I've now thoroughly reviewed both PDFs. Let me give you a clear summary.
Yes, both USB charging and battery protection are already covered in your battery architecture — they're part of the self-contained battery pack design you've been developing. Here's the breakdown:
The battery pack includes a full USB-C PD charging system built into the electronics bay at the bottom of the scaffold: ppl-ai-file-upload.s3.amazonaws
- USB-C panel-mount port (IP67, on the side of the battery end cap)
- PD trigger board (ZY12PDN or STUSB4531, ~31×15×4mm) — negotiates 20V from any charger 45W–240W automatically
- Boost converter (XL6019, 20V→42V CC/CV) — steps up to pack charge voltage
- Total electronics fit in ~60×45×25mm, tucked into the electronics bay
The key design point: all electronics live on the battery, not in the frame. You pull the battery out, plug your MacBook charger into the USB-C port on the side, charge on the kitchen table. The frame side is 100% passive — just flat copper pads. ppl-ai-file-upload.s3.amazonaws
A 10S BMS is included in the electronics bay, handling: ppl-ai-file-upload.s3.amazonaws
- Overcurrent, overvoltage, undervoltage protection
- Short-circuit and temperature cutoff
- Cell balancing during charge
- Per-cell fusing was deliberately skipped — at 3.5A per cell in 2P, the BMS alone handles everything adequately
The connector design settled on an elevated pad island + recessed pogo pin dock approach: ppl-ai-file-upload.s3.amazonaws
- Frame side: Elevated flat gold pads on a raised "speed bump" — water sheets off, no pooling
- Battery side: 6-pin pogo block recessed deep inside a dock cavity — finger-safe by geometry (IP2X-style)
- 2 power pins + signal/thermistor/comm pins
Your notes confirm the DT dimensions are not locked down yet, and you've been exploring both round and oval options: ppl-ai-file-upload.s3.amazonaws
| Discussed Size | Context |
|---|---|
| 50mm round | Original spec for 2×2 grid of 21700 cells |
| 55–60mm | Referenced for fitting 21700s with BMS/wiring room |
| 43×59mm oval | The 1-2-1 diamond layout (narrower, taller) |
| ~50×65 (your current thinking) | Wider than the diamond, gives more lateral room |
The 50×65 oval gives you more cross-sectional area than the 43×59 diamond and better lateral stiffness for pedaling loads. The tall axis (65mm) resists braking/vertical loads while the narrow axis (50mm) keeps the frame slim between your knees. Since you're building in aluminum (not steel), you have freedom to specify custom oval tubing from the fabricator. ppl-ai-file-upload.s3.amazonaws
The scaffold cage parameters (currently cagew = 53, cageh = 48 in the OpenSCAD file) would need updating to match whatever oval you settle on. With a 50×65 outer and ~2mm wall, you'd have roughly 46×61mm inner bore — plenty of room for the 2×2 cell grid (~43×43mm footprint) plus wiring channel and air gaps. ppl-ai-file-upload.s3.amazonaws
Bottom line: your electronics stack is already specced and costed at $22–38 total for BMS + USB-C PD + boost converter. The DT oval just needs to be finalized around whatever gives comfortable clearance for the scaffold + 1mm air gap on each side. ppl-ai-file-upload.s3.amazonaws
I now have all the data needed. Let me also confirm the BT F011 B720C dimensions from the workbook data, and note the notes about which are truly "intube" vs which Bafang labels as "intube" on their page.
Based on all the sourced data, here's the completed datasheet:
Bafang In-Tube Battery Lineup — Completed Datasheet
The F361 actually also fits dimensionally (51 × 59 mm < 65 × 55 mm on one axis — though 59 mm > 55 mm, so it's borderline on height depending on tube geometry). Still hits the same BMS handshake wall as the F040.[bafang-e]
Based on all the sourced data, here's the completed datasheet:
Bafang In-Tube Battery Lineup — Completed Datasheet
Notes on the filled data
BT F361 — The "Unknown — fits smaller frame tubes" placeholder is now resolved. The OEM datasheet gives 51 × 59 × 475 mm. This is noticeably larger than the F040 (48.5 × 48.5), so it still wouldn't fit a typical eRoad tube, but it's the slimmest option for city bikes with a larger DT. bafang-e
BT F020 / F021 — Both share the same body: 434 × 68 × 76.5 mm. The Workbook lists the cross-section as 67 × 74 mm, which is slightly different from the OEM page's 76.5 × 68 mm — the discrepancy is a labeling axis swap between sources, but the physical envelope is the same. The eurekabike source you had (67 × 74 mm) matches the Workbook. The OEM page's 76.5 × 68 mm just has W and H swapped. Both describe the same rectangle. [bafang-e](https://www.bafang-e.com/en/oem-area/components/component/battery/bt-f020b504c)
BT F011 (540 and 720) — Same physical housing, same 74 × 83 × 398 mm. The 540 Wh variant is 36V/15Ah, the 720 Wh variant is 48V/15Ah (13S rather than 10S). Different string count in the same shell explains the voltage/capacity difference at identical dimensions. [bafang-e](https://www.bafang-e.com/en/oem-area/components/component/battery/bt-f011b540c)
BT F440 — 75 × 77 × 435 mm, 48V, 21700 cells. Slightly slimmer cross-section than the F011 family but longer. bafang-e
BT F200 — 97 × 91 × 442 mm, 48V, 18650 cells. The oldest cells in the lineup; notably bulkier than the 21700-based models despite lower Wh density. bafang-e
BT F381 vs F380 — These share the same 427 mm length but differ in width: the F381 is 79 × 96 mm and the F380 is 116 × 96 mm. The F380 is the wider "medium" variant and F381 the slimmer one. Both are 960 Wh / 48V / 20 Ah. bafang-e.com
Your Frame Fit Analysis — Updated Numbers
With the correct F361 dimensions now confirmed, the fit picture is clearer than ever:
The F361 actually also fits dimensionally (51 × 59 mm < 65 × 55 mm on one axis — though 59 mm > 55 mm, so it's borderline on height depending on tube geometry). Still hits the same BMS handshake wall as the F040. [bafang-e](https://www.bafang-e.com/en/oem-area/components/component/battery/bt-f361b360c)