ghatikar wrote: ↑
Fri, 10 Nov 2017, 23:15
Do I have to sacrifice the USB( serial port) to BMS connectivity? Or Can I connect BMS to one inverter and ICC to another inverter.
Does the BMS have to connect to master only or can be connected to slave - The master and slave in Axpert change dynamically depending which one was switched first
Thanks ghatikar. Those are excellent questions. Although we have not tested it, we have every reason to believe that it does not matter which inverter the BMS is connected to, for the purpose of dynamically controlling the charge current. It can be the master or any of the slaves. That is certainly our intention, for the very reason that you gave. If this turns out not to be the case, this will constitute a bug in our patches that we will fix.
I don't know what an ICC is, but assuming it too doesn't care whether it is talking to a master or a slave then yes, you can connect the BMS to one inverter and the ICC to another.
I note that every MNCHGC command must contain a machine number (a single digit between 0 and 8). The machine receiving the MNCHGC command on its serial port, compares that with its
number. If they are the same, it deals with it locally. If different, it sends a message on the CAN bus to all the other inverters who then do the same comparison and either deal with it or ignore it.
For example, in a parallel system with two inverters, the BMS will need to send both a MNCHGC0
<nnn> command and a MNCHGC1
<nnn> command. If the BMS wants to reduce the total current to 2 amps towards the end of charge, it could send MNCHGC0
501 and MNCHGC1
501. To reduce the total current to 1 amp, it could send MNCHGC0
500 and MNCHGC1
The dynamic current control manual mentions that the current can't be changed more often than once every 2 seconds. But that is for a given inverter. It is not a limitation on how often a MNCHGC command can be sent. So in a system with two inverters, a MNCHGC command might be sent every second, provided the machine number alternates between 0 and 1, and provided each command is acknowledged before the next is sent.
If MNCHGC commands are addressed to the same inverter more often than every 2 seconds, nothing bad happens. Some of the MNCHGC commands will simply have no effect, even though they may be acknowledged. The 2 second limitation is due to the internal communication between an inverter's main processor and the secondary processor in its solar charge controller, and our decision not to patch the SCC firmware.
Some serial commands, such as the voltage setting commands PCVV, PBFT and PSDV, do not take a machine number as an argument in the way that MNCHGC and QPGS do, but they automatically get applied to all
machines, no matter whether the machine receiving them is a master or a slave.
Other commands, such as QPIRI, that do not take a machine number, only return information about the inverter whose serial port the command is received on. But it doesn't matter whether that machine is a master or a slave. The issue in that case is not master versus slave, but local versus remote.