I have installed a rack of 4 Chinese 16 cells Lifepo4 batteries, 48v, 300a per unit, so a total of 4x 15kwh = 60kwh. These have their own BMS that communicates with my Cerbo gx 2.
I have 3 multiplus II 6k5 units, connected to the grid. My house will be on the ac-out, for now i am testing the units.
They have charged to 99,47%. Cell voltages range between 3360mv and 3385mv. Total voltage of the battery is now 53,81v.
ESS is set to keep battery charged.
Absorption voltage is advised to be set to 57,6v by the manufacturer but i witnessed the voltage not rising higher then 53,8v and i figured it will never get so high and thus i lowered absorption voltage to 53,8v and float voltage to 51v. Absorption time is 1 hour.
So now comes the problem: my multiplusses ( 1 master, 2 slaves) are seemingly stuck in bulk phase and buzzing loudly, whilst the battery is idle and no current is going into them, as the BMS sees them as full. I have witnessed this for the entire day already.
Set the MPs own charge settings to what the battery manufacturer says. Limiting the MPs charger to a lower value can possible hinder the battery to be charged to the voltage it requests. If you really want to limit the charge voltage rather use the setpoint that there exactly for that, but keep in mind that its only intended for initial use, the BMS should be capable of controlling:
This means very likely DVCC will be enabled. This enables the batteries to set lower boundaries for both voltage and current. And thats also the reason why the MPs show “externally controlled” meaning controlled by the Cerbo and not by their own internal charging algorithms. They will stay in bulk for most of the time, even when discharging, so you can pretty much ignore that status while mains is available.
I am willing to ignore the constant bulk mode but I expected the Multiplus to go in a quiet (float?) mode when the battery is full. Now it’s constantly buzzing, I assume because of the bulk modus ?
I dont really know how quiet or loud a 6k5 can get, ive got my 4k5 that is used as ESS installed in the basement. During commissioning i did not feel like it did hum too much, noticeable yes, but it was also charging at 2kW at that moment.
But there will always be some base level noise since the transformer is connected to the AC input as long as there is mains voltage, whether or not there is current flowing over it.
There have been some threads about reducing noise levels, some also talked about decoupling, as in reducing the vibrations that can be transferred into the building structure, for example by using rubber dampers between the MP and the wall its mounted to.
