Skoolie conversion 1200W 24V
24V system, designed for a -15C (5F) cold snap - saved 2026-09-06
Compatibility checks
13 passing checks - expand to see the math
passBattery matches the 24V systemSystem voltage coherence
LiTime 24V 100Ah LiFePO4 (25.6V nominal) is a 24V-class battery.
battery nominal 25.6V is in the 24V class == system 24V
passInverter matches the 24V systemSystem voltage coherence
Giandel PS-4000QAR 4000W 24V Pure Sine Wave Inverter DC input is 24V-class.
inverter DC input 24V is in the 24V class == system 24V
passCharge controller supports 24V banksSystem voltage coherence
Victron Energy SmartSolar MPPT 150/60 supports 12/24/36/48V battery banks.
controller battery voltages [12, 24, 36, 48] include 24V
passString Voc stays at 72.7V at -15C - cannot reach the 150V limit at any temperatureCold-temperature string voltage
3 x Rich Solar MEGA 200 200W 12V Monocrystalline Solar Panel in series stays below the Victron Energy SmartSolar MPPT 150/60 max PV input voltage at your design low temperature. This string cannot reach 150V 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))
= 21.80V x 3 x (1 + (-0.28%/100) x (-15 - 25))
= 21.80V x 3 x 1.1120 = 72.7V
Controller max PV input: 150V
Crossover: string Voc reaches 150V at T = 25 + (150/65.4 - 1) x 100/-0.28 = -437C (below absolute zero - never reached)passString Vmp 55.2V has healthy margin over the 24V bankMPPT voltage margin
Clears the start floor cold and the hot-weather floor with sag included.
Vmp_string = 18.40V x 3 = 55.2V Start floor = V_batt + 5V = 24 + 5 = 29V Hot Vmp (~11% sag) = 55.2V x 0.89 = 49.1V vs hot floor 32V
passArray short-circuit current 23.20A is within the 50A limitArray current vs controller input limit
Within the Victron Energy SmartSolar MPPT 150/60 published max PV short-circuit current.
Isc_array = 11.60A x 2 parallel = 23.20A Controller max PV short-circuit current: 50A = 50A (manufacturer-specified, compared directly)
passController can pass the array's full output (46.9A of 60A rated)Array size vs controller charge output
No clipping at rated conditions.
Array = 200W x 6 panels = 1200W Potential charge current = 1200W / 25.6V = 46.9A Controller rated charge current: 60A
passArray 1200W is within the controller's 1720W rating at 24VMax array wattage for battery voltage
Within the published maximum array wattage.
Array = 200W x 6 panels = 1200W Controller max array wattage at 24V: 1720W
passVictron Energy SmartSolar MPPT 150/60 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 400A comfortably covers the inverter's 156.3A drawInverter draw vs battery BMS limit
Healthy headroom at full inverter load.
Inverter draw = 4000W / 25.6V = 156.3A Bank BMS limit = 100A x 4 batteries = 400A Headroom band starts at 80% of limit = 320A
passBank BMS peak 1120A covers the inverter's 312.5A surgeInverter surge vs battery peak limit
Surge loads within the bank's published peak rating.
Surge draw = 8000W / 25.6V = 312.5A Bank BMS peak = 280A x 4 batteries = 1120A
pass4 in parallel is within the manufacturer limit of 4Battery parallel count
Supported parallel configuration.
4 in parallel vs manufacturer max 4
passCharge current 60A is within the bank's 400A capacityCharge current vs bank capacity
Charge rate within limits.
Controller rated charge = 60A Bank max charge = manufacturer max charge 100A x 4 = 400A
Parts list
Wire and fuse guidance
| Segment | Continuous | Run (one way) | Copper wire | V-drop | Fuse/breaker |
|---|---|---|---|---|---|
| Array to charge controller | 23.2A | 15 ft | 10 AWG | 1.26% | 30APV-rated (gPV) fuse or DC breaker |
| Charge controller to battery bank | 60.0A | 5 ft | 4 AWG | 0.58% | 80AClass T |
| Battery bank to inverter | 156.3A | 5 ft | 3/0 AWG | 0.38% | 200AClass T |
Array to charge controller: show the math
Continuous current = 23.2A Design current = 23.2A x 1.25 (NEC continuous) = 29A Wire: 10 AWG copper (75C ampacity 35A); voltage drop 1.26% over 30ft round trip at 55.2V (target <= 3%) Fuse/breaker: 30A - two criteria, both required: carry the load: fuse >= design 29A -> next standard size = 30A protect the wire: fuse 30A <= 10 AWG ampacity 35A - OK construction: PV-rated (gPV) fuse or DC breaker
Charge controller to battery bank: show the math
Continuous current = 60A Design current = 60A x 1.25 (NEC continuous) = 75A Wire: 4 AWG copper (75C ampacity 85A); voltage drop 0.58% over 10ft round trip at 25.6V (target <= 3%) Fuse/breaker: 80A - two criteria, both required: carry the load: fuse >= design 75A -> next standard size = 80A protect the wire: fuse 80A <= 4 AWG ampacity 85A - OK bank BMS continuous 400A >= fuse 80A: 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 = 156.3A Design current = 156.3A x 1.25 (NEC continuous) = 195.3A Wire: 3/0 AWG copper (75C ampacity 200A); voltage drop 0.38% over 10ft round trip at 25.6V (target <= 3%) Fuse/breaker: 200A - two criteria, both required: carry the load: fuse >= design 195.3A -> next standard size = 200A protect the wire: fuse 200A <= 3/0 AWG ampacity 200A - OK bank BMS continuous 400A >= fuse 200A: 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 |
|---|---|---|
| 10 AWG copper wire | 1 | ~35 ft total (15 ft one way, round trip + slack) - Array to charge controller |
| 30A PV-rated (gPV) fuse or DC breaker | 1 | Array to charge controller |
| 4 AWG copper wire | 1 | ~15 ft total (5 ft one way, round trip + slack) - Charge controller to battery bank |
| 80A Class T | 1 | Charge controller to battery bank - include the matching fuse holder/block |
| 3/0 AWG copper wire | 1 | ~15 ft total (5 ft one way, round trip + slack) - Battery bank to inverter |
| 200A 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
A skoolie is the rare mobile build with a real roof: a full-size bus carries panel real estate a van owner can only dream about, and this build uses it - six 200W panels in two series strings of three. The higher string voltage suits the longer wire run from the back of the roof to the electrical bay, and the 150V-class controller has the headroom to accept those strings on a cold morning with margin to grow.
The loads look more like a small apartment than a camper: full-size fridge, induction cooking, power tools during the build itself. That argues for 24V over 12V - at this inverter size the battery current at 12V would be brutal - and for 400Ah of bank so an evening of cooking does not gut the reserve. The trade-offs are the usual 24V ones: a DC-DC converter for the bus's native 12V circuits, and appliances chosen to spread their draw rather than run everything at once.
Common questions
Why two strings instead of one long series string?
Six panels in one series string would push the cold-morning voltage far higher, eating the controller's input margin, and a single shadow anywhere on the roof would drag down the whole array. Two strings of three keeps voltage comfortable and quarantines shading to half the array - on a vehicle that parks near trees, that matters daily.
Is 1200W enough for full-time skoolie living?
For a couple running a fridge, lights, laptops, and moderate cooking, it is a workable daily budget in decent sun. Heavy winter use or air conditioning changes the math entirely. The honest approach is to meter your real loads for a week; the roof has room for more panels, and this controller class leaves room to add them.
Why not an all-in-one inverter for a skoolie?
Either works. This build uses separates so a failed inverter leaves solar charging intact - meaningful when your house has wheels and the nearest replacement is days away. An all-in-one saves wiring and money upfront; see the guides section for the full trade.
What about the bus alternator?
A DC-DC charger from the chassis alternator is a natural addition for driving days, sized to what the alternator can spare. It needs to match your 24V bank on its output side - check the charger's specs against your battery's charge limits in the builder.