BarnacleBoy
db353ad2d1
- 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
79 lines
2.9 KiB
Markdown
79 lines
2.9 KiB
Markdown
# Power System
|
||
|
||
## Decision: IP5389 Power Bank Board (Preliminary)
|
||
|
||
All-in-one power management PCB. Replaces separate charger module, BMS, and boost/buck converter with a single board.
|
||
|
||
## Why This Approach
|
||
|
||
| Requirement | IP5389 Solution |
|
||
|------------|-----------------|
|
||
| Charge lithium cells safely | Built-in CC/CV with cell balancing |
|
||
| Battery protection | Overcharge, overdischarge, short circuit, thermal |
|
||
| Output usable voltage | USB-C PD (5V, 9V, 12V, 15V, 20V) |
|
||
| Wall power input | USB-C input from any charger |
|
||
| Charge while using | Passthrough charging |
|
||
| Repairable | Bare PCB, cells are replaceable 18650s |
|
||
|
||
## How It Works
|
||
|
||
```
|
||
USB-C wall charger → IP5389 board → 18650 cells (3S or 3S2P)
|
||
↓ (passthrough)
|
||
USB-C PD output → OPi5 (5V) + peripherals
|
||
```
|
||
|
||
One board, one cell pack, one output cable to the SBC. No separate modules to wire together.
|
||
|
||
## Key Specs (varies by specific board)
|
||
|
||
- Cell config: 3S–6S (most common: 3S or 4S)
|
||
- Output: 45W–100W USB-C PD
|
||
- Input: USB-C (bidirectional port)
|
||
- Protection: overcharge, overdischarge, short circuit, thermal
|
||
- Price: $8–15 bare PCB
|
||
|
||
## Cell Configuration
|
||
|
||
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.
|
||
|
||
## Salvaged Battery: Not Usable
|
||
|
||
K501U battery (B31N1429, 4240mAh, 11.4V, 3S) assessed and rejected:
|
||
- Integrated BMS is paired to the laptop mainboard
|
||
- Most laptop BMS boards lock when removed from their system
|
||
- Not worth the effort to hack around
|
||
- Low capacity (4240mAh) doesn't justify the risk
|
||
|
||
## Alternative Approaches Considered
|
||
|
||
### Discrete Module Stack (TP5100 + 2S BMS + Buck Converter)
|
||
- Three separate modules, more wiring
|
||
- TP5100 charger (2S, 2A) + 2S 10A BMS + 5V/4A buck converter
|
||
- ~$10 in modules, works well but more complex assembly
|
||
- Backup plan if IP5389 board has issues
|
||
|
||
### Commercial Power Bank (decased)
|
||
- Buy a power bank, remove plastic shell, integrate bare PCB + cells
|
||
- Zero design work but constrained to whatever cell layout the bank uses
|
||
- Passthrough charging not guaranteed on all models
|
||
|
||
### UPS HAT (Waveshare / DFRobot)
|
||
- Designed for Raspberry Pi, works via USB output with OPi5
|
||
- Premium price for unused GPIO header
|
||
- Capped at 5V output, no 12V rail without extra boost converter
|
||
|
||
## Safety Notes
|
||
|
||
- Always use 18650 cells with matching capacity and age in parallel pairs
|
||
- Fuse between board output and SBC (5A automotive blade fuse recommended)
|
||
- No puffy, warm-at-rest, or sub-2.5V cells — ever
|
||
- Match cell count to board specs (3S board = exactly 3S, don't mix)
|
||
|
||
## TODO
|
||
|
||
- [ ] Select specific IP5389 board model with verified reviews
|
||
- [ ] Confirm cell count (3S vs 3S2P)
|
||
- [ ] Verify passthrough charging on selected board
|
||
- [ ] Order board + cells
|
||
- [ ] Test charging and output before case integration
|