Battery Management Systems

Batteries are charged when a power source is available. They provide energy on demand at any time irrespective of other power sources. Solar power happens on its own timetable however and an engine might be started for the sole purpose of battery charging. Battery monitoring allows us to manage the energy we have left in the battery and determine when to start and stop charging.

State of Charge (SOC) represents the charge level. It’s calculation is based on the total battery capacity and the accumulation of amps flowing into or out of the battery. It can be expressed as a percentage of full or as remaining amp hours.

Monitoring systems keep track of the key parameters and provide a warning or possibly shut down a system when dangerous conditions are imminent. 
Performance trends allow an analysis of past performance which can be used to fine tune system operation. High performance systems that minimize battery capacity rely heavily on battery monitoring to work closer to the battery limits. This is particularly true for Lithium Ion systems.

Although Lithium battery technology delivers outstanding performance, it also requires a higher level of diligence in it’s operation. An accidental over discharge or charge can cause severe cell damage.
Battery management systems (BMS) monitor battery parameters and act accordingly to protect the battery. The action might vary according to the fault. For example a battery that is approaching a state of charge limit might turn off non essential loads. Or a high cell voltage warning might cause a momentary shutdown of a charging source. Ultimately the BMS can act directly on the main battery switch and isolate the battery to prevent damage.

Some applications may sustain an unscheduled battery failure but others would not be able to cope with an unscheduled blackout. For example a vessel electrical system failure may be dangerous in some situations.

Advanced BMS systems employ methods to bring on-line a reserve battery before taking the main battery off-line. A Lithium battery and it’s BMS needs to be part of the overall DC distribution system rather than just an add-on component. Utilizing a DC power distribution board with integrated Lithium BMS components is a commonsense yet economical approach.

There are three components to a lithium battery system. Together they provide a complete system solution.

• Lithium Battery -  read about it here
• DC Distribution Board
• Battery Management System Controller

Download our Guide for Lithium Battery Systems  white paper for a complete review of an integrated system approach.

BMS DC Distribution Boards

All electrical circuits require protection against overload and short circuit conditions. The heavy cable that is used for interconnection of this equipment ideally suits a bus bar configuration with integral fuse protection of each circuit. Outback Marine has developed a range of DC Power Distribution Boards (DCD’s) that facilitate the interconnection, circuit protection, control and monitoring functions in a compact and reliable manner.

The DCD board is central to the entire electrical system. By planning the placement of equipment in close proximity, cable runs are kept short and power losses are minimized. Available boards range from simple manual battery switching versions through to remote controlled solenoid models with advanced monitoring and control capability.

Common to all distribution boards is the ability to remotely monitor and control the battery system from the battery management system controller. Battery data is monitored by a "Digital Shunt" module. It keeps track of battery voltage, current and state of charge. A two wire interface monitors the battery management modules and battery temperature.

A "Relay Board" module supports the balance of the system by providing a control mechanism for the magnetically latching solenoids. Both module connect to the battery management system controller over a digital I2C bus.

The arrangement of the DCD board and electrical system in general depends on the vessel configuration with variables that may include the following.

• Type of application - yacht, power boat, RV, caravan, industrial etc.
• Engine charging system
• AC generator system
• Solar panels and wind generation
• Battery technology

We have identified 5 system arrangements to individually target a broad range of applications.

Type 1 DCD System This board supports a system that has a single house battery bank. A battery switch is used to isolate the battery from the system in case of an emergency situation - for example an electrically driven fire caused by a short circuit. Fuses mounted on the positive bus bar protect outgoing circuits. A negative bus bar provides a ground return path. This system is typically used for caravans and camping trailers where the tow vehicle can charge the house battery via a DC-DC converter.

Type 2 DCD System The type 2 system adds a second switch that connects the house battery positive distribution bus to a "charge bus" that connects in turn to an engine or alternate charging system. The switch can perform the function of a cross charging relay that allows the house battery to be charged from the charging system. The switch would open circuit when the engine stops to prevent discharging the starting battery. In addition the house battery can be used for engine starting in the event of a start battery failure. The start battery has a direct fused connection to the charge bus. The engine can be connected by a seperate fuse as shown or can connect directly to the house battery as would be the case in say a motorhome or existing vessel engine system.

Type 3 DCD System The type 3 system adds a battery switch and a current monitoring shunt for the start/reserve battery. This system can keep track of the reserve battery state of charge and temperature so that the start battery can be used as an alternate house source in case of a battery shutdown. In case of a house battery shutdown condition, the system can parallel in the start battery before isolating the houase battery. This safety feature ensures that house power continues without interruption. This is a much better situation instead of just taking the house battery off line without notice. The ACR on this system has a bi-directional function. In the event that the start/reserve battery has been discharged, it's important to monitor the battery for temperature when charging from the house battery side. This is the system of choice for inboard and outboard powered cruising vessels where a Lithium Ion house battery can be combined with an AGM starting/reserve battery.

Type 4 DCD System Type 4 systems have an alternate approach to battery organization. Two batteries connect to a common DC distribution bus. They can be used together or separately for both house and engine cranking applications. They should be both of the same chemistry but do not need to be the same capacity.  This dual battery setup would normally charge and discharge both batteries in parallel. The charge status of the batteries are individually monitored. In the event of a single battery failure, the other battery is online and available to continue operation - all be it at a reduced overall system capacity.

Type 5 DCD System The type 5 system extends on the Type 4 by adding a separate engine/charging bus. It’s similar to a Type 3 system with the addition of a second house battery.  This system would be ideal for a larger vessel or motor home application where a redundant house battery system is combined with a cross charging capability with the engine alternator.

 

Battery Management System Controller

Some battery management systems only protect the Lithium battery from over and under voltage events. Others add cell based monitoring and cell balancing and may include a battery monitor as well. These are all good things. However it’s the electrical system that needs to be managed and not just the battery. Good engineering is about looking after things when something goes wrong. So when considering a Lithium system, it pays to look closer at what the BMS includes.

A comprehensive battery management system controller in conjunction with an integrated DC distribution system is a powerful combination.

• Monitoring and display of battery volts, amps, amp hours, temperature and solar amps with trend chart displays and historical data.
• Lithium Ion battery management including cell voltage monitoring and state of charge alarms.
• Manual and automatic control of battery switching and cross charge solenoid.
• Inverter and battery charger control.
• Separate charge bus control.
• Plain English language setup and operation.
• Internet web portal via Victron Color GX
• Bluetooth iPhone app. Android coming soon.
• NMEA-2000 battery data support (2016)

The Outback Marine battery management system uses an advanced controller with a graphic LCD display. This means that battery parameters can be displayed graphically over a time line that better indicates what's happening now relative to the past.