types. SSRs generally do not face the same issues as traditional mechanical relays, but it is still recommended to manage the ground path carefully to avoid any potential noise or ground shifts.

Conclusion

In conclusion, sharing a common ground between the two 12V DC power supplies can be a practical solution in many cases, especially when working with a reliable ground path or PCB. However, for systems involving high currents and sensitive electronics, it is essential to carefully manage the ground path to prevent any potential issues. By following the best practices outlined above, you can ensure that your electronic circuit operates smoothly and efficiently.

For further reading and detailed information, refer to the resources mentioned in the advanced electronics section.