The Voltage and Current Regulating System (VCRS) developed in conjunction with Electronics & Energy Solutions (EES) is a self regulating, and fully automatic charging module, allowing for the use of large-capacity rechargeable lithium batteries in conjunction with dynamos. Specifically it is designed to be installed on a boat, but its use cases could reach beyond and applies to safely charge lithium batteries anywhere, from any source (within the boundaries of the system). The VCRS is a standalone unit, providing its user with the necessary safety and surveillance of the lithium battery charging through its NarrowBand IoT mobile application connection. This gives the end user full control over what is happening during the charging process of the battery.
Today, most private boats are equipped with two or more batteries. One of these batteries are designated to start the boat engine, while the other will provide electrical power to the rest of the boat’s equipment and accessories. e.g. television, refrigerator, downlights, etc. Traditionally, batteries used for engine or general consumption are lead-acid batteries. However, batteries made with a chemical composition of lithium have great advantages compared to the lead-acid batteries. Lithium batteries weigh significantly less, have shorter charging time, a higher charging efficiency, larger number of charging cycles, and a higher power-volume ratio than lead batteries. Lithium batteries are simply the better alternative. However, safe charging of lithium batteries require a more complex circuitry than lead batteries.
A critical attribute of lithium batteries is their low internal resistance. These batteries will request as much charging current as possible from its source, up to 1C. This may cause the dynamo that is charging the lithium battery to provide more current than it is designed to, eventually causing it to overheat. On the contrary, lead-acid batteries should only be charged with 1/10C. Thus, one of the challenges of charging lithium batteries with dynamos is the potential overheating of the dynamo itself. In the worst cases, this could lead to combustion, which is not typically something you’ve want to happen on a floating vessel in the middle of the ocean.
Besides, a boat dynamo can deliver fluctuating voltage and current levels. Therefore, regulating and stabilizing the output from the dynamo to the batteries is necessary for safe charging and protecting the dynamo from overheating, and potentially catching fire. Currently the market does not provide any affordable and easy to implement solution for charging lithium batteries from a dynamo. Therefore, there exist a gap in the market for developing lithium battery chargers that provide the aforementioned qualities. Taking the above points into consideration, the client (EES) aims to develop an affordable and easy to integrate dynamo powered lithium battery charging system. This thesis addresses the development of a voltage and current regulating system, which makes it possible for the EES’s lithium batteries to be charged by a dynamo on a private boat.
The VCRS operates on an automated setup of Switch Mode Power Supply (SMPS) circuits. These are regulators which control the flow of current and voltage by switching on and off with incredibly high frequencies. Adjusting this frequency allows for more or less throughput of current. Each SMPS circuit on the VCRS has a theoretical max throughput of 50 apms. By installing 7 of these circuits in parallel, this allows the system to safely reach a total maximum of 250 amps, without any SMPS working on full duty.
This entire process is controlled and overlooked by an on-board Microcontroller Unit (MCU). The SMPS circuits feed their output current through a Shunt, which is a heavy duty ampere-meter, before it is connected to the lithium battery. This aforementioned shunt sends its reading directly to the MCU. The MCU is set up as a state machine, changing into different states based on the input it receives from temperature sensors onboard the system, the shunt readings and a potential of charge reading from the lithium battery. This all results in a power modulated control signal which is sent back to the SMPS circuits, effectively adjusting their throughput based on all these variables. Thus completing the loop.
Lastly, during this entire process, the MCU is also sending out data through the Narrowband IoT cloud service of NxTech. This data is then received by the connected mobile application on the private cell phone of the end-user. Here the end user can see everything happening on the VCRS in real time. The mobile application also receives information regarding the battery as the batteries in question come in a package with a Battery Management System (BMS) providing the MCU, and therefore application with information regarding things such as the battery charge, health, estimated time to depletion, water intrusion detection and behavioral warnings and so on.
Additionally, the VCRS is intended to be equipped with an GPS system, which is also available in this application. In today's society, boat thieves have gotten increasingly deceiving. In the case of a boat capture, thieves may try to disable the main electricity onboard to stop any onboard GPS tracking their location. With the inbuilt GPS tracking system of the VCRS, this could serve as a secondary security measure, often overlooked by intruders.