LiFePO4 system design considerations and sources for off-grid battery bank replacing lead acid

Dave

I need to replace my lead-acid battery bank prematurely and I am going LiFePO4.  I need between 600 and 800 kwh and I've described below what I am leaning toward. Based on 6 years with 470 Ah lead acid bank, my pulls are typically less than 40A and I have only very rarely seen 50A for a short time. I have a Tristar 60 MPPT controller.  Before my wife and I destroyed the batteries recently, we rarely went under 80% unless there were several days of clouds or snow. We live at altitude in the sunny SW.

96 Fortune 100Ah batteries https://www.electriccarpartscompany.com/Fortune-100Ah-Aluminum-Encased-Battery hooked in groups of 6 parallel, then series to get nominal 48V 600Ah

BMS leaning toward Orion Jr 2 https://www.electriccarpartscompany.com/Orion-Jr-2-BMS

which also requires 16 LED https://www.electriccarpartscompany.com/3V-1S-Lithium-Lighted-Battery-Balancers

I am curious about what you think about this overall system, is there a better way? I opted away from the cheaper BMS because I am worried about failure and Orion seems to have a good rep.

I am also curious about anybody's experience with Electric Car Parts Co?

Also, there are Powerwall options from Greensun and Meritech where you get a complete system of batteries and BMS that would be cheaper for more power but I am leery about an overseas transaction and the lack of support I'd be likely to receive. Does anybody here use one of the pre-built Chinese "Powerwalls"? I could get 800Ah powerwall shipped for under $11,000.

Among the things I am worried about is will shallow cycling (we do have occasional deep cycle needs but less than 20 times/year) will shorten the life of lithium batteries if they are fully charged between cycles?

Should we charge them to the max rated voltage of 3.65 cells each cycle or would it be better to only go up to 90%?

Will the BMS work if it is hooked only to each parallel group, i.e. each group of 6 batteries in parallel will have one balancer? The only drawback I can come up with for doing this is that if one cell is failing, the other cells in that parallel group will be stressed until I notice that the group is lower than the rest and replace the cell.

What else should I be losing sleep over?

Any thoughts are welcome. I already know that I am ignorant and on a nearly vertical learning curve about lithium set up.

Dave

I originally posted the above comment on a different thread and was advised to start new thread so I copied this comment from mcgivor over here for follow-up:

mcgivor Solar Expert Posts: 3,180 ✭✭✭✭✭

November 22 edited 5:19AM #9

Don't be intimidated it's not that complicated to build a DIY bank once the fundementals are understood.

For a BMS I contacted a manufacturer, they requested specifications, maximum load current, maximum charge current, battery capacity and charging source etcetera, their engineering department then recommend one based on my reply. 

Both the batteries and BMS I  ordered were from China, the support has been excellent from the supplier's I used. No experience with Electriccarparts.

Shallow cycles will extend the life expectancy, they can be used at partial states of charge without negative impact as well.

The only time they really need to be charged to 3.65 VPC is when initial ballancing is performed and perhaps every couple of years, under normal cycling it's best to only charge to ~3.40 VPC, somewhere in the 90% region, likewise discharge to 20% maximum which results in 70% of nominal capacity used.

The cells would be arranged parallel first then series, for 600Ah, 6 100Ah in parallel to form a cell block, the BMS sense wire for each cell will be connected to the cell block, 8 for 24V, 16 for 48V nominal. The ballancer would be redundant because the maximum voltage would be below it's operating range using  3.4 VPC , to understand this you need to consider how the cells are ballanced in the first place.

In EV applications the cells would typically be bottom ballanced to allow maximum capacity availability, in solar applications the cells are typically top ballanced, in both cases all cells or cell blocks are connected in parallel, then either charged to maximum voltage or discharged to a minimum voltage value. The cells can be top or bottom ballanced, but not both, with top ballancing a 3.65VP LiFePo4 single cell charger can be used to safeguard aginst voltage runaway which happens extremely fast without a proper charger, likewise with discharge things happen extremely fast, both over or under voltage can result in permanent damage to the cells.

The links below are a great source of general information, not nesesarally specifically for solar but useful for general information.
http://liionbms.com/php/bms_options.php#7
http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/

The attached pdf is the BMS I ordered, it costs ~$100

One suggestion, start a new discussion to concentrate response to your particular project.

Dave

Dave said:

I originally posted the above comment on a different thread and was advised to start new thread so I copied this comment from mcgivor over here for follow-up:

mcgivor Solar Expert Posts: 3,180 ✭✭✭✭✭

November 22 edited 5:19AM #9

Don't be intimidated it's not that complicated to build a DIY bank once the fundementals are understood.

I appreciate that!

For a BMS I contacted a manufacturer, they requested specifications, maximum load current, maximum charge current, battery capacity and charging source etcetera, their engineering department then recommend one based on my reply. 

Both the batteries and BMS I  ordered were from China, the support has been excellent from the supplier's I used. No experience with Electriccarparts.

Would you mind sharing the name/contact info for who you worked with for batteries and BMS?

Shallow cycles will extend the life expectancy, they can be used at partial states of charge without negative impact as well.

The only time they really need to be charged to 3.65 VPC is when initial ballancing is performed and perhaps every couple of years, under normal cycling it's best to only charge to ~3.40 VPC, somewhere in the 90% region, likewise discharge to 20% maximum which results in 70% of nominal capacity used.

ElectricCarParts (ECP) advised initial balancing by hooking all batteries up in parallel first for 8 hours or so before charging. Are you referring to that balance or the balancing that the BMS does, which I thought would be occurring all the time?

The cells would be arranged parallel first then series, for 600Ah, 6 100Ah in parallel to form a cell block, the BMS sense wire for each cell will be connected to the cell block, 8 for 24V, 16 for 48V nominal. The ballancer would be redundant because the maximum voltage would be below it's operating range using  3.4 VPC , to understand this you need to consider how the cells are ballanced in the first place.

This is where I am most confused. The BMS I was planning on would have one attachment (sense wire I guess) to each 6-cell parallel bank and the assumption (via ECP) would be that all cells in that group were at the same voltage. Then, I thought the BMS would distribute the charge current among the 16 groups as needed to keep them balanced and in range. I thought this would occur any time charging was happening even if the voltage was below max V. There is a more expensive BMS that monitors every cell but that seemed over the top, not so?

    This sounds very different than the balancing process you described so I could use some more tutoring! This aspect is important because I like the idea of setting the max voltage at 90% of max V but not if that means the BMS won't be doing its job automatically and constantly.

In EV applications the cells would typically be bottom ballanced to allow maximum capacity availability, in solar applications the cells are typically top ballanced, in both cases all cells or cell blocks are connected in parallel, then either charged to maximum voltage or discharged to a minimum voltage value. The cells can be top or bottom ballanced, but not both, with top ballancing a 3.65VP LiFePo4 single cell charger can be used to safeguard aginst voltage runaway which happens extremely fast without a proper charger, likewise with discharge things happen extremely fast, both over or under voltage can result in permanent damage to the cells.

The links below are a great source of general information, not nesesarally specifically for solar but useful for general information.
http://liionbms.com/php/bms_options.php#7
http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/

The attached pdf is the BMS I ordered, it costs ~$100

One suggestion, start a new discussion to concentrate response to your particular project.

mcgivor

Take some time to relax, it's far too easy to over think, there is a definite conflict between EV and solar useage, they are very different from one another, but related  somewhat in the common use of battery chemistry, focus on solar application. 

The battery supplier I used was http://www.aukpower.com/products.asp?did=38  they were very helpful and support is second to none, personal opinion. 
BMS supplier LWS battery bodyguard http://lws-pcm.com/en/new/news53.html

The cells are all connected in parallel initially to bring them to the same voltage regardless of wether they are top or bottom ballanced, for off grid I would personally recommend top ballancing because it better suits the needs.

Let's start with basics, what nominal voltage do you intend to use? That would be a good starting point, it really doesn't matter because the process is the same, I'm assuming 48V nominal if this is the case it would be a 6P 16S bank or 96 cells in total. Don't be intimidated it's actually very simple if you follow the procedure. You will need a single cell 3.65V charger, they are available for ~$50 for a 15A version, ballancing is a very time consuming process so patience is imperative.

 Hint. Disregard the EV perspectives, they don't really relate directly to off grid applications.

Get the cells from whoever you choose, mine were significantly less expensive albeit, imported, but $100 per100Ah cell local is reasonable price from a local supplier.

Once you have the cells it's an easy process, don't get confused, really it's not rocket science as long as you follow the process, which will follow, there's no point in putting the cart in front of the horse. 

mcgivor

One other thing, what equipment do you have for charging, it's important that it is programmable to correspond with the batteries needs.

Dave

mcgivor said:

One other thing, what equipment do you have for charging, it's important that it is programmable to correspond with the batteries needs.

Thanks for the distributor names, I contacted tAUK. I am curious how the Fortune 100 Ah battery is rated for 50% more life cycles, is smaller and lighter, and less expensive than the CALB 100 Ah battery with the same chemistry. That sounds too good to be true.

My controller is a Morningstar Tristar 60 MPPT which is programmable so it should work.

Thanks for your input.

mcgivor

Perhaps the cycle testing methods differ, one cycled to a deeper level who knows, as for weight and size  CALB do appear to have pretty thick cases, are they significantly different ? The cells I use were $56 per 100Ah, the price may have increased since, picture taken September 2018 after installation, Morningstar will work, they are an excellent product.with custom settings using MS view.

Battery_Man

@mcgivor
Dear, good to know calb battery works very well with your project. It seems that there is air conditioner to make good ambient temperature?
Stable favourable temperature will be much more helpful to maximum battery performance.