DFCD · Volume 5
Power System
NP-F battery, 7.2 V to 5.1 V step-down conversion, runtime math, and charging
Stub — section skeleton authored 2026-06-27; prose to follow.
5.1 The NP-F Battery Format
The NP-F format originates in Sony’s camcorder battery series and has become a de facto standard in the video production and cinema accessories market. The format provides a standardised slide-on contact interface and a range of capacities in the same footprint. This section covers the NP-F electrical characteristics (nominal 7.2 V, discharge curve shape, contact pinout), why the DFCD adopted this format (field availability, USB-C recharge options, capacity range), and the range of NP-F packs available to builders.
5.2 The Reference Battery: 10050 mAh NP-F Pack
The reference build uses an NP-F pack with 10050 mAh capacity and USB-C input for recharging. This section covers the specific pack [VERIFY: exact model and vendor], its rated discharge current, the USB-C input specification, and the physical dimensions as they fit the DFCD battery bay.
At 7.2 V nominal and 10050 mAh, the rated energy content is approximately 72.4 Wh. The actual usable energy will be less, depending on the discharge curve and the efficiency of the step-down conversion; the runtime math in §4 works from the usable energy figure.
5.3 Joy-it Step-Down Conversion (7.2 V → 5.1 V)
5.3.1 Module Specification
The Joy-it step-down module provides regulated 5.1 V output from the NP-F’s 7.2 V input. This section covers the module’s specification: input voltage range, output voltage setting, output current rating [VERIFY], conversion efficiency (typically 85–95% for a well-designed buck converter at these voltages), and load regulation.
5.3.2 Pi 5 Power Requirements
The Raspberry Pi 5 requires 5.1 V and draws up to 5 A (25 W) under peak load from a USB-C supply, with a more typical idle draw in the 3–5 W range. This section establishes the Pi 5 power envelope as the constraint the step-down module must satisfy, and confirms whether the Joy-it module’s output current rating is sufficient.
Cross-reference: the PiFlux deep-dive (§ Power and Thermal volume) covers the Pi 5 power draw in detail across workloads. See ../../PiFlux/ for the full characterisation.
5.3.3 Wiring and Protection
The step-down module’s input and output wiring, wire gauge selection for the expected current, and any fusing or protection at the battery interface are covered here.
5.4 Runtime Math
5.4.1 System Power Budget
The total system power draw is the sum of the Pi 5 load, the 10.1-inch IPS display, the NOS 450 TKL keyboard (USB HID, low draw), the trackball (USB HID, low draw), and the Joy-it module’s own quiescent current. This section builds the power budget from the individual component draws.
Table 1 — 4.1 System Power Budget
| Component | Typical draw (W) | Notes |
|---|---|---|
| Raspberry Pi 5 (FreeCAD mid-load) | [VERIFY] | From PiFlux power volume |
| 10.1-inch IPS display | [VERIFY] | Backlight-dependent |
| NOS 450 TKL keyboard | [VERIFY] | USB HID, typically <0.5 W |
| Trackball (Marble harvest) | [VERIFY] | USB HID, typically <0.1 W |
| Joy-it module quiescent | [VERIFY] | Manufacturer spec |
| Total (estimated) | [VERIFY] |
5.4.2 Estimated Runtime
Given the usable battery energy and the system power budget, the estimated runtime at the FreeCAD mid-load scenario is:
Runtime (hours) ≈ Usable energy (Wh) × conversion efficiency / System power (W)
Worked example with placeholder values pending [VERIFY]:
- Usable battery energy: approximately 72 Wh × 0.85 (pack efficiency) ≈ 61 Wh
- Joy-it module efficiency: approximately 90% → 55 Wh delivered to load
- System power at FreeCAD mid-load: [VERIFY] W
- Estimated runtime: 55 / [VERIFY] ≈ [VERIFY] hours
5.5 Charging
The NP-F 10050 mAh pack charges via its integrated USB-C input. This section covers the charging current (limited by the pack’s built-in BMS [VERIFY], typically 1–2 A for packs of this size), the charge time from depleted, and whether the DFCD can operate while the pack charges (pass-through use).
5.6 Cross-Reference: PiFlux Power and Thermal Volume
The Raspberry Pi 5’s power draw and thermal behaviour under sustained load are covered in depth in the PiFlux deep-dive at ../../PiFlux/. That volume includes:
- The Pi 5’s power envelope across workloads (idle, light compute, sustained CPU-bound, GPU-bound)
- Thermal characterisation under the Joy-it heatsink and under the stock cooler
- CPU governor settings and their impact on power draw
- Thermal throttling thresholds and their practical effect on FreeCAD performance
The DFCD power system is designed around the Pi 5’s typical FreeCAD mid-load draw. For a builder who wants to understand the full envelope — worst-case sustained load, thermal limits of the Joy-it heatsink in a warm shop — the PiFlux power volume is the reference.