Why are My Batteries Charging Daily?

[Bananassassin]

I have 2 Growatt 5000 inverters and 4, 48V server rack batteries. I'm connected to the grid which is just passing power through to a 30W load. No solar installed quite yet. I just finished the system a week ago so I'm just monitoring its behavior for now. I'm confused by the behavior of the batteries charging daily despite running off of grid power and only a 30W load. Even if the batteries were powering that small load, I don't understand why they need to be topped off significantly every day. The sawtooth charging after the primary charge is also puzzling. Can anyone shed some light on this behavior? The below charts are exports of the last three days. Thx in advance!

 

[sunshine_eggo]

What is the priority setting of the inverter?

What is the battery voltage doing?

Keep in mind that the units have a high idle power draw - probably 80-90W EACH, so your 30W load is costing you > 200W. IIRC, the idle power is actually drawn from the batteries regardless of connection to AC, so I suspect this is what's happening. The battery voltage is dropping to the set point in #12, so it charges back up until voltage rises to #13.

 

[Bananassassin]

What is the priority setting of the inverter?

What is the battery voltage doing?

Keep in mind that the units have a high idle power draw - probably 80-90W EACH, so your 30W load is costing you > 200W. IIRC, the idle power is actually drawn from the batteries regardless of connection to AC, so I suspect this is what's happening. The battery voltage is dropping to the set point in #12, so it charges back up until voltage rises to #13.

Great info. Thank you. One thing I failed to mention is that I'm not confident the batteries are getting a full charge. The SOC graphs usually say 75%, occasionally 100% (25% increments which is frustrating). I'm not sure my BMS is communicating properly with the inverters. Do you think the charging is affected because I don't have panels connected yet? This is why I'm just getting familiar with the system for now - to educate myself and work out the kinks.

Thx for the quick response. This forum is such a great resource due to people like you!

 

[sunshine_eggo]

Priority setting? Should be SUB.

They are not getting fully charged. There is no harm in this as LFP doesn't mind.

The Growatt AC charger is not a 3 stage charger. It's ON at setting 12 voltage and OFF at setting 13 voltage.

In order to get a proper 3 stage charge, solar will get you there.

To minimize the amount the batteries are discharging, I would raise your setting 12 to the highest allowed.

 

[sunshine_eggo]

Something you might want to consider for more robust function is:

Automatic power management for Axpert inverters

SolarAssistant allows you to change inverter modes based on Pylontech, Narada, Revov, etc. battery state of charge. It can also protect your battery from shutting down by shutting down the inverter before the battery shuts down.

solar-assistant.io

I have no personal experience with it, but many use it for improved function.

I suspect that you could prevent the inverter from behaving in this manner and simply float the batteries, but I'm guessing.

 

[Bananassassin]

Thank you, I can bump up #13 to 58. Is that advisable? The 48V chargers on the signature solar site charge to 58.4.

 

[Brett V]

I have a Growatt 6000T and it does the same thing, Idle consumption is what's pulling your batteries down and the AC charger in the Growatt acts like a float valve in a toilet tank. This is the nature of the beast and it's acting normally. I have my float set at 54.2 and charge set at 55.0

 

[sunshine_eggo]

Thank you, I can bump up #13 to 58. Is that advisable? The 48V chargers on the signature solar site charge to 58.4.

You can, but I wouldn't as it's not really important that you get your batteries fully charged at this time. Once you're fully operational, it might make sense.

 

[Bananassassin]

You can, but I wouldn't as it's not really important that you get your batteries fully charged at this time. Once you're fully operational, it might make sense.

Thanks! good call

 

[Pierre]

I have been experimenting with my Growatt SPF 5000 ES for about a month now. Very quirky unit. Sometimes it will charge the battery from solar at max 10A my PV can deliver and other times under the same conditions it will only charge at 2-3A . Once I isolate the battery and turn it back on it will once again charge at 10A. I am wasting a lot of useable PV this way as I cannot babysit the unit all the time. I do not know if it is the Growatt or the JBD BMS causing this. Me thinks it is the Growatt.

 

[sunshine_eggo]

I have been experimenting with my Growatt SPF 5000 ES for about a month now. Very quirky unit. Sometimes it will charge the battery from solar at max 10A my PV can deliver and other times under the same conditions it will only charge at 2-3A . Once I isolate the battery and turn it back on it will once again charge at 10A. I am wasting a lot of useable PV this way as I cannot babysit the unit all the time. I do not know if it is the Growatt or the JBD BMS causing this. Me thinks it is the Growatt.

This type of issue including the solar just going to zero or refusing to start with the morning sun have been occasionally reported. Hard reset with battery disconnect has been the temporary fix.

IMHO, there's either a firmware issue, or it's a defective unit. Some operate just fine.