Projects

Lithium Ion Battery Smart Charging System

The next logical step after building a Lithium ion battery management system would be to build a compatible charging system, so, this is it!


  Overview:

The smart charger hardware, firmware and communications were built with the following specifications

  • Intelligent, micro-controller controlled buck conversion charger design
  • 4 to 75VDC input
  • 0 to 75VDC charging output
  • Hardware over current limiting with 30uS response time making this charger short proof with a hardware programmable set point for over current threshold
  • Current sensing from 0-10 amps with 8mA resolution
  • Isolated CAN communications
  • Can act as a slave to a master controller, a PC or act as a stand alone charger with built in direct differential communications to LTC6802 slaves without the use of a master
  • Built in interface to LCD display
  • High accuracy 5.12v A/D reference design for 5mV resolution A/D
  • Programmable for 1 to 12 series Li-ion cells with CC/CV (constant current/constant voltage) output   

smart charger for li-ion batteries
      The above picture shows the main smart charger board.  I ended up taking a fair bit of the BMS board and incorporating it into the charger electronics so that it could function in a number of different configurations.

li-ion smart charger connected directly to LTC6802 pack

The smart charger uses the same method of differential communications so it can communicate directly with the Linear LTC6802 boards in a daisy chained fashion.  One board is shown here but a maximum of 16 could be used.

Li-ion smart charger taking commands from PC CAN interface
This is a complete, working setup with power coming from a DC power supply (left) and flowing through the smart charger.  The CAN-4-USB/FX interface is connected to a PC that is running configuration and monitoring software.  The DC input can be up to 75 volts but can be throttled back to charge a single cell if needed.  The 12 cell pack shown will have a final charge voltage of 50.4 volts.  There are a number of isolation points in this system.  The CAN bus, and therefore the PC, are isolated and the 6802 communications are isolated as well.  This means the CAN bus ground, the power supply ground and the 6802 communications bus ground are all isolated. 


Li-ion smart charger taking commands from BMS system

In this configuration the smart charger is taking its commands from the BMS.  If you haven't already looked, you can see all the features of the BMS board here

Li-ion smart charger in stand alone mode with LCD display

Yet another configuration would be to have the smart charger work in a stand along mode and have charging information and simple configuration choices displayed on the LCD screen.





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