The $600 Kit With an Inverter That Kills Your CPAP

The WindyNation 400W Complete Kit with 1500W VertaMax Inverter kit costs $600 advertised price, $805 real build cost. It ships with a VertaMax 1,500W modified sine wave inverter. That waveform is the problem. Inverters and power conversion determine whether your off-grid system powers your devices or damages them.

CPAP machines running on modified sine wave inverters deliver reduced pressure and suffer accelerated motor wear. The stepped waveform confuses the device's pressure regulation, meaning the therapy that keeps your airway open at night is quietly failing. A $600 kit becomes a liability for anyone who depends on one.

The inverter is not an accessory. It is the single component that determines whether your solar system can power standard household appliances or is limited to USB devices and 12V LED strips.

Get the waveform wrong and you damage medical equipment. Get the sizing wrong and your inverter shuts down mid-load. Get the voltage wrong and you spend $200+ on cable that should have cost $10.

This guide covers the four decisions that separate a working off-grid power system from an expensive mistake:

1. Inverter type -- pure sine wave, modified sine wave, or hybrid inverter-charger
2. Sizing math -- running watts, surge watts, and the 1.25x safety margin
3. Voltage selection -- 12V vs 24V vs 48V and the wiring cost implications
4. Wiring fundamentals -- cable gauge, fuse placement, and install sequence

Every kit referenced below is drawn from the OffGridEmpire database with verified specs and real build costs. No advertised price is presented without the real build cost alongside it. Seven kits are referenced directly, ranging from $209 to $3,399, covering 12V portable stations through 48V homestead systems.

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What an Inverter Actually Does in Your Solar System

Solar panels produce DC (direct current). Batteries store DC. Every standard household appliance -- refrigerator, CPAP, laptop charger, microwave -- runs on AC (alternating current) at 120V/60Hz in North America. The inverter is the component that converts DC to AC.

Without an inverter, a solar panel and battery bank can only power DC-native loads: USB devices, 12V LED strips, RV water pumps. The moment you plug in anything with a standard three-prong plug, you need an inverter in the circuit.

The conversion is not lossless. Every inverter consumes some power during the DC-to-AC transformation, typically 5-15% depending on the load relative to the inverter's rated capacity. An inverter running at 25% of its rated wattage is less efficient than one running at 75%. This efficiency factor matters when sizing both the inverter and the battery bank that feeds it.

System Position

The inverter sits at a specific point in the power chain:

Solar Panels → Charge Controller → Battery Bank → Inverter → AC Loads

Panels generate DC power. The charge controller (MPPT or PWM) regulates voltage and current flowing into the battery bank. The battery bank stores energy. The inverter draws DC from the battery and outputs AC to your appliances, outlets, or subpanel.

All-in-One Stations vs Component Systems

Modern solar kits split into two categories based on how they handle inverter integration.

All-in-one power stations build the inverter, battery, charge controller, and battery management system (BMS) into a single sealed unit. The Bluetti AC2P 300W / 230.4Wh Portable Power Station + Choose Your Custom Your Custom Bundle | Complete Solar Generator Kit - Bluetti AC2P [Main Unit Only] ($209, 300W pure sine wave inverter, ~230Wh storage) is plug-and-play. Connect a solar panel to the input, plug appliances into the AC outlet. No wiring decisions, no fuse sizing, no cable gauge calculations.

The EcoFlow RIVER 2 [MAX] 512Wh / 500W Portable Power Station + Choose Your Custom Bundle | Complete Solar Kit - EcoFlow River 2 Max [Main Unit Only] ($269, 600W pure sine wave, 512Wh) follows the same model. Both are 12V internal systems with built-in inverters.

Component systems ship the inverter as a separate unit. The WindyNation 400W Complete Kit with 1500W VertaMax Inverter is a component system. It includes panels and a charge controller but requires a separate battery (not included, estimated $180), battery cables, fuses, and manual wiring. The inverter choice -- in this case, a modified sine wave unit -- becomes a decision the buyer must evaluate independently.

Size your solar system

Pure Sine Wave vs Modified Sine Wave vs Hybrid Inverters

Pure Sine Wave

A pure sine wave inverter produces a smooth, continuous AC waveform identical to utility grid power. The voltage oscillates in a clean sinusoidal curve at 60Hz, matching exactly what appliance manufacturers design for.

Every kit in the OffGridEmpire database above $500 uses a pure sine wave inverter. The BLUETTI Premium 80 [AC70P] Portable Power Station | Complete Solar Generator Kit | 3,000 Cycles | Choose Your Bundle - Double Kit [2 x 200W Rigid Panels] ($809, 1,000W) uses pure sine wave. The Anker SOLIX C1000 Gen2 Portable Power Station | 1,024Wh / 2,000W | 49-Min UltraFast Recharge | 600W Solar Input | Choose Your Bundle Option | 5-Year Warranty - C1000 Gen 2 + 1 x 400W Solar Panel ($870, 2,000W) uses pure sine wave. The Anker F3800 [PLUS] - 3,840Wh / 6,000W Portable Power Station | 120V/240V Output | 3,200W Solar Input | Choose Your Bundle Option | 5-Year Warranty - Nomad Kit [F3800P + 2 x Folding 200W Panels] ($3,048, 6,000W) uses pure sine wave.

Pure sine wave is the standard for off-grid solar. Sensitive electronics, variable-speed motors, medical devices, and audio equipment all require it. There is no device category that runs worse on pure sine wave than on modified sine wave. The only scenario where modified sine wave is technically acceptable is powering simple resistive loads -- incandescent light bulbs, basic space heaters, soldering irons -- devices with no microprocessor, no motor controller, and no transformer-based power supply.

The cost premium for pure sine wave has compressed. A 1,000W pure sine wave inverter now costs $80-$150 as a standalone component. Five years ago, that same unit was $200-$300. The price gap between pure and modified sine wave no longer justifies choosing modified sine wave.

Modified Sine Wave

A modified sine wave inverter produces a stepped, blocky approximation of a sine wave. Instead of a smooth curve, the waveform jumps between voltage levels in abrupt steps. The result is electrically "close enough" for simple resistive loads (incandescent bulbs, basic heaters) but problematic for anything with a microprocessor, motor controller, or transformer.

The WindyNation 400W Complete Kit with 1500W VertaMax Inverter ships with a VertaMax 1,500W modified sine wave inverter. At $805 real build cost, the kit's inverter can damage or degrade six categories of devices:

1. CPAP machines -- reduced pressure delivery, increased motor wear. The stepped waveform causes the blower motor to run inefficiently, producing inconsistent air pressure throughout the night.
2. Variable-speed motors -- excessive heat, reduced torque, premature failure. Ceiling fans, modern washing machines, and HVAC blower motors are all at risk.
3. Laser printers -- paper feed errors and fuser damage from irregular power delivery to the heating element.
4. LED dimmers -- visible flicker or complete failure to dim. The dimmer circuit cannot interpret the stepped waveform correctly.
5. Laptop and phone chargers -- run hot, charge 20-40% slower. The power supply works harder to filter the rough input into clean DC.
6. Thermostat-controlled devices (hair dryers, clothes irons) -- the thermostat misreads voltage from the stepped waveform, causing the device to overheat or cycle erratically.

The price difference between a 1,500W modified sine wave inverter and a 1,500W pure sine wave inverter is typically $50-$150. Saving that amount while risking a $800+ CPAP machine or a $300 laptop is not a trade-off that survives basic math.

Hybrid Inverter-Charger

A hybrid inverter-charger combines three components into one unit: an inverter, a battery charger, and an automatic transfer switch. When grid or generator power is available, the unit charges the battery bank and passes power through to loads. When external power drops, the unit switches to inverter mode automatically -- typically in under 20ms, fast enough that most electronics never notice.

The Victron MultiPlus-II 48/3000 delivers 3,000W output with a 35A charger at $800-$1,200. The EG4 3000EHV provides 3,000W with an 80A MPPT charge controller built in, split-phase capable, at $699.99 (April 2026 pricing).

Hybrid inverter-chargers serve cabins and homesteads that pair solar with a generator or occasional grid tie-in. They are not necessary for RVs, vans, or pure camping setups where the system runs exclusively on solar and battery.

The key advantage over buying separate components is the automatic transfer switch. Without one, switching from generator to solar requires manually flipping a breaker or unplugging cables -- a process that interrupts power to all connected loads. With a hybrid unit, the transition happens in under 20ms. Refrigerators, freezers, and networking equipment never lose power.

The EG4 3000EHV at $699.99 includes an 80A MPPT charge controller alongside the inverter and transfer switch. That eliminates one component and one set of wiring connections from the build. For a cabin with 4-6 solar panels and a backup generator, a hybrid inverter-charger reduces the total component count from five (panels, charge controller, inverter, charger, transfer switch) to three (panels, hybrid unit, battery bank).

Compare pure sine wave kits side by side

How to Size Your Inverter: Running Watts, Surge Watts, and the 1.25x Rule

Undersizing an inverter triggers its overload protection and shuts down your power. Oversizing wastes money and increases standby power drain on your battery bank. The formula for correct sizing:

(Sum of simultaneous running loads x 1.25) + largest single surge = minimum inverter requirement

The 1.25x multiplier provides a 25% safety margin for real-world conditions: voltage sag under load, inverter efficiency losses (typically 85-95%), and minor loads you forgot to account for.

Worked Example: Off-Grid Cabin

Running load: 1,021W x 1.25 = 1,276W continuous minimum.

Surge requirement: 1,276W + 3,000W (well pump surge, the largest single surge) = 4,276W surge minimum.

The Anker SOLIX C1000 Gen2 Portable Power Station | 1,024Wh / 2,000W | 49-Min UltraFast Recharge | 600W Solar Input | Choose Your Bundle Option | 5-Year Warranty - C1000 Gen 2 + 1 x 400W Solar Panel ($870, 2,000W continuous, 2,700W surge) covers the continuous load but falls short on surge if the well pump starts while other loads are running. It works if you stagger startup -- run the well pump before turning on the fridge.

Note the refrigerator surge: 1,200W is 8x the running wattage. Refrigerator compressors are induction motors. Every time the thermostat cycles the compressor on (typically 4-8 times per hour), it draws that surge. The surge lasts under one second, but the inverter must handle it every single time or it trips overload protection and shuts down.

Well pumps are worse. A 1HP well pump surges to 2,200-3,000W -- roughly 3-4x running watts. If the well pump and refrigerator compressor happen to surge simultaneously, the combined inrush hits 4,200W. This is why the formula adds the largest single surge to the continuous total rather than summing all surges -- simultaneous surges from multiple motor loads are unlikely but must be accounted for in the safety margin.

The Air Conditioner Trap

A 3-ton air conditioner draws approximately 3,500W running. The surge at compressor startup hits 15,750W -- roughly 4.5x running watts. That surge demands an inverter rated above 15,000W, pushing into the $5,000+ range for the inverter alone.

A soft starter module ($80-$150) reduces AC compressor inrush to approximately 6,300W. That single component drops the inverter requirement by more than half.

With a soft starter installed, the cabin example plus air conditioning requires:

Running: (1,021W + 3,500W) x 1.25 = 5,651W continuous.

Surge: 5,651W + 6,300W = 11,951W -- or 5,651W + 3,000W = 8,651W if the AC is already running when the well pump starts.

The Anker F3800 [PLUS] - 3,840Wh / 6,000W Portable Power Station | 120V/240V Output | 3,200W Solar Input | Choose Your Bundle Option | 5-Year Warranty - Nomad Kit [F3800P + 2 x Folding 200W Panels] ($3,048, 6,000W continuous) covers the cabin with air conditioning when paired with a soft starter. Without the soft starter, no single consumer-grade kit in the database handles the raw 15,750W surge.

The soft starter is the single highest-ROI accessory in off-grid AC installations. At $80-$150, it reduces the required inverter capacity by 9,000W+, translating to thousands of dollars in inverter cost savings. Install it on the compressor contactor wiring before the first AC startup on inverter power.

Standby Drain: Why Bigger Is Not Always Better

Every inverter consumes power just being on, even with zero load connected. A 1,000W inverter might draw 10-15W standby. A 6,000W inverter might draw 30-50W standby.

Over 24 hours, that is 720-1,200Wh consumed producing nothing -- enough to drain a small battery bank overnight. Size the inverter to your actual load, not to the largest number available.

Calculate your inverter size | Browse kits by inverter wattage

12V vs 24V vs 48V: Why Voltage Changes Everything About Your Wiring

System voltage does not affect what appliances you can run. The inverter converts any DC input voltage to 120V AC output regardless. What voltage changes is the current flowing through your DC wiring -- and current determines wire gauge, connector ratings, fuse sizes, and cost.

The Wire Math

Power equals voltage times current (P = V x I). For the same wattage, lower voltage means higher current:

On a 10-foot cable run (battery to inverter), the real build cost difference is stark:

• 12V system: $160-$240 in cable alone
• 24V system: $40 in cable
• 48V system: $10 in cable

That is a $150-$230 difference on wiring for the same 1,200W of power delivery. And the 12V cables are thick, stiff, and difficult to route through walls or conduit. 4/0 AWG cable is roughly the diameter of a garden hose.

The 12V Ceiling

Above 2,000W inverter capacity, 12V systems become impractical. A 3,000W inverter at 12V draws 250A -- territory where cable costs, connection losses, and voltage drop make the system unreliable and dangerous. This is why no off-grid installer builds a 12V system above 2,000W.

Voltage drop compounds the problem. Every foot of cable has resistance. At 100A (12V, 1,200W), even properly sized 4/0 AWG cable drops approximately 0.3V over 10 feet.

At 250A (12V, 3,000W), the drop exceeds 0.7V -- nearly 6% of the nominal 12V. That lost voltage converts directly to heat in the cable and represents wasted battery capacity. At 48V, the same 3,000W load draws only 62.5A, and voltage drop is negligible.

At 24V, the numbers fall between: 1,200W draws 50A, and voltage drop over 10 feet of 6 AWG cable is approximately 0.4V -- about 1.7% of nominal. Manageable, but still 3x the drop of an equivalent 48V run.

Database Voltage Mapping

The kit database reflects this reality clearly:

12V kits (small/portable):

• Bluetti AC2P 300W / 230.4Wh Portable Power Station + Choose Your Custom Your Custom Bundle | Complete Solar Generator Kit - Bluetti AC2P [Main Unit Only]: 300W, $209
• EcoFlow RIVER 2 [MAX] 512Wh / 500W Portable Power Station + Choose Your Custom Bundle | Complete Solar Kit - EcoFlow River 2 Max [Main Unit Only]: 600W, $269
• WindyNation 400W Complete Kit with 1500W VertaMax Inverter: 1,500W, $600

48V kits (mid-to-large):

• BLUETTI Premium 80 [AC70P] Portable Power Station | Complete Solar Generator Kit | 3,000 Cycles | Choose Your Bundle - Double Kit [2 x 200W Rigid Panels]: 1,000W, $809
• Anker SOLIX C1000 Gen2 Portable Power Station | 1,024Wh / 2,000W | 49-Min UltraFast Recharge | 600W Solar Input | Choose Your Bundle Option | 5-Year Warranty - C1000 Gen 2 + 1 x 400W Solar Panel: 2,000W, $870
• Anker F3800 [PLUS] - 3,840Wh / 6,000W Portable Power Station | 120V/240V Output | 3,200W Solar Input | Choose Your Bundle Option | 5-Year Warranty - Nomad Kit [F3800P + 2 x Folding 200W Panels]: 6,000W, $3,048

Decision Rule

RV or van under 1,000W inverter capacity: 12V works fine. The wiring is manageable and 12V accessories (lights, fans, USB outlets) run directly without conversion.

Cabin or homestead above 1,000W: 48V saves hundreds on wiring and enables scaling. The only trade-off is that 48V battery banks cost slightly more upfront, but the wiring savings offset that within the first installation.

The 24V middle ground exists but is declining in popularity. Most modern all-in-one stations run internal 48V architectures regardless of label. Component builders increasingly skip 24V entirely, going from 12V small systems directly to 48V for anything above 1,000W. The charge controller and inverter ecosystem for 48V is broader and more competitively priced than 24V in 2026.

How real build cost is calculated

Wiring Fundamentals: Cable Gauge, Fuse Placement, and Install Sequence

This section applies to component system builders -- those wiring a standalone inverter to a battery bank, charge controller, and panel array. All-in-one power stations (Bluetti, EcoFlow, Anker portable units) handle all internal wiring at the factory. If you bought an all-in-one station, skip to the verdict section.

The 6-Step Install Sequence

Order matters. Wiring a solar system in the wrong sequence risks shock, arc flash, or equipment damage. Follow this sequence exactly:

Step 1: Install the battery. Mount the battery bank in a ventilated, temperature-controlled location. Secure it so it cannot shift or tip.

Step 2: Connect battery to inverter. Run appropriately sized DC cable from battery positive to inverter positive, battery negative to inverter negative. Install a fuse or circuit breaker on the positive cable within 18 inches of the battery positive terminal. This fuse is the last defense against cable fires from short circuits.

Step 3: Connect charge controller to battery. Wire the charge controller's battery output to the battery bank. The charge controller must see battery voltage before it sees panel voltage.

Step 4: Wire panels to charge controller LAST. Solar panels produce power the instant sunlight hits them. Connecting panels before the charge controller is wired to a battery means the controller has nowhere to send the energy, risking overvoltage damage.

Step 5: Wire inverter AC output to loads. Connect the inverter's AC output to your outlets, subpanel, or extension cord. For permanent installations, a dedicated subpanel with branch circuit breakers is the standard approach.

Step 6: Test under no-load, then progressive loads. Turn on the inverter with nothing plugged in. Verify AC output voltage with a multimeter (120V ± 5%). Then add loads one at a time, starting with the smallest. Monitor for voltage sag, unusual heat at connections, or inverter fault codes.

The 18-Inch Fuse Rule

The fuse or circuit breaker on the positive DC cable between battery and inverter must be within 18 inches of the battery positive terminal. Not 3 feet. Not "close enough." The National Electrical Code (NEC Article 690) specifies this distance because every inch of unprotected cable between battery and fuse is a potential ignition source if a short circuit occurs.

Cable undersizing is the number one cause of DIY solar fires. A 12V battery bank delivering 100A through undersized cable generates enough heat to melt insulation and ignite surrounding materials within minutes. The fuse prevents this -- but only if it is close enough to the battery to protect the full cable run.

Cable Gauge Selection

Match cable gauge to maximum continuous current, not average current. Use the wire sizing table from the voltage section above. When in doubt, go one gauge thicker.

The cost difference between 6 AWG and 4 AWG on a 10-foot run is under $20. The cost of a cable fire is the entire system and potentially the structure.

All connections should use crimped ring terminals or bus bar connections -- never twist-and-tape on DC power wiring. Crimped connections resist vibration loosening (especially in RVs) and provide consistent contact resistance. A loose connection at 100A generates enough resistive heat to start a fire within minutes. Use a torque wrench on bus bar bolts to manufacturer spec.

For component systems like the WindyNation 400W Complete Kit with 1500W VertaMax Inverter, the kit does not include battery cables, fuses, or bus bars. These required missing parts add $50-$100+ to the real build cost depending on system voltage and cable length. Factor wiring hardware into your real build cost calculation before purchasing.

See which kits need manual wiring

Which Inverter Setup Fits Your Build: RV, Cabin, or Homestead

RV / Van / Camping

Inverter range: 300-600W pure sine wave

Voltage: 12V

Price range: $200-$400

The Bluetti AC2P 300W / 230.4Wh Portable Power Station + Choose Your Custom Your Custom Bundle | Complete Solar Generator Kit - Bluetti AC2P [Main Unit Only] ($209) handles phone/laptop charging, LED lighting, and a small fan. For CPAP users, the EcoFlow RIVER 2 [MAX] 512Wh / 500W Portable Power Station + Choose Your Custom Bundle | Complete Solar Kit - EcoFlow River 2 Max [Main Unit Only] ($269, 600W, 512Wh) provides enough capacity for a full night of CPAP operation plus device charging.

Pure sine wave is non-negotiable for CPAP machines. The WindyNation 400W Complete Kit with 1500W VertaMax Inverter and its modified sine wave VertaMax inverter should not be used with any medical device.

Both the Bluetti and EcoFlow units listed here are all-in-one stations -- no wiring, no fuse sizing, no cable gauge decisions. Plug in a solar panel, plug in your devices. For RV and van builds, simplicity matters as much as specs.

Off-Grid Cabin

Inverter range: 1,000-3,000W pure sine wave

Voltage: 48V

Price range: $800-$1,500 for inverter/station

The BLUETTI Premium 80 [AC70P] Portable Power Station | Complete Solar Generator Kit | 3,000 Cycles | Choose Your Bundle - Double Kit [2 x 200W Rigid Panels] ($809, 1,000W, 864Wh) covers a basic cabin with LED lighting, laptop, phone charging, and a small appliance. The Anker SOLIX C1000 Gen2 Portable Power Station | 1,024Wh / 2,000W | 49-Min UltraFast Recharge | 600W Solar Input | Choose Your Bundle Option | 5-Year Warranty - C1000 Gen 2 + 1 x 400W Solar Panel ($870, 2,000W, 1,024Wh) adds capacity for a refrigerator and well pump with staggered startup.

If you run a generator for backup power, consider a hybrid inverter-charger. The EG4 3000EHV ($699.99) includes an 80A MPPT charge controller, eliminating one component from your build. The Victron MultiPlus-II 48/3000 ($800-$1,200) is the industry standard for reliability.

Homestead

Inverter range: 3,000-6,000W+ pure sine wave or hybrid

Voltage: 48V mandatory

Price range: $3,000-$6,000+

The Anker F3800 [PLUS] - 3,840Wh / 6,000W Portable Power Station | 120V/240V Output | 3,200W Solar Input | Choose Your Bundle Option | 5-Year Warranty - Nomad Kit [F3800P + 2 x Folding 200W Panels] ($3,048, 6,000W, 3,840Wh) provides plug-and-play power for a full homestead. The BLUETTI [APEX 300] Modular Power Station | 3,840W / 2,765Wh | 120V/240V Dual Voltage | 5-Year Warranty | Choose Your Bundle - APEX300 + 2 x B300K2 ($3,399, 3,840W, 2,765Wh) supports expansion with additional battery modules for multi-day autonomy.

Any homestead running air conditioning needs a soft starter ($80-$150) on every AC compressor. Without it, the 15,750W surge from a 3-ton unit will trip the inverter's overload protection instantly. For homesteads with generator backup, a hybrid inverter-charger (Victron MultiPlus-II or EG4 3000EHV) eliminates the need for a separate transfer switch and battery charger, reducing component count and wiring complexity.

The progression across these three tiers follows a clear pattern: as power demand increases, system voltage moves from 12V to 48V, all-in-one convenience gives way to component flexibility, and wiring knowledge becomes mandatory. There is no single inverter setup that serves all three use cases. Match the tier to your actual load profile using the solar calculator, not to aspirational future loads.

Compare kits for your build type | Browse all solar kits

Inverter and Power Conversion FAQ

Can I run a refrigerator on a modified sine wave inverter?

Yes, but the compressor runs hotter and less efficiently. Modified sine wave reduces compressor lifespan from 15-20 years to an estimated 8-12 years. Pure sine wave eliminates this degradation.

What size inverter for a CPAP machine?

A CPAP draws 30-60W running. A 300W pure sine wave inverter is sufficient. The Bluetti AC2P 300W / 230.4Wh Portable Power Station + Choose Your Custom Your Custom Bundle | Complete Solar Generator Kit - Bluetti AC2P [Main Unit Only] ($209, ~230Wh) runs most CPAPs for 4-6 hours. Pure sine wave is mandatory.

Is a bigger inverter always better?

No. Larger inverters draw more standby power (30-50W for a 6,000W unit vs 10-15W for 1,000W). That idle draw runs 24/7. Size to actual load x 1.25.

Do I need a hybrid inverter if I have a generator?

A hybrid inverter-charger like the EG4 3000EHV ($699.99) handles automatic switching between solar/battery and generator power. Without one, you need manual switching or a separate transfer switch and battery charger.

Why do all-in-one power stations cost more per watt than standalone inverters?

The per-watt premium pays for integrated battery, BMS, charge controller, UL/FCC safety testing, and warranty on the complete system. A standalone 1,000W pure sine wave inverter costs $100-$200; an all-in-one station with 1,000W output and built-in battery costs $500-$900.

Can I parallel two inverters for more power?

Most consumer-grade inverters cannot be paralleled. Connecting two non-parallel-rated inverters to the same load causes phase conflicts and damages both units. If you need more power than a single inverter provides, choose a larger single unit or a purpose-built stackable system like the BLUETTI [APEX 300] Modular Power Station | 3,840W / 2,765Wh | 120V/240V Dual Voltage | 5-Year Warranty | Choose Your Bundle - APEX300 + 2 x B300K2, which supports expansion modules.