Issue - Victron Battery balancer and Victron MPPT Controller

I have a Victron Battery Balancer and Vitron MPPT Controller.

The reason for the balancer is I have two 12v 100ah Lifepo4 batteries connected in series. I notice when the batteries start to get to full charge the battery balancer kicks on and then the wattage through the controller drops for a moment then rises back up. This continues over and over again unless I turn off the power coming from the solar panels at which point the balancer seems to balance things out and turns itself back off.

The inverter also seems to lose power for about a second before gaining it back. When this happens and I monitor the voltage the controller is showing for the batteries it jumps up to 30V for a brief moment.

Is this because the balancer is turning on and transferring energy at the same time as the controller providing energy to the battery causing the voltage to jump up? Currently, I have the controller set to the default for 24v lifepo4 that it automatically set itself to which seems to align with the battery factory specs. Should I be lowering the absorption settings perhaps?

It's possible. What are the current settings? I like 13.8/27.6V to avoid/reduce risk of the BMS turning off due to high voltage or a high cell.

Brucey said:

It's possible. What are the current settings? I like 13.8/27.6V to avoid/reduce risk of the BMS turning off due to high voltage or a high cell.

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Thank you for the reply. Absorption is 28.4 and float 27v. Think I should leave float at 27 and change absorption to 27.6?

Maxout77 said:

Thank you for the reply. Absorption is 28.4 and float 27v. Think I should leave float at 27 and change absorption to 27.6?

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That's what I would do. Just no need to push them any higher for 1% more.

The Victron balancer should kick in once voltage hits >27.3V so should be good there.

Brucey said:

That's what I would do. Just no need to push them any higher for 1% more.

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Alright. I'm going to make that adjustment. I appreciate the intel. This is my first dive with a DIY solar system.

Maxout77 said:

Alright. I'm going to make that adjustment. I appreciate the intel. This is my first dive with a DIY solar system.

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My first battery build also.

Let us know if that works. The victron balancer has quite a few negative reviews and I was hesitant to use it.

If the fix is simply to slightly lower charging parameters that would be good, but that spike in voltage is concerning and I don't think it will be that simple.

I am using this type with decent results:

Maxout77 said:

nverter also seems to lose power for about a second before gaining it back. When this happens and I monitor the voltage the controller is showing for the batteries it jumps up to 30V for a brief moment.

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This is typical of BMS shutdown on one of your series batteries. Since the controller cannot respond fast enough the voltage spikes, the shutdown and spike upsets the inverter.
The battery balancer cannot in any way help with unbalanced cells in each of the batteries, if either of the batteries is experiencing. BMS shutdown.
Forget about the balancer for the moment and try to get each battery charging without BMS shutdown.
Charge the batteries in parallel with a 12v charger set to a voltage just below BMS shutdown, this may be as low as 13.7 volts. Arrange absorbtion and float equal voltage, and apply for several hours.
The aim is to get the batteries to accept an absorbtion voltage of 14.0 to 14.2 without BMS shutdown. Once this is achiever reconnect in series and charge with 28 to 28.4 volts, float at 27.0. Unless the voltage is significantly higher than 3.40 per cell , Internal balancing won't be effective.
Adding the external battery balancer will protect against mid point voltage drift and ensure each battery has the same charge voltage.

Lowering the absorption a little seems to have done the trick. I think when that battery balancer was kicking on combined with the solar input coming in at the same time it would for a split second push the energy up high enough to the point to shut down the BMS. Without that battery balancer, the batteries seem fine at 28.4 absorption.

Maxout77 said:

Lowering the absorption a little seems to have done the trick. I think when that battery balancer was kicking on combined with the solar input coming in at the same time it would for a split second push the energy up high enough to the point to shut down the BMS. Without that battery balancer, the batteries seem fine at 28.4 absorption.

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Makes sense. The Victron balancer really isn't designed for lithium batteries. Glad you found a good solution.