# DC-02 — Open Solar Trailer: DC Architecture **Status: design-review draft — not a construction drawing.** Basis: owner-supplied DC-02, with its Victron equipment explicitly selected by the owner on 17 September 2026. Two SmartSolar MPPT 150/35 controllers; two 51.2 V, 100 Ah batteries in parallel; a MultiPlus-II 48/5000/70, 120 V inverter/charger. Exact battery compatibility remains unconfirmed. This sheet defines connection roles, polarity, monitoring boundaries, and protective functions. It does not specify cable gauges, fuse ratings, terminal layouts, grounding/bonding, or physical installation order. Protecting and isolating a circuit may require several devices; a block is not necessarily a single purchased part. The companion [AC-03 architecture](https://open-solar-trailer.pages.dev/electrical.html#ac-03) describes the inverter's AC-out-1 distribution and optional AC-in shore path. Its AC neutral is separate from the DC-negative nodes defined here. [PG-04](https://open-solar-trailer.pages.dev/electrical.html#pg-04) adds the protection and bonding draft. The DC/PV ground-fault arrangement remains unselected; it does not approve a hard jumper from N1 to chassis. ## A. Solar-input architecture Each arrow represents a positive-and-negative PV circuit, not a single wire. Only like polarities join at the parallel junctions. R1–R4 are roof panels; L1–L2 and W1–W2 are the two panels on each side. PV protection selection remains a design-review item. ```mermaid flowchart TB R12["ROOF STRING A
R1 and R2 in series"] R34["ROOF STRING B
R3 and R4 in series"] RJ["ROOF PARALLEL JUNCTION
Two series strings in parallel — 2S2P"] SR["S-R: ROOF PV ISOLATOR
Simultaneously disconnects PV + and PV -"] MR["MPPT-R: ROOF CONTROLLER
SmartSolar 150/35
PV input terminals"] L12["LEFT-SIDE STRING
L1 and L2 in series"] SL["S-L: LEFT PV ISOLATOR
Simultaneously disconnects PV + and PV -"] W12["RIGHT-SIDE STRING
W1 and W2 in series"] SW["S-W: RIGHT PV ISOLATOR
Simultaneously disconnects PV + and PV -"] WJ["WING PARALLEL JUNCTION
Left and right strings in parallel — 2S2P"] MW["MPPT-W: WING CONTROLLER
SmartSolar 150/35
PV input terminals"] R12 --> RJ R34 --> RJ RJ --> SR SR --> MR L12 --> SL W12 --> SW SL --> WJ SW --> WJ WJ --> MW ``` The roof and wing PV circuits stay separate. Their controller battery outputs connect to the common DC distribution in Section C; the PV circuits do not connect directly to the battery bus. Either complete wing-side string can remain connected while the other is isolated. This does not give each individual panel independent charging capability. Both wing sides share one tracker. ## B. Battery-bank architecture **These are connection paths, not directional energy arrows.** A battery block has distinct positive and negative terminals. P0, P1, N0, and N1 are different electrical junctions, not interchangeable names for one bus. Crossing lines without a labeled junction do not represent an electrical connection. ```mermaid flowchart TB B1["B1: BATTERY 1
51.2 V / 100 Ah / 5.12 kWh"] B2["B2: BATTERY 2
51.2 V / 100 Ah / 5.12 kWh"] F1["B1 SOURCE PROTECTION
Individual Class T fuse
Service isolation to be defined"] F2["B2 SOURCE PROTECTION
Individual Class T fuse
Service isolation to be defined"] P0["P0: BATTERY-POSITIVE JUNCTION"] QB["COMMON BANK FEEDER
Overcurrent protection and disconnect
Final devices and ratings TBD"] P1["P1: SYSTEM-POSITIVE BUS
Protected equipment branches connect here"] N0["N0: BATTERY-NEGATIVE JUNCTION
Battery returns only"] SH["SH1: BATTERY-MONITOR SHUNT
BATTERY MINUS to SYSTEM MINUS"] N1["N1: SYSTEM-NEGATIVE BUS
All charger and load returns connect here"] B1 ---|Positive terminal| F1 B2 ---|Positive terminal| F2 F1 --- P0 F2 --- P0 P0 --- QB QB --- P1 B1 ---|Negative terminal| N0 B2 ---|Negative terminal| N0 N0 ---|BATTERY MINUS terminal| SH SH ---|SYSTEM MINUS terminal| N1 ``` The parallel bank remains 51.2 V nominal, with 200 Ah / 10.24 kWh nominal capacity. These are not two batteries connected in series. P0 and N0 identify battery-combining junctions, not a commitment to buy a separate busbar product for every labeled node. The combined battery feeder must be protected for the combined available fault current; coordination with the individual battery fuses is unresolved. The shunt's small fused Vbatt+ supply is listed below; it is not a high-current connection through the shunt's negative terminals. ## C. Equipment connections to the common buses MPPT-R and MPPT-W below are the SAME TWO controllers shown in Section A. | Equipment / terminal | Positive connection | Negative connection | Role | |---|---|---|---| | MPPT-R battery terminals | BAT+ to P1 through its own battery-side overcurrent protection and isolation | BAT- to N1 | Roof charging | | MPPT-W battery terminals | BAT+ to P1 through its own battery-side overcurrent protection and isolation | BAT- to N1 | Wing charging | | Inverter/charger DC terminals | DC+ to P1 through its protected, isolatable inverter branch | DC- to N1 | Draws DC for 120 V loads; can return charging energy when approved optional AC input is installed | | Optional 48 V-to-12 V converter input | Input+ to P1 through its own protection and isolation | Input- to N1 | Supplies a separate, protected 12 V distribution system | | SmartShunt monitor supply | Small manufacturer-specified fused lead from battery positive / P0 to Vbatt+ | Reference is through its installed shunt; no added bypass | Keeps battery monitoring powered | Each MPPT requires protection on its BATTERY side, even though its PV input also has an isolator. PV and battery-side protection have different jobs. See the manufacturer manuals before selecting any devices. ## D. Required design notes ### Shunt boundary Both battery negatives connect only to N0, then through SH1 to N1. The negative connections of the inverter, both MPPT battery outputs, and all other DC loads/chargers belong on N1. Do not add a normal-current path that bypasses the shunt. The shunt measures NET energy entering and leaving the battery bank. Solar energy that feeds a load directly at the system buses is not battery throughput. Use controller data and separate load metering for total solar generation and delivered-load measurements. ### Battery disconnect is not an all-source shutdown Opening the common bank disconnect does not establish that the system bus is de-energized: solar controllers and an optionally shore-powered inverter/charger are additional sources. The fused monitor supply at P0 also remains battery-powered. For the SmartSolar controllers, Victron prescribes PV off before disconnecting battery power, and battery connected before restoring PV. A complete system shutdown must also account for AC input, loads, and retained energy. Sunlit PV wiring upstream of an open isolator remains a source. This sheet is not a lockout procedure. ### Grounding and bonding remain required This sheet does not release a grounding design. A later protection/bonding sheet must address PV frames, steel mounting rails, trailer chassis, enclosures, DC system grounding, and ground-fault protection. Do not infer a PV-positive or PV-negative chassis connection from these diagrams. Victron specifically says not to ground PV conductors separately. ### Battery controls and limits remain open Confirm the exact batteries, parallel-operation instructions, charge/discharge limits, temperature limits, and compatible shutdown/control method. Account for BOTH MPPTs and optional inverter charging together, including operation if one battery is unavailable. No battery communications link, coordinated BMS shutdown, or current limit is asserted by this diagram. No 12 V equipment connects directly to the 51.2 V bank. No direct trailer-bank connection to the golf-cart battery is included. No alternator connection is included. ## Manufacturer reference checks [S1] Victron SmartSolar 150/35 and 150/45 installation manual — battery-side protection, PV configuration, grounding, and connection sequence. https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_150-35__150-45/en/installation.html [S2] Victron SmartShunt installation manual — BATTERY MINUS / SYSTEM MINUS boundary and fused Vbatt+ supply. https://www.victronenergy.com/media/pg/SmartShunt/en/installation.html [S3] Victron SmartSolar operation manual — shutdown and restart procedure, section 6.5. https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_150-35__150-45/en/operation.html [S4] Victron MultiPlus-II 120 V installation manual — DC fusing, disconnects, and connection requirements. https://www.victronenergy.com/media/pg/MultiPlus-II_120V/en/installation.html Reference pages checked 17 September 2026. These references support individual connection rules, not approval of this complete custom trailer design.