One of the hallmarks of the Australian RV industry is that it’s generally very quick to adopt new technologies. This includes things like LED lighting, solar panels, 12V equipment and high performance batteries.
There are times, though, when an RV company does not merely adopt new technologies, it develops them. This is true of the solar panels and lithium battery system developed for the new Kimberley Kampers Black Caviar Kruiser caravan.
The challenge Kimberley Kampers set itself was to have enough battery power and charging capacity to drive a 12V air-conditioner. This would have been possible using existing technology but not within practical weight limits and weight is a huge concern in the RV industry.
There are batteries for many different applications but essentially there are two classifications – starter and deep-cycle.
Starter batteries are designed for high current, short time duration, such as for starting a vehicle. But those characteristics do not suit the ‘house supply’ batteries needed in caravans and motorhomes so that’s where deep-cycle batteries are used.
Deep-cycle batteries are designed to supply a lower current over an extended period of time. There are several different types of deep cycle batteries, as well as the latest development – lithium.
LEAD ACID BATTERIES
The basic form of deep-cycle battery is the standard lead acid variety in which lead plates are suspended in wet acid. This means the electrolyte levels will require some maintenance by periodically being topping up with distilled water.
Deep-cycle batteries are rated in amp hours (Ah), so a 100Ah battery should deliver 5A for 20 hours while keeping the voltage above 10.5V for a 12V battery. But that doesn’t mean you should try and get 20A for five hours because deep-cycle batteries are most effective if they are rarely cycled below 50 per cent of their rated capacity.
GEL CELL BATTERIES
These are sealed and have multiple plates in a jelly-like electrolyte. Being sealed, they require no maintenance and can be left in a discharged state for a long period of time. But a deeply discharged gel cell battery may not fully charge and could require some treatment. They cost about 30 per cent more than conventional deep cycle batteries and do not cope well with conventional vehicle alternators – they need very strict monitoring of the charging voltage and they are temperature-sensitive.
ABSORBED GLASS MAT BATTERIES
Originally built for military and aviation use, absorbed glass mat (AGM) batteries are also sealed and have multiple plates that sit between glass fibre mats which hold the electrolyte. They are the most rugged of all the batteries, so are most suited to RVs. They can be charged very quickly from a normal vehicle alternator, but they do cost considerably more (about 50 per cent) than flooded deep-cycle batteries. In terms of physical size, AGM batteries will provide about 15 per cent more Ah capacity than a gel cell but about 25 per cent less than a good flooded deep-cycle. AGM batteries can be routinely and quickly charged to 90 per cent of their capacity and discharged without long term damage to 30-40 per cent of their capacity.
Lithium batteries have been around for a few years (in your mobile phone, for example) but their usage in RVs is much more recent. Until then, the Rolls Royce of batteries was the AGM deep-cycle. The disadvantage of AGM batteries when compared to lithium batteries is their physical size – lithium batteries are much smaller and about 75 per cent lighter which is a major asset in any RV. They can be charged to 100 per cent capacity and will give nearly their maximum voltage down to 20 per cent. Lithium batteries can be charged at nearly 100 per cent efficiency (most batteries run at about 85 per cent) which means lesser energy loss. But there are disadvantages of lithium batteries – they are the most expensive of all and when fully discharged, the voltage drops very rapidly resulting in a dead battery which needs to be replaced.
All of the above assets were the reasons that Kimberley Kampers, along with several other manufacturers, opted for lithium batteries, with appropriate protection for the discharge problem, for its 12V power supply needs
Batteries require some method of charging, so the design of the offroad Black Caviar started with the development of a lighter and more efficient solar panel.
Monocrystalline silicon solar panels are commonly used because of their reliability and ability to deliver a good wattage per square metre. Caravan and motorhome roofs are ideal for solar panels as they are relatively large and flat. But the traditional glass format can be very heavy and fragile. A slight crack can cause the panel to fail – this is not common but it does happen.
Solar panels convert light, not heat, into electrical energy and are, in fact, less efficient in hot weather. It’s an oddity in Australia but solar panels work best in Tasmania.
I can’t tell every industrial secret here but a couple of years ago, Kimberley started working with a manufacturer to develop super-thin solar panels that are made from Monocrystalline wafers bonded in a unique and proprietary way to aluminium. Kimberley started working with a manufacturer to use the Oxide Aluminium back-sheet and Dupont’s EVA/Tedlar products to bond the same monocrystalline wafers. This produced a highly durable panel less than 2mm deep, and weighing 75 per cent less than glass. An added feature is that they are virtually unbreakable.
So how did the Kimberly panels work out in the weight saving department? They are quite impressive to say the least - normal glass panels would weigh about 65kg but the 540W panel array on a Kruiser weighs 15kg. That 50kg weight saving reduces the overall weight, in particular on the roof. Additionally, there is less wind resistance – conventional solar panels can be up to 40mm/1.5in deep.
Most solar panels have an output voltage but the Kimberly panels run with a load voltage of 36V. Apart from anything else, that means that smaller power cables can be used and there are less line losses.
The vital component between solar panel and battery is the solar regulator. It’s there to control the output from the solar panel and ensure that the batteries are charged quickly but not overcharged. It is possible to not have a regulator but the end result may be, at best, a battery that is not charged properly and, at worst, a ruined battery. Kimberly advises using a Maximum Power Point Tracking (MPPT) controller because of the high no load voltage (42.6V) of the solar panel. The MPPT reads battery voltage, solar panel output and adjusts accordingly for optimum voltage and current flow to maintain batteries at their highest state of charge.
Apart from the benefits to the RV industry, it’s good to see developments like the Kimberley solar panels. I’ve no doubt that in a country like Australia, where there’s plenty of solar energy available, our ability to harness that same energy is going to be very important in the future.