In order to best maintain and protect the batteries, I have opted for an Orion BMS2 Battery Management System, made by Ewert Energy Systems. This unit is highly capable with a flexible range of I/O and is very configurable using a Windows software utility.
The Orion is a centralised BMS – so there is one central unit which is wired to all cells in the battery. While not ideal for my battery pack which is partially distributed (1/4 of the pack is under the bonnet, the rest is behind the passenger seats) the Orion unit provides the best avaliable compromise for price & functionality.
As there is no active thermal management planned for the batteries in the project so far, I have opted to also purchase Ewert’s CAN thermistor expansion module. This enables an additional 80 temperature sensors over the BMS’s stock 8. With 88 sensors, I am able to put a thermistor on almost every cell group. If I add active cooling/heating to the batteries later, then these extra thermistors will continue to be important.
The BMS has two CAN interfaces, which are software configurable for different purposes. One is intended for integration with the majority of other CAN components in the vehicle, and the other is intended for auxiliary purposes (Programming, CHAdeMO charger communications). The BMS is programmed with a USB-CAN adapter, which is removed for normal operation.
There is the option of adding CHAdeMO charging capability later, I would simply need to add safety contactors and the charging socket as the BMS can handle all communications for the protocol. If the BMS supported CCS charging as an option, I would choose this over CHAdeMO as it is the winning standard for new charger installations in the UK – but the communications protocol is more complex and at the time of writing, there does not exist a turnkey DIY solution for CCS.
The BMS will control the main on-board charger also – an ElCon TC 6.6kW unit on the main CAN interface. The BMS also has dedicated charger enable & safety interlock signals that will be used to control contactors on the charger’s input for safety.