I have a MultiPlus-II 5000 and a DIY battery with a JK BMS running DESS. The BMS supports “float mode”, which means that when the SOC reaches 100%, it waits for one hour and then goes into float mode by reducing the requested charge voltage from 55.2V to 53.6V. This works fine for ESS mode with a fixed grid setpoint, but with DESS the behavior is unexpected: As soon as the RCV is reduced, the MultiPlus discharges the battery and feeds the energy back to the grid at full power to reach the lower voltage as soon as possible. Depending on the configured limits it may take only a few minutes, but it is kind of silly to do this when the battery was just charged to 100%.
I disabled float mode on the BMS for now, but is this something that could be improved in DESS?
And this doesn’t occur with DESS deactivated? In my opinion, this is quite normal behavior of a Victron System? Maybe not with full power, but discharging in general yes.
And this doesn’t occur with DESS deactivated? In my opinion, this is quite normal behavior of a Victron System? Maybe not with full power, but discharging in general yes.
Yes, but without DESS the MultiPlus tries to keep the grid point stable. So it will discharge, but only what can be used in the house. It will not dump it back to the grid at full power.
Edit: Now that I think about it some more, you may be right. Without DESS, the battery will probably also be discharged into the grid. But in this case, that is not much of a problem because the battery was most likely just charged from PV, not the grid. I must confess that I don’t have much experience with this case, as there was not much PV production when I ran without DESS.
Good to see another one using MultiPlus-II 5000 with a JK BMS equipped battery.
I have a similar setup with 3 fase MultiPlus-II 5000 and 2 Batteries with JK BMS (1 Master 1 Slave)
I’m using ESS but no DESS.
Would it be ok for you to share and compare settings? Here in the forum or via private Mail.
I use the same 55.2V & 53.6V voltages in the JK BMS but seem to have some unexpected behavior. Cerbo reports the battery voltage, current and temperature just fine and all the details like highest and lowest cell of the Battery just fine. However my MPPT RS 450/100 does not want to charge. I complains about > Error code: #67 - No BMS
Sure, I can share my settings, although I don’t use a Victron MPPT but an AC-coupled PV inverter. When you can see the BMS information on the Cerbo, your BMS seems to be working fine, so that is probably not the issue. There might be an issue with the communication between the MPPT and the Cerbo? Googling your error message brings up a number of posts from the old forum, so you might want to look at them as well.
It doesn’t seem to be possible to sent private messages here, so if you want to contact me directly, just google my name. I suspect that we will be able to communicate in Dutch.
Yes DVCC is on with just BMS Selected and a Charge Current Limit of 90 Amp (3 x 30).
I’ll mail you probably monday as out now till tomorrow evening. And yes I’ll write in Dutch then
The same thing happens here. I had three multiplus II units with two 15kWh batteries with JK Inverter BMS (currently just upgraded to three Multi RS Solar units). As soon as the float voltage kicks in the battery is discharged to match that voltage. As I understand it this is done to prevent the battery from having a high voltage for too long. I’m charging with 55,2V bulk/absorption, and then lower to 54V for float to not loose too much energy in this process…
I personally feel like it would be nice for DESS/ESS to use this power effectively by just covering AC loads until the voltage is reached and not getting there as fast as possible!
