Battery

This page contains the information about the EoI battery development, everything from the requirements to the implementation can be found here.

What is the battery?

The battery is the energy buffer of the boat, it stores the energy coming in from the solar panels and provides a constant voltage for the motor path and peripheral electronics. The battery consists of multiple parts:

• Battery cells
• Battery management system (BMS)

The BMS makes sure that the battery cells can't be overcharged or over-discharged, as this might damage them and present dangerous situations. Besides monitoring the voltage a BMS usually monitors the current and temperature as well.

Technical regulations (as per September 2022)

• Maximum nominal voltage: 58,8V (14S lithium-ion)
• Maximum capacity: 1,5 kWh (= 5400 MJ)
• All battery cells must be commercially available
• The BMS must monitor the battery voltage and current
• The BMS must be capable of shutting down the system
• The BMS must be able to monitor charge and discharge currents
• The BMS must have a means to limit over-current in charge and discharge paths
• The BMS must monitor all individual cells
• All electrical systems must be provided with a fuse in series connection with the main battery ('Main fuse')
• The battery must be fused
• The BMS must be fused

Specifications

Functional requirements

ID	Specifiction	Value	Pass/Fail
	Nominal pack voltage	<= 58,8V
	Maximum capacity	1,5 kWh
	Monitor (pack) voltage
	Monitor (pack) current
	Monitor (pack) temperature	>> 1 sensor (8)
	Limit overcurrent in (dis)charge path
	Capable of shutting down the whole system
	CAN-bus communication	5V / 1 Mbit
	Internal cell balancing
	Charge and discharge paths can be operated simultaneously
	Motor and MPPT should be enabled independently
	The battery should be enabled with a N.O. contact	open = off closed = on
	Separate enable contact for Motor path (output) (Optional: Software disable only)
	Battery should be fully disabled (all outputs disabled) by emergency switch
	Shelf life (Save battery mode)	>= 1 year (2.8mA max)
	Humidity sensor
	Galvanic separation of safety path (bilge and horn)
	(Optional) I.M.U.
	(Optional) Phase change cooling hardware

Electrical requirements

ID	Specification	Value	Pass/Fail
0	Motor path (output)	60V / 300A
1	Charge path (input)	60V / 50A
2	Peri path (output)	24V / 2.5A
3	Safety path (output) (bilge and horn)	24V / 4A

Environmental requirements

ID	Specification	Value	Pass/Fail
0	Ambient operating temperature	0 - 50 °C
1	Ingress protection	IP67 or better

Battery Management System

The Battery Management System (BMS) is the brains of the battery and makes sure to manage the battery so it is Dedier proof and does not catch on fire.

The BMS has different functionalities on the PCB and therefore different settings. Since these settings are extensive (especially with the Cell Voltage Monitoring (CVM) chip, this chip does more than only measuring the cell voltages but we will be calling it the CVM from now for better readability.

The BMS has different hardware components that is used in the EoI-battery, these are shown in their corresponding figures throughout the page. Shown below is the full battery system with cells in the box.

Battery box

Hardware

The full BMS system consist of at least three PCBs that are:

• Main board
• Current sense board for the discharge
• Charge path board

Each of the hardware are further elaborated in their own sections.

Main board

BMS PCB top view

The main board (shown right) is big brain of the battery system. On the main board there are multiple ICs with their own configurations and applications, namely:

• Cell Voltage Measurement IC
• ADC
• Microprocessor
• ...

Current sense PCB top view

Charge path PCB top view

CVM

The CVM that is used on the BMS is the BQ76952, located in the middle of the main board. This CVM-chip has an extensive list of configurations and features which makes it cumbersome to scroll through the code to know which features are enabled and which safety configurations are made. Therefore a list is generated with a description of the used configuration below.

These are preliminary configurations and could be changed through the course of time and should be changed accordingly here as well.

FUSE pin configuration of the CVM IC.

Short description	Configuration	Long description
Min Blow Fuse Voltage	STACK: 60.2V(4.3V per cell)	Permanent faults the device and enables FUSE pin to trigger the fuse. FUSE pin stays on indefinitely and thus manual intervention is needed.
PF_FUSE	Enabled	Whenever a permanent fail occurs the FUSE pin should also be triggered.
Internal regualtors 1 & 2	Disabled	Regulator 1 and 2 are disabled since we do not use that with the CVM on the BMS.
Pre-regulator REG0	Disabled	Pre regulator is used to generate voltages for regulators 1 & 2.
CFETOFF	Disabled	CFETOFF pin is not used on the BMS.
TS1,2,3	18k resistor model & 18k pull-up resistor internal Used for cell protection	Temperature pins are configured to be used in cell temperature protection
DFETOFF	DFETOFF pin is configured as a termistor input 18k resistor model & 18k pull-up resistor internal Used for cell protection	DFETOFF can have different functions and is used for temperature measurement as a termistor input.
DDSG	Configured as analogue discharge enable	CVM IC can determine if the battery may be discharged. This pin activates the discharge path if everything is within spec
DA	Resolution measured current: 0.1mA Resolution measured voltage: 10mV Internal temperature not used for cell/FET protection	DA configuration specifies the units for measuring the current and voltage. And can configure if the internal temperature readout should be used for cell protection.
VCELL	Disable cell protection on cells 14 and 15	Configures which cell should be used for cell protection and which cell should be ignored. Cell 14 and 15 are shorted since EoI uses a 14s battery.
FET settings	Disabled	The CVM IC can drive its own FETS.
FET charge pump	Disabled	N/A EoI
Shutdown internal temperature	80C	If measured internal temperature of the CVM is above 80C than the CVM should go into shutdown mode.
Over voltage protection	Over voltage: 4.25V Delay: 2000ms Over voltage reset: 4.00V	Over voltage protection triggers alert after Delay resets trigger after reset voltage
Under voltage protection	Under voltage: 2.5V Delay: 2000ms Under voltage reset: 3.00V	Under voltage protection triggers alert after Delay resets trigger after reset voltage
Permanent failure under voltage protection	Under voltage: 2.0V Delay: 5000ms	Permanent failure under voltage protection triggers alert after Delay Needs manual intervention for reset
Permanent failure over voltage protection	Over voltage: 4.3V Delay: 5000ms	Permanent failure over voltage protection triggers alert after Delay Needs manual intervention for reset
Permanent failure over temperature protection	Temperature: 90C Delay: 5000ms	Permanent failure over temperature protection triggers alert after Delay Needs manual intervention for reset
Permanent failure VSSF protection	VSSF: 100mV Delay: 5000ms	Permanent failure over VSSF triggers alert after Delay. VSSF is measured internal of the IC. Needs manual intervention for reset
Permanent failure 2LVL protection EDIT: Should not have to use.	Delay: 5000ms	Permanent failure over 2LVL triggers alert after Delay. 2LVL is measured internal of the IC. Needs manual intervention for reset
Permanent failure LFOF protection	Delay: 5000ms	Permanent failure over LFO oscillator frequency deviates from expected value after Delay triggers alert. LFOF is measured internal of the IC. Needs manual intervention for reset
Permanent failure HWMX	Delay: 5000ms	Permanent failure for input MUX used for OV, UV protection if check fails and fails after Delay trigger alert. Needs manual intervention for reset
Over temperature protection for charge	Temperature: 60C Recovery: 55C	Triggers fail and disables charge path until Recovery
Under temperature protection for charge	Temperature: 0C Recovery: 5C	Triggers fail and disables charge path until Recovery
Over temperature protection for discharge	Temperature: 60C Recovery: 55C	Triggers fail and disables discharge path until Recovery
Under temperature protection for discharge	Temperature: -40C Recovery: -35C	Triggers fail and disables discharge path until Recovery
Over temperature protection FET	Temperature: 80C Recovery: 75C	Triggers fail and disables discharge path until Recovery
Over temperature protection internal	Temperature: 70C Recovery: 65C	Triggers fail and disables CVM until Recovery
Under temperature protection internal	Temperature: -20C Recovery: -	Triggers fail and disables CVM path until Recovery
Balancing configuration minimum cell voltage	3.30V	Minium cell voltage before balancing
Balancing cell voltage delta	10mV	Minimum cell voltage between cell before stopping balancing (or start balancing if bigger than)
Number of cells balancing simultaneously	4 cells	CVM supports multiple cell balancing up to 16 cells.

Open questions

• Do the MPPTs have to be modified for the 14S battery?
• Integrated or seperate charge/discharge paths? (I've got a slight preference for seperate pcb's)