Hey everyone! I've been trying to figure out why my Dyness B3 battery management system (BMS) and the BMV-712 display different voltage readings when charging. During discharge, the voltages match up, but as the batteries approach full charge, things get a bit confusing. For instance, at full charge, the BMS shows around 51.5V, while the BMV-712 displays approximately 53.5V. Here's what I'm working with: 3 Dyness B3 75A batteries, a Cerbo GX, a 150/85 charge controller (both set to work with the battery BMS), a Multiplus 5000VA 220V inverter, and 12 Canadian Solar 305W panels. Any insights on why the voltage readings differ at this stage?
2 Answers
It seems like the two devices measure voltage differently. The BMV-712 is more like a fuel gauge that calculates the actual energy stored in the batteries, translating that into voltage readings. The built-in BMS, however, bases its readings solely on state of charge (SoC) voltage. So when the BMS says it's full, it might not exactly match what the BMV-712 shows since they're not on the same measuring wavelength.
I don’t have direct experience with Dyness batteries, but it sounds like the BMS might stop charging when a certain voltage threshold is reached. From what I’m seeing, they look like 15S packs, which would mean about 3.43V per cell when fully charged but not under load. So, as far as the solar charge controller is concerned, once the BMS halts charging, the battery might not register the same voltage as the system. Hope that makes sense! Feel free to ask if you need clarification!
But that's not quite right! The OP is getting actual voltage readings in volts, not SoC percentages. A shunt works by measuring real voltage, so let’s not mix things up. Make sure to check the manuals for accurate info!