December 10, 2018

TT #109 REV Group Introduces Lithium Batteries to its Luxury Models

By: Rob Lowe

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Some 2019 American Coach and Monaco Coach models have the option of a Lithium Battery Package to replace the conventional AGM maintenance free Coach Batteries. After extensive bench and in vehicle testing, this superb power source is now available in production. Those models offering this upgrade option are the American Coach Eagle and Dream and the Monaco Signature. There are some configuration differences, which I will address later in this TechTip.

Why would I buy Lithium Ion Batteries?

Lithium Ion (or more correctly Lithium Iron Phosphate (LiFePO4)) Batteries offer substantially longer usage time, longer life, are much more tolerant to being almost completely discharged and are a fraction of the weight of the comparable Lead Acid batteries they replace. They can be recharged much faster and are a very safe power source. To learn more about this technology and its advantages, I recommend reading four earlier Technical Tips on our website that cover the rationale for selecting Lithium batteries, the actual battery conversion of our coach battery system to Lithium Batteries and some "in use” information. These are detailed in Technical Tips #82, #83, and #84 together with #94. Without going into much more detail, I can say that as of the date I am writing this article, our Lithium batteries, which were installed in July, 2014 are performing as if they were new, almost five years later.  These batteries should be considered lifetime batteries since, according to the supplier, even after 2,000 to 3,000 discharge/charge cycles, they will deliver 80% of the rated capacity. Some in the battery maker’s testing are performing well after 5,000 cycles! My experience seems to bear out the claims with a competitive brand of battery.

Different Configurations Depending Upon the Model:

In preparation for this article, I interviewed the REV Group’s (REV) Electrical Engineering Manager and one of his Electrical Engineers. REV installs 100 Amp-hour (Ah), 12 Volt, dragonfly brand (http://dragonflyenergy.com/batteries/) Lithium batteries connected in parallel, as a direct replacement for the original 6 Volt, AGM batteries that were series/parallel connected to give 12V on the standard equipment coach battery system. This allows the new batteries to drop right in and fit in the same compartment without modifications.
dragonfly Lithium 12V Battery
On the Eagle, the system consists of eight (8) batteries (800Ah total). On the Dream and Signature, the system consists of six (6) batteries (600Ah total). Generally, the industry considers the effective Ah capacity of Lithium Batteries to be double the nominal rated capacity, since they can be discharged to about 20% without any long term damage. Thus, the configurations result in 1,600Ah or 1,200Ah which, when compared to the capacity of conventional Lead-Acid AGM Batteries is a lot of dependable power! (Note: Our coach has performed flawlessly with a 300Ah (= 600Ah) battery.)

Reno, Nevada is the home to dragonfly and their consumer version of the battery is known as Battle Born. The batteries are assembled in Reno, with components imported from many worldwide locations. The individual cells are made in China, since that is the only source for lithium iron phosphate cells at present. The batteries are UL listed.

In the REV Group coaches, the batteries are placed on AC powered, heat mats in the battery compartment and interconnected by Bus bars attached to all Positive terminals in each row. Similarly, all Negative Terminals in each row are connected together. This results in 3 (or 4) batteries in 2 rows and allows the coach connections to be made in the middle of the two sets (considered to be the best point for making connections). Each individual battery contains a Battery Management System (BMS) that manages the charging of each battery and equalizes the charging among the batteries. It protects each battery against overcharging, short circuits, reverse polarity connections and discharge below a safe level. The nominal voltage of each individual cell is 3.2V with four cells making up each battery, thus 12.8V is considered the battery voltage. Charging these cells brings them up to 3.6V which results in 14.4 Volts for a fully charged battery. Typical voltage readings will be in the 13.4V to 13.6V range. Each battery cell contains a fire-retardant and their construction further reduces any risk of fire.

The aforementioned heat mats compensate for the fact that Lithium Batteries will function down to about -4°F (-20°C) ambient temperature, however the BMS shuts down and will not accept a charge below 25°F (-4°C). If the Coach is used in very cold conditions, starting the generator (Dry Camping/ Boondocking) or turning on the power from the campground power source to supply AC power to the mats will warm the batteries to allow full charging.
REV Group Lithium Battery InstallationOn the Eagle, the option is $11,780 for the Coach Battery system. Conventional AGM batteries are used for the Chassis batteries, since they are better suited to the engine and chassis requirements.

As this technology becomes more common, the battery voltage likely will climb to 24, 36 or 48 volts. There are numerous reasons why this makes sense, not the least being that the higher voltage makes more power available for larger power demanding equipment such as air conditioners. If we look at other applications where lithium batteries are common, such as electric vehicles, we’ll find that 24, 48 or 96 volt lithium battery systems are common. Some, such as Tesla cars, use lithium battery systems producing about 400 volts. DC to DC Converters are used to run the 12V systems on each vehicle.

Some smaller Class B vehicle battery systems are capable of running a single roof air conditioner for periods of time. Some of these vehicles have eliminated the traditional generator and replaced it with an engine mounted generator that uses an integrated control system to start the coach engine when power demands it. While it may be a while before we see such a system on a large Class A, it is not outside the realm of possibility. Many of the newer generators found in late model coaches use inverter generators which allow them to be much more responsive to the actual load demanded. If the battery system was to increase in voltage substantially these inverter generators could be connected directly to the battery system, then those systems would provide all the power needed in the coach.

Perhaps this is a little bit of blue sky thinking however with this replacement of a lead acid system that has been the ‘go to’ power system since RV’s were invented power systems such as lead acid maybe on the way out. Lithium batteries are well worth considering if you are buying a new luxury coach.


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