40V is very very low for a 16 cell battery, that is 2.5V per cell, if you have 16 in series. I don’t think it is a good idea to go below say 3.2V per cell or 51.2V for the battery as a whole (but I have not expertise in saying this, just what I recall from other conversations with experts).
If it gave you a low battery voltage around 50.4V, that is already past what I would think is good for the battery anyways. It might have had a big load on it, pulling it down more than 50.4V, then you getting the low voltage alarm and the BMS disconnecting the battery the voltage recovered to 50.4V. The battery’s voltage drops off a cliff when the SoC gets below 20%, so between 50V and 40V, very little energy is stored compared to between say 56V and 51.2V.
I would have used something like VRM helping me to measure the energy discharged from the battery. Put the ESS on Keep Batteries Charged until the evening, when PV is 0, put it into your self-consumption mode of choice. You’ll then be able to estimate how much energy you discharge from it by taking your saving on the AC side and dividing it by 0.9 (for conversion losses). It isn’t perfect, but it should give you a fair indication of whether the battery is providing the energy it should before its voltage gets too low.
Don’t feel too discouraged with your solar system. Just like making monetary investments, it will require your time and expertise if you want to get the most of it. A solar system is an expert system just like investing directly in shares is an expert investment.
@HennieJH quick question, is this the revov units with the external BMS setup? I think maybe the BMS got damage with the lightning. Who did you speak with at Revov?
This is also fairly typical when a BMS disconnects the cells from the DC-bus (the inverter, solar chargers, the rest of the stuff).
Let me explain just a bit. When a low battery alarm occurs, the graphical display is programmed to add the current voltage to the display, as extra information. But sometimes there is a slight delay (as much as a second) between the disconnect and the voltage reading, and this sometimes causes the voltage that accompanies the error to not be all that useful. In Lead Acid world where things are permanently connected, it works perfectly. With disconnecting BMSes, you often measure a bit of noisy air…
In other words, I don’t think it actually raised the low voltage alarm at 50V. It was probably lower when it did that, and if you have a BMS disconnecting, any voltage measurement (coming from the Multi) would not represent what is actually happening inside the battery.
Aren’t those sudden up shoots in the battery voltage due to it being charged from the grid? Although, presumably we should see that in the current…
The fully charged voltage seem a bit low for a 16s battery? And the battery is already practically empty by midnight if the voltage is sitting on 50V? Shouldn’t this battery operate between 56V and 51.2V (with no load on it)?
The low voltage drop-outs (below 50V) look like BMS disconnects to me. Is there any way to connect the BMS from these batteries to Venus to check the reported SoC? (and possibly cell voltages)
There is a ticket open to add it and someone in Gauteng willing to help with a test unit, etc. From the call I had with them they have similar issues with many clients that use the Revov Battery. It seems that the Tian BMS does not correctly balance all the cells. I suspect that the BMS cannot balance fast enough with full current input.
@HennieJH, I suggest you lower your Bulk/Absorption voltage setting to 54.2V (3.39V per cell) and run it for a few days. If you still get issues then drop that to 54V(3.375V per cell). It should give the BMS chance to balance the cells without one going into overvoltage.
The other option is to buy the ANT BMS that PJJ wants to sell and swop it for the Tian Power (only if not still under Revov warrantee).
If it’s any use to you, I have the Tian Power monitoring software and I can share it if you need it.
You will need to have a windows PC with a USB to RS485 adapter connected to the BMS to use it though.
Also, if you are only interested in reading the realtime data, there is only one simple string you need to send to the BMS and I have the structure of the response if you want it.
Revov is using BYD batteries and bms on this unit, and if remember correctly, there was some of them that gave problems. Hein Herholdts is sitting with a massive comeback on this units where they started to give problems.
I got some photos where some of this revov units running on a Solar MD unit and there some 24v revov units floating around that is running a ANT BMS
