question

libor avatar image
libor asked

Multi RS doesn't stop charging LiFePo4 batteries at SOC=100%

Hello Victron community,

I am using BMS mode (hopefully only until another set of CAN terminators arrive) and charging doesn't stop at 100%.

First, I set everything according to the manufacturer's documentation; as meaningfully as possible. I.e. "Bulk Voltage" is nowhere to be found in the Multi RS. It's mentioned in Multi RS documentation as a description of charge mode, in description of built-in BMS, but I don't see anything about setting it.

I may have confused the BMS management by initially entering 9600 Ah (which is KWh) instead of 200 Ah. Of course I closely monitored charging and stopped it by turning off solar switch, when it did not stop upon reaching 100% SOC on the battery (higher SOC on the two batteries, to be exact). The SOC indicator in VC was evidently off by a big margin. This was just a brief state, since the batteries were nearly full, when I turned Multi RS on.

I found the mistake and set 200 Ah, but it did not change anything. I consulted documentation and used Settings -> Battery -> Expert Mode -> "Sychnronize" button for "Synchronize SOC to 100%" (when 2nd battery charged to 100%) and after that the SOC on VC perfectly matched what the battery shows (in range circa 68-100%, that I could test Today).

However, the charging still didn't stop at 100%. I didn't try to let it charge beyond 100%, so I'm not sure if "synchronizing" to lower value would help, or if it is because I missed some setting, or if I misunderstood the manual about built-in BMS capabilities with LiFePo4 batteries.

________________________________________________________________

Bellow are VC settings I am using and Manufacturer's recommended settings.

vc1.png

vc2.png

Battery charging range:
voltage-lifepo4-battery.png

It doesn't seem to be accurate for two parallel batteries, though.

Voltages:

  • Bulk = 54.0 V
  • Absorbtion = 53.4 V
  • Float = 51.7 V

This is recommended specifically for Victron Energy invertors:

• DC input low shut down: 37,5V

• DC input low restart: 46,5V

• DC input low pre-alarm: 43,5V

• Shutdown Voltage:

--> 0.005C 47,4V

--> 0.25C 48,2V

--> 0.7C 48,3V

• Sustain Voltage: 38,0V

However, those such (exact) settings aren't present in Victron Connect, I think. And they seem to be all related to the low state of charge.

battery chargingSOCMulti RS
vc1.png (21.1 KiB)
vc2.png (15.3 KiB)
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3 Answers
libor avatar image
libor answered ·

It does work, probably as intended, but I had to do several adjustments (using Synchronize button) so it switches to Float just bellow 100% and last iteration I'm testing is with 95% on battery 1 and 96.5% on battery 2. Still, it seems the batteries get still charged on Float at least some time, so I wonder if that means I should reduce the float voltage by a tiny little bit...

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kevgermany avatar image
kevgermany answered ·

Bulk charging is current limited. Output Voltage of the charger stays below absorption voltage setting.

Once absorption voltage is reached charger output voltage doesn't go higher. And charger switches to absorption mode.

Your table for the batteries shows much lower charging voltages than you are setting as absorption. This will cause the BMS to cut charging to prevent overcharging/damage. It looks as if your batteries are 15S, not 16S. Your settings are more appropriate for 16S batteries.

Batteries should be at the same state of charge before being connected. The BMS may correct this over time, but much better to completely charge them individually before going further.

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Alexandra avatar image
Alexandra answered ·

@Libor

Out of curiosity how did you determine 54v for bulk? The table shows 51.89v for 100% SOC?

The battery is full the inverter doesn't know that as its target voltage is much higher. So it isn't stopping at battery 100% since according to the settings it hasn't reached the target voltage you set.

The voltage for charge shouldn't / wont change no matter how many batteries you have in parrallel. If charged is 51.89v then that is is for al batteries in the bank.

Voltages suggest a 15s battery.

Sustain should be much higher, closer to 48v.

Your low cut off is 47.5v (0%) under load.

Leave equalisation at absorption/bulk voltage.

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Related Resources

Mutli RS Solar Datasheet

Mutli RS Manual


Additional resources still need to be added for this topic

VictronConnect VE.Bus charging manual