Hello,
Today I updated my REC ABMS to 2.8 software. At the time, my pack was measuring around 72% (3.25v per cell), and had not been recharging.
After the upgrade, the pack was reading 50% (This was somewhat expected, at least it is in line with the behavior of a new device). It immediately began to charge. I restored the settings from the export which was taken before upgrade.
The BMS proceeded to order the MP3k (under external control) to charge at 90A (my current limit on the MP3k). This continued until the highest cell was at 3.52, and the lowest cell was 3.43. It did not ramp down at any point, but SOC was set to 100%. I became concerned that the algorithm was making some strange decisions I did not understand (Different from the previous version with the same settings), and turned off my inverter charger. I then read through the charing section of the new 2.8 manual again. I am still confused about the settings I have configured, and the observations.
I don’t understand why no ramp-down occurred. It is support important to me to feel comfortable with this before hooking up my 250a Balmar alternator.
I have 6 days left before my slip is up and I must head south.
It would be pretty nice to have a functioning alternator at that time.
Any support would be super great.
This is becoming quite stressful.
For posterity, here is the relevant charging section form page 33 on the “Manual for REC Active BMS_Victron_Wakespeed_compatible_v2_8.docx file I received from Tine. Below, I work through this section, substitute the config parameter with my values and complete the math. I have also added in some questions about individual statements that are not very clear in the manual. It would be great to have someone confirm the calculations and understandings are correct, and correct anywhere I have misinterpreted the manual.
“When the highest cell reaches the End of charging CHAR voltage setting, charging current starts to ramp down to 1.1 A x Number of Inverter/Charger Devices STRN until the last cell rises near the End of charging CHAR (CC/CV) – UBDI (End of charge unbalance difference). At that point the Maximum charging voltage allowed is set to Number of cells x (End of Charge Voltage per cell CHAR – Maximum Cell Float Voltage Coefficient CFVC x End of charging hysteresis per cell). End of charge SOC hysteresis SOCH and End of charge cell voltage hysteresis CHIS is set to prevent unwanted switching. SOC is calibrated to 100 % and Power LED lights ON 100 %. Charge optocoupler is turned off. Maximum allowed charging current is set to 50% to allow supplying DC loads from charging devices like MPPTs.
Charging current is limited to 30 % of the maximum charging current, but more than 5 A near both ends of temperature (Max cell temperature TMAX and Min temperature for charging TMIN) and when the battery is empty (Max discharging current is set to zero).
Charging is stopped in case of systems errors (see System Errors indication chapter).
SOC is calibrated to 96 % when the maximum open circuit cell voltage rises above 0.502 x (Balance start voltage BMIN + End of charging voltage CHAR), minimum open circuit voltage above Balance start voltage BMIN and system current is positive.”
WHEN the highest cell reaches the End of charging CHAR voltage setting (3.45)
Charging current starts to ramp down to 1.1 A x Number of Inverter/Charger Devices STRN (1) 1.1 * 1 = 1.1
UNTIL the last cell rises near the End of charging CHAR (CC/CV) – UBDI (End of charge unbalance difference)
CHAR=3.45, UBDI=null in config, 0.008 from UBDI? (8.00000e-3)) -- 3.45 - 0.008 = 3.442
Questions:
1: Are MPPTS considered “inverter/charger devices”, or just the MultiPlus?
2: Where it says \"Near the End of charging CHAR - UBDI\", what does \"near\" mean? is it at 3.442 from the calculation above, or is there some hysteresis applied here to achieve a \"near\" value? is this just a grammatical error and it should read: \"UNTIL the last cell rises to the CHAR - UBDI\"?
3: If I understand this correctly, once any cell reaches 3.45 (CHAR), current should begin to ramp down until the last cell reaches 3.442 -- is this correct?
THEN At that point the Maximum charging voltage allowed is set to Number of cells x (End of Charge Voltage per cell CHAR – Maximum Cell Float Voltage Coefficient CFVC x End of charging hysteresis per cell).
End of charge SOC hysteresis SOCH and End of charge cell voltage hysteresis CHIS is set to prevent unwanted switching.
CHAR=3.45, CFVC=0, CHIS=0.25. - 4 * 3.45 - (0 * 0.25) = 3.2 * 4 = 12.8 Maximum Charging Voltage Allowed (float voltage)
Questions: How is SOCH used in calculation?
Charge optocoupler is turned off.
Question: Will this mean the charge bus is disconnected?
“Maximum allowed charging current is set to 50% to allow supplying DC loads from charging devices like MPPTs.”
Question: How will MPPTs supply DC loads if the charge contractor has been disconnected by the previous statement “Charge optocoupler is turned off”
“Charging current is limited to 30 % of the maximum charging current, but more than 5 A near both ends of temperature (Max cell temperature TMAX and Min temperature for charging TMIN) and when the battery is empty (Max discharging current is set to zero).”
This sentence is confusing in general, but focusing on the first section ““Charging current is limited to 30 % of the maximum charging current, “ — the previous sentence says it would be set to 50% — which is correct? If both are correct, can the conditions for the 30% state be better defined? Is this a correct interpretation of what is written:
\"IF TMAX or TMIN has been reached and Max Discharging current is set to 0, charging current will be between 5A (min) and 30% of maximum charging current\" ?
“SOC is calibrated to 96 % when the maximum open circuit cell voltage rises above 0.502 x (Balance start voltage BMIN + End of charging voltage CHAR),”
BMIN=3.35, CHAR=3.45 -- 0.502 * (3.35+3.45) = 3.4136
