need help with BMS for 48V 200Ah LiFePO4 battery bank

Hi,

I am new and I need some help. This is not a solar project but will also at some point will need help for my solar too. I have a lead acid small EV and need to upgrade to lithium. After looking at the videos and doing some research I have found that using 3.2v 100Ah sinopoly is the best bet, costs cheaper too. So I will need 16 of them in series to make 48v and 2 of these blocks in parallel to make 200Ah. But I recently saw you have to connect first in parallel and then in series so does that mean I add 2 batteries in parallel and 16 of these blocks in series? why is that? Also I saw that you only need 1 bms in this case. I need some recommendation on which BMS to buy so the max current it can draw while using the ev is 350A. Can the bms also monitor all 32 cells or just 16 in this case?

Thank you all for your help.
Chandra

If you put 16 cells in series, you need one 16s BMS. If you put 2 cells in parallel, it is like 1 cell. So if you want 100ah with 100ah cells, you use one cell (per "cell"). If you want 200ah you will need 2x100ah cells per "cell", 300ah=3x100ah per cell. Then series your cell groups to get your voltage to your target voltage, then get a BMS for that number of cells. This is normally the best solution. The other option would be to build 2, 100ah 48v batteries with a 16s BMS for each one and then put them in parallel. There might be cases where this would make sense but you would normally need a specific reason like, "I can use half of it at a time"....for some reason, like carrying it off for use in a portable system.

I can't recommend a specific model but Will has many videos about BMS. Keep watching and you will get more info for a good decision.

Thanks. I have watched the videos and havent found a bms that is capable of handling 400A peak current. All of them seems small ones.

Take a look at the Chargery BMS16T with a 600A shunt.

maharzan said:

Thanks. I have watched the videos and havent found a bms that is capable of handling 400A peak current. All of them seems small ones.

Click to expand...

Did you see the videos about using a BMS to control a large relay?

Well, I'll take you on a wee side trip. You say 100AH cells are cheaper, see below.

16 cells in series will give you 48V/XXXAH depending on the cells you get. That would need a 16S BMS to manage each cell. The chargery BMS is also a balancer which can balance, while charging, discharging or at rest (storage mode when no amps are drawn) The BMS16T would suit this application.

Once you start to figure in sizing (and DO take measurements ! , you'd feel pretty dumb if you made packs that would not fit the space you have) and then figure in weight and how to distribute it you may find t easier to use different cells. I will point out the LFP does not care if it's upright or sideways but Never upside down ! Fortunately that allows for some more configuration options for fitting batteries into odd spaces.

Avoid series / parallel packs. Shown below is my 24v/350AH 16 cell pack from Shunbin. Note how the cells are paired and makes it into an 8S pack. This lacks fine management of each cell. This is NOT optimal, I kept it, in that format because that's how it s bundled up even after gutting the crap out and rebuilding the pack. This pack is under scrutiny & first sign of trouble it will change format into a pair of 24v/175AH 8S packs. BTW: That Shunbin mess cost $3K USD and another $400 to correct, with new wiring, busbars & BMS that replaced the "junk" they provided in the prebuilt pack.
The Shunbin 24V - 16 cell pack configured as 8S


Regular Pack with cells in series:


Below are 200AH CATL Cells for $74USD each.

Below 280AH Cells for $85 USD (I just ordered 16)

Thank you everyone.

Please let me know how good the batteries are from alibaba orders.

coming back to this (as i am looking to build a 48v bank with 16 cells)
Would you not build 4 12v banks with their own BMS and then connect them in series to make the 48v bank.
giving individual cell management? and flexibility for later cell replacement or additional banks ?
Seems 12v banks has flexibility (space, airflow etc) but at the cost of additional BMS... or am i missing something

TLJester said:

coming back to this (as i am looking to build a 48v bank with 16 cells)
Would you not build 4 12v banks with their own BMS and then connect them in series to make the 48v bank.
giving individual cell management? and flexibility for later cell replacement or additional banks ?
Seems 12v banks has flexibility (space, airflow etc) but at the cost of additional BMS... or am i missing something

Click to expand...

If I was to build a 48v battery, my preference would be to make it 16s with a single BMS made for a 16s battery. A 16s battery is less complicated, less wiring, less cost, less work.

TLJester said:

coming back to this (as i am looking to build a 48v bank with 16 cells)
Would you not build 4 12v banks with their own BMS and then connect them in series to make the 48v bank.
giving individual cell management? and flexibility for later cell replacement or additional banks ?
Seems 12v banks has flexibility (space, airflow etc) but at the cost of additional BMS... or am i missing something

Click to expand...

Only *some* BMS will support serial connections, and then they usually limit you to two (although maybe more). Once a single battery is full, it stops all the others in the string from charging, so you'd better make darn sure all those packs are the same capacity (not easy to do with commodity cells). The same thing on discharge, the battery pack with the least capacity will cut off discharge first. Better just one BMS, and only one capacity and one high voltage cell disconnect and one low voltage cell disconnect to worry about. Everything works much better if the cells are matched, but once again, limited by the capacity of your cell with the lowest amp hour.

With 4 in series, you have 4 times as many things to go wrong, is the short summary (as long as the BMS will support 4 in series).
A common cheap (not really) high capacity BMS is Daly, in talking to them, they say their 12 volt and 4 cell BMS does NOT support series connection. I'm pretty sure Overkill will work in that manner, but it may not be supported by the actual manufacturer, and is likely discouraged by Overkill (I don't know, but if I was him, I'd discourage it). Just buy an 8 or 16 cell BMS to begin with, if you are planning on increasing to 24 or 48 volts in the future, you will need to buy a new inverter anyway, just plan on buying a new BMS (I won't even go into problems with mixing used cells with new cells).

maharzan said:

Thank you everyone.

Please let me know how good the batteries are from alibaba orders.

Click to expand...

My order of 16 commodity cells, 280ah Eve cells, the lowest capacity cell measured 270ah, the highest 281ah. The majority are in the 275-280ah range. You can easily assemble and run a 250ah battery. At approximately $100 per cell (mine was $1620 total including credit card fees and shipping for 16 cells) this is a great value. I'm hearing (but have no personal experience) that Lishen 272ah cells are measuring about the same, but for slightly less money. Currently if I were to order again, I'd buy the Lishen cells since they perform almost identically, and are slightly cheaper.

Despite being labeled and sold as "grade A" cells, at these prices they are NOT grade A. Some companies are now saying they can get and sell true grade A cells, but unless each cell is accompanied by a testing report (should be around 285 amp hours or above), it is not really grade A. These would (or should) cost about 20% or more above commodity cells. If they are real manufacturer grade A cells, likely over the lifespan of the battery (about 10 years) you might break even.

To handle the kind of current the OP is asking for, you may need to parallel four 100 amp BMS units. This is not as crazy as it sounds. They may not perfectly share the current, so it won't take 400 amps, but 200 to 300 should be fine for a long time. If any one BMS does disconnect due to over current, the current on the others will increase and they should all trip out fairly quick, so that protection still works. If any cell goes too low or too high on volts, it may not be sensed at exactly by all of the BMS units, so again, the current on the ones that don't shut off will increase. That could trip on current, and if the current is low, it will stay working until the balance is error is enough to trip the other BMS units. A side benefit is you get 4 times the balance current. The cheap ones only have 30 ma of balance current, now you have 120 ma. There is a you tube thread about building a home powerwall, and he uses a lot of small BMS units spaced all through his bank of paralleled 18650 cells. I thought about going this way, but for my system I ended up going to one 200 amp rated smart BMS. My max current should never exceed 140 amps. For 300, this won't cut it.