Uneven battery draw w new Growatt System

[Jonnyvan]

OK here goes...first post and new system.

Setup: Cargo conversion RV system

• Growatt 3000 24v
• 2 x 200 solar panels in series
• 2 x SOK 12V 100AH batteries

Problem: Batteries start with equal capacity (measured w meter). Balanced the batteries before initial install too, but overnight with minimal loads in the AM Growatt has shut down (cannot power back on) and left battery reads 1 volt!!! while other reads 13. This has happened both times I have done this test. I am happy to provide more info as needed to help w diagnosis. Only thing "plugged in" during latest test was powered cooler (this seems to run very efficiently).

Notes:

• Growatt is set to user for battery type with 19,20, and 21 menu parameters set to Will Prouse suggested.
• Intended system use is for boon-docking with solar to charge system in day (supplemented with 2000w generator as needed) and power off batteries at night to run cpap machine, powered cooler, and a few 12 led's.
• Shunt monitor wires were disconnected as I thought that might be culprit
• I have not finished wiring 12v loads yet as you can see from pic (the wire bundle on left goes to loads nut hooked up yet.
• Will be installing victron 24/12v converter next week.

 

[Jonnyvan]

On a side note I am wondering if the Growatt was the best choice for an efficient RV system? Should I have went individual Victron MPPT, Charger/Inverter route? But want to address the "problem w current system before I go too far down that path.

 

[MichaelK]

Looking at your battery voltages, it appears that one battery is OK, and the second has had the BMS shut the battery down. It appears that you have the model designed for serial wiring, so I don't think that is a problem. One of the BMS experts though will better address your problem, but do you know how to reactivate an SOK battery that has had BMS shutdown? Did you make sure the two batteries were at the same state of charge before connecting them together?

Try disconnecting the sleeping battery, and connect that battery alone to a 12C charger. That might wake it up. If it wakes up, leave it on the charger till fully charged. Once charged, check the charge level of battery #2. Make sure that one is brought to the same state of charge before reconnecting them in series.

 

[Jonnyvan]

Thanks for the reply, the first time this happened I pulled both batteries out of system and charged them individually with Noco 10amp charger back up to capacity then balanced them and reinstalled in system. So they have went through one "round" of this so far. I do not know how to reactivate a SOK that has had BMS shutdown. What I am gleaning from your comment is that the left (1.3v battery) is not actually at 1.3v and has been shutdown?

 

[timselectric]

Thanks for the reply, the first time this happened I pulled both batteries out of system and charged them individually with Noco 10amp charger back up to capacity then balanced them and reinstalled in system. So they have went through one "round" of this so far. I do not know how to reactivate a SOK that has had BMS shutdown. What I am gleaning from your comment is that the left (1.3v battery) is not actually at 1.3v and has been shutdown?

That's correct.

 

[Jonnyvan]

So now what?

 

[Kornbread]

What are the working voltages of the sok? Never mind, a little research shows the sok 12v100a specs cuts off at 10.4, reconnects at 11.6v. One battery at 12.98v is ~25% soc, and if the bms shuts down at 10.4, that's maybe <10soc? Darn, that seems a bit harsh.

When figuring loads, don't forget to add in the draw from the aio. It adds up.

 

[MichaelK]

So now what?

I'm no BMS expert, but I think it might wake up if you put it on a 12V charger. If that does not work, try jumpering the sleeping battery in parallel with the awake battery, while you have the charger connected to the asleep battery. If the BMS awakens you can then disconnect the parallel jumpers. The reason for the parallel battery is because the charger may not function properly until it sees an appropriate voltage, and if the shut off battery is essentially zero voltage the charger doesn't come on.

 

[Jonnyvan]

Thanks folks I need a layman’s interpretation..my assumption there is a pretty small range that this battery operates before it shuts down? Correct? What is aio?

 

[timselectric]

AIO
All In One unit

 

[Jonnyvan]

Well that seems like a lot of draw if it can’t even make it 12 hrs with 24volts of lith batt? Kind of like what’s the point! Solar charges system during day and aio runs it self down at night. With only tiny load.

 

[Jonnyvan]

Something must be wrong with either my system design or one of its components. I used to get WAY more battery time with my 2 old golf cart 6 volt batteries In my basic charger/inverter setup and shore power charge before the weekend boondock trip.

 

[MichaelK]

Something must be wrong with either my system design or one of its components. I used to get WAY more battery time with my 2 old golf cart 6 volt batteries In my basic charger/inverter setup and shore power charge before the weekend boondock trip.

What's going wrong is that the BMS is shutting down one of your batteries. Rather than low capacity, that suggests to me that the two batteries were charged unevenly before installing them in series. Lead-acid is far more forgiving about that, and a simple equalization charge solves most battery inequities. Have you awoken that battery yet?

BTW, your previous system was 12V? Can out itemize the components that you used previously and what you have now? That might help determining way one battery is shutting down. Pics would be great.

 

[Kornbread]

When only looking at the one 12v battery, at 12.98v it is past the long flat spot where LiFePo4 likes to meander and hitting the lower knee. Not a lot of power remaining down there.

vs 12v FLA. The graph at right is at a higher voltage, but it gets the point of their different discharge rates across.

 

[Kornbread]

What state of charge were the batteries in during the day? While there does seem a considerable soc difference between the pair of batteries, I just do not know how LiFePo4 reacts when they reach such a low state. Do they become a bit erratic? Which model Growatt? What is its idle current? Have you figured up the total loads?

 

[chess-equality]

What's going wrong is that the BMS is shutting down one of your batteries. Rather than low capacity, that suggests to me that the two batteries were charged unevenly before installing them in series. Lead-acid is far more forgiving about that, and a simple equalization charge solves most battery inequities. Have you awoken that battery yet?

BTW, your previous system was 12V? Can out itemize the components that you used previously and what you have now? That might help determining way one battery is shutting down. Pics would be great.

Looks like battery 1 soaked most of the draw (is this even possible?) and just drained out, or something triggered the BMS cut out. Can you isolate what's causing this? Maybe test just battery 1 first on a 12v system. But first you need to wake up the BMS, e.g., some chargers can charge it up even if battery is at low <12v.

 

[Ellcon123]

"Equal capacity (measured with meter)", not sure what you are measuring? Until you fully charge LiFePo4 you have no good idea of state of charge. Voltage can be very close between the 2 batteries but one could be at 20% and the other at 80%. Generally putting the battery on charge will turn the BMS on. Need to be over 14V on each to know that they are near full charge.

 

[Jonnyvan]

Hello folks. Was able to charge both batteries by pulling out of system and using Noco ac charger. One battery read 13.25 and other read 13.35 with multimeter and then put in the balancer (that I used before initially hooking up system). They now both read 13.25 This is exactly what I did before putting system in place and after the first time I had the problem, so I am back to square 1 that I have been at 2 times before.

to address some questions: as far as total loads, my 12v side will max out at 16 amps if everything was on at once. AC side is only the cooler and random appliances as needed BUT am not even to that point yet, cannot get past this overnight with extremely small load. Aio is growatt300024v, they do not become erratic from what I can see.will hook up shunt today With the little display, what should I be looking for with that to see if something is ”off” or will that not tell me much?

 

[Kornbread]

Thinking out loud.

Some say top balance, others bottom balance, but at 13.25v, it's ~80% soc. Does this make a difference? At ~80%, how do you zero the shunt, doesn't that have to be done from a full or empty charge?

One 100ah battery really isn't a lot of storage. You need to figure up your loads. Filterguy has an energy audit that might be useful, but I have no idea how to add in the 12v loads.

 

[timselectric]

If you are going to put the two batteries in series. They need to be at 100% SOC before connecting.
If you don't start balanced, you'll never be balanced.
Also, are you using a 24v to 12v converter to supply the 12v loads? If you try to connect the 12v loads to just one of the batteries, it will definitely cause issues of unbalance.