ADR-004: Power Architecture
Status |
Accepted |
|---|---|
Date |
2026-07-14 |
Author(s) |
Context
The machine draws power from a single external 230V AC mains connection and must safely distribute it to multiple internal voltage domains: the Raspberry Pi (Station) and the pumps, valves, and stepper motors (Pods). The power design must support the Human Safety quality goal by providing a clearly labeled disconnect point, protection against residual current and overcurrent faults, and a continuous protective earth (PE) conductor.
Decision
We will use a single-chain power architecture: an IEC C14 inlet feeds a main switch (manual mains disconnect), followed by a residual current and overcurrent protection device, followed by an SMPS that converts 230V AC to 24V DC. The 24V DC rail directly powers pumps, valves, and stepper motors, and is further stepped down via a DC/DC converter to 5V DC for the Raspberry Pi. A continuous PE conductor runs through every stage, independent of the voltage domain.
Consequences
-
Good: A single main switch gives the operator one clearly labeled point to fully disconnect the machine from mains power, directly supporting Human Safety.
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Good: A single, linear power chain keeps the internal wiring simple to document and verify, supporting Maintainability.
-
Bad: The single SMPS is a single point of failure for the entire machine; if it fails, both the Station and all Pods lose power simultaneously, working against Reliability.
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Bad: All Pods share the same 24V DC rail, requiring careful current budgeting and fusing as more Pods are added, which limits scaling without revisiting the power design.