Dometic Battery-Powered Auxiliary Air Conditioning System manual The Basics, Batteries, Alternator

THE BASICS

The basic principle of an air conditioner is the transfer of heat from one place to another – in this case from the inside of your vehicle to the outside. This is accomplished by absorbing heat from the inside air into a refrigerant gas flowing through an evaporator coil. The refrigerant is then pumped to a condenser, where the heat is released to the outside air. The refrigerant, a chemical with a low evaporation temperature, flows around a closed loop, driven and pressurized by a compressor. As a part of the cooling process, the air conditioner also removes moisture from the inside air, which makes the area feel more comfortable and keeps the compartment dry and mildew-free.

A belt-driven compressor on the truck’s engine supplies air conditioning whenever the engine is running. To keep the driver comfortable when the engine is shut down, it is necessary to have a separate auxiliary air conditioning system that uses an alternative source of power.

To that end, Dometic has developed an auxiliary air system that runs on 12 Volt power from an onboard bank of batteries, using a device called an inverter, which converts the 12 Volt DC battery output into 115 Volt AC power. It can also run on 115 Volt electricity from a shorepower hookup. No separate diesel genset or other internal combustion engine is involved. The batteries are automatically recharged by the alternator whenever the truck is running or from shorepower when used with Dometic’s recommended inverter/charger unit.

In specifying an all-electric battery-powered HVAC system, you should think of it as an integrated solution comprised of a number of different components, including:

•Heavy-duty deep-cycle batteries, designed for numerous discharge and recharge cycles

•A high-performance alternator with external regulator to recharge the batteries quickly and keep them fully charged

•A correctly sized and specified DC-AC inverter

•The air conditioning components, with associated ducts, grills, electrical power supply and controls

•Shorepower connection

BATTERIES.

Traditionally, truck batteries are designed to provide sufficient power to start the truck’s engine and to power lights, blower motors, electrical sensing circuits and other “hotel” loads like a refrigerator or a television set. It takes much more sustained power to run an air conditioning unit for ten hours (and conform to HOS regulations) without recharging.This is why Dometic specifies absorbed glass mat (AGM) batteries.These batteries are a proven technology and are readily available across North America. Dometic’s choices have up to 500 cycles in them (about 2 1/2 years of use) and were selected for their deep cycle recovery characteristics and ability to be recharged rap- idly.The number of batteries depends on the capacity of the air conditioner, size of the sleeper and the use profile of the truck.

ALTERNATOR.

You will replace your existing alternator with a higher-output unit rated at 185 amps minimum. The size of the new alternator will depend on the total number of batteries to be charged, and we will provide some guidelines in Chapter 3. Unlike traditional truck alternators, these units have an external regulator, which acts as a three-stage charger with a boost phase, a charging phase and a float stage. This regulator is programmed to charge to the specific requirements of an AGM battery. It has sensors for temperature at the regulator and batteries, and also for voltage and will use these sensors to protect the alternator from damage. Leece Neville extends a three year warranty for this alternator and external regulator combination.

INVERTER.

Off-the-shelf inverters are generally designed for relatively light loads, for instance,TVs, microwave ovens, coffee makers and computers. Dometic’s air conditioning systems will draw 70 to 100 DC amps for up to ten hours, and, there are momentary spikes when the compressor cuts on. We have developed a specific inverter with an experienced inverter firm that can handle the requirements of an air conditioning system while also being able to handle the normal house loads. It is available as an inverter/charger and as an inverter only. Both have a low- voltage cutout to protect the truck’s battery system and ensure re-starting. Dometic’s specified systems have never failed to start a truck engine.

SHOREPOWER.

Although there are relatively few shorepower hookups available at truck stops, rest stops and terminals, these will become more readily available in the future. The Dometic all-electric system is designed so that the auxiliary air conditioning system can run on an external 115 Volt power source, which can also simultaneously recharge the truck’s batteries when the inverter-charger unit is installed.

AIR CONDITIONING SYSTEM.

Dometic offers a range of models and capacities designed to meet each truck’s specific profile – its load requirements and space constraints -- and we will look at these choices on the next page.