Motorhome maintenance Our Diamond Dave offers expert guidance on LPG supply systems and leisure batteries

Over the years we’ve featured lots of advice from Diamond Dave, our technical expert - Dave has his own workshop (https://davenewell.co.uk) and is a highly experienced motorhome engineer. This month, LPG supply systems and leisure batteries

gas issues

Most motorhomes use LPG as a power supply; it is a very useful commodity.

In our ’van, we use it for cooking, heating and hot water. Some people use it as fuel for a generator and if your motorhome has a petrol engine, it can be converted to run on LPG.

LPG stands for liquefied petroleum gas, a by-product in the oil industry. However, LPG is not a single gas: the term covers a range of gases, all of them derived from oil.

Propane and butane are the two types used in motorhomes and caravans. In Calor cylinders, butane is the blue one and propane the red.

Butane has a slightly higher calorific value than propane, which means it contains more energy per unit volume; but it has a major drawback, in that its boiling point (the temperature at which it changes from liquid to gas at atmospheric pressure) is around 2°C.

Propane, by comparison, boils at -42°C, so is much more of a viable choice if you are planning to use your motorhome in cold climates. It is also, therefore, much better for all-year use.

Full and complete combustion

Whenever we burn a fuel, be it petrol, diesel or gas, we need to make sure that it has sufficient air for full and complete combustion.

Provide too little air and the process will be what is termed ‘fuel-rich’, which causes incomplete combustion and results in the production of soot and carbon monoxide (CO), which is highly poisonous.

Appliances are fitted with metering jets, which allow the correct amount of gas through for the burner to achieve full combustion. However, if the jet or air port becomes obstructed, this will lead to incomplete combustion and production of the above-mentioned CO – not what we want.

In my experience, the fridge is the most likely appliance to have problems with combustion, which is because the burner is pretty much out in the open. In almost all of the other appliances found in your motorhome (other than the cooker, of course), the burner is buried deep inside the unit.

The fact that the burner in the fridge is relatively exposed, and this appliance is one of the lowest users of gas, makes it very common for the burner to get dirty, which leads to poor combustion and the production of CO.

Most companies that manufacture three-way fridges recommend annual servicing, with more frequent checks if the appliances are being used very extensively on gas.

Gas Safety Regulations cover the safe installation, maintenance and use of gas systems. And when it comes to working on your motorhome’s gas system, the rules are clear.

All motorhomes, caravans and horse boxes are exempt from the regulations, except for those being hired out in the course of a business; in which case, they fall within the remit of the regulations and can only legally be worked on by a Gas Safe registered engineer with the right qualifications.

This is both a good thing and a bad thing – it is good, in that there are no real restrictions to end-users carrying out their own gas maintenance, but it’s bad because not everyone who does so really knows what they’re doing.

The gas, although highly flammable, is pretty stable and safe to use, as long as a few basic rules are followed. LPG is stored in cylinders as a liquid under pressure, at two bar (28 psi) for butane and 6.5 bar (100 psi) for propane.

When it’s released to atmospheric pressure, the liquid boils and converts to vapour. Propane expands by 270 times its volume when changing from the liquid to the vapour phase, so one litre of liquid would convert into 270 litres of vapour.

It should therefore be obvious that the general condition of the cylinder is important. Any dents could provide a weak spot, potentially leading to a rupture of the cylinder.

LPG is heavier than air, which is why motorhome and caravan gas lockers have a drop-out vent in the floor.

If a leak occurs, the gas can escape downwards to the outside world, where it will dissipate harmlessly.

Make sure that you don’t obstruct the drop-out vents in your gas locker. I’ve seen lots of cases where all sorts of stuff has been stored there – tools, knee-mats, plastic sheets and so on.

Strictly speaking, there’s nothing wrong with using the space in that way, but this will cause problems if it obstructs the free flow of vapour to the vent. Your locker should hold one or two cylinders, nothing else.

Gas regulators have a 10-year lifespan, and should then be replaced with a new unit. Gas hose (including pigtails) generally has a five-year lifespan, but can be used beyond five years if regularly inspected and found to be in good order.

I have seen quite a few home conversions over the years employing top-quality gas installations. Sadly, I’ve also seen a few absolute horror stories, including one ’van that was piped entirely in rubber hose, from the bottle-mounted regulator to all of the appliances.

The fridge in this ’van also had no external vents at all, not even to allow products of combustion to escape.

Exchange cylinders, or user-refillable?

A popular conversion is to switch from exchange gas cylinders to user-refillable ones. In the former, you rent the cylinder with a one-off payment, then, when it is empty, you exchange it for a full one and just pay for the gas – but you never own the cylinder itself.

With user-refillables, you buy the cylinder and it is installed in the ’van, with a filler connection. You refill from an Autogas pump. Autogas is a trade name – the gas is propane, exactly the same as you get in a red Calor cylinder.

‘Make sure you don’t obstruct the drop-out vents in your gas locker. I’ve seen lots of cases where all sorts of stuff has been stored there – tools, kneeling mats, plastic sheets and so on’

Most motorhome owners rely on at least one leisure battery, sometimes more, for 12V power for the lights, water pump, TV and other equipment.

But many seem to misunderstand the function and performance limitations of their leisure batteries.

The battery is an energy store – a fuel tank for electricity, if you will. As with any fuel tank, you can only take out what you put in.

Charging up the leisure battery

Most motorhomes have two means of charging the leisure battery: from mains via the hook-up, or from the alternator with the engine running.

Most vehicles will use a multistage charger as the mains unit. These can be left on almost indefinitely without risk of harming the batteries.

Charging from the alternator is not as good, because it starts with quite a high charge rate, but tapers off to a trickle charge of just a few amps.

The reason is simple. On starting up, the alternator ‘sees’ a depleted battery and winds up to near maximum charge rate. At this level, the battery voltage rises quickly and the charge current (amps) decreases proportionately.

The alternator charge to the battery is also limited, typically to about 20A.

The other point about recharging leisure batteries is the time it can take. If you have a 100Ah leisure battery and discharge it to 50%, you will need to replace 50Ah.

If the alternator is delivering 5A to the battery, it will take 10 hours of driving to recharge it. Likewise, when using the mains charger, you need to leave it on for long enough to recharge the battery. Most on-board chargers are 15-20A units, so would take more like three hours to recharge a battery. Bigger, or multiple, batteries will take longer to recharge.

It’s inadvisable to leave conventional batteries in a discharged state, so when you have been away for a weekend off-grid, put your ’van on hook-up for 24 hours to top up the battery – if you can’t leave it on hook-up long term.

Other options for recharging your batteries are solar, wind, fuel cell and LPG-fuelled generators. Solar panels are getting cheaper, and are physically smaller for the same output. The most popular size has been around 100W, but with prices dropping, 150W panels are becoming more common.

Solar regulators have also moved on. For many years, the standard has been PWM (pulse width modulated), but MPPT (maximum power point tracking) units are also popular, as they harvest the panel’s energy more efficiently.

Many motorhome owners looking at solar power ask, “How big a panel do we need?”, to which I have to reply, “I don’t know.”

The question isn’t the size of the leisure batteries, but how much 12V energy you use. A little camper using just a couple of LEDs might manage with a panel of 50-60W, but someone with a 9m tandem-axled rig with blown-air heating, a 26” TV and a compressor fridge, for example, will need more like 150-200W of solar real estate, possibly more.

Some distribution units (Sargent and Schaudt to name but two) can take the solar feed and distribute it to leisure and engine batteries as required.

If you are considering solar, check if yours has this facility and ask the installers to wire it in accordingly.

Be aware that these systems often have a maximum solar wattage that they can handle, so check yours won’t exceed this.

Wind generators aren’t as popular, because they have to be stored for travelling, plus they can be noisy.

Engine-driven generators can be very useful and often have higher outputs than solar or wind, but are heavy, noisy and smelly.

Fuel cells convert energy chemically and can be convenient because they are almost silent, but they are costly.

There has been a bit of a revolution in leisure battery technology, with the advent of lithium iron phosphate (LiFePO4) batteries. Size for size, these offer better energy density (the amount the battery can store) than traditional lead-acid batteries.

LiFePO4 batteries are much more resilient than lead-acid – leave the latter discharged for more than a few days and you will almost certainly do it a mischief. LiFePO4 batteries can withstand being discharged a lot lower than lead-acid, and cope with being left discharged for longer periods of time; although of course, this is not recommended practice.

The only disadvantage is, LiFePO4 is a pretty expensive option – and there are few signs of the price coming down in the foreseeable future.

‘The battery is an energy store, a fuel tank for electricity. As with any fuel tank, you can only take out what you put in’