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Parallel Arrangement (Are 8 cells too many?)

Newman

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Apr 28, 2020
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Wyoming
This is my First attempt (Probably Second) at posting. I have watched numerous videos concerning various methods of hooking up LiFePO4 batteries. I have just purchased (4) of the below listed battery packs from Ebay. There are a total of 128 cells in my purchase. Each cell is 3.6 volts and 40Ah. I have a 48 volt system with a Magnum MS4448PAE inverter. My old AGM batteries did not survive the past Winter. They were 14 years old... I see in Will's video on top balancing that he hooks All of his batteries in Parallel, to do the balancing act. My Question is? Why not leave them that way? ( 8 cells in parallel in my case).. I would like to build my battery pack after bottom and top balancing, By hooking 8 cells in Parallel creating one battery (Set) of 3.6 volts and 320Ah. Then connecting 16 of these (Sets) in series to achieve my 48+ volt required battery pack. What problems do you foresee? I propose using heavier bus bar material.. I anticipate adding a BMS to the system, and it is my understanding I would be able to operate with ONE BMS that would monitor the 16 battery (Sets). Still studying the Overkill BMS and awaiting the release of the New Chargery with all of the upgrades that have been suggested. Thank you in advance for all of your expertise..

lithium ion battery cells 160ah LFP Etrust Brand (Solar Backup) | eBay
The system demonstration was operational only for a couple of months.
ebay.us
 
since there is no way to manage parallel cells, 2 is already too much from a certain point of view.
but 2 or 8, it does not really change the concept. Tesla batteries are parallelling a lot more.
just make sure each battery is fused
for example it is a strange idea to purchase 40A cells to put them in parallel , when you can purchase 280Ah cell, that is equivalent of 7 40Ah cells in parallel (and if you really need 8x40, 320Ah cells exist also)
 
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All 128 should be in parallel to balance every cell in the pack. Then rearrange them into your 48 volt pack of 8P16S. Eight cells is not too many.

I don't think you need to fuse every cell like Tesla does. LFP does not have the volatility of the NMC chemistry used in a Tesla. Are you going to be doing any drag racing with your pack? :) Stationary storage packs don't have the hugh Amp draws that EVs have.
 
just make sure each battery is fused
for example it is a strange idea to purchase 40A cells to put them in parallel , when you can purchase 280Ah cell, that is equivalent of 7 40Ah cells in parallel (and if you really need 8x40, 320Ah cells exist also)
Strange idea? As you mention,, Tesla does it successfully. How many pouch cells are in parallel in a 320 Ahr prismatic? Are they fused? There are a lot of ways to solve a problem. Currently in my Nissan Leaf pack I have 14 cells in parallel. For whatever "strange" reason Nissan modules are 2P2S. Their pack is 2P2S48S.
 
since there is no way to manage parallel cells, 2 is already too much from a certain point of view.
but 2 or 8, it does not really change the concept. Tesla batteries are parallelling a lot more.
just make sure each battery is fused
for example it is a strange idea to purchase 40A cells to put them in parallel , when you can purchase 280Ah cell, that is equivalent of 7 40Ah cells in parallel (and if you really need 8x40, 320Ah cells exist also)
Yes, The price was a big part of the attraction. About $15 for each cell. If individual cells begin to weaken over the years, I figures I could reconfigure the (Sets) to 7 cells. Thereby not having to discard an entire 320Ah unit. Regards, Martin
 
Every cylindrical pack is going to have a ton in parallel, normally about 200. My ups pack is 30p24s right now.

I think the only difficulty is in turning the corner correctly if you want to bring it back. So either don't or make sure you have lots of wires doing it.
 
Every cylindrical pack is going to have a ton in parallel, normally about 200. My ups pack is 30p24s right now.

I think the only difficulty is in turning the corner correctly if you want to bring it back. So either don't or make sure you have lots of wires doing it.
Thank you for the suggestion, although I am not entirely up to speed on a couple of the terms. i.e. "turning the corner correctly", and "having lots of wires doing it". I propose having (8) cells in parallel using the standard bus bar connectors for that Amperage, and then connecting the Neg. terminal of cell #1 to a Heavy Copper bus bar, and the Pos. terminal of cell #8 to another Heavy Copper bus bar. Each (Set) of 8 cells will be similarly connected to their respective (Pos. & Neg.) Heavy Copper bus bars, thereby placing all 16 (Sets) in series. I am open to suggestions as to how I should then connect these Heavy Copper bus bars to the 48 volt Inverter. Should I connect at a mid-point on each of the Heavy bus bars, or at opposite ends of the Heavy bus bars. In other words, take the Pos. connection from close to battery (Set) #1, and take the Neg. connection from close to battery (Set) #16? This may be confusing, I should probably draw a schematic, but it is getting late for this old man.. Regards, Martin
 
Thank you for the suggestion, although I am not entirely up to speed on a couple of the terms. i.e. "turning the corner correctly", and "having lots of wires doing it". I propose having (8) cells in parallel using the standard bus bar connectors for that Amperage, and then connecting the Neg. terminal of cell #1 to a Heavy Copper bus bar, and the Pos. terminal of cell #8 to another Heavy Copper bus bar. Each (Set) of 8 cells will be similarly connected to their respective (Pos. & Neg.) Heavy Copper bus bars, thereby placing all 16 (Sets) in series. I am open to suggestions as to how I should then connect these Heavy Copper bus bars to the 48 volt Inverter. Should I connect at a mid-point on each of the Heavy bus bars, or at opposite ends of the Heavy bus bars. In other words, take the Pos. connection from close to battery (Set) #1, and take the Neg. connection from close to battery (Set) #16? This may be confusing, I should probably draw a schematic, but it is getting late for this old man.. Regards, Martin
BELAY my Last.. (Old Navy term for-Ignore what I just said..) I was definitely in the Fog on my previous description last nite.. Regards, Martin
 
In the image on the first post it has the positive and negative on the right side and on the left a fancy connector. That connector turns the corner for that pack.

For wiring, whatever you've decided your need for bus bars, you want to continue to the inverter. So if your are 8p with 8 bus bars connecting each one, and they are 100a bus bars, then you might want 8 wires going back to the inverter, one at each end terminal.

That way any paralleling is only for balance, not for load, and the pack has no weak points.
 
For wiring, whatever you've decided your need for bus bars, you want to continue to the inverter. So if your are 8p with 8 bus bars connecting each one, and they are 100a bus bars, then you might want 8 wires going back to the inverter, one at each end terminal.
The pack in that picture is 8P4S. That means there would be a positive and negative going to the inverter and 5 balancing wires going to the BMS. I don't know how you come up with 8 wires. Each cell in the parallel group of 8 is going to measure exactly the same voltage as the next cell because the buss bar connects them. The BMS connects to the buss bars.
 
The pack in that picture is 8P4S. That means there would be a positive and negative going to the inverter and 5 balancing wires going to the BMS. I don't know how you come up with 8 wires. Each cell in the parallel group of 8 is going to measure exactly the same voltage as the next cell because the buss bar connects them. The BMS connects to the buss bars.
Sure about that to me it looks like 4p8s. But you are correct that the BMS will connect to the bus bars. And you will have 1 more lead than the series number
 
And to answer the question 8 is not too many. That being said The more cells in parallel the harder it is to find a bad cell if one goes bad. Personally I would do 2 sets of 4 in parallel. Which just makes it a little easier to keep things balanced.
 
On closer look, it is 4P8S. I did not see the break in the buss bars. My interpretation of that picture was influenced by the comment of @zorlig who referred to 8P and I was trying to clarify his comment about 8 wires. As you confirm, there only needs to be one wire to each buss bar and one to the negative terminal.
 
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8 cells in parallel was the number you gave in your post, not a reflection of the picture. One cell in parallel, one wire. 8 cells 8 wires. Just scale everything up together and you'll never have a problem!

Bms balance leads don't carry current so you don't have to scale those up.
 
8 cells in parallel was the number you gave in your post, not a reflection of the picture. One cell in parallel, one wire. 8 cells 8 wires. Just scale everything up together and you'll never have a problem!

Bms balance leads don't carry current so you don't have to scale those up.
Yes, I have purchased Four of the Battery Packs that are pictured above. If you can click on the above picture, and then click on the magnified picture again, you can scroll through 11 different close-up photos of how the cells are currently arranged. This is one of those enlarged pictures.

My intention is to make Two Larger battery packs that will have the same configuration as the one pictured below, but each will be constructed of (Sets) that have 8 paralleled cells instead of 4 as pictured. The Two Larger battery packs will then be connected in series to achieve the desired 48 volts. I would like to add new bus bar material on top of the existing bus bars thereby creating the (Sets) of 8 Paralleled cells. The Positive terminals are indicated by Orange stripe material. By adding an additional row of 4 (Sets) on both the top and bottom (of this picture), I can create this Larger battery pack. Do you see a problem with just using new bus bar material to make these connections? Hope I haven't made this too confusing, There are probably better ways to skin this cat..
1589576446540.png
 
Yes, I have purchased Four of the Battery Packs that are pictured above. If you can click on the above picture, and then click on the magnified picture again, you can scroll through 11 different close-up photos of how the cells are currently arranged. This is one of those enlarged pictures.

My intention is to make Two Larger battery packs that will have the same configuration as the one pictured below, but each will be constructed of (Sets) that have 8 paralleled cells instead of 4 as pictured. The Two Larger battery packs will then be connected in series to achieve the desired 48 volts. I would like to add new bus bar material on top of the existing bus bars thereby creating the (Sets) of 8 Paralleled cells. The Positive terminals are indicated by Orange stripe material. By adding an additional row of 4 (Sets) on both the top and bottom (of this picture), I can create this Larger battery pack. Do you see a problem with just using new bus bar material to make these connections? Hope I haven't made this too confusing, There are probably better ways to skin this cat..
View attachment 13255
 
Yes, I have purchased Four of the Battery Packs that are pictured above. If you can click on the above picture, and then click on the magnified picture again, you can scroll through 11 different close-up photos of how the cells are currently arranged. This is one of those enlarged pictures.

My intention is to make Two Larger battery packs that will have the same configuration as the one pictured below, but each will be constructed of (Sets) that have 8 paralleled cells instead of 4 as pictured. The Two Larger battery packs will then be connected in series to achieve the desired 48 volts. I would like to add new bus bar material on top of the existing bus bars thereby creating the (Sets) of 8 Paralleled cells. The Positive terminals are indicated by Orange stripe material. By adding an additional row of 4 (Sets) on both the top and bottom (of this picture), I can create this Larger battery pack. Do you see a problem with just using new bus bar material to make these connections? Hope I haven't made this too confusing, There are probably better ways to skin this cat..
View attachment 13255
 
Here is an actual Cut & Paste photo of the proposed 48 volt Battery Pack consisting of 128 cells arranged in (Sets) of 8 cells Paralled, and then those 16 (Sets) placed in Series. My graphics are a bit primitive, I had to make several copies of the above picture, then cut them into strips and then tape them into the proposed String. This configuration has 16 (Sets) of cells that could be monitored by one BMS, (Is that Correct?) I know that a parallel arrangement of 8 does not allow me to detect a weak or defective cell within a particular (SET), but my main concern is this off-grid system is in our remote cabin in Wyoming. I may not be there to monitor the system for several weeks at a time. In the event of some component failure in my Midnite Classic CC or in the Magnum MS4448PAE Inverter, I would like to have a BMS that could shut the system down 48 volt Battery Pack.jpgthus avoiding overcharge thus avoiding overcharge or discharge damage to my New Batteries.. Member zorlig had expressed concern about the difficulty of turning the corner correctly. I'm not sure if my proposal solves that concern. All comments will be appreciated, even if you say Wrong--Really Wrong.. Regards, Martin
 
In the image on the first post it has the positive and negative on the right side and on the left a fancy connector. That connector turns the corner for that pack.

For wiring, whatever you've decided your need for bus bars, you want to continue to the inverter. So if your are 8p with 8 bus bars connecting each one, and they are 100a bus bars, then you might want 8 wires going back to the inverter, one at each end terminal.

That way any paralleling is only for balance, not for load, and the pack has no weak points.
Thank you for your suggestion. I have added a new picture of the proposed arrangement. At the Mid-Point connection where I am turning the corner I will use a Heavy Copper bar, probably 1/4" thick and 2" wide. On the opposite end I am planning to use the same material to connect all of the 8 positive terminals, and likewise for the Negative terminals, and then connect those bars at their mid-point to a 4/0 welding cable for the short 3 ft. run to the Inverter.
 
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