RV Electrical System 101: 12V, 120V, and Why It Matters

When we bought our first camper, we plugged into shore power at the campground and everything worked. Lights, microwave, AC, outlets, all good. Then we tried boondocking for the first time, disconnected from shore power, and half the stuff in our RV stopped working while the other half kept going. We had no idea why.

The answer is simple once you understand it: your RV has two separate electrical systems that work together but behave very differently. This guide breaks down both systems so you know exactly what you're working with.

The Two Systems: 12-Volt DC and 120-Volt AC

Every RV runs on two types of electricity:

12-Volt DC (Direct Current), This is the same type of power your car battery uses.

120-Volt AC (Alternating Current), This is the same power that comes out of the outlets in your house. It comes from shore power at a campground, a generator, or an inverter that converts your battery power to AC. It powers larger, power-hungry appliances.

What Runs on 12V DC?

Your 12V system handles the essentials, the things that need to work even when you're parked in the middle of nowhere:

• Interior lights, All of them, including overhead, reading, and porch lights
• Water pump, Pressurizes water from your fresh tank to faucets and shower
• Furnace fan, The propane furnace itself uses gas, but the blower fan runs on 12V
• Refrigerator control board, Even if your fridge runs on propane, the electronics that control it need 12V
• Slide-out motors, The motors that extend and retract your slide-outs
• Carbon monoxide and propane detectors, Critical safety devices
• USB charging ports, Built-in USB outlets run directly from 12V
• Vent fans, Roof-mounted fans like Maxxair and Fan-Tastic

What Runs on 120V AC?

The 120V system powers appliances that draw too much energy to run efficiently from batteries:

• Air conditioner, The single biggest power draw in most RVs
• Microwave
• Standard wall outlets, Anything you plug into a regular outlet
• Residential refrigerator (if equipped, instead of an absorption fridge)
• TV
• Hair dryer, coffee maker, toaster, All high-draw small appliances
• Electric water heater element (some water heaters have both propane and electric modes)

How the Systems Connect: Converters, Inverters, and Chargers

These three devices are the bridge between your two electrical systems. Understanding them is the key to understanding RV power.

The Converter (AC to DC)

When you plug into shore power, your converter takes 120V AC electricity and converts it to 12V DC to power your 12V devices AND charge your house batteries. Think of it as a big battery charger that also powers your lights and water pump.

Every RV has a converter. It's usually built into the power center (the panel with your fuses and breakers).

The Inverter (DC to AC)

An inverter does the opposite: it takes 12V DC battery power and converts it to 120V AC so you can run household appliances from your batteries when you're not plugged in. Not every RV comes with one, but they're an incredibly useful upgrade for boondocking.

Inverters come in different sizes measured in watts. A small 300-watt inverter can charge a laptop. A 2,000-watt inverter can run a microwave. A 3,000-watt+ inverter can handle most appliances except the air conditioner.

The Battery Charger (Sometimes Called a Smart Charger)

Some RVs have a standalone battery charger that's separate from the converter. Modern units often combine the converter and charger into a single "converter/charger" unit. The charger's job is to replenish your house batteries when you have shore power or generator power available.

30-Amp vs. 50-Amp: What's the Difference?

When you book a campsite, you'll see "30-amp" or "50-amp" power options. Here's what that means:

30-amp service delivers a maximum of about 3,600 watts (30 amps x 120 volts). This is standard for smaller RVs, travel trailers, and Class B/C motorhomes. You get one 120V "leg" of power. With 30 amps, you can run most things, but not everything at once. Running the AC while microwaving will trip your breaker.

50-amp service delivers about 12,000 watts (50 amps x 240 volts, split into two 120V legs of 50 amps each). This is standard for larger Class A motorhomes and fifth wheels. You can run two AC units, the microwave, and the water heater simultaneously without breaking a sweat.

Battery Basics: Your 12V Power Bank

Your house batteries are the heart of your 12V system. When you're off-grid, they're your only source of power for lights, fans, water pump, and anything running through your inverter.

There are three main battery types for RVs:

Lead-acid (flooded), Cheapest upfront ($100-150 each) but require maintenance (checking water levels), can only be discharged to about 50% without damage, and weigh a lot.

AGM (Absorbed Glass Mat), Maintenance-free, sealed, can be mounted in any orientation. More expensive ($200-350 each) but more durable. Still should only be discharged to about 50%.

Lithium (LiFePO4), The premium option. Can be discharged to 80-100% of capacity, last 3-5x longer than lead-acid, weigh half as much, and charge faster. The catch? They cost $800-1,200+ per battery. But the lifetime cost is often lower because they last so much longer.

Practical Tips for Managing Your Power

Know your draw. Lights and fans use very little 12V power. Your water pump uses moderate power. Your inverter running a microwave uses a lot. If you're boondocking, turn off what you're not using.

Get a battery monitor. A device like a Victron BMV or Renogy monitor shows your battery percentage, current draw, and estimated time remaining. Flying blind on battery level is how you end up with dead batteries at 2 AM.

Don't mix battery types. If you have two house batteries, they should be the same type, brand, age, and capacity. Mismatched batteries cause charging problems and reduce overall lifespan.

Solar helps enormously. Even a small 200-watt solar panel setup can keep your batteries topped off during the day for lights, fans, and device charging, extending your boondocking time from 1-2 days to a week or more.

Understanding your RV's electrical system takes the mystery out of camping. You'll know why your AC won't run without shore power, why your lights still work when unplugged, and how to manage your power for days of off-grid freedom.

Want to go deeper? Read our guides on RV inverters and RV batteries for detailed buying recommendations and installation tips.