How should I sort the cells?

Think of it this way. You have 3 fuel tanks. One is 100Gallons, another at 200gallons and a third at 500gallons. All the tanks are the exact same size diameter, just different hieghts.
All have the same size pipe/valve coming out. If you open all of them at once, they will all flow out of the tanks at different rates because the pressure is different. So the tank with 500gallons will be pushing harder (higher amps)
Now, when we go to refill them, you fill from the top of the tanks. The 100 gallon tank will up faster than the others, and the 200 gallon next. Just because they are full, doesn't mean there isn't pressure from the incoming line being applied to them. So, the 100 gallon tank is starting to bulge from the pressure even though it's full. Same when the 200 gallon tank gets full. It won't stop till the 300 gallon tank has reached peak.
In practical application, this would cause the lower capacity cells to raise in voltage until charging is completed. Then they would start to slowly lower in voltage (un-swell) as they balance with each other.

This is why you don't want to mix them to far apart. Yes, they will work. But you are stressing the lower capacity cells. Just because a cell is full by our standards, doesn't mean it won't keep excepting current till one of two things happen: current stops flowing, or the cell fails.

Now, if I am wrong here, please let the big dawgs of experience speak up. But this is how I understand it. And I won't be mixing too large of range together.
Altho, I do understand that the PackBuilder will use a range of capacities to build the pack. Just personally I see an issue with it. If anyone could show me scientifically why/how this is ok with large ranges, then I'll accept it.

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spinningmagnets said:

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A common pack build might use a style of nickel bus that is shaped like a ladder, and it accomplishes the series and parallel connections at the same time with a single layer of nickel sheet.

Click to expand...

I'm thinking about building a DIY 10S6P battery pack using new Samsung 29E cells bought with Z-solder tabs already spotwelded on them (as I don't own a spotwelder myself). In another thread, Hillhater pretty much convinced me to avoid bolts/nuts connections so I'm now considering soldering the tabs together to form series connections first, and then add parallel connections later on. The solder tabs are 8mm wide and 0.15mm think (30mm long but I will shorten these). The idea is to drill a hole in the solder tabs where the cells would be connected together, stick a copper nail (orange) in that hole and then solder each tab to that copper nail. Finally the parallel connection would be added on top (grey), as on the following figure:



The copper nail may not be needed but I was thinking it would add some strength to the soldered connection, slightly lower resistance too but most importantly would make it easier to solder the tabs together without transferring too much heat to the cells. The whole pack would look like this, with parallel connection (light grey) made using Nickel strips (maybe 6mm wide, 0.15mm thick):



Yellow dots show the locations of the soldered connections with the Copper nails etc. The battery positive and negative terminals would use either a copper strip with tabs folded over it and soldered to it again using a copper nail or I may also directly solder a thick cable to each battery tabs. I didn't figure that out yet. A BMS would be added at the end.

I intend to draw max 20A from this pack so that's about 3.4A per cell. I guess that series connections made out of two nickel tabs one on top of the other over probably half of the connection's length should be enough to handle that but I'd like to be safe and have some room. Do you think that build would be adequate? Do you see a problem with such layout?

Alternatively I could also use copper strips (instead of nickel) to build the parallel connections. I understand that copper would be most useful for series connections and not parallel ones but I'm kind of constrained by using nickel for the series since these would be formed by the tabs. However if I sandwich a copper strip for parallel connection in-between the two tabs, the series connection would look like this:



So the series connection would also benefit from a little bit of added copper, which should help lower the resistance too. Is that worth it for you?

I'm thinking about building a DIY 10S6P battery pack using new Samsung 29E cells bought with Z-solder tabs already spotwelded on them (as I don't own a spotwelder myself). In another thread, Hillhater pretty much convinced me to avoid bolts/nuts connections so I'm now considering soldering the tabs together to form series connections first, and then add parallel connections later on. The solder tabs are 8mm wide and 0.15mm think (30mm long but I will shorten these). The idea is to drill a hole in the solder tabs where the cells would be connected together, stick a copper nail (orange) in that hole and then solder each tab to that copper nail. Finally the parallel connection would be added on top (grey), as on the following figure:The copper nail may not be needed but I was thinking it would add some strength to the soldered connection, slightly lower resistance too but most importantly would make it easier to solder the tabs together without transferring too much heat to the cells. The whole pack would look like this, with parallel connection (light grey) made using Nickel strips (maybe 6mm wide, 0.15mm thick):Yellow dots show the locations of the soldered connections with the Copper nails etc. The battery positive and negative terminals would use either a copper strip with tabs folded over it and soldered to it again using a copper nail or I may also directly solder a thick cable to each battery tabs. I didn't figure that out yet. A BMS would be added at the end.I intend to draw max 20A from this pack so that's about 3.4A per cell. I guess that series connections made out of two nickel tabs one on top of the other over probably half of the connection's length should be enough to handle that but I'd like to be safe and have some room. Do you think that build would be adequate? Do you see a problem with such layout?Alternatively I could also use copper strips (instead of nickel) to build the parallel connections. I understand that copper would be most useful for series connections and not parallel ones but I'm kind of constrained by using nickel for the series since these would be formed by the tabs. However if I sandwich a copper strip for parallel connection in-between the two tabs, the series connection would look like this:So the series connection would also benefit from a little bit of added copper, which should help lower the resistance too. Is that worth it for you?

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