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Hope avatar image

Charging and SOC of Lithium batteries

Last April we fitted 4x 150ah Victron Smart 12.8v Lithium batteries in our yacht whilst in Malta. These batteries make up house bank of 600Ah at 12v. We had a Mulitplus 12/3000/120 charger/inverter and added a second Multiplus to be able to charge these batteries faster whilst we are running the onboard generator. The 2 Multiplus are linked together. A BMS200 was also installed. The system was professionally installed and the local Victron dealer commissioned the system including checking and updating the software for each item. We had a Victron BMV 702 already installed.

At a later date I managed to buy a Mk3 to USB Interface and run VE Config 3 to set up the 2 Multi's. The Malta Victron dealer originally did the set up and suggested I buy an Interface so I could make any changes necessary.

My issue is regarding the charging of theses batteries and the SOC shown by the battery monitor. When the Multi's are running on shore power and from the onboard generator the charging AMPs start at say 180 in bulk and then after a few minutes the charging AMPs start to drop as the chargers go into ABS mode and within 10-15 minutes the charging rate is down to say 80 amps. Mean while the SOC on the BMV starts at say 35% and after some time the charging is at 80 amps the SOC is shown as say 45%. At these two SOC the voltage on the BMV shows 12.3V and 12.7V respectively. Whilst the Victron Connect App shows shows the voltage of the batteries around 13.1V with a temp of 21C. The house bank voltage shown on the boats normal display shows say 13.3V. After say 1.5 hours of charging the amps have dropped to 30amps whilst the SOC on the BMV shows say 50%. If however the batteries are charged from the alternator of the drive motor the BMV shows 100% after 3-4 hours of running (charge rate reduced by the BMS to max of 90amps from the capacity of 150amps). But the alternator seems to keep charging at say 70-80 amps and after another several hours with the BMV still showing 100% the charge from the alternator drops to a float mode. So my problem is why can't the Multi's continue to charge at a high rate - say 120amps in ABS mode until almost a SOC of 100% before dropping to Float?

The software versions of all equipment etc seems to be up to date. Part of the reason to invest in the Lithium batteries and the two Multis was to be able to charge at a high rate to reduce the running of the onboard generator. What setting can I try changing on the Multis to get this higher more constant charging whilst on the generator?


SOCLithium battery Smart
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2 Answers
Hope avatar image

The settings on the BMV702 are -

1. Batt capacity = 600ah

2, Charged voltage = 14.2V

3, Tail current =4.0%

4. Charged detection time = 3 minutes

5. Peukert exp = 1.05

6 Charge efficiency factor = 99%

7. Current threshold = .10A

The settings on the Multi's (both) are -

Enable charger =Y

Lithium batteries = Y

Charge curve = Fixed

Abs voltage = 14.5V

Float Voltage = 13.5V

Charge current = 120A

Repeat ABS time = 3 hours*

Repeat ABS interval = 0.25 days*

ABS time = 4 hours*

In the battery type box it lists - No corresponding default.

* I changed these setting because when the yacht is on shore power the charger could not keep up with battery power drain which is about 15 amps.

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The alternator charges the batteries directly by DC and charges according its charge controller's algorythm.

The MultiPlus has its own algorythm: starts to charge in bulk with the current set as "Charge current" on the Charger tab of the VEConfigure3. It keeps charging with that current until the battery's voltage rises by itself to the value set as "Absorption voltage" (for Victron LiFePO 12,8V batteries the preset value is 14,2V), also the preset absorption time is 1 hour, after this period it goes into "Float".

The battery monitor is independent, does not communicate with the MultiPlus (if you do not have a CCCGX or VEnus GX installed) and says SOC based on the parameters set in the BMV-702.

What are your settings?

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The settings on the BMV702 are -

1. Batt capacity = 600ah

2, Charged voltage = 14.2V

3, Tail current =4.0%

4. Charged detection time = 3 minutes

5. Peukert exp = 1.05

6 Charge efficiency factor = 99%

7. Current threshold = .10A

The settings on the Multi's (both) are -

Enable charger =Y

Lithium batteries = Y

Charge curve = Fixed

Abs voltage = 14.5V

Float Voltage = 13.5V

Charge current = 120A

Repeat ABS time = 3 hours*

Repeat ABS interval = 0.25 days*

ABS time = 4 hours*

In the battery type box it lists - No corresponding default.

* I changed these setting because when the yacht is on shore power the charger could not keep up with battery power drain which is about 15 amps.