Understanding the Basics for Electrical Power and Energy in RV and Marine

A very simple way of understanding power, batteries, inverters and solar is the analogy to water flow, tanks and pumps.

·      A water tank is like a battery. It fills and depletes to empty.

·      A tank filler is like power coming in. There are different size water fillers. A low power charging device is like a small/tiny water filler. You are standing there all day trying to fill the tank through a ½ inch hose. A big power charger is like a huge opening to fill the tank quickly.

·      An inverter is like a super big water pump. It will pump the tank dry if you aren’t careful. If it is dry, trying to pump water can damage things.

·      A fridge and LED lights is like a smaller pump but always pumping away day and night out of the tank.

The fundamental principle is to always have water in the tank.

·      That means similar quantity of water has to go in as comes out. Then the tank level will stay at a similar point.

·      And this is the fundamental principle of well-designed power systems:

o   Don’t just buy a big tank – ie: a bigger battery. Ask the question: Is the power going in more or equal to the power expected to go out? When the tank is empty, it is useless.

·      Make sure the tank can accept bigger flows  – for batteries that is the continuous charge current is high. Preferably as high as the discharge current. Most batteries have much lower charge current levels than discharge current levels.

·      Then make sure that the charging sources are adequate. Ask the question: How long will it take to charge these batteries?

o   Solar at 50% power level. We pick 50% because this is the rating for a beautiful day in July or a cloudy day in summer. 20% of the days are perfect in QLD, 60% are at 50% and 20% are rainy/overcast at 10%. We always design for 50% solar yield which is 80% of the days.

o   DC DC charging. In a conventional analog DC DC the output drops to 50% when hot (users report this for Enerdrive DC DC for example). So again, how long at 50% charge rate? (Scotty doesn’t derate and runs at 96% efficiency)

·      Then make sure the replenishment energy sources can pour the power in and fill up the tank as quickly as it goes out.

·      Most couple who are moderate users require around 3,500Wh of replenishment energy a day. For 1,000W on a caravan roof, at 50% yield for 5 hours, that 2500Wh produced. Then the battery is being consumed at 1,000Wh per day. In perfect weather it is adequate. About 1400W at 50% produces 3500Wh a day.

Solar Power

Think of solar power as the gutters on a roof collecting rain water to go into the tank.

·      The bigger the roof area the better. With solar for an all electric van for 2 people we target 1200-1400W on the roof.

·      Panels of different sizes are like roofs of different sizes but all feeding through one gutter system built for the smallest roof. Designing the solar takes us the longest time than anything else on a job. I consider myself above average at this, having designed/ delivered over 5000 solar jobs, yet it still takes time in the design to squeeze out every possible ounce of solar.

·      The higher the solar panel voltage, the better. Think of this as the steeper the roof, the sooner you get water in the rain tank. Some 12V solar panels are like having a flat roof. Or a roof with a belly in it and nothing flows out unless there is a torrential rain storm. We like individual solar panels at 33V Voc and higher. The best Sunpower panels are 82Voc.

·      The most common mistake with jobs coming in is the customer wants to keep or buy solar from a cheaper source. They then end up spending good money on a system but with a dubious power source.

Think of an Inverter/Charger as a very big pump

·      However, not all inverters or inverter/chargers are the same.

·      Some inverters are stand alone and cant be connected to the incoming power. That’s like running two pumps. One pumping water into the tank and one pumping out. The water coming in from a connected source is not just passing out.


  • Compliance to Australian Standards
    Safety is always No 1. Large power systems and inverters have to be safe. The earth wire is the ultimate safety point with RCD’s (Residual Current Detection) tripping if there are faulty appliances. These are compulsory on every installation.

    The Victron inverters Safiery use have an additional safety feature of detecting if the incoming power when you are plugged into a socket at say a farm stay, is safe or not. The incoming power will NOT be activated if it is unsafe. We get 2-3 calls a week from our now nearly 500 monitored systems requesting us to check this as no power is coming in.
    Safiery systems don’t require double pole switches because we activate software to actively check on the polarity of the active wire for incoming power.
    New Standards become mandatory after 19th November 2023. The major change is the location of Lithium batteries which will require either an exterior location or access externally. Safiery will release our new 48V IP67 Lithium battery to comply with the external mounting option. There is no change in these standards that impacts the installation of Safiery's 48V packs.

How Good’s That!

New Electrical Standard Apply Soon and impact Lithium Batteries

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