Issues with Charging My LiFePO4 Bank Using MPPSolar & Victron MPPT

[hellror]

Hey everyone,

I need some advice on properly configuring my solar setup. I’m using an MPPSolar Inverter PIP3024GK and a Victron SmartSolar 100/50 MPPT, both connected to a 24V 300Ah LiFePO4 battery bank consisting of three Power Queen 25.6V 100Ah batteries (I've used 4x Ultimatron 100Ah 12V Gel batteries in the past).

Initial Battery State & Charging Setup:​

Before connecting everything, I checked the battery voltage—all three were at 26.1-26.2V (35-40% SoC, according to the battery manual). I decided to charge them individually first before wiring them together to ensure a well balance.

I've set both MPPSolar and Victron MPPT to the same charging parameters to avoid conflicts:

• Bulk (Absorption): 28.4V
• Float: 27.6V

Charging current setup:

• MPPSolar: 10-20A (handles a free-standing 3kW solar array)
• Victron: 15A (handles a 460W solar tracker, planning to upgrade to 1100W soon, meaning higher charge current)
  Both are connected to the battery bank through a Victron Power In.

The Issue:​

Once the battery voltage exceeds float, the MPPSolar stops charging in Bulk, leaving only the Victron SmartSolar to handle Bulk and Absorption.

One battery seems to handle this fine, but two of them have a new issue:

• When Victron enters Absorption Mode, the voltage spikes to 30V, triggering the BMS shutdown.
• I’m unsure if this is due to high charging current or if my Absorption Voltage was set too high from the start.

Disabling MPPSolar and using only Victron didn’t fix the issue.

Battery Manufacturer’s Specs:​

• Recommended Absorption Voltage: 28.8V (± 0.4V) - 29.2V
• Recommended Charging Current (per battery): 20A
• Maximum Recommended Charging Current: 50A (up to ~96% SoC)

I've let the batteries rest for 12h, almost 24h, and the first one (which had overspike to 30V) is now at 26.93V. Rest of them have almost the same values.

My Questions:​

1. What are the best Absorption, Float, and Charge Current settings for a LiFePO4 bank (24V 300Ah) when using two charge controllers?
2. Does the voltage spiking to 30V, then dropping to Float, then back to Bulk (and repeating) indicate a fully charged battery, or is it a sign of incorrect settings? Could this be due to the Re-bulk setting being at the default 0.1V?
3. Is it normal for Absorption time to be extremely short for one battery? Absortion Time is set to 1 hour with Tail Current on 1A. Charging current drops from 15A to 1A in just 10-15 minutes.

Thanks in advance for any insights! And sorry for the spaghetti of information—I know it’s a bit all over the place.

 

[mikefitz]

Victron enters Absorption Mode, the voltage spikes to 30V, triggering the BMS shutdown.

The BMS in one or more of the batteries is shutting down the charge path due to cell overvolts.

What you need to do lower the charge volts down, to perhaps 27.6 volts, with a long sbsorbtion period, and/ or set float to the same value .
The cells need time to balance and they only show up unbalanced vo.tager when near full charge. If you have a power supply that can be set to this voltage, an option would be to use that. It may be useful to treat each battery seperatly. The process could take many hours . As the balance improves you may be able to increase the voltage.
Note, the BMS protection is indicated by a sudden drop in charge current to a very low value.
Once things improve use the default lithium charge settings, 28.4 volts absorbtion, 27 volts float.
The problems you are seeing is very common with new batteries, its not a fault, just tollerances in cell characteristics.

 

[hellror]

The BMS in one or more of the batteries is shutting down the charge path due to cell overvolts.

What you need to do lower the charge volts down, to perhaps 27.6 volts, with a long sbsorbtion period, and/ or set float to the same value .
The cells need time to balance and they only show up unbalanced vo.tager when near full charge. If you have a power supply that can be set to this voltage, an option would be to use that. It may be useful to treat each battery seperatly. The process could take many hours . As the balance improves you may be able to increase the voltage.
Note, the BMS protection is indicated by a sudden drop in charge current to a very low value.
Once things improve use the default lithium charge settings, 28.4 volts absorbtion, 27 volts float.
The problems you are seeing is very common with new batteries, its not a fault, just tollerances in cell characteristics.

Thank you for your reply.

Would it be best to handle the balancing process solely with the Victron, or can I use both devices set to 27.6V for Absorption and Float?

Since the Victron is currently limited to 15A, would it be ok to use the MPPSolar alongside it to increase the total charging current to around 20-30A?

Once all three batteries are connected in parallel (24V 300Ah), what would be the optimal combined charging current from both MPPSolar and Victron?

Thank you again.

 

[mikefitz]

Would it be best to handle the balancing process solely with the Victron,

The balancing process only starts when the battery is approaching fully charged so a high charge current is not needed.

optimal combined charging current from both MPPSolar and Victron?

When you have normal charging the limit will be the maximum the battery can accept, ( based on the battery data you gave), 50A, ( 150 for 3 in parallel). Power Queen recomend 20A, (60 for 3 in parallel).
The 3000 watt array, in theory, is 107 amps at 24 volts and the proposed 1100 array, in theory , 40 amps.
The Power Queen charge current, maximum and recomended, see low compared to many 24v batteries. Do you have the correct data for your battery?

 

[hellror]

The balancing process only starts when the battery is approaching fully charged so a high charge current is not needed.


When you have normal charging the limit will be the maximum the battery can accept, ( based on the battery data you gave), 50A, ( 150 for 3 in parallel). Power Queen recomend 20A, (60 for 3 in parallel).
The 3000 watt array, in theory, is 107 amps at 24 volts and the proposed 1100 array, in theory , 40 amps.
The Power Queen charge current, maximum and recomended, see low compared to many 24v batteries. Do you have the correct data for your battery?

Yes. Those are the charging currents I have in the manual.

 

[hellror]

Hi,

I’m back with an update.

I’ve set the MPPSolar inverter to 27.4V - 10A charging , and the Victron at 27.6V - 30A charging, and it seem to work properly (no overvoltage).

My next issue/question is: When the MPPSolar goes past its bulk/float voltage setting because of the Victron, which is the Master at 27.6V (for Absorption), is it normal that the MPPSolar, when the house consumption is, for example, 800W, only produces 700W from the solar panels, and the rest is drawn from the MPPT, with current flowing to the battery terminals?

See example in attached file ( Green line is the MPPSolar, Yellow Line is the Solar Tracker and the Blue line is the home consumption).


Would it be a problem if this happens for several hours a day after the batteries are charged? Does it pose a future issue for the batteries?

Is it a better solution to set both to 27.6V and have them both do an absorption (in their own way) at the same time? << So the MPPSolar will produce a lil bit more than consumption.

Thank you.