Practical Advice: Off-grid Power

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Today’s RV travellers often take an array of appliances and devices on their travels. All well and good when you’re plugged into mains electricity, but what about when you’re parked up with no power point nearby?

HOUSE BATTERIES

Most RVs have two power sources – AC (alternating current), which is powered by plugging into a 230V mains power point. And DC (direct current) which runs off a house battery (12V or 24V). Your RV’s house battery stores electricity used to power basics such as lights, the LCD screen, water pump etc, and is recharged as you drive, and when plugged into mains electricity overnight.

But to power up bigger electrical appliances such as the kettle, toaster and portable devices like laptops, you’ll need AC power.

INVERTERS

An inverter converts direct current (DC) to an alternating current (AC). This allows you to use home appliances that run on 230V AC with your RV’s house battery.

There are three types of inverter: Square Wave Signal (now outdated), Modified Sine Wave (MSW) and Pure Sine Wave (PSW). Broadly speaking, PSW inverters are best for RV use. Some devices don’t operate correctly and may even be harmed when used with MSW inverters. Most devices that operate on 230V at home will work correctly and not be harmed if plugged into a PSW inverter.

Inverters are rated in running watts from 100W upwards. But running watts are not the only factor to consider. Equally important is a phenomenon known as ‘surge’ wattage, which occurs when a device starts up. Up to three times the device’s running wattage, it lasts just milliseconds before the device reverts to its running wattage. The inverter must be able to handle it, so choose one that covers both the running wattage and the start-up surge. For example a 1000W microwave oven with a 3000 surge wattage would require a 2000W inverter with a 3000W surge capacity. Covering the surge is just as important as covering the running wattage.

SOLAR PANELS & CONTROLLERS

Solar panels work by converting sunlight into direct current (DC) electricity. An inverter then converts the DC electricity into alternating current (AC) electricity to be used from your RV’s power points.

The size of your solar power system is measured in watts: the higher the wattage, the more electrical energy it will produce (depending on the amount and intensity of sunlight received). Many solar providers have calculators on their websites or in store to help you work out how much power you need.

To use solar power, you’ll also need a solar regulator (charge controller). This functions as a solar-driven battery charger. Connected between the solar panel and the house battery, it regulates the battery-charging procedure so that the battery is not overcharged.

Two types of regulator are commonly used in New Zealand – the earlier Pulse Width Modulation (PWM) type and the newer Maximum Power Point Tracking (MPPT) type. These regulators work differently. PWM regulators use a basic ‘rapid switch’ to control the battery-charging regime. They tend to slide o the optimum operating voltage, reducing both power and e ciency. However, PWM regulators are a cost-effective option for small systems like small solar lighting arrays and phone charging. MPPT regulators are more sophisticated and can be up to 30 percent more e cient than their PWM equivalents.

GENERATORS

Generators produce both 240V AC and 12V DC power, and they deliver it on demand. They are a good solution for power-hungry appliances. The downside is that they are noisy, smelly, and heavy to carry around, both physically and as part of your RV payload. And fuel must also be carried, further depleting the RV payload capacity.

The time taken to charge the batteries is determined by the generator’s 12V DC output rate or the RV’s AD-DC charger output rate. Either way, an 8-amp charger will take around five hours to replenish 40 amps into the battery. You can reduce the time by upgrading to a 20-amp charger, but this will require an upgraded generator.

Because of the noise and smell, many campgrounds, including DOC camps, ban the use of generators, and others restrict the time and duration of use. NZMCA stopover parks allow generator use between 8am and 8pm for two hours per RV per day – often not long enough to replenish the electricity (amps) used overnight.

BEWARE OF POWER VAMPIRES

Different appliances and devices draw different amounts of electricity. Some run very well on small amounts, while others will use up large amounts very quickly. Generally, appliances that generate heat or cold (think fridges, air conditioners, hair dryers, plug-in heaters) will draw a lot of power. Most kitchen appliances such as microwaves, toasters and coffee machines also use a lot of electricity.

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