Recommendations for BMS for 14s Li Ion packs

[sjsamuel]

Hello folks, I’ve new to the forum and this is my first post after I got pointed in this direction by a member on a support forum for the Outback Inverters I’m using.
I have recently undertaken this project of adding battery backup to my current Enphase IQ7 AC coupled solar setup. This project started when I was offered a great price on these Chevy Bolt batteries that a friend of mine acquired and then reconfigured to 14s / 48v. I purchased 6 initially and soon to add two more..and will have a total of 8 packs which I plan to run in parallel to power my pair of Outback Radian 8048s.

In the process of reconfiguring this packs for 14s, the original balance connectors were disconnected, so I spent quite a bit of time with a soldering iron and 20g wire to create balance connectors for these packs and my original plan was to manually keep a close eye on these packs to make sure the cells stay balanced while they are being used. However, the more I ponder this, I would love to be able to plan and implement a BMS setup for these packs that I could trust to keep up with these packs and maybe even automatically shut of the inverter/charger if something is out of order with the cells.
In my searching and reading through this forum, it seems like this should be an option, but I would love to hear some ideas on what setup you guys would recommend for trying to accomplish my goals.

Im including some pictures of my batterie and how I created my balance tabs. My friend who got me into this whole project is using a very similar setup with his Victron Inverters and his batteries have stayed very well in balance now going on 2 months of use. So I’m hoping that with very conservative use of these batteries, that is keeping my cell voltages on the low and high end very conservative, I will have an even less likelyhood of the cells needing much if any balancing. For now I have a 2 A Active balancer that I could use to balance each pack individually if I need to.







Video of me checking the cells with a battery checker

 

[GXMnow]

Check out my thread in the Show and Tell sections. "Adding Storage to my Enphase system"

Adding storage to my Enphase system

I am still fairly new on the forum, tried to answer a few questions as I asked some, and have been talking about my plans and purchases. I figure this is the right place to talk about what I am doing and where it is going. My existing system is a very typical Enphase setup. I have 2 arrays of 8...

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I went with a Schneider XW-Pro inverter and just 2 14 S strings of those Chevy Bolts batteries. That gives me 360 amp hours. I may add a bit more, but for now this works great. Seeing the packs bolted to the garage wall on wood does make me a little nervous. These cells do contain cobalt and can do thermal runaway and catch fire. It is very unlikely, something would have to go very wrong, and they are actually a little safer than most laptop batteries and even the Tesla packs, but still, I have mine going into a steel rack chassis. If nothing else, put a sheet of metal or a concrete backer board between them and the house structure. Mine have been up and running about 2 months now, cycling 50% capacity each day and they are holding great balance and staying cool. I am using a JK BMS with 2 amp active balancing. It is fully configurable as far as balance limits and voltage, current, and temperature limits. The iPhone app works well, but the range is a bit short. It does have a CAN port and an RS-485 port, but I have not fond documentation yet on how to make use of them. I have it set to safe limits for the cells, and have my Schneider set to a lower full charge and higher low bat cut point, so the BMS should never have to cut the power, but it can if something does go bad. The Bolt cells are staying in excellent balance, and I rarely see the active balance kick in at all with the balance set to allow a max of just 0.006 volts from the highest to lowest cell. It is certainly not cheap at about $200, but how much do we have invested in batteries? Since I do not expect to push more than about 120 amps, I am only using one BMS to manage my 2 strings. I branch out the balance leads to both packs, and had to put 30 fuses on the wire loom to keep it safe. If I add another string or two, it would need another BMS unit. I have each string fused at just 125 amps, and a 200 amp fuse after the two strings combine. Full rated power of my XW is 6,800 watts, with a 12,000 watt surge rating. It could pull about 140 amps long term, and surge to 250, but I told it max current 150 in the settings. I only have a few essential loads which will not be stressing the system.

My Enphase array is 16 iQ7's with SilFab 300M panels. I have had a partial success power fail test, with 7 of my Enphase inverters locking out until the sun went down and came up to reset them, cycling the breaker on the AC side did not wake them up, Enphase is looking into why that happened. 6 of the panels never skipped a beat and were AC couple charging my battery bank without any issue. I was able to get 4 more of them to work by covering them form the sun for 2 minutes, and when I uncovered, they came back up. But I can't easily access the other array.

I am having issues with the Schneider software. In AC coupled only mode, while on grid, it does not want to switch from grid support inverting back to charging again. I have to nudge 2 settings manually to make it work. I detail this in my thread.

Keep us posted, I am very curious how your system works out. If I see a good price again on more Bolt Cells, I will likely buy 2 more strings.

 

[sjsamuel]

Hello GXMnow, I was really hoping you would respond to my request/situation. From t
Following the forum now for a couple of weeks I have read a lot of your posts and already was aware of your setup and the fact that you were using the same battery setup as I am.
First to answer your question, I got 6 batteries for $4500. I have two more I plan to add for a total of 8. After this I’ll have $6000 in batteries. From the calculations done by my buddy running a similar setup(he has 12 of them powering his Victron setup) and from whom I got the packs, I think I will have about 45kwh with 6 and about 60kwh with 8. This will be with me cycling the cells between 3.3-4.05. I think that’s fairly conservative, on my high and low voltages, but I may be even more conservative while I figure out this whole BMS situation.
Interesting that you have Enphase Iq7s with Silfab 300s, as this is my exact setup as well. I have 58 panels and a 15kw system. Max production I have seen is around 13kw.
This project to add batteries to my AC coupled system has been a huge learning curve and I got really excited that I could even accomplish this, as like you I was under the impressing initially that my only option was to go with an all Enphase battery setup, and when the cost of that came out it was way to much to be worth it. Then I got the option to get a deal on these batteries, and realized that hybrid inverters were and option with AC coupling and fancy procedures such as phase shifting. Like you, I looked at many options, but I wanted a fairly large system and for what I was doing the Outback Radians seemed to be the ticket. Like I said earlier, I have 2 8048s currently and if everything works as planned may add a 3rd.
Where I differ from your situation is that I live in Arkansas and have a 1:1 net metering contract already established with my Enphase panels. I don’t have to worry about peak rates and selling back to the grid vs. storing power in the packs and after adding this battery system, I don’t plan to change anything as far as the net metering. They way I will be wired is that my battery setup will be primarily for grid outages/home backup, but also idea of grid independence if needed is very appealing to my wife and I. This being said at this point other than while testing the system and for potential grid outages my batteries should not even be cycling and holding at float voltage. With this idea in mind I feel a bit more comfortable with no active BMS currently. I have a way to manual check the cells which I will do frequently, especially if I’m actively using them...and I have a way to balance the packs individually if needed using this unit which I have purchased.

2A Blance Active Equalizer Battery Active Balancer Li-ion, Lipo, Lifepo4, LTO, 2S ~ 24S BMS APP Super Capacitors Continuous Active https://www.amazon.com/dp/B07SFCY36G/ref=cm_sw_r_cp_api_fab_ikDDFbHQWQQ69

Like my original post said I would love to find a setup where I have an automated balancing setup that I can trust to leave connected, but honestly I feel more comfortable with the cells holding their balance with my minimal using plan as described above. Leaving a cheap balancer connected all the time, I think has a higher risk of failure and causing a problem. I don’t know if this thinking is flawed, but this is where I am.
Currently, I’m waiting on an electrician to come help me with the AC side of things as I am having to do some significant work on the load planning side to have my “critical loads” and such ready right tie to the inverters. I have almost completed the DC side of my install. I will try and keep this forum updated, but my hunt of a BMS setup is going to be my biggest hurdle I think. I am happy to spend some money on a good system if that’s what it takes..I’m a little disappointed in finding out late in the my plan that Radians have no canbus charger control. But there is a relay controlled switch to shut the system down, and if I can find a cell monitoring system that triggers a relay to shut down the system if there is a specified cell discrepancy that would atleast be a start. This all gets complicated in that I will have 8 packs to monitor! That is a LOT of cells. I’m looking forward to see what people more experienced in this forum would have for suggestions for me.

Thanks everyone for the help ahead of time and any advice is appreciated.

Samuel

 

[GXMnow]

Since you plan on just floating the batteries, you may want to keep the voltage even a bit lower, like 4.00 per cell as keeping them at a high voltage is the most stress. The way mine cycle, they spend most of the time below 4 volts, and they rest overnight at just 3.6 volts, which is an ideal storage level. Once the sun is up, they charge to 4.1 volts, and an hour later they are discharging to power me through the peak rate.

Have you done an energy use plan to see how much power you actually use? With that much capacity, you should be able to keep them a bit lower to reduce stress. Even if you get just 60% usable, your 45 KWH bank still give you 27 KWH's. The raw advertised capacity of the cells is 60 amp hour. The Bolt packs come as 3P for 180 amp hour. I paralleled 2 strings for 360 amp hour. Using 3.6 for the nominal voltage still yields 18 KWH. You have triple that for 54 KWH, but being conservative, you 45 KWH usable is a fair estimate.

That balancer is the same as the balance section of my BMS. I think it even uses the same app to monitor it.
Here is a screen shot of mine from a few days ago.

As it shows, it has been operating for 83 days, but only cycling for about 50 days now since the inverter has been running. I entered it as the full 360 amp hours, and it seems to be close. I have not run a full capacity test. If you paired the strings like I did, you could use just 3 of these, but if you plan to run much more current than I do, I would then use six as it did get a bit warm at 80 amps.

In this image you can see my highest and lowest cells are all within 3 millivolts. They have been staying in perfect balance, and it rarely ever has to use the balance current. As the cells age, it may have to work more, and I am happy to have that ability waiting when needed.

For very large banks, people do like the Chargery and Batrium BMS systems, but they only have the passive balancing. You could use that, and add the active balancer you have. That would be a best of both worlds system. You would only need to monitor the balancer if you see th balance drifting out on the main system monitor. Of course, that will cost more, but at the size of system you are looking at, it is a small part of the total cost for the peace of mind.

I have been very happy with my SilFab panels. The cost was ok, and they have been producing their rated power and have a 25 year performance warranty. With just my 16 panels I have produced over 31 KWH's in a single day, my typical is about 24 KWH's. In this crazy hot weather and smoke in the air from the wild fires, I am still topping 20 KWH's most days. Did almost 23 yesterday. 23/16=1.4375 per panel. 1.4375 x 58 panels = 83 KWH's That is a ton of power. You said you have seen 13 KW peak. My system peaks at 3.85 KW on the 16 panels. That is all of the inverts in clip. Got to love So Cal sun. You are not that far behind though at 224 watts per panel. Mine hit 240 on cool but sunny days.

Unless you have some huge demands in your home, that should be enough solar to go off grid in all but the worst conditions. My original plan was just to get free A/C in the summer, but thanks to the Time of Use rates, it did not work out right and I am not saving what I expected to. I may end up adding 4 to 8 more panels. And a third string of the Bolt cells would be nice as well.

 

[keepsake]

Can anyone confirm on this Blance ? 280ah 48v 16s system
Can I use this 2A active balancer ?
Does it have outputs for me to open a 300a contactor to disconnect ?
Can I set the discharge individual cell threshold to like 2.5v ?
Can I set the charge to detect a battery higher than the others and shut down ?
iow -- will this do the dirt simple stuff a Daly would do and add the balancing benefit to the full picture ?

 

[keepsake]

2A Blance Active Equalizer Battery Active Balancer Li-ion, Lipo, Lifepo4, LTO, 2S ~ 24S BMS APP Super Capacitors Continuous Active​

Can anyone point me to the user or install manual pdf ?

 

[GXMnow]

I don't see a link or product name in your post, but it does sound like you are describing the Heltec/JK BMS like the one I have. Mine was rated at 200 amps, but in the setup app, you can set the max current before shut down at up to 250 amps. And I have seen an ad showing a 300 amp version, but it uses the same number of MOSFETs. I do not think I would trust that PC board to handle 200 amps for a long period of time. I have only run up to 80 amps through mine, and it handled it fine, and just got a little warm. All of the voltages and current limits are adjustable over very wide ranges. But it does not have outputs to control external contactors.

 

[SolarPrep]

GXMnow: very interesting. One thing I've always wondered is if automotive batteries are consistent between manufacturers. For example, if the Volt (presumably) uses LG pouch cells, are the charge profiles and capacities the same if used by different car manufacturers? I've mostly purchased Samsung SDI NMC cells, and those have some variance between those made for autos, and those (again, presumably) made for ESS. I cannot find it right now, but read some technical papers on a Samsung site that showed cycle life/charge level curves that seem to differ from what people on these forums tend to assume.

While looking for a BMS to use for my largest single project (about 43kw) I was told by one BMS manufacturer that if I only charged those SDI cells to 3.7v rather than something like 4.15 I would lose 50% of the capacity. I have not done any extended testing yet, while we figure out the final format for this particular project. My particular modules are 8s, which are then placed in series (16s) for a typical voltage around 66, and those trays of 2 modules are then in series again for high voltage. There are not many inverters that work with high voltage except those that have proven communications, so my thought is to reconfigure the whole cabinet.

Your comments to SJSamuel are along the lines of what I was originally thinking; to continue to use the modules as 8s, but just use a lower charge voltage. I would like to have long life with the batteries, and our intended use is similar to your project. All of that made sense when I was focused on Victron equipment, but recent code changes here will not allow us to use non-UL approved equipment. We are mainly focusing on Radian now.
It has been suggested to remove one cell from each module, make them 7s, lowering the overall voltage to within the range of typical inverter equipment, and then charge to a higher voltage level such as 4.15v. These particular modules are easy to reconfigure, because they are held in place with a few bolts (14) and one cell can be easily pulled out. Those cells could be made into additional 7s packs.

Hope I didn't just hijack your thread. I'm following your project carefully, and learning along the way. The Schnieder equipment could be a good option for us, but locally I'm getting nothing but resistance towards using it, from people who are frustrated with their tech support. We do have access to top notch support on Radian products here.

Thanks!

 

[GXMnow]

Most NMC cells should have very similar voltage to state of charge curves, but they do vary quite a bit with their current handling ability. For a given size of cell, the capacity can cover a 3 to 1 range. With 18650 cells going from barely 1 AH to over 3 AH. But what you will also find is that the lower capacity cells often have higher continuous and peak current ratings. The higher capacity seems to be more fragile. The cells that Ford uses in their hybrid vs plug in hybrid are also a good example of this. I have the hybrid with just a 1.4 KWH pack, which is 5 AH at 76P, full charge at 315 volts, or about 4.15 per cell. These cells are rated for 20C 100 amp constant discharge. The plug in version has a 7.5 KWH pack, but the peak power is no higher. It has 5 times the capacity, but it only about twice the physical size. The 18650's I just bought for my E-Bike are only 1.5 AH per cell, but they can handle 30 amps each. I have 2 packs running them in 4P each. 8P if I run both packs together for 12 amp hours. Those are also 14S so that works out to over 600 watt hours, and more than enough current to max out my 1,500 watt motor controller.

So most ESS batteries are higher capacity but lower rate. EV cells need higher rate capability to handle acceleration demands. The Chevy Bolt cells I am using are rated at 60 amp hours each, and 3C constant discharge rate. Basically middle of the road. I am running 12P now (4 3P strings) so I have 720 amp hours, and maximum current capability of over 2,000 amps. Needless to say, I will never come close to that current. My single Schneider XW-Pro maxes out at about 140 amps.

Have you looked at the OutBack SkyBox? It is a 5,000 watt hybrid inverter system with all of the monitoring and a charge controller all built in. It does support AC coupling, but as of a few months ago, it did not support stacking multiple units in AC coupling, but they should be fixing that with a firmware fix. When I first looked at it, I thought the Schneider was going to be a much better unit, and the actual inverter part of the Schneider XW-Pro is excellent, but the firmware and control side does have some odd quirks.

How much power and energy do you need? Peak power, long term power, and total kilowatt hours. With old school lead acid batteries, you needed a lot of extra capacity to be able to supply the peak current and handle charging in just the time the sun is up. Most lead acid cells could only put out 1C for any length of time, and only charge at 0.1C without boiling out the acid. With lithium cells, even weal LFP cells will take 0.5C charge and 1C discharge without a problem.

 

[SolarPrep]

GXMnow: Thank you for the reply. To answer your questions: I have read up on The Skybox, but local Outback people think it isn't well executed. They are die-hard Radian fans, and they sell a lot of them. Maybe those two things go hand in hand? From the videos I've watched of it, the Skybox appears to be a nice unit. 5k is a bit limiting if you cannot stack them, but I could make use of it. One possibility I've considered with other brands is to have two units operating essentially independent of each other. Put one in, and see how it works out. If needed, add another. Our property has some shading issues, and we are likely to have a combination of both roof and ground mount. I'm getting quotes right now. We have to pick our inverters so we can apply to the utility for a grid tie agreement. The amount they pay is diddly squat, but it has advantages.

We have lots of batteries, and plenty of panels. Just need to get everything mounted up. The recent laws enacted here regarding UL have really put a crimp in our plans though, along with availability of things.

Our SDI cells for the most part are ESS batteries designed for moderate discharge. I do have some 14s units too that I'm not sure what they came out of. There is 24kwh of those, so is a significant amount. Those are beautiful modules, of the typical welded variety, 3kwh per unit. I'm going to sell off a bunch of batteries we picked up for other projects, like SPIM08, etc.

We have run our property on generators for weeks at times, and were able to get by pretty handily between 3kw peaks, and 6 kw peaks from 2 different gen-sets. (Running only one at a time) It was a learning curve. However, we were not running A/C at the time, and that is something we want to cover in the future. Our new house is smaller and better insulated, but we don't have any real data to compare with.

To begin with, we will put up at least 7kw of panels. We have twice that many on hand now. I know this is all over the board, but we cannot help it. Our goal is to run during the day on solar, and switch to batteries at night. if the power if down for extended periods of time, I want to be able to run for 3 days off batteries. If Victron had UL approval, I'd be on my way with no hesitation. I asked our State official about getting approval for using Victron AC coupled with Fronius, but he thinks it won't fly. Dang.

I'm going to look into Skybox a bit more.

Thanks!

 

[GXMnow]

If I was in your position, I would do a split setup. Put half of the panels on microinverters to provide all the power you need when the sun is up, and then put the other half of the panels, the ones with no shading issue, on DC charge controller(s) to the battery bank. Then you can use pretty much any inverter that supports the frequency shifting. This would work with a Radian, Schneider, Sol-Ark, or SkyBox. I am planning to go this route with my system, by adding 2 to 3 KW of solar panels to a DC charge controller. That eliminates my issues with the Schneider software refusing to charge from AC each morning.

The microinverters will run all of your loads while the sun is up, and the DC solar charges up the batteries. When the sun goes down, the batteries run all the loads until morning. In my case, the idea setup would be 4 KW of DC and just 3 KW of AC micros, but I already have 4.8 KW of AC panels (3,840 watts AC max), and I can't really justify taking any offline. Our net metering 2.0 agreement is still pretty good if I push back power during the day. I don't really have room to add more than about 3 KW of panels.

During a grid outage, the AC coupling comes into play. The AC panels will still run the loads while the sun is up, but any excess solar will also help charge the batteries instead of going out to the grid. If I am home during an outage, I will set the charging to allow the batteries to charge to a higher state. I normally am only hitting 85%, I could push to 95%. I also allow the battery inverter to run them down to 20% with the grid down, where I have been keeping them above 45% when the grid is up. I now have 36 KWH of battery, so I think I could run off grid for at least 2 days of cloudy weather. If the sun comes out, I could run all of my backup loads without issues. Just no air conditioner.