I’ve been meaning to ask this for a while now and finally gotten around to it:
When my Venus GX is set to operate with or without battery life, it charges the batteries full to 52.4V. When I select Keep Batteries Charges then, it charges up another .3V to 52.7V.
Why is this happening and is that a safe voltage for my Pylontech 3000Bs?
I recommend you check your inverters config file. Remember the Inveter does the charging in keep batteries charge mode, on the other hand the MPPT, does the charging in the other 2 settings. If you look at the voltage both reports, you would normally see a 0.3 volt difference.
Your Pylons can charge up to 53.4 or somewhere around there so 52.7 is perfectly safe still.
It actually charges up another 0.4V.
The method used by Victron inverters to feed excess DC-coupled PV into the grid is to instruct the solar chargers to charge 0.4V higher. The Multi then detects this overvoltage and pulls it down by feeding that power into the grid. So the solar chargers attempts to push it up, and the multi tries to pull it down.
You may wonder why I bring up the feeding in of excess DC PV? Well, simply because KeepBatteriesCharged uses the same mechanism. It also instructs the solar chargers to charge 0.4V higher, and then the Multi pulls it down, but only up to a limit (which corresponds with your loads).
There is no control loop. That is the beauty of this setup. Control loops can get unstable, so if you can get away with not having one, so much the better! The 0.4V is deemed low enough that it will never be a problem, so if you have more PV than loads (when not feeding in excess PV and ess mode = KeepBatteriesCharged), then it simply rises a little higher than usual. Which is what you observe.
It is nothing to be concerned about. 52.8V is safe for your Pylontech batteries. In fact the battery wants 53.2V, but as you can imagine, if we used that voltage and added another 0.4V on top of it (53.6V) and then maybe another 100mV calibration difference, 200mV voltage drop over a cable, etc etc… you get way too close to 54V where the battery disconnects from the DC bus. Which is one reason that 52.4V is used as a base voltage.
Thanks! Okay, that explains it. As long as I don’t need to be concerned about anything. I’ve noticed that when the PV available is less than the loads the voltage drops back to 52.4V, which sounds like it is in line with what you are saying.