BATTERY MONITORING

Monitoring the state of charge of the lead-acid battery requires continuous monitoring, considering that most of the time the battery powers a system that is supposed to be uninterruptible for long periods, or that the batteries are part of an off grid or mixed system, an on grid – off grid system, which is subject to charging from an automatic charger powered by the grid or from a photovoltaic system. The battery under monitoring is most often made up of individual cells or from mono-blocks with 3 cells (with a nominal voltage of \(6 [V]\)) or 6 cells (with a nominal voltage of \(12 [V]\)) connected in series until the required nominal voltage to be delivered by the battery is achieved.

For continuous monitoring, in addition to the hardware component, software support is often necessary, which provides servers (client-server services) for the protocol required for data transmission, storage, display, processing, and signaling any potential malfunctions.

Since it is important for all elements in the battery to be of the same type (capacity and voltage) during its construction, it is equally important for them to maintain a similar degree of wear during operation, as the early loss of electrochemical characteristics of one or several elements will cause the battery to be taken out of service before its expected lifespan. In other words, the weakest element of the group within the battery will dictate the performance of this battery.

To determine in advance which element or monoblock, from which group, has lost its electrochemical characteristics compared to the other elements or monoblocks in the groups (string) that make up the battery, it is necessary to monitor each monoblock or group several elements together, in case it is not possible to monitor each element that constitutes the battery.

Client-server services used in monitoring

After collecting information regarding the voltage level of each monitored group, it is necessary for this information to be transmitted remotely for processing and decision-making regarding the state of charge or wear of the battery or a specific monitored group.

Mosquitto Service - MQTT

MQTT is the English acronym for MQ Telemetry Transport. It represents a communication protocol specifically designed to minimize the bandwidth required for communication in a high-latency network. Thus, the protocol is ideal for use in machine-to-machine communications or IoT from the English "Internet Of Things" - the internet of things.

The installation and configuration of this service are presented below for Debian 9 or 10 distribution running the Linux® operating system. All commands will be executed in a console/terminal opened on the server. Commands are executed by the root user or by a user with administrative rights.

To begin with, we will download the key:

foo@bar:~$ wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key

We are installing the key:

foo@bar:~$ apt-key add mosquitto-repo.gpg.key

We create the file with the list where the repository of files to be installed is located:

foo@bar:~$ nano /etc/apt/sources.list.d/mosquitto.list  

After opening an empty file, we write, using the preferred editor, in this case nano, the following:

deb http://repo.mosquitto.org/debian stretch main