--- tags: [project-drogheda, hardware, bom, cost, power] project: Project Drogheda author: Helgen CTO date: 2026-09-09 status: Draft — first-pass estimate --- # 5 V source: on-board (V6 / U25) vs external Mean Well SD-15B-05 (V5) !!! warning "Designators from before 22-Oct (T43)" This document keeps the designators the board had on its date. Since 22-Oct (T43) the V5.6, V5.7 and v6 carry new ones, and several old names now belong to another part: on the V5.6/V5.7 the LTC4040 is U14 (was U6); on the v6, U6 is the modem and the LTC4040 is U17. To read it against today's board, use the [old → new table](https://drogheda.helgen.online/hardware/designadores-t43-22oct/#8-tablas-viejo-nuevo) (in Spanish); parts already gone by 22-Oct are not in it. > **Bottom line:** the on-board 24→5 V block already captured in V6 costs > **≈ US$2.2 / MX$37 per board** in parts. The external Mean Well it replaces costs > **≈ MX$330 per unit** all-in as currently purchased. **Net saving ≈ MX$290/unit** > (≈ MX$8,700 at 30 units, ≈ MX$29,000 at 100). The money is not the interesting part — > the isolation loss and the 3 A → 3.5 A headroom are. Prices: LCSC/JLCPCB live database (2026-09-09) · FX **USD 1 = MXN 16.91**. --- ## 1. What each version actually does | | **V5 (as built)** | **V6 (as captured in the schematic)** | |---|---|---| | 24→5 V | **External** Mean Well SD-15B-05 → `P2` (JST 2-pin) → `VEH5V` | **On-board** `U25` TPS54360B: `VIN_PROT` → `VEH5V` | | Rating | 5 V / **3 A** isolated (1.5 kVDC) | 5 V / **3.5 A**, non-isolated, 60 V input | | Entry chain | `Q10` (IRFR5305) + `D10` (SMBJ33A) → fan buck only | `F2 → Q23 → D32 (SMCJ33A) → C149/C150 → U25 → D34/L22 → C153/C154` | | Extra parts on board | `P2` connector | 15 fitted + 2 DNP (`R124`/`R125`) | V6 keeps the fan buck (`U2`) and the 3V3_ETH buck (`U12`); `U7` was deleted. Neither ever made the main rail — this comparison is only about the `VEH5V` source. --- ## 2. On-board block — BOM cost per board `U25` TPS54360B · `L22` SRP1265A-100M · `D34` B560C · `D32` SMCJ33A · `C149`/`C150` 2.2 µF/100 V · `C151` 100 µF/50 V · `C152` 100 nF · `C153`/`C154` 47 µF/16 V · `C155`/`C156` · `R120`–`R123` — plus the entry chain `F2` · `Q23` · `D33` · `R119`. | Line | 30 boards | 100 boards | 500 boards | |---|---:|---:|---:| | `U25` TPS54360BDDAR (C524806) | $0.487 | $0.428 | $0.419 | | `L22` SRP1265A-100M 10 µH/10 A (C840531) | $0.639 | $0.554 | $0.504 | | `D34` B560C 5 A/60 V (C85100) | $0.220 | $0.179 | $0.158 | | `D32` SMCJ33A TVS (C699039) | $0.114 | $0.091 | $0.079 | | `C149`/`C150` 2.2 µF/100 V 1210 ×2 † | $0.180 | $0.180 | $0.160 | | `C151` 100 µF/50 V elco (C134502) | $0.149 | $0.149 | $0.149 | | `C153`/`C154` 47 µF/16 V 1210 ×2 (C5440143) | $0.185 | $0.185 | $0.127 | | `C152`, `C155`, `C156`, `R120`–`R123` | $0.022 | $0.022 | $0.022 | | **Buck subtotal** | **$1.996** | **$1.788** | **$1.618** | | `Q23` IRFR5305 (C2624) | $0.262 | $0.227 | $0.193 | | `F2` 2 A/1812 fuse †, `D33` BZX84C15, `R119` | $0.144 | $0.144 | $0.144 | | **Entry subtotal** | **$0.406** | **$0.371** | **$0.337** | | **Parts / board** | **$2.40** | **$2.16** | **$1.96** | | JLC extended-part setup (7 new uniques × $3, amortised) | $0.70 | $0.21 | $0.04 | | SMT placement (~50 joints) | $0.10 | $0.09 | $0.09 | | **All-in / board** | **$3.20 · MX$54** | **$2.46 · MX$42** | **$2.09 · MX$35** | † `C149`/`C150` and `F2` have no LCSC part pinned yet — estimated at $0.09 and $0.12. Board outline stays 140×100, so **the block costs zero PCB area money**. --- ## 3. External Mean Well — cost per unit | Item | MXN | Source | |---|---:|---| | Mean Well SD-15B-05 | **300** | `BOM-master.md` §1 item 12 (as purchased locally) | | — same part, direct import | *189–200* | Mouser $11.15 / Arrow $11.85 @100 | | DC PSU bracket (ASA print) | 20 | `BOM-master.md` §1 item 3 | | `P2` JST-XH + housing + crimps + wire | ~12 | est. | | **Total** | **≈ 332** *(≈ 221 if imported direct)* | | Plus ~5 min/unit of mounting and wiring labour, and one more connector in the vibration path — `P2` is exactly the class of joint the RCA blamed. --- ## 4. Net | Volume | External (local price) | On-board | **Saving** | |---|---:|---:|---:| | per unit | MX$332 | MX$42 | **MX$290** | | 30 units | MX$9,960 | MX$1,260 | **MX$8,700** | | 100 units | MX$33,200 | MX$4,200 | **MX$29,000** | Against best-case direct import (MX$221) the saving is still **≈ MX$180/unit**. --- ## 5. What actually decides this (not the money) **For on-board:** - **3 A → 3.5 A.** The 10-Ago boot-loop was the SD-15B's 3 A ceiling. It also makes the standing `RS1` errata (3.12 A input limit sitting *above* a 3 A supply) go away by itself. - One fewer sub-assembly, one fewer connector, no import lead time on a PSU. **Against on-board:** - **Isolation is lost.** SD-15B-05 is 1.5 kVDC isolated; TPS54360B is not. HBOX ground becomes the cabinet 24 V return. The ignition already shares that return — worth a deliberate look at the ground topology before this is locked. - The EMC burden moves onto our board. The copper plan already calls `U25`'s input loop the loudest on the PCB; that stops being Mean Well's problem. - No field-replaceable part. Today a dead PSU is a 10-minute swap; after this it is a board. --- ## 6. 🔴 Side finding — the MP1584s cost more than this whole question Genuine `MP1584EN-LF-Z` (C15051) is **$2.21 @100** on LCSC. V6 carries two (`U2`, `U12`) = **$4.41 / MX$75 per board**, against **$0.43** for the TPS54360B or **$0.58** for the AP64350 already qualified as `U20`. Re-speccing those two rails onto a part already in the BOM saves **≈ $3.5 / MX$59 per board** — more than the entire 5 V-source saving — and it also retires EMC findings 3 and 4, which named the MP1584s directly. Worth a separate decision. --- ## 7. Battery — LiPo vs Li-ion, first pass | | Energy | Price | **MXN / Wh** | |---|---:|---:|---:| | **Li-ion** Hyvel 18650 1S4P (current pack) | ~43 Wh | MX$204 | **≈ 4.7** | | **LiPo** 2000 mAh 1S, SparkFun @ Sandorobotics | 7.4 Wh | MX$270 | **≈ 36** | | **LiPo** 2000 mAh 1S, generic (indicative) | 7.4 Wh | ~MX$90–160 | **≈ 12–22** | To reach today's 43 Wh with 2000 mAh pouches you need **6 in parallel**: MX$540–1,620 against MX$204. Li-ion 18650 is **3–8× cheaper per Wh**, and it is also the better cell for a box that runs hot — pouch cells swell, and heat is this product's standing failure mode. LiPo buys thickness and form factor, nothing else. Treat the 2000 mAh cells as bench hardware. ⚠ The generic LiPo row is indicative — MercadoLibre/Amazon MX would not serve prices to an automated fetch; get one real quote before this line is used in a decision.