Growatt not charging batteries after reaching low dc cutoff

[MTM98290]

We have had many low sun days and lots of snow lately. This has led to the batteries finally being depleted to 40v which is where I have the low cutoff set. The inverter is switched to on as it left on all of the time.

Will the panels ever charge the batteries now that it has hit cutoff? I have been told that is should restart, but I have also been told it wont unless its above 43v which makes no sense. My batteries are full at 50.4v and empty at 36v so I charge them at 49.9v and discharge them to 40v which is low enough and also as low as the Growatt allows.

shouldn't the MPPT circuit still function if the inverter is lit up and has power from batteries?

any help with this would be great, thank you.

 

[sunshine_eggo]

We have had many low sun days and lots of snow lately. This has led to the batteries finally being depleted to 40v which is where I have the low cutoff set. The inverter is switched to on as it left on all of the time.

Will the panels ever charge the batteries now that it has hit cutoff? I have been told that is should restart, but I have also been told it wont unless its above 43v which makes no sense. My batteries are full at 50.4v and empty at 36v so I charge them at 49.9v and discharge them to 40v which is low enough and also as low as the Growatt allows.

shouldn't the MPPT circuit still function if the inverter is lit up and has power from batteries?

Remember, this is an all-in-one (AiO). It is an inverter/charger and MPPT. There are various set points and functions for those components. If you have the recovery voltage set to 43V, then the inverter will not allow AC output until that recovery voltage is met.

If actively powered by the battery or AC input, it should charge from AC or MPPT as available even below 43V.

I'm guessing you're using 2X 6S Tesla modules for 12S "48V" or some other 12S 3.7V battery. Unfortunately, these are not an ideal match for inverters designed for 48V systems as your battery is actually 44.4V and operates outside the normal working range for a 48V system. Most 48V systems are designed around lead acid, and they are designed to cut off around 42V.

 

[MTM98290]

Remember, this is an all-in-one (AiO). It is an inverter/charger and MPPT. There are various set points and functions for those components. If you have the recovery voltage set to 43V, then the inverter will not allow AC output until that recovery voltage is met.

If actively powered by the battery or AC input, it should charge from AC or MPPT as available even below 43V.

I'm guessing you're using 2X 6S Tesla modules for 12S "48V" or some other 12S 3.7V battery. Unfortunately, these are not an ideal match for inverters designed for 48V systems as your battery is actually 44.4V and operates outside the normal working range for a 48V system. Most 48V systems are designed around lead acid, and they are designed to cut off around 42V.

What is recovery point? It is basically set to charge at 49.9v it is set to use2 with 49.9v in all charge settings, and cut off inverter below 40v which it did. The Shinephone app showed when it hit 40v and a while later the UPS ran out of power. The inverter is lit up and functional even if the batteries are at 40v.

System is;

Off grid

4x Slifab Solar Silfab Solar SIL-490-HN 490Watt 156 1/2 Cells in series-roof mounted on 12\12 (45°) Roof using Ironridge XR1000 rails facing SSE at 48° lattitude in north central Washington State.

1X Growatt spf 3000tl lvm-es 48V-3kw AC output
120V single phase 60 HZ 250V mppt

4x bigbattery.com BDGR gen 2 NMC 48V batteries in paralell these function at 36v to 50.4v

So if I set the cut off higher it would self restart? I do not understand why it would allow the 40v setting if it werent capable of functioning at that setting.

When we purchased these batteries we did so because they were a good price and could handle cold better than most. I also thought that limiting the depth of discharge would not be an issue as it would prolong battery life. If I have to use 43.2v to 50.4v it really kills the capacity.

 

[sunshine_eggo]

If you're off-grid, you should have a generator.
If you don't have several days of battery backup, and you don't have excellent year round solar conditions, you should have a generator.
If you're using Growatt hardware, that generator should be an inverter generator as they don't tolerate dirty power.
If you hit low voltage cut-off, you should charge with said generator.

From: https://watts247.com/manuals/gw/SPF 3000TL LVM-ES User Manual.pdf

Setting 21 is the low voltage disconnect, which you have set to 40. I do not see that there is a low voltage recovery value or setting.

I have to accept that the 43V you have been told is correct and not something you can change.

My concern is that if you change #21 to something higher, the recover voltage will move with it, i.e., since it can be adjusted to as high as 48, it doesn't make sense that 43V would be the recovery voltage. If you set it to 43.2V, the recover voltage would likely move to 46.2V. You could move the low voltage disconnect back to 40 and possibly get it to restart, but this is a poor solution as you surmise.

The way to avoid this in the future is to:

1) make sure you never let the unit hit 40.0V by turning it off if needed.
2) Get an inverter generator if you can't do #1.
3) Set #1 to SbU, #12 to 49.8V and #13 to 49.9V - this will ensure that the unit will charge from generator when you fire it up.

Unfortunately, as I mentioned above, your battery is a bad choice for a 48V system. The inverter and conventions its following are consistent with standard practice for decades, but you are trying to use a battery with usable capacity below the normal cut-off and still below the absolute cut off.

To wrap around to your original question, if the unit is provided either AC input power or PV input power to the MPPT, it will start charging even if it won't deliver AC power. Once it charges enough to hit 43V, the inverter will turn back on.

 

[MTM98290]

If you're off-grid, you should have a generator.
If you don't have several days of battery backup, and you don't have excellent year round solar conditions, you should have a generator.
If you're using Growatt hardware, that generator should be an inverter generator as they don't tolerate dirty power.
If you hit low voltage cut-off, you should charge with said generator.

From: https://watts247.com/manuals/gw/SPF 3000TL LVM-ES User Manual.pdf

Setting 21 is the low voltage disconnect, which you have set to 40. I do not see that there is a low voltage recovery value or setting.

I have to accept that the 43V you have been told is correct and not something you can change.

My concern is that if you change #21 to something higher, the recover voltage will move with it, i.e., since it can be adjusted to as high as 48, it doesn't make sense that 43V would be the recovery voltage. If you set it to 43.2V, the recover voltage would likely move to 46.2V. You could move the low voltage disconnect back to 40 and possibly get it to restart, but this is a poor solution as you surmise.

The way to avoid this in the future is to:

1) make sure you never let the unit hit 40.0V by turning it off if needed.
2) Get an inverter generator if you can't do #1.
3) Set #1 to SbU, #12 to 49.8V and #13 to 49.9V - this will ensure that the unit will charge from generator when you fire it up.

Unfortunately, as I mentioned above, your battery is a bad choice for a 48V system. The inverter and conventions its following are consistent with standard practice for decades, but you are trying to use a battery with usable capacity below the normal cut-off and still below the absolute cut off.

To wrap around to your original question, if the unit is provided either AC input power or PV input power to the MPPT, it will start charging even if it won't deliver AC power. Once it charges enough to hit 43V, the inverter will turn back on.

 

[MTM98290]

I understand that there is a slight mismatch in voltages now that I have some experience with the system. I thought that this would be ok because I didn't want to discharge battery 100%.

Hopefully the pv will charge it up soon but the panels may be covered in snow goven the current conditions which will make it take a while.

I did start another thread in regard to a installing a generator, which would fix this. I do agree with that.

I could buy a bigger better matched battery setup and move the batteries to our full time residence which would allow me to have a nice battery backup for power outages, but a generator seems to be the best overall solution as I can use it all year long and just pay for Propane once a year whenever I think the price is best. I can get a truck out there in the summer no problem and leasing a tank is cheap. The big hit is just the initial fill and generator purchase.

 

[MTM98290]

The system still hasn't come back online. If my batteries worked between say 44v and 58v the Growatt wouldn't behave this way?

 

[sunshine_eggo]

The system still hasn't come back online. If my batteries worked between say 44v and 58v the Growatt wouldn't behave this way?

Is the battery voltage above 43V?

Per above, I expect that if you move the cut-off to 44V, it will likely cut off sooner AND raise the recovery to 47V, so you'll have even less usable capacity than you do now. The only benefit I see is you will have the opportunity to lower the cut off to 40V, and the unit should restart since 44V is above 43V, but you'll still have to manually do it.

 

[MTM98290]

Is the battery voltage above 43V?

Per above, I expect that if you move the cut-off to 44V, it will likely cut off sooner AND raise the recovery to 47V, so you'll have even less usable capacity than you do now. The only benefit I see is you will have the opportunity to lower the cut off to 40V, and the unit should restart since 44V is above 43V, but you'll still have to manually do it.

I understand what you meant above. I am asking if I replaced the battery with something in the conventional 48v range would this not be an issue?

I do not know at present if the battery is above 43V, I am not there, and the growatt is offline. If it can charge itself with using the solar input then it should be above 43V but I can not confirm until I am there.

When it went offline before the display was still active when I arrived in the dark. I hooked it to the generator and charger and filled batteries that way.

 

[sunshine_eggo]

I understand what you meant above. I am asking if I replaced the battery with something in the conventional 48v range would this not be an issue?

Ah... got it.. It will still be an issue if you don't have sufficient capacity. Approximately 15% of your NMC battery is unusable. If you had 14S NMC (42-58.8V operating) or 16S LFP (40-58.4V) of the same capacity, you would effectively get a 20% boost for the same kWh of capacity. 100% of the usable capacity would be captured in the operating limits of the inverter.

The most cost effective and safe would be 16S LFP.

 

[MTM98290]

Ah... got it.. It will still be an issue if you don't have sufficient capacity. Approximately 15% of your NMC battery is unusable. If you had 14S NMC (42-58.8V operating) or 16S LFP (40-58.4V) of the same capacity, you would effectively get a 20% boost for the same kWh of capacity. 100% of the usable capacity would be captured in the operating limits of the inverter.

The most cost effective and safe would be 16S LFP.

 

[MTM98290]

What does cold start voltage mean? Maybe that is the goal.

I knew that the low end would be unusable but didnt care as I didn't really want to run them down 100%

I purchased them because I liked that they were modular. Having 4 instead of 1 seemed to be wise in case of a failure of one would just mean unplugging it and I could keep going on 3. Plus you have to pay shipping if you don't buy 4 which was not cheap.

I think I'd rather add a generator and live with using 10v of the batteries14.4v capacity than spend more on a bigger battery I don't need.
I need huge battery capacity for 2 or 3 months a year max. The rest of the year that capacity is basically pointless. The gap can be easily filled with a generator running a few hours a week maximum for 2-3 months.

 

[MTM98290]

Inverter is back on on its own at 45.76V.
Cold start voltage must mean when the inverter will turn back on voltage after reaching low DC cutoff. I have roughly a 6V gap between cutoff and restart.

If I could use BMS for SOC % It could be set to come back without so much charging first. Mine is set to Lead Acid mode because I have no BMS so my cold start voltage is stuck at 46V.

If my batteries were 43V-58V range with BMS I could be set to DC cutoff at 48V and It could be back on at as low as 49V.

So to anybody looking at battery options, get one in the 43-58.8V range and get one with BMS for the best adjustability and seamless performance.