I have a Multiplus II with venus on a Raspberry PI and a separate generator which can charge the battery. The battery is connected via dbus-serialbattery.
Example: The battery demands maximum charge current limit of 10A. The generator is already charging with 6A, so the multiplus should only charge with 4A. Instead if charges with 10A, and displays the total battery charge current of 16A. As the victron sees the total battery charge it should lower its own charging to ensure the batteries CCL is respected and no overcharging occurs.
The generator is outside of the scope of control. See note #2
“…the total charge current of the inverter/chargers and all MPPT solar chargers will be controlled, nothing else. Any other sources will be extra charge current, unaccounted for. Even when installing a BMV or other battery monitor.”
Is there any way to connect a generator to victron, so that the multiplus accounts for the charge coming from it?
As I understand, the DVCC tries to evenly distribute charge currents to the various sources. But this is not always possible, so how should this work?
The Multiplus itsself should never overcharge the battery if it sees that there is already to much current flowing into the battery for safety reasons. I think this is a very important safety feature, because otherwise the battery can be destroyed by this irrational behavior.
In addition the perfect solution would be, if the multiplus would have an option to account for overcharging from other sources and feed back this energy to the grid. E.g.
a) Supply additional charge up to BMS CCL limit: If the multiplus sees that the battery is charged with 6 Amps (from whatever reasons or sources), and the BMS says that CCL is 10A, and there is solar power available, it should charge with the 4A.
b) Feed excessive charge to the grid: If the multiplus sees, that other charger are already trying to provide 13A to the battery (at CCL 10A), it should take 3A and feed this to the grid. I think this seems be already partially there.
This would not only solve the problem for many application like the above, but also would be big gain in battery safety, because the multiplus would prevent overcharging of the battery even from other devices (in regular and fault cases).
No, is is the multiplus, because the multiplus is directly connected to the BMS and sees the actual current flowing into the battery (it is also the only device conntected to the battery). The battery says, that it interdicts more charge, but the multplus actively draws extra power from the grid / AC connected inverters to overcharge the battery above the allowed amount.
In my opinien, the Multiplus MUST ensure, that it never overcharges the battery on its own. This must be done for safety reasons already, because overcharging can set the whole system on fire or even explosion.
Even if everything is from victron and the multiplus tries to command the other chargers to reduce charge, it is a safety problem, because there the control could not be perfectly exact and also there could be malfuctions for various reasons. It should NEVER occurs, that the Multiplus who is in charge of controlling all connected devices to see that the battery cannot be bear additional charging, actively pumps more charge into the battery against the interdiction from the battery, which could lead to explosion.
The document used to design systems clearly says otherwise:
“…the total charge current of the inverter/chargers and all MPPT solar chargers will be controlled, nothing else. Any other sources will be extra charge current, unaccounted for.”
You’re asking the MP to be in total control of your battery charging for protection, but want it to be subservient to your external charger that it doesn’t know about?
The generator is the AC source for the multi. If the multi is sent a 10A limit that is what it will try pull from the generator to charge.
It is doing what it is supposed to.
The multi is not directly connected to the BMS, the Pi is, via dbus-serial, which is also an unsupported modification for battery connectivity.
System issues need to be shown on supported configurations.
Without further detail, as the description is frankly a bit confusing, everything seems to be doing what it is supposed to.
When was talking about Multiplus I meant a Multiplus GX or GX replacement with Raspberry. The ESS is running on the GX / venus / raspberry.
I am talking of a DC generator, i.e. a power source producing 48V (like an MPTT) which is also attached to the battery.
The Problem is simple and the current behaviour unnecessarily extremly unsatisfactory and dangerous, because the multiplus provides charging power to a battery which tells, it does not want any charge.
The argument that dbus-serial battery is not supported is a very bad argument, because the same would be the case if you replace the battery with a Pylontech battery. The basic problem, that the pylontech battery gives a max CCL and the multiplus sees the total battery current, and even though it is already at its limit (because of other atteched DC generators) provides power the battery which can destroy it.
The solution is extremly simple: The ESS / DCVV would just have to monitor the current total battery change current and ensure, that the multiplus never provides any charge current which would make total current > CCL.
To have a ‘supported’ configuration: Take Pylontech with Multiplus GX and attach another DC MPPT to the battery.
As far as I understand, the MP/GC tries do ensure that the MPTT current + its own does not exceed BMS provided CCL. If the MPTT does not give enough current, the MP/GC will take grid power (e.g. from a AC connected PV) and feed it also into the battery. When the there the control of MPTT current is not exact, or the connection breaks, or there is another malfuction, the MP could not take the other current into account and provide everything from its own, this destroying the battery.