Cloning: Sailboat 400W 12V (marine)
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Solar array
Panels + how they are wired (series x parallel)
Charge controller
MPPT/PWM between array and battery
Battery bank
Identical batteries in parallel
Inverter / all-in-one
DC to AC. All-in-one units include the charge controller.
Wire runs
One-way distances for wire and fuse sizing.
| Segment | Continuous | Run (one way) | Copper wire | V-drop | Fuse/breaker |
|---|---|---|---|---|---|
| Array to charge controller | 11.0A | 10 ft | 14 AWG | 1.44% | 15APV-rated (gPV) fuse or DC breaker |
| Charge controller to battery bank | 50.0A | 4 ft | 6 AWG | 1.23% | 70AClass T |
| Battery bank to inverter | 78.1A | 3 ft | 3 AWG | 0.72% | 100AClass T |
Array to charge controller: show the math
Continuous current = 11A Design current = 11A x 1.25 (NEC continuous) = 13.8A Wire: 14 AWG copper (75C ampacity 20A); voltage drop 1.44% over 20ft round trip at 38.5V (target <= 3%) Fuse/breaker: 15A - two criteria, both required: carry the load: fuse >= design 13.8A -> next standard size = 15A protect the wire: fuse 15A <= 14 AWG ampacity 20A - OK construction: PV-rated (gPV) fuse or DC breaker
Charge controller to battery bank: show the math
Continuous current = 50A Design current = 50A x 1.25 (NEC continuous) = 62.5A Wire: 6 AWG copper (75C ampacity 65A); voltage drop 1.23% over 8ft round trip at 12.8V (target <= 3%) Fuse/breaker: 70A - two criteria, both required: carry the load: fuse >= design 62.5A -> next standard size = 70A protect the wire: fuse 70A <= 6 AWG ampacity 65A - NOT satisfied, upsize the wire bank BMS continuous 170A >= fuse 70A: the bank can hold the fuse's rated load construction: Class T (interrupt rating matters on battery mains)
Battery bank to inverter: show the math
Continuous current = 78.1A Design current = 78.1A x 1.25 (NEC continuous) = 97.7A Wire: 3 AWG copper (75C ampacity 100A); voltage drop 0.72% over 6ft round trip at 12.8V (target <= 3%) Fuse/breaker: 100A - two criteria, both required: carry the load: fuse >= design 97.7A -> next standard size = 100A protect the wire: fuse 100A <= 3 AWG ampacity 100A - OK bank BMS continuous 170A >= fuse 100A: the bank can hold the fuse's rated load construction: Class T (interrupt rating matters on battery mains)
Mount the fuse close to the battery positive terminal - it protects the wire run, so the unprotected stub should be as short as possible.
Sized for 75C copper ampacity with the NEC 1.25 continuous factor and a 3% voltage-drop target. Round up when between sizes and verify against local code.
Balance of system - shopping list
| Item | Qty | For |
|---|---|---|
| 14 AWG copper wire | 1 | ~25 ft total (10 ft one way, round trip + slack) - Array to charge controller |
| 15A PV-rated (gPV) fuse or DC breaker | 1 | Array to charge controller |
| 6 AWG copper wire | 1 | ~10 ft total (4 ft one way, round trip + slack) - Charge controller to battery bank |
| 70A Class T | 1 | Charge controller to battery bank - include the matching fuse holder/block |
| 3 AWG copper wire | 1 | ~10 ft total (3 ft one way, round trip + slack) - Battery bank to inverter |
| 100A Class T | 1 | Battery bank to inverter - include the matching fuse holder/block |
Derived from the wire and fuse guidance above. Wire lengths include round trip plus slack - verify against your actual layout, and verify ratings against local code. Buy fuses and wire from reputable electrical suppliers; marketplace listings for these items are a common source of counterfeit or mislabeled parts.
Parts list
| Part | Qty | Est. price | Where to buy |
|---|---|---|---|
Newpowa 100W 12V Monocrystalline Solar Panel (9BB) | 4 | $300 | |
Victron Energy SmartSolar MPPT 100/50 controllerdatasheet | 1 | $300 | |
SOK SK12V206P 12V 206Ah Marine batterydatasheet | 1 | n/a | |
Renogy 1000W 12V Pure Sine Wave Inverter (RNG-INVT-1000-12V-P2) inverterdatasheet | 1 | $175.99 | |
| Estimated total | $775.99(some prices unknown) |
12 passing checks - expand to see the math
passBattery matches the 12V systemSystem voltage coherence
SOK SK12V206P 12V 206Ah Marine (12.8V nominal) is a 12V-class battery.
battery nominal 12.8V is in the 12V class == system 12V
passInverter matches the 12V systemSystem voltage coherence
Renogy 1000W 12V Pure Sine Wave Inverter (RNG-INVT-1000-12V-P2) DC input is 12V-class.
inverter DC input 12V is in the 12V class == system 12V
passCharge controller supports 12V banksSystem voltage coherence
Victron Energy SmartSolar MPPT 100/50 supports 12/24V battery banks.
controller battery voltages [12, 24] include 12V
passString Voc stays at 49V at -5C - cannot reach the 100V limit at any temperatureCold-temperature string voltage
2 x Newpowa 100W 12V Monocrystalline Solar Panel (9BB) in series stays below the Victron Energy SmartSolar MPPT 100/50 max PV input voltage at your design low temperature. This string cannot reach 100V at any physically possible temperature.
Why this matters: Panel voltage rises as temperature falls. A string that measures fine in summer can exceed the controller's absolute maximum input voltage on the first cold clear morning, which can permanently destroy the controller - and at these DC power levels, failures can start fires. This is the mistake experienced builders catch most often in DIY parts lists.
Voc_string = Voc x N_series x (1 + tempCoeff/100 x (T_design - 25))
= 22.12V x 2 x (1 + (-0.36%/100) x (-5 - 25))
= 22.12V x 2 x 1.1080 = 49V
Controller max PV input: 100V
Crossover: string Voc reaches 100V at T = 25 + (100/44.2 - 1) x 100/-0.36 = -325.1C (below absolute zero - never reached)passString Vmp 38.5V has healthy margin over the 12V bankMPPT voltage margin
Clears the start floor cold and the hot-weather floor with sag included.
Vmp_string = 19.23V x 2 = 38.5V Start floor = V_batt + 5V = 12 + 5 = 17V Hot Vmp (~11% sag) = 38.5V x 0.89 = 34.2V vs hot floor 20V
passArray short-circuit current 11.00A is within the 60A limitArray current vs controller input limit
Within the Victron Energy SmartSolar MPPT 100/50 published max PV short-circuit current.
Isc_array = 5.50A x 2 parallel = 11.00A Controller max PV short-circuit current: 60A = 60A (manufacturer-specified, compared directly)
passController can pass the array's full output (31.3A of 50A rated)Array size vs controller charge output
No clipping at rated conditions.
Array = 100W x 4 panels = 400W Potential charge current = 400W / 12.8V = 31.3A Controller rated charge current: 50A
passArray 400W is within the controller's 700W rating at 12VMax array wattage for battery voltage
Within the published maximum array wattage.
Array = 100W x 4 panels = 400W Controller max array wattage at 12V: 700W
passVictron Energy SmartSolar MPPT 100/50 supports LiFePO4 chargingBattery chemistry support
Controller has a lithium profile or user-adjustable charge voltages.
battery chemistry = lifepo4; controller lifepo4_profile = true
passBank BMS limit 170A comfortably covers the inverter's 78.1A drawInverter draw vs battery BMS limit
Healthy headroom at full inverter load.
Inverter draw = 1000W / 12.8V = 78.1A Bank BMS limit = 170A x 1 batteries = 170A Headroom band starts at 80% of limit = 136A
passBank BMS peak 200A covers the inverter's 156.3A surgeInverter surge vs battery peak limit
Surge loads within the bank's published peak rating.
Surge draw = 2000W / 12.8V = 156.3A Bank BMS peak = 200A x 1 batteries = 200A
passCharge current 50A is within the bank's 70A capacityCharge current vs bank capacity
Charge rate within limits.
Controller rated charge = 50A Bank max charge = manufacturer max charge 70A x 1 = 70A
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