One of the most common questions we get from RV owners planning a power system upgrade is: when should I move to a higher battery voltage? The answer is actually straightforward: if your system will draw more than 200 amps, it's time to step up your voltage. Push past that threshold, and everything — cables, fuses, bus bars, breakers — gets more expensive fast.
The 200-Amp Rule Explained
The 200-amp figure isn't arbitrary. It's the practical upper limit for most DIY-friendly electrical components. Bus bars, disconnects, DC breakers, and switches commonly max out at around 250 amps in the consumer market. Once you exceed that, you move into specialised, higher-cost territory.
To see why voltage matters so much, let's run the numbers on a real example: a 12V system with a 3,000W inverter.
Because inverters are typically 90% efficient, the DC input side must supply more power than the AC output. After accounting for this and applying a standard 1.25× safety factor, the numbers look like this:
To handle 347 amps safely, you need a 350A fuse and 4/0 AWG cable (120mm²) — one of the heaviest and most expensive cable gauges available. The cost of fuses, bus bars, and breakers at this current level adds up quickly.
Double the Voltage, Halve the Current
Now run the same 3,000W inverter on a 24V system. The power is the same, but because current equals power divided by voltage, doubling the voltage cuts the current in half:
At 174 amps, the required fuse drops to 175A and the cable reduces to 2 AWG (35mm²). That's a significant saving in materials, and the smaller cable is also much easier to route through a motorhome or caravan.
For the same power output, doubling your battery voltage halves the current. Lower current means thinner cables, smaller fuses, cheaper components, and less heat throughout the system.
Recommended Inverter Sizes by Voltage
Using the same assumptions (90% inverter efficiency, 1.25× safety factor), the table below shows the maximum inverter size that keeps your system current below the 200-amp threshold:
| Battery Voltage | Max Recommended Inverter | Notes |
|---|---|---|
| 12V | 2,000W | Above this, current exceeds 200A quickly |
| 24V | 4,000W | Good sweet spot for most larger RVs |
| 48V | 8,000W | Best for high-power off-grid setups |
These are practical guidelines based on real-world experience, not hard electrical limits. Staying within them will keep your system cost-effective and running efficiently.
Cheaper Solar Charge Controllers Too
The advantages of higher voltage extend beyond the inverter. Your solar charge controller also benefits. With 800W of solar panels, the charging current at different battery voltages looks like this:
| Battery Bank | Solar Charging Current (800W array) |
|---|---|
| 12V | ~62A |
| 24V | ~31A |
A charge controller rated for 31A is noticeably cheaper than one rated for 62A. Over a full system build, these savings across multiple components add up to a meaningful difference.
The Hidden Cost: Heat Loss
High current doesn't just mean higher component costs — it also means wasted energy in the form of heat. The formula for heat generation in a circuit is:
Because current is squared, doubling the current produces four times the heat loss — not twice as much.
As an example, assume a circuit with 0.5 milliohms of internal resistance (cables, fuses, bus bars, connections):
| Current | Heat Generated |
|---|---|
| 200A | 20W |
| 400A | 80W |
That's 80W of continuous heat — four times as much — simply from doubling the current. High-current systems are less efficient and place significantly more thermal stress on every component in the circuit.
When Higher Voltage Isn't Always the Answer: Mobile Systems
Higher voltage delivers real advantages for most systems, but there are situations where it creates more problems than it solves. Mobile setups — particularly vans and RVs — have two specific constraints worth considering.
In a van or motorhome, you typically charge from a 12V starter battery. Going from 12V to a 48V house battery requires a specialised 12-to-48V DC-DC charger. These exist, but they're generally more expensive and less common than 12-to-12V or 12-to-24V options.
To charge a 48V battery (which can charge up to 57.6V when full), your solar array needs to produce at least 5V over the battery voltage. That typically requires multiple panels wired in series — which may not be practical on the limited roof of a caravan or motorhome.
For most motorhomes and caravans in New Zealand, 24V is the practical sweet spot. It delivers meaningful savings over a 12V system in terms of current and component cost, without the added complexity and space requirements of a 48V setup.
Summary: The Rules to Remember
• Keep system current below 200A for cost-effective components
• 12V system: maximum ~2,000W inverter
• 24V system: maximum ~4,000W inverter
• 48V system: up to ~8,000W inverter
• For vans and motorhomes: 24V is usually the best balance
Getting the voltage right from the start means your cables, fuses, charge controller, and bus bars all stay within the affordable, widely-available range. It also means less heat, less energy waste, and a more reliable system overall.
If you're unsure which voltage is right for your setup, our team at RV Solutions is happy to walk through the options with you. We design systems that work together properly — solar, batteries, inverters, and charging all sized and integrated correctly for your travel style and budget.
Need Help Planning Your Battery System?
Our Christchurch team can help you choose the right voltage, size your components correctly, and install everything to NZ standards.
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