Following the discussion held in this post:
I share the Node-RED flow that I developed to be able to use AC power sources with low current capacity, such as those sometimes found in some campsites, for example.
The problem is that Victron inverters/chargers have a minimum current limit value at the AC input that can be configured, and sometimes the power source used may have a current/power capacity lower than this minimum. For example, my Multiplus II 48V/5kVA has a minimum current limit value of 6A at the AC input, and I have been in places where the circuit breakers on the power outlets were only 4A.
To solve this problem, the first thing to know is that this minimum limit (6A, in the case of my inverter/charger) only exists when the PowerAssist function is enabled!
The PowerAssist function is activated when the PowerControl function is not sufficient to keep the current at the AC input below the configured limit. The PowerControl function reduces the battery charging current as the AC load increases. When the AC load reaches the current limit at the AC input and the battery charging current is reset by the PowerControl function, the PowerAssist function comes into action, with the inverter adding current to the AC input so that the load is powered without exceeding the AC input current limit. When the PowerAssist function is disabled, it is possible to configure lower current limit values ​​at the AC input, and the PowerControl function will use the configured limit to control the battery charging current.
The problem that arises is that, with the PowerAssist function disabled, the current limit at the AC input will not be respected if the AC load exceeds this limit. And the circuit breaker of the AC circuit connected to the AC input will probably trip. The solution to get around this problem is to disconnect from the AC input when the AC load exceeds the current limit at the input, supplying the AC load only by the inverter.
This way, it is possible to use the AC input to power the AC load and charge the battery as long as the AC load is less than the AC input limit, and it is possible to have an AC load greater than the AC input limit when necessary without tripping the AC input circuit breaker.
In principle, the best way to disconnect the AC input would be through the existing control option to “ignore the AC input”. In fact, this control works well when done by Multiplus assistants, as I showed in this comment:
However, this control using the Multiplus assistants has the problem of being a fixed configuration, which does not automatically adjust to changes made by the console in the current limit.
Therefore, a solution that automatically adjusts this, enabling or disabling PowerAssist according to the configured current limit and disconnecting the AC input according to the AC load when PowerAssist is disabled (when it is necessary to configure small current limits on the AC input) is interesting. This is possible through Node-RED.
When trying to implement this solution through Node-RED, I came across two main problems. The first is that when PowerAssist is enabled, it is not possible to know what the current limit was configured for the AC input, if the limit was lower than the minimum value accepted when PowerAssist is enabled. I posted about this problem here:
If a value lower than this minimum was configured, the value obtained when checking the configured current limit is always the minimum value accepted when PowerAssist is enabled. If this minimum value is 6A, and the current limit is set to 4A, it is not possible to know that the limit was set to 4A; the value obtained when checking the limit will be 6A. However, the configured value of 4A is not lost; it is stored in the Multiplus, and it is possible to obtain it by deactivating PowerAssist. So, to always have the reading of the value of the AC input current limit that is actually configured, one solution is to disable PowerAssist when the configured value is equal to 6A (or the minimum acceptable value when PowerAssist is enabled). This way, you lose the possibility of using PowerAssist with the minimum acceptable value, which is not a big problem since you can configure a value 0.1A higher (that is, the minimum value at which PowerAssist will be enabled will be 0.1A higher).
The second major problem encountered in implementing the solution by Node-RED was that the control via the option to ignore the AC input did not work. In my test, when I set the register to ignore the AC input, this register was automatically reset and I was unable to establish that the AC input should be ignored. I talked about this problem in this other post:
As can be seen in the post above, the suggestion was made to change the inverter/charger mode to inverter-only mode, which for the intended purpose is equivalent to ignoring the AC input. I had to follow this path, although it adds some layers of logical complexity to the control, since it is not enough to set to ignore or not ignore the AC input as needed, it is also necessary to check what operating mode the equipment is in and to make all the control a little more complex to make the mode changes, so as not to lose manual control of the operating mode. Even so, part of the manual control of the operating mode is lost, since when the device is initially in “on” mode, it goes to “inverter-only” mode by the implemented automatic control (due to the increase in the AC load above the configured limit), while the device is in “inverter-only” mode (but is actually in “on” mode) it will not be possible to manually change to “inverter-only” mode (since the device is already in it). But this is also a minor problem, since it should not be a common need.
Finally, I still found it difficult to control using the AC output current, which would initially be the most practical and natural way, since it would be enough to compare the AC output current with the AC input current limit to know if it is above the configured limit. The difficulty was that the AC output current value fluctuates a lot, with a very high amplitude! So even when the AC load is relatively stable and well below the configured limit, the control could keep disconnecting the AC input because the reported AC output current kept fluctuating above and below the configured limit! The solution was to use the power and voltage values ​​at the AC output, which are much more stable than the current value at the AC output!
Well, having said all that, I finally share below the Node-RED flow that I created to perform this control, allowing the configuration of current limit values ​​at the AC input lower than the normally acceptable minimum.
I am sharing this so that it can be used by anyone who needs this feature (it is good to try to understand everything the flow does so that you can make the necessary adjustments), as well as to receive criticism and suggestions for improvement. This implementation can certainly be improved, as I developed it as quickly as I could, studying the minimum about Node-RED, which I did not know until then.
Small_AC_Current_Limit.zip (1,8,KB)
I think this flow implements a very useful functionality that could be implemented in the devices by Victron itself in the future.