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Building a 72KwH battery system, help understanding these Li-ion modules.

You can always add more later comes with an asterisks yes? Isn't the limit to adding new cells to an existing group about around 2-years? Thank you all for the help, really appreciate this forum.

For these cells most off-grid applications are not particularly stressful compared to their 1C discharge and 0.5C charge limits. The cells in EACH one of the proposed 2P8S batteries are designed to handle 14kW continuous discharge and 7kW continuous charge. You will likely only use a small fraction of that on an average basis. There are many examples of packs that have lasted 8+ years with only minor degradation, so any arbitrary limit must come with caveats.

There are many who successfully operate banks constructed from different brands of batteries with different capacities. The key is to test the fully deployed system and confirm each battery is operating within specifications.
 
It sounds iike you're looking at exactly the batteries I recently built. I got 48 of the Eve 304 AH cells from Docan and made 3 x 24 volt 600 amp hour batteries out of them. Each battery is 16 cells, 2P8S, with one Overkill 8s BMS. They're all running in parallel, fed by 2 Midnite Classic 150's, each fed by a 4KW solar array.

They're working fantastic, couldn't be happier with the setup. With 3 batteries, each one never sees more than 70 amps charge or discharge current, and the Docan cells seem perfect, all the cells track each other within a few millivolts across the charge range.
 
Quick background: I live off-grid and am ready to replace my 12-year old Flooded Lead Acid batteries that our home/systems run on. I'm looking at buying 35 of these Samsung EV modules from BatteryHookup which would give me 72KwH of storage. They are offering me a bulk discount and free shipping which is making it more enticing. I understand my FLA batteries quite well, but I don't have the same depth of knowledge on Li-ion batteries to make an educated decision here, so I'm hoping folks here can give me feedback.

I'm not quite sure what cells they are used in these batteries, does anyone know? Does Samsung make good Li-ion cells that would be good for off-grid home use? At 35 modules I shouldn't have to work about pulling too many amps from these? My inverter is 5000VA but I rarely peak over 3000W.

These modules are 48V, but I asked and you can "cut the bus bar between the 7th and 8th cell" to make them 24V. My inverter is 24V and I would prefer not to replace it. If the only benefit to 48V is smaller wiring, fusing and BMS it will still be more affordable to pay extra for those things than to replace my inverter. Is there anything else that I'm not seeing that makes it a bad idea to make these modules 24V?

Anything else I might be missing? I'm aware of the basic for Lithium Ion...keeping them above freezing, risks of thermal runaway if they get to hot. What else should I know before I make the investment into these? Any help appreciated.
BatteryHookup is a very strange company, I would not trust them, they sell waste for recycling propose only, no guarantee, nothing. Very expensive.
 
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BatteryHookup is a very strange company, I would not trust them, they sell waste for recycling propose only, no guarantee, nothing. Very expensive.
I think they're a good company, they're not hiding the fact that batteries are used. For folks who know what their doing and how to work with cells I think they're great. That deal I linked specifically won't work for me and super appreciate the help of folks here to figure that out.
 
Also, I don't think anyone mentioned this. These are 12s, so they list it as 44.4v. If you would split that in half you'd have 22.2v as 6s. This may limit your ability to access all of the battery as most 48v or 24v inverters would shut off due to low voltage while potentially still having a decent amount of energy left.

It can work, you just have to plan for that. Typically, I think 13s is more common for liIon, 8s lifepo4 or 16s lifepo4 to get 24v or 48v is more common. I have seen inverters geared specifically for the slightly lower tesla modules. Some inverters can adjust the low-voltage where it shuts off, some can't.
 
I think they're a good company, they're not hiding the fact that batteries are used. For folks who know what their doing and how to work with cells I think they're great. That deal I linked specifically won't work for me and super appreciate the help of folks here to figure that out.
You will get many opinions on this forum to consider before making an informed choice. It is wise to do what you are doing right now...ask questions.

Just a couple of observations to add to the list:

There is nothing wrong with Battery Hookup. Like you said, they don't hide what they are doing. They provide a valuable service that keeps material out of landfills/hazardous waste sites, and in many cases allows people to build what they want. I do find it frustrating that they rarely answer their phone.

I wouldn't make the ASSUMPTION that keeping your 24v inverter is cheaper than changing it out for 48v. Keep on doing your research, and make a lit of all the components that you will need to have a properly constructed bank, including fuses, breakers, cabling, etc. Do it for 24v and for 48v. You may find that your assumption is incorrect. I have a crap load of both 24 and 48 volt modules, and recently did a quick and dirty comparison, and it was cheaper to go with 48v. Another thing to keep in mind is if you can actually get the components you want, with all the shortages, price gouging, etc.

It can be way harder to tap, and reconfigure modules than you might realize.

BMS'es are expensive, and time consuming to install.

Read up on technical papers on lithium chemistries, and you will find that there are advantages and disadvantages for each of the chemistries. Most people have jumped on the LifePO4 bandwagon, but there are many backup systems successfully using other chemistries too.

What is your time worth? There are a lot of very nice, modular units coming out now that are ready to go out of the box, and are very price competitive.

Those Samsung modules you originally considered are beautiful...and would likely make a very nice golf cart battery, EV conversion, or similar. I would not use them as you described in your original text.

Don't be in a hurry...keep looking and learning. Best of luck...
 
Quick background: I live off-grid and am ready to replace my 12-year old Flooded Lead Acid batteries that our home/systems run on.

Just wanted to say congrats on those lasting so long. What are you, some kind of FLA guru?

Back on topic...
 
I still need a BMS
You will need twice as many BMS's as you have modules. there is no easy way to parallel cell groups between modules from EVs.
I was considering using Tesla modules and that complexity tiered me toward LFP. In the long term the safety and affordability of LFP provided better value.
Most of my thoughts are already expressed above.
 
Typically reusing EV modules is more economical and practical if you get them with BMS boards on them. I also have 12s modules, but they are from the BMW i3 (also Samsung).
I use them with CAN bus, so every cel is monitored and the temperature sensors (a few in each module) are reused.
I bought a SimpBMS which talks on the CAN bus to these modules, telling them when to balance and so on. It also talks to my Victron system telling it how the battery is doing.

That is much better than having all these small modules without BMS.
For another project I am using different modules and will be adding a generic Chinese BMS on there. But then they are just two modules of 10kWh each, so it is just 2 BMSs. Not 35 like your case.

I am still using the 2016 bmw i3 modules and they work nicely and compact.
But if price difference is small, it would be better to buy new LFP.
 
Those are the cells I've been talking about. Note how 8 cells + a BMS is about $1300 :)

Sorta, but it's not recommended. You'd need to parallel sets of 8 and then series each group. Your system would be limited to about 5000W maximum current, and you would have NO redundancy.

I would likely consider 2P8S X 4
Can you help me out here again...I'm considering 48V now as it will save me a lot on hardware for my charge controller for the number of panels I want to add.

What battery configuration would you recommend for 48V? I already purchased 64 of the Eve batteries from doucan. Would I just do 2P16S x 2 or 16S4P? I know this is a religious debate. I'm would prefer to have better monitoring of each cell, so maybe 16S is the way to go?

I'm also sometimes confused on the order of P before S or S before P in: xPxS or xSxP, so I might have follow up questions
 
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The ones I linked are 48V, but I would be cutting the bus bars on them to make them 24V (for reasons I mentioned in my original post).

Yes, aware of the possibility of thermal runaway.
Thermal runaway in your application would be a non issue using a 5kva inverter, maxed out continually your draw on each cell would not even warm them, a thermal run away issue could come from temperature or over/under discharge tho
 
Ohhhhhkay. Yeah this is the information I needed. Doesn't seem wise to have 70BMS's!


This would require pulling and re-doing the existing spot welds? If so that's exactly what I was hoping to avoid...


Can you explain why that is? What specifically makes these geared for high-voltage? If my inverter supported ~40-50v wouldn't I just connect these all in parallel as they are? Appreciate your help, thank y
only issue with multiple bms's is cost as long as they are decent, if you go with parraleling cells you will need a bms that can balance your parallel groups and it would be advised to use something like "rec" bms with contactors.
 
if you go with parraleling cells you will need a bms that can balance your parallel groups.....
A BMS sees parallel cells as one cell. If you mean a BMS that handle the Amperage of a bunch of parallel cells then that could be an issue. I use an Orion BMS that does not have much of a balancing current so I disabled the balancing function and just use the Orion for cell and pack alarms. Instead I used a Heltec active balancer that can move up to one Amp from one cell to another. My pack is 3P16S of LF280 cells. Therefore one parallel group is three cells totaling 840 Amphours each. I parallel top balanced them but when I assembled the pack there was still some small imbalance near the top which the Heltec resolved in a few days of cycling them.
NOTE:
After posting the above and rereading the thread, I realize I am unclear what the final decision was regarding pack configuration. My comment is only applicable if the OP is paralleling the cells not paralleling various 24 volt packs.
 
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Thank you for the response, and good to know that just in general. An update on my project, I now have 64 EVE 280Ah LiFePO4 batteries I'm prepping to install! Not going the route I originally mentioned but thanks to all the advice here I feel very good about the new setup I have!
 
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