I have a system with a single Multiplus 12/300/120-50 (v556) connected to a Cerbo GX(v3.55) via V.E.BUS, with a BMS V2(v113) inline. There is also a SmartSolar M.P.P.T 100|30(v1.64) connected to the Cerbo via V.E Direct. A IP65 BMV Smart Shunt is also connected via VE Direct to the Cerbo GX. These are all connected in a manner consistent with Victron recommended layout charging Victron Smart LiFePo batteries. D.V.C.C is active and configured on the Cerbo GX.
I have two issues I need help with please.
I have the remote switch on the B.M.S V2 connected to a standard S.P.S.T switch to facilitate turning off the system if needed. I have noticed that this correctly turns off the Ready To Discharge & Ready To Charge Circuits and Multi-Plus. However the M.P.P.T continues to charge despite the switch being off and the B.M.S inactive. The M.P.P.T reports that it is in fact being controlled via the B.M.S. Why does the M.P.P.T not reduce itās charge current to 0A when the remote switch is off? As a data point, disconnecting the B.T.V cables to the B.M.S V2 performing the commissioning test results in the M.P.P.T charge current dropping to 0A.
On turning off the remote switch, and then back on, the D.V.C.C current limit value set on the Cerbo GX no longer seems to have authority in the system. Adjusting the D.V.C.C limited current up or down by any amount seems to then reassert the authority of the D.V.C.C. Cycling the D.V.C.C on and off also has the same effect. Why does the D.V.C.C not take affect again after turning the B.M.S V2 back on after being turned off. This seems like some type of communications bug?
If anybody can help me with this Iād appreciate it. Thank you.
There is code in a part of dvcc.py in the cerbo which controls whether the MPPTās shut down when requested by the BMS - for certain types of battery this defaults to false - This in my opinion is incorrect behavior. whether this āquirkā is causing this behavior in your system depends on the BMS type and the exact wiring.
Iāve not noticed this. The required behavior of the BMS by Victron is to control the charge current of the battery by adjusting the Voltage limit - not the current limit. So there may be a bug in the Venus code that is causing this issue - the value is not re-written to the dbus system periodically, but only on change (of value).
The same happens with the Lynx BMS, so either link the MPPT remote to the ATC port or change your SPST switch to a DPST switch with the MPPT remote port on the second pole or add a breaker between solar panels and MPPT and switch this off first. I know it would be cleaner if no signal from BMS turned off the MPPT.
Hey mpwfarnell, thank you for your reply and recommendations. I guess bottom line here is how can I have confidence the BMS v2 will taper down to 0A in a genuine over voltage(Ready To Charge Disabled) condition. I know the M.P.P.T tapers to 0A when the B.T.V cables are disconnected but the lack of shutdown when the switch is used makes me concerned whether the B.M.S will taper to 0A in a genuine do not charge scenario. Just curious, have you ever seen a B.M.S V2 taper the M.P.P.T to 0A in a do not charge situation. Thank you again for your help.
I have a Lynx BMS not the VE Bus BMS so I have not seen it, when the BMS stops charge like you have shown on BTV cable failure, the BMS tells the Cerbo to set charge current to 0 and DVCC tells the MPPT to stop charging, works as intended. I have no problem in believing that when required, solar will be shut down by the BMS as advertised, mine does, your does as you have proven.
The problem comes when you shut down the BMS, then it is no longer sending comms to the Cerbo, in fact the Cerbo may shut down if not auxiliary powered so there is no message to the Cerbo to stop charging, so the MPPT goes into stand alone operation and does not shut down. This same issue has been discussed recently on the Lynx BMS. On my BMS, of the 3 options, I added a breaker between the panels and the MPPT because if I am going to shut the system down, then I want to make it properly safe rather than relying on the software shutdown of the MPPT with high voltage still present on its input.
Thanks for reply and the link, I will study that next. Understood and agreed, I guess I have no logical reason to believe that it wouldnāt work as expected just because of this particular behavior with the remote switch. Disconnecting the B.T.V cables does indeed drop the M.P.P.T output to 0A. So that control aspect has been tested and confirmed.
Do you have any thoughts on the second item I had listed by any chance please? The work around on this is to simply alter the current limit value or cycle D.V.C.C off/on after the remote switch has been turned back on but that is not ideal. What concerns me is that itās loosing itās āAuthorityā to begin with, if thatās the correct term, after this remote switch operation. As an example I set the current limit to 30A, watched it regulate charge at that. Then cycled the B.M.S off/on, on resumption of charging I witnessed maximum charge of over 100A from the multi-plus. Simply moving the current limit to 31A immediately resulted in to the system then returning to normal behavior.
Thanks again for your thoughts and feedback pwfarnellā¦
On the second issue I have no firm thoughts. I expect the limit you set in the DVCC menu is sent to the system once and it ends up getting overriden by the BMS restarting rather than it being resent. I do not use this feature so I have never come across it. Post it in the Venus OS beta section as a bug report, it will then be seen.