Even though the batteries will accept 148 amps and there is at least 2500 watts solar power available, however the current and power for charging is limited to around 1500 watts and less even when the battery is at 50% or lower. Why is that? See the later picture, I switched on the water heater and that takes 1500W, when I switch the water heater back off the charge current is not maximized.
DVCC is forced on, no overrides in current limit.
see pictures, numbers might not be the same, but the problem is not giving full available power to charge the batteries. This was not the case from the beginning, this change in behavior is recent. Probably a change that came with a firmware update, I suspect the CerboGX not handling the BMS values from the batteries correctly?
Just made another observation, which is that there is 1500W available but the battery is charged with 50w at 63% SOC. And this SOC is getting lower and lower over time, meaning the batteries will never get to a decent charge ever again with this charging algorithm.
Is the shunt still connected to the Cerbo via VE Direct?
If so, try disconnecting the shunt from the communication system. It may be “talking” to the system unexpectedly.
Is the charging voltage additionally limited in the DVCC …
In the “newer” FW, the charging voltage for 15S batteries has been limited to 52,4V … no matter what you set … which is why the charging current also increases … when you switch on a load …
Steffen, Thank you for your response. No the shunt is not communicating with the system. Not connected, it is just sitting there as part of the buzzbar. DVCC is forced on, no override/change to any limitations.
No problem, I can understand that change in lower voltage, but clearly the MPPT can deliver 2500w easy, however only 1500 is send to the batteries. Makes no sense at all. The diagram with the voltage and current is from the MPPT and shows when I switch on the water heater and back off again. Showing that there is way more power available, but again it is not used to charge. There is some kind reason in the algorithm that limits it. I want to know what that is, because as it sits now, my system is pretty useless, because no matter how many solar panels I install the charge is always limited and I cannot get these batteries ever again at 100% which is needed to balance them correctly.
As soon as the DVCC target of 52.4V is reached, the MPPT starts to throttle.
According with your first screenshot, the voltage at the MPPT output is 52.4V, so…
Measure the voltage at the MPPT output and then the voltage at the batteries terminals with a reliable voltmeter.
You may have a drop on the wiring between MPPT and batteries.
The SOC and internal resistance of the battery are always decisive factors… at 85% SOC, for example, the battery will not accept 2500W because a charging voltage of 52.4V does not generate enough “pressure.” Many Pylontech batteries, especially the Us2000 series, have failed with their pouch cells because the voltage exceeded 53V … and more.
So keep an eye on the voltage in the upper SOC range.
In the lower SOC, the battery should still be able to absorb the charging power.
Here’s a graph on my case, where you can see that at 97% SOC, with a voltage on batteries of 51.52V, the MPPT is still pushing about 2500W, with only 0.3V drop on the cables (0.6%).
This is why I’ve said that the voltage drop is critical for a proper functioning.
Thank you so much for responding. I got some ideas now what I can measure, I did some poking around and I see other strange readings, for example the MPPT is 1 whole voltage off from what I measure on the terminals, how is that possible if the MPPT has to regulate on a tenth of a volt??? The BMS of the battery is reporting a more accurate voltage that is closer to what I measure on the terminals on the entire battery bank. I did a quick test with drawing 1500 watts and 3000 watts, the later gives a voltage drop of about 0,3 or 0,4 Volt between the MPPT terminals and the battery terminals. Tomorrow I am gonna do some better measurements when the sun is out I hope. I do not have a fluke meter, but a Voltcraft and that one is accurate enough I think.
I have a Pylontech (US2000 and US5000) battery bank and have observed similar behaviour and have spent significant time investigating it. However my battery bank started stopping around 94% then 93% etc down to 89%.
I think the voltage shown in the MPPT device in the GX device comes from the DVCC system. It is not the physical voltage on the MPPT terminals. I think this voltage comes from the managed battery (Pylontech) and is not shown in the user interface anywhere else. The charge voltage limit of 53.2V in the battery parameter section is what the PylonTech reports. However Victron actually limits the charge voltage to 52.4V (mentioned in Victron Pylontech webpage) this was updated to 52.5V but only if your Pylontech batteries report their min and max cell voltages to the system (to do so they need new enough firmware on the batteries - min version required is listed in Victron PylonTech docs)
Given the behaviour you are seeing re Pylontech not accepting much current I suspect you have cell imbalance inside your Pylontech batteries.
If you watch the voltage in the MPPT when that is happening I think you will see that the MPPT is hitting that voltage limit of 52.4V and reducing its charging power to keep the battery voltage at or below 52.4V as others have already stated too.
My understanding and experience is that the Pylontech batteries balance the cell voltages in the upper end of the SOC cycle so in the 90% plus range.
What do you see when you go to GX device, PylonTech battery → Details? Do you see info on min and max cell voltage and temperature?
If you don’t get enough time in the day to charge up your batteries using the MPPT due to it throttling down. Then another option could be to charge your system with the grid or a generator with a low current overnight or even longer to see if that helps. Ideally you would do this if you can see the min/max cell voltages as you should see them get closer and closer together over time as the batteries balance.
