I have a Multiplus, Cerbo & a 12kWh DIY battery (230Ah at 50V, 14 Lion cells in series) with a JK BMS but no CAN comms. I want to use this for load-shifting only - I have no PV installed.
My problem is that the Multiplus is only charging the battery at 100W. I’m expecting 500W per my settings.
But I’d expect the Cerbo/Multi to use the low shut-down voltages and the float absorption voltages to figure out that at 50.5V the battery is about 50%.
Reading some other community threads talk about using smart shunt. But I can’t see what extra information that can give the system as the Mulitplus already has access to voltage and current flows and I have the voltage sensor cables attached to the battery. And I’m not concerned about seeing the SoC on the VRM only if it’s the SoC that is throttling the charging current.
If I set to ‘Keep Battery Charged’ or ‘External Control’ then the battery starts charging at 500W (slightly lower but hey!). But of course I don’t want to keep my battery charged all the time and I don’t have any external control.
So I don’t think the Grid Set Point of 100W is relevant @chrigu. My understanding is that is a margin of safety to ensure no accidental export to the grid.
So maybe when it gets up to the absorption level it will reset the SoC to 100% and all be well if it is the incorrect SoC observation that is the issue.
Thanks for the reply. The BMS JK-B2A24S25P has a 3 pin CAN port and an RS485 port.
But I thought I read that you’d need to do some protocol conversion (on a raspberry pi?) to get the two to talk. And probably some more wiring. I kind feel the multi & cerbo should have all the info they need to rock on at this stage and it ought just be configuration.
It is quite literally the power level that the system is trying to regulate to. Which it does. If you want more charging power, increase the grid setpoint
So how do I configure ESS so that from 2am-4am it will draw say (5000W) from the grid and then from 5pm-7pm it will use the battery in order to keep grid use very low (say 100W) but not export.
That must be a very common use-case but I haven’t come across a step by step in the docs. Has anyone a link or reference to do this?
Further down the ESS menu there are scheduled charge levels.
You leave the grid setpoint at whatever value you want for the day and set a charge schedule. The scheduled charge will disregard the grid setpoint and charge at full power (or whatever other charge-only limit you set)
I have been using the scheduled charge mechanism already with no difference in charge rate - only the battery mode and Grid Setpoint influence it. But I’m feeling more confident now the reason the scheduled charge with ESS>Mode>Optimized is pulling in only to the Grid Setpoint and not to the Max Charge Power is due to the mis-estimation of battery SoC.
I won’t be able to report back with what happened until next week but will do so then.
I’ll use Keep Battery Charged to bring the Battery Voltage up to full and hopefully the
Set charging Schedule “Settings > System Setup > ESS > Scheduled charge levels”
Deactivate Dynamic ESS “VRM > Settings > Dynamic ESS : OFF” (Dynamic ESS blocks the use of the schedule)
Set the desired charging current level “Settings > System Setup > Charge control > Maximum charge current”
P.S. Grig setpoint - will always pass the specified power out of the grid - usually used to power the seventh inverter but can also be used for charging;
It look like it was the multiplus/cerbo thinking the battery level was at 98% that was throttling the charging power.
Once I charged the battery up fully (by either increasing the grid set-point or using ESS > Mode > External Control or Keep Batteries Charged) and then let it run down a little (VRM was reporting 75%), then charging occurred at the Max. Charge Power after that.
