He looked at my data and now thinks that my charge current is too high. I had it set at the default 80A. He said I have a common problem of having way to much solar power available for not a lot of batteries, and I'm "cooking" the batteries by charging them too quickly. His analogy was wetting a sponge with a fire hose.
So I've dropped the charge current to 40A and will see how that goes.
The batteries ramp up to 14.4 V or so in just a couple hours in the morning. I don't understand how I have 24 kWh of batteries drained to 42V, and they charge up to full capacity in just 3 hours, and using max 1500W of solar? (I have 4500W of panels available) Something is not right. I tend to believe the batteries are not actually getting fully charged to capacity, but they are reading 14.4V which should be full charge, right?
I can measure current on the cable going from the Growatt to the batteries. I just checked now, on "float" at 54V, and it is about 8A.I have read through this entire scenario and I believe the only way to get to the bottom of the situation is to monitor the current into the batteries and out of the batteries. They have a number of devices on the market that do just that. With my system the Overkill BMS does a good job of keeping track of the cell voltages (Lifepo4) and also how many amps that the Cell packs have taken in during the day. It also keeps track of the current draw during the night and how many amps are left in the cell pack in the morning. In my opinion, if you are not keeping track of the current going into your batteries and the current that is coming out of your batteries then you will never be able to solve this problem. With all batteries of the different chemistries it is very important to keep the batteries happy. I am not sure of the specs on the AGM batteries that you have but you can look them up and make sure that they are happy. Charge current is important, Discharge current. I believe that you need to occasionally take the batteries to 14.4 volts for a period of time and then drop them down to an absorb voltage. I would become very familiar with the actual parameters if it were my system. When I purchased my Lifepo4 cells, I read everything about the voltages and currents that the cells were to receive. If you exceed the voltage or current then damage will occur. I am not a fan of Growatt but I will not criticize those who have elected to go that route. The All in one concept sounds good on paper, but I suspect that it has some issues which I do not want to deal with. I like the concept of if something goes wrong then replace one component rather than the system. Like if the Charge controller quits working then replace the Charge controller. If the Inverter quits working then replace the Inverter. With the Growatt system that you are dealing with who knows how much power that thing is consuming during the night. For all you know it could be sapping all the power out of your batteries and you would not know. Again enough of the philosophy, in my opinion the only way to determine what the problem is would be to measure the current into the batteries and the current out of the batteries. If the batteries are for example 100 amp batteries, then you should be able to put 100 amps into them and then take 100 amps out of them in a perfect world.
Yes, confirmed - two parallel strings of four 12V batteries, rated at 250 A-hr each, so 24,000 Wh.24,000 Wh of batteries, 48V bank = 500 Ah ... confirm that's what you have?
4500w of panels delivering 48V would be 94A, about 0.2C ... I would consider that about right for my AGM batteries. Specs for yours may vary.
40A would be 0.08C ... I would consider that low for FLA (0.12C typical I think), maybe appropriate for some Gel.
In this picture, the meter is set to AC amps.I can measure current on the cable going from the Growatt to the batteries. I just checked now, on "float" at 54V, and it is about 8A.
View attachment 87723
I can also look at all of the data over time as logged by the Growatt. I plotted the following from one day's worth of data. I believe this is charge and discharge current.
View attachment 87728
There is only one amp setting on the meter, and that is for AC. I thought amps were amps, although I understand the current flows both ways for AC. Perhaps I don't have a meter capable of measuring DC amps.In this picture, the meter is set to AC amps.
Set the meter to DC.
Press the orange "SEL" (select) button, to switch between AC and DC.There is only one amp setting on the meter, and that is for AC. I thought amps were amps, although I understand the current flows both ways for AC. Perhaps I don't have a meter capable of measuring DC amps.
Sorry, that meter doesn't have a DC option.There is only one amp setting on the meter, and that is for AC. I thought amps were amps, although I understand the current flows both ways for AC. Perhaps I don't have a meter capable of measuring DC amps.
Now I wish it was - I should have looked closer when I bought it, as I do a lot of car / motorcycle work as well and DC amps would come in handy.I thought that it was the CL390.
For sure, thanks for pointing this out - I ordered the CL390 last night. I do a lot of DC work, and I do need to know how much current is going into the batteries.It never hurts to have an extra meter. On several occasions I have found myself using 3 clamp meters, at once
Thanks, these are AGMs, but I will read your write-up for sure!Just skimmed this thread and could have missed something you folks have already figured out, but it sounds like perhaps the system just isn't getting enough total hours of charging to catch up with the usage each day.
I wrote up this phenomena a while back, maybe it will be a useful read: https://symbioquine.net/2021-11-29-off-grid-lead-acid-battery-charging
I don't know, but what I can't understand is why my controller is only charging 7 kWh in a day when the batteries are still not at capacity at the end of the day? This has been suggested before here - the controller should be bulk charging longer throughout the day, but it doesn't.
The peak power is always around 1500W early (8 to 9 am) and then drops. Every day. (The spikes are just from using my skill saw or vacuum). If I have 4500W available, why is it only using 1500W? What's limiting it?
The only thing I have seen that causes this is a bad battery.Well maybe we're not done.
I swapped out the bad battery of one string and I'm just running off that one string of four for now.
I measured the voltages of the four batteries while charging (lots of sun) and the first in the string is at 16.3V! The others at about 13.7V. What the heck?
I disconnected the panels and they all are around 13V.
View attachment 62987
I'm afraid to hook up the panels again - isn't 16V way too high? what could cause this?
A charge controller is basically a constant current supplying current to the batteries. Once the batteries reach a certain voltage as determined by your charge controller then they go into a constant voltage mode. The charge controller thinks your batteries are charged and is going into absorption This reduces the amount of current that is actually going through your batteries because according to the charge controller your batteries are at full capacity.I don't know, but what I can't understand is why my controller is only charging 7 kWh in a day
Appears you've checked everything. I was going to ask where you were located because temp affects batteries BUT you said the bartteries were in an 80F room; so, hum.Hi,
I'm trying to understand why my off-grid system has not been making it through the night, hoping some of you solar sleuths can help me out. I built this system in the spring and it did well for a while with batteries rarely dropping below 75%, but for the past month or so the inverter has been shutting down due to low voltage early in the morning. If we run the generator in the evening for a couple hours it helps, but even then we drop way down in voltage overnight.
I've contacted the seller of the batteries, and he says we simply need more batteries. I contacted Growatt, and they took a look at my settings and say everything is fine. But what I don't understand is why the power we are using doesn't even come close to the amp-hour rating of the batteries.
We have 4500W of panels, Growatt SPF6000 Inverter/Controller, and eight "lead-carbon" AGM 12V batteries. The batteries are rated at 250Ah (at 77°F). I am running two parallel strings of four batteries, so 48V and 500 Ah. I ran the 240V output from the inverter directly into my electrical panel, and all circuits in the house are brand new and working great.
The controller is set to charge to 56V, and then float at 54V. Looking at my data from yesterday, the battery voltage reached 56V by 10:30am, and stayed there for two hours until 12:30pm, when it dropped to 54V. It stayed right around 54V until around 5pm when the sun gets low in the sky, and from there the voltage starts to drop. I'm assuming that when they go to 54V they are full and under float charge...?
Looking at our power usage, from 5pm until 3:30am when the inverter shut down we are using between 200W and 350W, which is two ceiling fans, the TV for a while, the fridge cycling on and off, some lights, wifi modem, and other small electronics. The battery voltage drops from 54V at 5pm to 52V at 6pm, 51V at 9pm, and then rapidly to 46V at midnight. It continues to fall until 3:30am, when it gets to 42.5V and the inverter shuts down.
Attached are plots of battery voltage and power usage from yesterday and this morning.
Now for my calculations. If I have 500 Ah of capacity at 48V, that is 24,000 Wh. I understand that we don't really want to use more than 50% of the battery capacity, so I should safely have 12,000 Wh to use before the batteries drop to 50%, of course a bit less than that due to inverter efficiency, etc.
So I'm using lets say 350W max for 10.5 hours, which is 3,675 W-hr of energy. So why are my batteries dropping down to under 25% when I'm not using anywhere near the energy I have?? I'm a mechanical engineer, not electrical (haha), but the math is pretty simple, right?
I understand this is not an exact science, and battery capacity can vary with temperature and other factors. My battery room is in the low 80 degrees F for most of this time.
Any thoughts? Am I missing something?