Growatt Grid AC Charge from Low Voltage Cutoff on LifePower4 48v

[maple_syrup]

Hi All!
This is my first setup - a Growatt 3000TL LVM-48P with a LifePower4 100ah 48v battery. I picked it up used on FBM from someone who purchased it a few months back (I have their receipt from Signature Solar) but never hooked it up.

I believe they hooked up the inverter to test it a few times, as the battery has reached its low-voltage cutoff. I am able to turn on the battery, get the Growatt to wake up before it trips the cutoff and everything shuts off.

I'm still working to get my solar mounted, this morning I was reading about 60V at PV-in, which I believe should be sufficient, but it wasn't enough to wake up the Growatt. I'll try again when the panels are in direct sunlight this afternoon. I don't have enough time to make sure the settings prioritize grid charging, otherwise I'd post my settings here.

My main question is:

Is there a way to charge from utility using the Growatt in this case? I have a socket hooked up to the AC Input, but plugging it in to my utility (on-grid) outlets does not wake up the Growatt to charge the battery. Reading the manual I did not find a good answer if this is possible.

If not, what are some good options for getting the battery back up to a safe SOC?

 

[RCinFLA]

A lot depends on the current draw as you approach cutoff. Cell voltage will rise a bit when load current stops, after one to three minutes of no load. The greater the discharge current when it approached cutoff the greater the cell voltage will recover and the longer it will run again when it turns back on until it collapses again.

BMS's also have reset voltage bracket to avoid chattering on and off near trigger voltage.

If you milk a battery dry at low discharge rate it won't have any residual recovery capacity left.

 

[maple_syrup]

Thanks RC!

The BMS is definitely cutting things off here as it should. Maybe a different question then is: Can the charging circuit in the Growatt run without battery power to recharge the battery following LVS? I assume not given what I have tried so far, but I was hoping to confirm here as there is no clear answer from what I've read elsewhere.
Is this the case with the MPPT circuit as well? Based on what I've read about people attempting to go "batteryless" with some of the MPP/Growatt inverters, I assume this is not the case with the MPPT and it could recover a dead battery.

In a more complete system I am aware this shouldn't really happen. The Growatt can trip a generator backup or utility recharge/passthru when the battery approaches the low voltage limit.

 

[RCinFLA]

When a BMS cuts off for low cell voltage it disables the discharge pass MOSFET but leaves the charge MOSFET on.

Problem with this is when any small amount of discharge load is on BMS output it will show near zero volts on its output that may cause inverter to interpret there is not valid battery connected and inverter may refuse to attempt to charge it.

If inverter internal electronics is supplied by AC input power or available PV power, it may go ahead and try to charge battery input. This assumes you do not have another item loading down the BMS output line. Just a battery monitor may have enough load current to drag the DC lines down on a discharge disabled BMS. The reasonable solution is the inverter puts out a short, low charge current attempt and checks if battery terminals shows a reasonable battery voltage range in response to the attempt.

 

[maple_syrup]

Thanks again RC.
I ended up ordering the 48v 18A charger from Signature Solar. After attempts with as much solar as I currently have capacity for, it wouldn't keep the Growatt up. Talking with SS support as well I think the best bet is to top it off and prevent the Growatt from discharging this close to the LVS.