Saturday, September 20, 2014

Refinement of draft Schematics - BMS + a draft CAN Alternator Regulator

Along with looking at CAN standards, I have been refining the draft schematics for the BMS, and crafted up an initial cut at a simplified CAN Alternator Regulator.   Here are a couple of snap-shots; higher resolution .pdf files can be found under the Schematics resource tab above.

Click for larger, or see .PDF file in Schematics resource tab above

Major changes to the BMS include:
  • Addition of small Switching PS for better energy usage.
  • Revised USB chip for more widely supported (driver wise) component.  Is also simpler to solder, and lower cost!
  • Improved CAN electronics, considering 'system wide' deployment.  There likely will be some additional enhancements / changes here - open to input from anyone with experience in this area.
I considered changing out the CPU for an integrated CPU/CAN device (ala, the 90CAN32), but am staying with the current solution as it appears to be able to provide lower power consumption.   In addition to more consideration on the CAN interface, I want to consider the optional BMS Cell loop - currently it is a Yes/No design in support of the Clean Power Auto cell monitors (  I want to consider how a simple protocol can be transferred over this same line to gain perhaps individual cell voltage status.  Maybe even enabling the OneWire standard - Or reusing the Auto industries LIN protocol (a kind of CAN lite) ??

I also drafted up a potential Alternator Regulator for use with the CAN system.  It is based on the Arduino Alternator Regulator ( with several key differences:
  • Battery measurements are utilize the BMS
    • There is no on-board remote battery voltage connectors..
    • Same of battery Amps, and Temperature
  • Eliminated Charge Pump (May add back), will cap max field drive to a duty cycle of 99.6%

Click for larger, or see .PDF file in Schematics resource tab above

 Some new features include:
  • Isolated CAN Bus interface
  • USB built in, just as the BMS is.

 It still supports 12v .. 48v batteries and fields, independent of each other.  It also includes local voltage sampling (at the Alternator) for the purpose of early detection of load-dumps, as well as fall back modes in the case of a failure in the BMS CAN bus communications.

Note that it has an isolated CAN bus, I will be key for any high current device (ala, charging sources) - as the voltage drop over even large cables can be significant.  And when paralleling the small signal gauge wires using in CAN wiring, one could end up trying to carry several amps of ground loop current.  Isolation prevents this situation.

Going forward I may look again at the Power Supply - perhaps also changing out of a switching mode PS. - one of the challenges is there is a need to pass though voltages under 12v to allow the FET driver to work.  So, and power supply design has to work in two modes:  Buck as well as pass-though....

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