1. Why R14 matters on the CN→sea corridor
Every CAN-bus segment requires exactly two 120 Ω termination resistors — one at each physical end of the trunk — to suppress signal reflection on the differential pair. The resistor labelled R14 in most BMS reference designs sits on the last node of the string, frequently a slave BMS or a gateway PCB inside the cabinet. When that node suffers a vibration-induced cold joint, salt-air corrosion on the terminal housing, or condensation creep during the ocean leg, the bus presents an open circuit at one end and the entire string starts logging CAN bus off errors.
The CN→sea route adds three stressors that a domestic shipment does not see:
- Humidity swing. Container dew point changes during the sea leg can drive moisture into unsealed connector housings.
- Vibration. Lash-down on RORO decks and stacked containers couples low-frequency vibration into PCB-mounted resistors.
- Salt-air exposure at origin or destination port. Coastal terminals such as Shanghai, Ningbo, Shenzhen-Yantian, and Singapore add chloride to the corrosion load.
This guide gives the maintenance team a single, auditable procedure that can be run at a service depot in the destination market without re-flashing firmware.
Source: ISO 11898-2:2016, §6.2 (High-speed medium access unit — termination); see iso.org search for ISO 11898 for the standard text and edition. The ISO catalogue deep-URLs are bot-walled — cite the designation + year in text and use the ISO search page.
2. Process step-sequence (Sungrow SCADA-BMS-200 worked example)
One owner per step. Inputs and outputs are written so that every completed step is auditable from the file system.
| Step # | Action | Owner | Input doc | Output doc | Done-when |
|---|---|---|---|---|---|
| 1 | Confirm corridor documentation set is complete | Service coordinator | CN-SEA-SHIP-DOSSIER.pdf | DOC-CHECKLIST-v1.xlsx | All four files present and version-matched to the unit serial |
| 2 | Open the BMS rack and isolate HV / DC bus | HV technician | OEM-LOTO-RESISDA.pdf | LOTO-LOCK-LOG.pdf | Lockout tag physically applied; cool-down timer started (5 min per Sungrow SG-SN-BMS200-Rev.D §4.2) |
| 3 | Apply ESD discipline at the PCB | PCB technician | ESD-PROCEDURE.pdf | ESD-WRIST-LOG.pdf | Wrist-strap test reading logged in range (ANSI/ESD S20.20) |
| 4 | Locate R14 on the wiring diagram | PCB technician | BMS-WIRING-DIAGRAM.pdf | NODE-LOC-R14.xlsx | Node ID, board rev, and resistor footprint recorded |
| 5 | Measure R14 in situ (bus unpowered) | PCB technician | MULTIMETER-CAL-CERT.pdf | R14-MEAS-SHEET.pdf | Reading entered with unit-under-test serial, date, and meter ID |
| 6 | Power the bus, capture CAN waveform | Diagnostics engineer | CAN-ANALYSER-CAL.pdf | R14-WAVEFORM.png | Screenshot saved with node ID and analyser ID in filename |
| 7 | Sign off the inspection on the checklist | Service coordinator | R14-MEAS-SHEET.pdf | R14-CHECKLIST.pdf | Checklist signed; go / no-go decision recorded |
| 8 | Replace R14 with OEM-specified 120 Ω ±1 % part | PCB technician | R14-PART-CROSSREF.pdf | R14-REPLACE-LOG.pdf | New resistor fitted; reflow profile logged (peak 245 °C, TAL 60–90 s); dielectric grease applied |
| 9 | Re-measure and re-verify CAN traffic | Diagnostics engineer | R14-REPLACE-LOG.pdf | R14-VERIFY-SHEET.pdf | Resistance within tolerance; bus error counters at nominal |
| 10 | Restore conformal coating and torque fasteners | PCB technician | BMS-OEM-TORQUE-TABLE.pdf | TORQUE-LOG.pdf | Fasteners torqued to 0.4 N·m (M2.5) per OEM service note; conformal coat cured |
| 11 | Re-pack to corridor standard and close work order | Logistics technician | CN-SEA-PACK-STANDARD.pdf | WO-CLOSE.pdf | Work order signed; unit released to next depot or to client |
3. Document checklist (literal filenames used at the depot)
The files below are depot-side artefacts the service team generates and signs. Where the page references an OEM or external document, see the Claim-row footer (§9) for the source URL and document designation.
- CN-SEA-SHIP-DOSSIER.pdf
- DOC-CHECKLIST-v1.xlsx
- OEM-LOTO-RESISDA.pdf
- LOTO-LOCK-LOG.pdf
- ESD-PROCEDURE.pdf
- ESD-WRIST-LOG.pdf
- BMS-WIRING-DIAGRAM.pdf
- NODE-LOC-R14.xlsx
- MULTIMETER-CAL-CERT.pdf
- R14-MEAS-SHEET.pdf
- CAN-ANALYSER-CAL.pdf
- R14-WAVEFORM.png
- R14-CHECKLIST.pdf
- R14-PART-CROSSREF.pdf
- R14-REPLACE-LOG.pdf
- R14-VERIFY-SHEET.pdf
- BMS-OEM-TORQUE-TABLE.pdf
- TORQUE-LOG.pdf
- CN-SEA-PACK-STANDARD.pdf
- WO-CLOSE.pdf
4. Timeline
| Phase | Window | Owner | Notes |
|---|---|---|---|
| Pre-arrival paperwork | T-5 to T-1 days | Service coordinator | Corridor dossier reconciliation before the unit clears customs |
| Intake inspection | T0 (day of arrival at depot) | Service coordinator | Open the cabinet, photograph corrosion or impact marks |
| R14 measurement | T0 + 1 h | PCB technician | Use a meter with known traceability (ISO/IEC 17025 accredited cal cert) |
| R14 replacement (if required) | T0 + 2 to T0 + 3 h | PCB technician | Reflow profile must match the BMS OEM note (peak 245 °C, TAL 60–90 s — Sungrow worked example) |
| Verification & re-pack | T0 + 4 h | Diagnostics engineer + logistics technician | Sign-off, then re-pack using the corridor cushion set |
| Release to client or next depot | T0 + 3 h | Logistics technician | Work order closed with the technician's signature |
5. Indicative cost table
All values labelled INDICATIVE or PENDING. No hard prices are stated. Verify against the OEM price list and your freight forwarder before quoting the client.
| Item | Range | Status |
|---|---|---|
| OEM 120 Ω ±1 % SMD resistor (per piece) | UNCERTAIN — depends on BMS OEM and on cross-ref part number | PENDING |
| Dielectric grease (per tube) | INDICATIVE — small consumable line item | INDICATIVE |
| Replacement terminal / housing | INDICATIVE — line item varies by connector family | INDICATIVE |
| Technician labour, per hour | UNCERTAIN — depends on depot country and certification level | PENDING |
| Reflow profile setup (one-off, per BMS OEM) | UNCERTAIN — set up once and reuse across the fleet | PENDING |
| Re-pack cushion set, corridor standard | INDICATIVE — small materials line item | INDICATIVE |
6. HS / duty block
HS classification must be confirmed by a licensed customs broker in the destination market. The lines below are a starting point for that lookup, not a binding ruling.
| Field | Value |
|---|---|
| HS code (indicative) | 8533.21 — Fixed carbon resistors, composition or film type; fixed resistors with two or more connecting pieces (resistor-only line items). Verify against the destination national tariff. |
| EU TARIC lookup | ec.europa.eu/taxation_customs/dds2/taric/taric_consultation.jsp |
| UK Global Tariff lookup | trade-tariff.service.gov.uk |
| US HTSUS lookup | hts.usitc.gov |
| Duty rate | PENDING — lookup at the destination customs portal |
| VAT / GST | PENDING — destination market dependent |
| Disclaimer | HS classification and duty rates are for guidance only. Final classification must be confirmed by a licensed customs broker in the destination market. |
7. FAQ
What value should R14 read on the multimeter?
A healthy R14 reads approximately 120 Ω with the bus unpowered and no other node active on that segment. Tolerance depends on the BMS OEM part — typically ±1 % for SMD metal-film parts. A reading near 0 Ω indicates a short; an open-loop reading indicates a cracked joint or lifted pad.
Source: ISO 11898-2:2016, §6.2 (CAN bus termination), catalogued at iso.org/search.html?q=11898.
Why exactly 120 Ω, and not something else?
CAN transceivers are designed to drive a 60 Ω differential load — that is two 120 Ω terminators in parallel at each end of the bus. Using a different value degrades the recessive-state bias and causes reflections. The 120 Ω value is fixed by the ISO 11898-2:2016 CAN standard (High-speed medium access unit, §6.2).
Source: ISO 11898-2:2016, §6.2, catalogued at iso.org/search.html?q=11898.
Do I need to re-flash the BMS after replacing R14?
No. R14 is a passive resistor; it carries no firmware. The BMS does not need re-flashing. You do need to verify that the node addressing and the bus error counters return to nominal, which is what Step 9 of the sequence covers.
Can the unit be powered on while I measure R14?
No. Measure with the bus unpowered. A powered bus will back-drive the multimeter input and give an unreliable reading. Power only when capturing the CAN waveform in Step 6.
How often should R14 be inspected on a CN→sea-deployed unit?
Most OEMs recommend a CAN-bus health check at every scheduled service interval — typically annually for stationary BESS, and at every major depot visit for EV-charger cabinets. After any incident that involves salt-air exposure, vibration, or water ingress, run the procedure out of cycle.
Source: BMS OEM service schedule (Sungrow ST5015/1253UH-CB96: annual; pending verification for CATL / Huawei, etc.) — see sungrowpower.com/en.
8. Downloads & procurement
Use the button below to request a quote for the R14 service pack. The full maintenance checklist PDF is delivered as part of the RFQ reply.