Growatt SPF 5000ES Deep cycle batteries charger glitches when floating at 54 volts- No solar

[tarek]

Hello,
I have installed Growatt SPF 5000 ES connected to grid and batteries without solar panels.
I am using four C10 Luminous batteries LPPT 12200 200AH.
The inverter is working normally, yet something disturbing is happening when utility is charging the batteries. The charger start to raise the voltage with a constant current to reach the bulk charge voltage (57.5 volts) the going down to float voltage 54 Volts.
The float voltage remain stable until the batteries become full then strange change in the inverter charger is happening as shown in the graph. The fan speed is continuously change its speed with the intermittent supply and drain of current from the batteries. I contacted Growatt but no reply from the support team.
Firmware version 040.05.701
In other words, when the inverter finish floating the batteries, the charger becomes unstable.
Any idea or proposed solution?

 

[tarek]

It seems there in no solution for this problem which is coming by design. The Growatt inverter after finish charging the batteries to 100%, it starts draining the batteries again via feeding the inverter from batteries in the presence of utility.
This apply to all types of batteries and this is a weakness in the design because the inverter is cycling the batteries.

 

[Herb]

It seems there in no solution for this problem which is coming by design. The Growatt inverter after finish charging the batteries to 100%, it starts draining the batteries again via feeding the inverter from batteries in the presence of utility.
This apply to all types of batteries and this is a weakness in the design because the inverter is cycling the batteries.

Which user mode are you using? Do these batteries have communications?

 

[octal_ip]

Yes, this is normal behaviour, it also happens when using solar to float charge the batteries and with small AC loads. The internal DC/DC converters don't have the precision necessary to match the load exactly, so there will be a bit of ebb and flow from the batteries as the charger cycles between providing slightly too much current, and not quite enough.

I don't think this is anything to worry about, it might cause some wear on the batteries, but the amount of energy involved is very small. I doubt it'd be measurable against the larger contributors to battery lifespan like temperature and normal cycling.

 

[Steve_S]

Tubular FLA class.

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[octal_ip]

Out of curiosity I've had a closer look at this today: according to the BMS, after the system reaches the "unstable" floating stage, the battery pack voltage varies by about 0.3v, with about 370mA of current variation peak to peak. The batteries are still float charging the whole time and not providing any power, so micro-cycles aren't occurring, which means no potential for wear on the batteries. I don't think this is anything to be concerned by, it's just a few jagged edges in a graph.