RV 30A lithium upgrade 12V
12V system, designed for a -10C (14F) cold snap - saved 2026-08-16
Compatibility checks
warningBank peak current limit unpublished - surge headroom unverifiedInverter surge vs battery peak limit
The Victron Energy MultiPlus-II 12/3000/120-50 2x120V can surge to 5500W (429.7A at 12.8V). Victron Lithium Battery Smart 12.8V 330Ah does not publish a BMS peak discharge rating, so we cannot verify motor-start surges will not trip the BMS.
surge 5500W / 12.8V = 429.7A; BMS peak limit unpublished
13 passing checks - expand to see the math
passBattery matches the 12V systemSystem voltage coherence
Victron Lithium Battery Smart 12.8V 330Ah (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
Victron Energy MultiPlus-II 12/3000/120-50 2x120V 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 88.9V at -10C - safe down to -58.8C (-73.8F)Cold-temperature string voltage
3 x Renogy 200W 12V Monocrystalline Solar Panel (RSP200D) in series stays below the Victron Energy SmartSolar MPPT 100/50 max PV input voltage at your design low temperature. The string would not reach the 100V limit until the temperature drops below -58.8C (-73.8F).
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))
= 27.00V x 3 x (1 + (-0.28%/100) x (-10 - 25))
= 27.00V x 3 x 1.0980 = 88.9V
Controller max PV input: 100V
Crossover: string Voc reaches 100V at T = 25 + (100/81 - 1) x 100/-0.28 = -58.8CpassString Vmp 67.8V has healthy margin over the 12V bankMPPT voltage margin
Clears the start floor cold and the hot-weather floor with sag included.
Vmp_string = 22.60V x 3 = 67.8V Start floor = V_batt + 5V = 12 + 5 = 17V Hot Vmp (~11% sag) = 67.8V x 0.89 = 60.3V vs hot floor 20V
passArray short-circuit current 9.66A 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 = 9.66A x 1 parallel = 9.66A Controller max PV short-circuit current: 60A = 60A (manufacturer-specified, compared directly)
passController can pass the array's full output (46.9A of 50A rated)Array size vs controller charge output
No clipping at rated conditions.
Array = 200W x 3 panels = 600W Potential charge current = 600W / 12.8V = 46.9A Controller rated charge current: 50A
passArray 600W is within the controller's 700W rating at 12VMax array wattage for battery voltage
Within the published maximum array wattage.
Array = 200W x 3 panels = 600W 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
passVictron Energy MultiPlus-II 12/3000/120-50 2x120V charger supports LiFePO4Battery chemistry support
Inverter/charger has a lithium charge profile.
battery chemistry = lifepo4; inverter charger lifepo4_profile = true
passBank BMS limit 400A comfortably covers the inverter's 187.5A drawInverter draw vs battery BMS limit
Healthy headroom at full inverter load.
Inverter draw = 2400W / 12.8V = 187.5A Bank BMS limit = 400A x 1 batteries = 400A Headroom band starts at 80% of limit = 320A
passCharge current 50A is within the bank's 400A capacityCharge current vs bank capacity
Charge rate within limits.
Controller rated charge = 50A Bank max charge = manufacturer max charge 400A x 1 = 400A
passClosed-loop comms available via victronClosed-loop battery communications
The inverter can read state of charge and limits directly from the battery BMS. Enable closed-loop per both manuals.
inverter speaks [victron, pylontech, generic-can]; battery speaks [victron]; overlap [victron]
Parts list
| Part | Qty | Est. price | Where to buy |
|---|---|---|---|
Renogy 200W 12V Monocrystalline Solar Panel (RSP200D) | 3 | $570 | |
Victron Energy SmartSolar MPPT 100/50 controllerdatasheet | 1 | $300 | |
Victron Lithium Battery Smart 12.8V 330Ah batterydatasheet | 1 | $1,654 | |
Victron Energy MultiPlus-II 12/3000/120-50 2x120V inverterdatasheet | 1 | $1,088 | |
| Estimated total | $3,612 |
Wire and fuse guidance
| Segment | Continuous | Run (one way) | Copper wire | V-drop | Fuse/breaker |
|---|---|---|---|---|---|
| Array to charge controller | 9.7A | 18 ft | 14 AWG | 1.30% | 15APV-rated (gPV) fuse or DC breaker |
| Charge controller to battery bank | 50.0A | 5 ft | 6 AWG | 1.54% | 70AClass T |
| Battery bank to inverter | 187.5A | 4 ft | beyond 4/0 - see notes | - | 250AClass T |
Array to charge controller: show the math
Continuous current = 9.7A Design current = 9.7A x 1.25 (NEC continuous) = 12.1A Wire: 14 AWG copper (75C ampacity 20A); voltage drop 1.30% over 36ft round trip at 67.8V (target <= 3%) Fuse/breaker: 15A - two criteria, both required: carry the load: fuse >= design 12.1A -> 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 1.54% over 10ft 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 400A >= 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 = 187.5A Design current = 187.5A x 1.25 (NEC continuous) = 234.4A No single-conductor AWG in table satisfies ampacity + 3% drop Fuse/breaker: 250A - two criteria, both required: carry the load: fuse >= design 234.4A -> next standard size = 250A bank BMS continuous 400A >= fuse 250A: 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.
Current or distance exceeds single 4/0 copper; parallel conductors or shorter runs required. Consult a professional.
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 | ~40 ft total (18 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 | ~15 ft total (5 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 |
| 250A 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.
About this build
This build is the classic RV upgrade: keep the rig's 12V architecture and 30A shore-power service exactly as built, but replace the lead-acid bank with lithium, add an inverter/charger, and put real solar on the roof. Staying at 12V avoids re-engineering the RV's existing DC wiring - everything from the water pump to the slide motors keeps working untouched.
The MultiPlus-II does the heavy lifting: it charges the bank properly from shore power with a lithium profile (the factory converter almost certainly cannot), passes through 30A service when plugged in, and inverts when boondocking. The high-current Victron Smart lithium bank is chosen deliberately - a 12V inverter at this class pulls serious amps, and the battery's BMS ratings need to cover both continuous draw and motor-start surges. That surge math is exactly what the compatibility checks on this page are showing.
Common questions
Do I need to replace my RV's converter?
Almost certainly. Factory converters are built for lead-acid charge profiles and will chronically under- or over-charge lithium. In this build the MultiPlus-II takes over charging entirely, so the factory converter gets disconnected rather than replaced.
Why stay at 12V instead of going 24V or 48V?
Because the whole RV is already 12V. Converting means DC-DC converters for every existing circuit and a lot of rewiring. At this system size, 12V with properly sized cable is the pragmatic choice; the checks flag exactly where the current limits are.
Will 600W of roof solar keep up?
For boondocking with normal RV loads - lights, fridge, charging, occasional inverter use - it is a solid baseline that shore power tops up between trips. Heavy inverter cooking or AC changes the math; clone the build and resize the array to see the effect.