BarnacleBoy
3c11190822
- docs/sbc-selection.md: full rewrite for OPi 3B specs (RK3566, 8GB, 256GB eMMC, built-in WiFi) - README.md: SBC description, checklist, components table, quick ref, cost estimate - docs/parts-list.md: SBC marked purchased, eMMC/controller/WiFi changes - docs/design-decisions.md: WiFi exclusion reason, native eDP, power input - docs/salvage-analysis.md: WiFi card not needed, cooling fan, summary tables - docs/storage-architecture.md: rewritten for 256GB eMMC primary boot - docs/usb-expansion.md: 2x USB3 native, port allocation, power budget - docs/port-layout.md: OPi3B port differences (eDP, power-only USB-C, built-in WiFi) - docs/power-system.md: lower power draw context
88 lines
3.2 KiB
Markdown
88 lines
3.2 KiB
Markdown
# Power System
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## Decision: IP5389 Power Bank Board (Preliminary)
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All-in-one power management PCB. Replaces separate charger module, BMS, and boost/buck converter with a single board.
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## Why This Approach
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| Requirement | IP5389 Solution |
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|------------|-----------------|
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| Charge lithium cells safely | Built-in CC/CV with cell balancing |
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| Battery protection | Overcharge, overdischarge, short circuit, thermal |
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| Output usable voltage | USB-C PD (5V, 9V, 12V, 15V, 20V) |
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| Wall power input | USB-C input from any charger |
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| Charge while using | Passthrough charging |
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| Repairable | Bare PCB, cells are replaceable 18650s |
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## How It Works
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```
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USB-C wall charger → IP5389 board → 18650 cells (3S or 3S2P)
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↓ (passthrough)
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USB-C PD output → OPi3B (5V) + peripherals
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```
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One board, one cell pack, one output cable to the SBC. No separate modules to wire together.
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## Key Specs (varies by specific board)
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- Cell config: 3S–6S (most common: 3S or 4S)
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- Output: 45W–100W USB-C PD
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- Input: USB-C (bidirectional port)
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- Protection: overcharge, overdischarge, short circuit, thermal
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- Price: $8–15 bare PCB
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## OPi3B Power Context
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The Orange Pi 3B draws ~3-5W under load (vs OPi5's ~8W), which simplifies the battery system:
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- Lower peak current means the IP5389 board doesn't need to push its limits
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- A smaller cell pack (3S vs 3S2P) may suffice
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- Less heat generated, less thermal management needed
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- The OPi3B's 5V/3A input spec is well within what a USB-C PD board can provide
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## Cell Configuration
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TBD — need to select specific board first. Likely 3S (3 cells in series) or 3S2P (6 cells, pairs in series). 3S2P with quality 3000mAh cells gives ~6000mAh at 11.1V nominal.
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## Salvaged Battery: Not Usable
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K501U battery (B31N1429, 4240mAh, 11.4V, 3S) assessed and rejected:
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- Integrated BMS is paired to the laptop mainboard
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- Most laptop BMS boards lock when removed from their system
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- Not worth the effort to hack around
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- Low capacity (4240mAh) doesn't justify the risk
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## Alternative Approaches Considered
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### Discrete Module Stack (TP5100 + 2S BMS + Buck Converter)
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- Three separate modules, more wiring
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- TP5100 charger (2S, 2A) + 2S 10A BMS + 5V/4A buck converter
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- ~$10 in modules, works well but more complex assembly
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- Backup plan if IP5389 board has issues
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### Commercial Power Bank (decased)
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- Buy a power bank, remove plastic shell, integrate bare PCB + cells
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- Zero design work but constrained to whatever cell layout the bank uses
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- Passthrough charging not guaranteed on all models
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### UPS HAT (Waveshare / DFRobot)
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- Designed for Raspberry Pi, works via USB output with OPi3B
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- Premium price for unused GPIO header
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- Capped at 5V output, no 12V rail without extra boost converter
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## Safety Notes
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- Always use 18650 cells with matching capacity and age in parallel pairs
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- Fuse between board output and SBC (5A automotive blade fuse recommended)
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- No puffy, warm-at-rest, or sub-2.5V cells — ever
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- Match cell count to board specs (3S board = exactly 3S, don't mix)
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## TODO
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- [ ] Select specific IP5389 board model with verified reviews
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- [ ] Confirm cell count (3S vs 3S2P)
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- [ ] Verify passthrough charging on selected board
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- [ ] Order board + cells
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- [ ] Test charging and output before case integration
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