Battery for 12kW inverter

I started off looking into building a solar generator, but after realizing that I'd need at least two or three due to location requirements, I have convinced my wife to allow a full solar install. The main function of the full install is to reduce electricity costs (over $0.51/kWh) and to provide power during outages. Being in Bermuda, we are affected by hurricanes and the power company just recently "upgraded" their plant with a new diesel generator and have been having reliability issues. (With these powers combined...something, something, captain planet...) I will essentially max out south-facing roof space with 14 panels. I will be using the following equipment:

• Growatt SPF 12000T DVM-MPV
  • Provides 12kW with support for 36kW surge. (low frequency inverter...this beast tips the scale at ~200lbs)
• 14x 320 Mission Solar panels.
  • Model MSE320SR8T -> Link to specs
    
  • 5s2p for PV1 and 4s for PV2
• 48x 280Ah LiFePO4 cells. (EVE cells from Basen)

My current dilemma is the battery configuration. I was originally going with 3x 48v packs, but have been considering a 3s48p pack instead. (3 cells in parallel as one logical cell, 48 logical cells in parallel) My choice of BMS options is throwing me for a loop.

3x 16s packs (multiple packs):

• Pros
  • Can monitor each cell individually.
  • Provides redundancy. If one BMS fails, the system can run on 2 packs. (I wouldn't want to push one pack to run solo.)
  • I can use the busbars that are provided with the cells.
  • Far easier to fit 3 packs. (The batteries and Growatt will be in the garage. The less space I have to take up, the better.)
• Cons
  • 3x the following; BMS, fuse, shunt (might just go with one shunt directly before the inverter's input, but not sure yet)

1x 3p16s pack (single pack):

• Pros
  • Only one BMS, fuse, and shunt needed.
  • Don't have to worry about one pack hitting low/high voltage and disconnecting, requiring the remaining packs to pick up the slack.
• Cons
  • Will have to use something along the lines of 4/0 cables for the battery connection to the inverter.
  • Will need to custom order or fabricate some larger busbars to deal with the potential 750A surge draw, and possibly some longer studs.
  • Will take up more space in the garage. (I don't want to vertically stack the cells...I can't see all that weight being good for the cells on the bottom.
  • Cannot monitor cells individually.

I've been looking at the following BMS's for the setup:

• 3 packs
  • 250A Daly Smart BMS (250AcomUARTBT -> Link to model)
  • QUCC Smart BMS (200A continuous, 600A surge ->Link to model)
  • JiaBaiDa smart bms (200A continuous, 600A surge -> Link to model)
  • *I believe that the QUCC and the JiaBaiDa are the same product with a different sticker, but don't have confirmation.
• Single pack
  • Chargery BMS16T V4.02 (600A capacity -> Link to model)

Any advice or recommendation is appreciated. Thanks in advance!

Welcome to the forum.

3X 16S packs in parallel.

Pros outweigh the cons.

You have redundancy. if a single cell has a problem, you still have 2/3 of your bank online after disconnecting only one element in the problematic 16S battery.

Still only need 1 shunt with 3X 16S.

Unlisted con of a 3P16S single pack is that any ONE failed cell will likely take out it's two "cell mates," so one failed cell likely means 3 failed cells. If a single cell fails, and you catch it in time, you have to reconfigure the entire bank as a 2P16S, and finding the bad cell in the parallel group of 3 may take several hours. Bad cell is obvious in a 16S setup.

I think you have a really good grasp of what is going on.

I did 4 packs of 16S. I'm not a fan of a paralleled cell when you can parallel the entire pack. You do save $ with less control electronics, but you lose the granularity of knowing if one cell is acting up.

I did 4 2 amp Active Balancers.

I have the Chargery BMS16T with the DCC. (I don't yet trust it, and only have one installed) I do trust the balancers absolutely though.

Consider your amp load that you will have. My amp load is across all 4 sets of 16s batteries. In your 16S3P setup that is essentially the same. If you use an active balancer, it might take a lot longer to get everything under 5 mV. But once they all are, they will stay together more, or at least that is what the balancer will show.

@snoobler - Would you not recommend putting a shunt after each battery pack to monitor input/output, and just rely on what the BMS reports.

@jasonhc73 - Would you recommend a separate balancer, or would the Chargery BMS16T/ QUCC / JiaBaiDa options suffice? I've seen the previous version of the QUCC used on Off-Grid Garage. It looks to be a decent option and the price is good enough that I would most likely get 4 of them so that I have one as a "hot-spare."

Thank you for the input. I wanted to make sure that I wasn't missing anything with the pro's and con's. (The difficulty/hassle/downtime finding and dealing with a bad cell in the 3p16s option is definitely off-putting.)

Would a 2 gauge welding wire be sufficient for each battery connection to the busbar/common post? The Growatt's manual, page 7, states that it requires 3x 2AWG for the battery connection. Am I right to feel like this might be pushing it a bit? Would something like 2|0 be better suited, or is that overkill? I plan on having the batteries as close as I can realistically get them...ideally under 6 feet of cable away.

Gannam said:

@snoobler - Would you not recommend putting a shunt after each battery pack to monitor input/output, and just rely on what the BMS reports.

Click to expand...

I would not. I would build the bank using best practices ("Wiring" in link #2 in my signature). Under heavy charge and discharge scenarios, confirm the batteries are within their rated specifications with a clamp ammeter. I would use a single shunt for the whole bank.

snoobler said:

I would not. I would build the bank using best practices ("Wiring" in link #2 in my signature). Under heavy charge and discharge scenarios, confirm the batteries are within their rated specifications with a clamp ammeter. I would use a single shunt for the whole bank.

Click to expand...

Thank you for the link, it's been bookmarked for quick and easy reference!

Does this sound ok for 3x 48v 280A batteries in parallel, considering the aforementioned inverter?:

• Each battery having a 400A fuse.
• 2 gauge wire from each battery connected to common post. (Each battery with a 400A fuse)
• 1x 4/0 gauge wire from the common post to the inverter. (Shunt on this line)

Are my values within spec? I'd rather do things right once, over doing them twice.

Given the beastly surge, I'd go with 1/0 for each battery to the bus bar.

Gannam said:

@jasonhc73 - Would you recommend a separate balancer, or would the Chargery BMS16T/ QUCC / JiaBaiDa options suffice? I've seen the previous version of the QUCC used on Off-Grid Garage. It looks to be a decent option and the price is good enough that I would most likely get 4 of them so that I have one as a "hot-spare."

Click to expand...

I use a separate active balancer. The passive balancer in just about every BMS only discharges the highest voltage cells. An active balancer discharges the highest cell into a capacitor and then discharges the capacitor into the lowest cell.

In my setup with the one Chargery, I disabled the balancing function.

I have build about 100 DIY packs with Daly.
If you top balance your batteries and use the 500A non-smart BMS you should be fine.

I have had some issues with smart Dalys failing (maybe they have fixed it).

Also you should over rate it (500A).
You can still fuse it at 300A (required in inverter specs).
I would not use a fuse one each battery.
I would not use a shunt.
I have a few of the same inverters and monitoring and control with USE settings with voltage levels works fine. The only thing you will miss is accurate SOC by percent on the ShinePhone app.

Many (well respected) people say that the 36mv balance current is insuffecient for large capacity batteries. I have not seen this to be an issue and we have several 40kWh+ packs running (but I would like to hear about other's experience). I always thought I would add an active balancer if needed but the Daly seems to work great.

The only disadvantage of this I have seen is that I occasionally manually check the cell balance with a meter. So far they always fall back into balance once they are charged (so this checking is not necessary).

Some say it will be difficult to identify a failed cell. I suspect the failed cell would likely result in a low voltage on the parallel cell group and that the bad cell would be easy to isolate and test after removing a few buss bars.

The trade off of less componets/simplicity may result in greater reliabity.