add power system: IP5389 board + 18650 array decision
- IP5389 power bank board selected (preliminary) - All-in-one: charging, BMS, USB-C PD output - Rejected K501U battery (integrated BMS not reusable) - Documented alternatives considered (TP5100+2S BMS+buck, UPS HAT) - Updated parts list with power system BOM - Cost estimate now 06-230 (was 70-190) - Added power-system.md, updated design-decisions.md
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@ -36,6 +36,14 @@ User sits at the **stern**, facing the **bow**. Hinge axis runs port-to-starboar
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### Bow Wall Functions
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- Power input (barrel jack or USB-C PD)
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- Power input (USB-C for IP5389 board charging)
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- Exhaust fans blowing away from user
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- Heat management surface
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## Power System
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IP5389 power bank board (preliminary). All-in-one: charging, BMS, USB-C PD output. See [power-system.md](power-system.md) for details.
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## Input Device
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ThinkPad TrackPoint keyboard (specific model TBD based on availability). Chosen for built-in TrackPoint pointer and 15.6" deck space compatibility.
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@ -32,8 +32,10 @@
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| Item | Specification | Source | Est. Cost | Status |
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|------|--------------|--------|-----------|--------|
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| Power supply | USB-C PD or 12V 2A | Amazon | $8-12 | To purchase |
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| (Future) Battery | 10,000-20,000 mAh PD | TBD | $20-40 | Future |
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| IP5389 power board | USB-C PD, 3S, bare PCB | AliExpress | $8-15 | Preliminary selection |
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| 18650 cells | 3S or 3S2P, quality brand | User's pick | $12-24 | To purchase |
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| 5A blade fuse + holder | Automotive | Amazon | $2 | To purchase |
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| USB-C wall charger | 45W+ PD, for charging | Amazon | $10-15 | To purchase |
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### Networking
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@ -62,24 +64,24 @@
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| MicroSD | $12 |
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| USB hub | $20 |
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| USB enclosure | $12 |
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| Power supply | $10 |
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| Power system (board+cells+fuse+charger) | $32-56 |
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| WiFi dongle | $12 |
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| **Subtotal** | **$194** |
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| **Subtotal** | **$206-230** |
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### With Optional Items
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| Category | Cost |
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|----------|------|
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| Base build | $194 |
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| Base build | $206-230 |
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| Heatsink/cooling | $10 |
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| Panel-mount cables | $15 |
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| **Total** | **$219** |
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| **Total** | **$231-255** |
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### Future Additions
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| Category | Cost |
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|----------|------|
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| Battery pack (portable) | $20-40 |
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| Battery pack (portable) | Integrated in base build |
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| Case materials | TBD |
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| Custom PCB | TBD |
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@ -96,7 +98,9 @@
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- MicroSD card
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- Powered USB hub
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- USB enclosure or flash drive
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- Power supply
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- IP5389 power board + 18650 cells
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- 5A fuse + holder
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- USB-C PD wall charger (45W+)
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- WiFi dongle
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---
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79
docs/power-system.md
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79
docs/power-system.md
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@ -0,0 +1,79 @@
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# 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 → OPi5 (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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## 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 OPi5
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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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