LiIons, and Chargers, and Panels, OH MY! - Part 1

This is the first article in a series of many around the choices that we’ve made for the power system for Wally the Airstream.  There are many brands and products out there for powering your RV so we’ll try to explain our choices for each below.  Wally’s power system can be broken down into 3 major systems:

1)    The charging system (solar, shore power, and generator)

2)    The storage system (batteries, battery management system, charging system)

3)    The power system (inverter, 12VDC panel, 110VAC panel)

For the charging system we’ve selected to go with a 400W 4 panel array in series/parallel configuration on the roof, a 50A shore power input, and a 3000W generator.  The combination of these items will be sure that we’re able to run all of the lights, accessories, and A/C whenever needed, even when we don’t have access to power. Future articles will go into the details of our specific product selections in this category.

The power system will consist of a 3000W inverter with standard marine panels for both the AC and DC sides of the system.

The heart of this first article is to discuss our storage system first.  We’ve elected to go with a LiPO4 (lithium ion) battery array for storing the power we generate via our charging system. Based upon our needs and the system that we’re configuring, we’ve decided to go with a 440 Ah battery.  LiPO4 batteries have many advantages and a couple shortcomings. First, the advantages.  LiPO4 batteries:

1)    Have a very high energy density. LiPO4 batteries typically are around 110Wh/kg whereas a lead acid battery usually performs at about 40Wh/kg.  This means that for the same amount of weight and size, you can get nearly 3 times the power.  This becomes a huge advantage when thinking about a lightweight towable solution like Wally the Airstream.

2)    Have long life and deep discharge curves.  LiPO4 batteries can get over 2000 charges, 10+ years of battery life, can discharge to 10% remaining charge without significantly shortening life, and have a very high charge/discharge efficiency (95%). Compared to a lead acid or AGM batteries that have a maximum discharge of 50-60% SoC (state of charge) you have much more usable power with a LiPO4 battery. They also are capable of rapid discharge needed for high current drain applications (A/C) without damaging the battery. The batteries also have a broad range of operating temperatures.

3)    LiPO4 batteries can be stored for long periods of time without risk of damage. 

There are a couple risks to consider when choosing LiPO4 batteries as well.  Those are:

1)    Thermal runaway or total failure of discharge circuits leading to extreme heat dissipation and fire are possible.  Many of you likely remember the Samsung Galaxy Note fires and the surrounding hoopla that was created around them.  The cause of these fires was determined to be lithium ion cells that had become damaged from punctures and overheating and experience thermal runaway.  Thermal runaway occurs when a short between the anode and cathode of the battery occurs and the battery super heats to the point of creating fire.  Unfortunately this is possible in cheaply manufactured batteries without thermal protection and/or cheap battery management systems.  Our selection of a Lithionics battery is focused around finding a very safe LiPO4 cell for Wally the Airstream.

2)    LiPO4 batteries are very pricey.  For a high-quality battery, you can expect to pay $1500-$2000/100 Ah.  Cheaper Chinese cells with low quality BMSs can be found in the $900-$1000 range but with our focus on safety, we weren’t interested in going that route.  We’ll get into our selection and the difference between a good and bad cell and BMS in our next article.

A good quality Battery Management System is critical to the health and use of any battery. We’ve elected to use the NeverDie BMS that comes with the Lithionics LiPO4 battery that we’re installing in Wally the Airstream.  The NeverDie system is built with military-grade contactors rather than cheaper MOSFET contactors seen in lower quality systems as well as temperature intervention sensors and battery protection circuits.  This BMS will ensure that the large investment batteries are kept in top operating conditions and function as a secondary safety backup to our power system. 

For the charging system, we’ve elected to use the Victron Multiplus 50A/3000W charger inverter system.  Victron is well-known in both the marine and off-grid communities as being some of the most reliable and well-made charger/inverters and battery management systems.  The Multiplus has Bluetooth and CAT-5 connectivity for management of the entire charging/generating/storage system.  So far we’ve been really impressed with it.

In our next article we’ll talk a bit more about the reason why we chose Lithionics for our LiPO4 storage solution.  Here’s a hint: because they’re the safest!