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3P8S pack of 150ah Lishen cells

Leon

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Dec 15, 2019
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Can I get a sanity check here please?

I'm about to place an order for some cells to build a backup bank. I need 8S in order to work with an Electrodacus SBMS0. I've all but decided to go with 24 150ah Lishen cells via Michael Caro. These are pretty good $/kwh and are apparently more readily available than the larger cells. The obvious alternative, which happens to be marginally more costly per kwh at the moment would be a 1P8S pack of larger cells (lets ignore the much larger capacity of the 3P8S pack for the moment).

The only thing holding me back is the terminals. The tapped holes on the 280ah cells are notoriously weak and sometimes crooked. I am equipped to helicoil or otherwise repair but would prefer to avoid this. There has been some doubt expressed regarding the current-carrying capacity of the laser welded stud terminals, though these seem otherwise much easier to work with.

My logic is this: By going with a 3P8S, instead of 1P8S, the current flowing through any single terminal would be divided by 3. I would have to cop the extra work and complexity in handling three times the number of connections.

Let's say my peak sustained load is 3000W (it's probably more like half that). At 24V nominal, that would be 125A total, or about 42A through any one terminal. That seems pretty low given the cells can discharge continuously at 75A (O.5C). Spec sheet here: https://diysolarforum.com/resources/lishen-150ah-specification-sheet-w-photo-caro.177/
Picture of terminal attached (M6 on left, which is what I think I would be getting.)

Would you go with the 150s with welded studs or something like this: Vaircore 310ah

studs M8 and M6 2.jpg
 
I had no problems with the terminal threads on my EVE 280Ah cells. Some of the reported issues are due to people not realizing that the threads shouldn't be torqued more than 35 inch pounds. The cases where terminals aren't straight is a quality control issue with the supplier.

Every cell will see the same current. If you're drawing 125 amps, then every cell will see 125 amps. At lease on an 8s system. 3p8s, I'm not so sure about.

My preference is to create redundancy. That's why I went 4s2p. But you've pigeonholed yourself with the electrodacus, so you can't go that way.
 
the Electrodacus SBMS0 can do 12-volt or 24-volt.
any 3 cells connected in parallel will act as one cell.
the voltage will stay the same but the amperage adds up.
then when you connect the groups in series the voltage will add up.
so the correct way is to connect in Parallel 1st 3P; then connect the parallel groups of 3 cells in series to get a 25.6 volt battery 3P8S.

this is the low end of the charge. normally LiFePo4 cells are charged to 3.55 which is (3.55voltx8cells= 28.4 volts. i find that my 2 Electrodacus systems normally run at 27.2 volts a lot of the time. (3.4 volts per cell when charged by solar panels). your results may be different.
I have 2 16 cell (using 272Ah Lishen cells) 24-volt LiFePO4 batteries up and running. they are 2P8S configuration with the Electrodacus SBMS0 turning off the Electrodacus DSSR20 chargers at 3.55 volts.?
 
after working with the set screws (aka grub screws) M6 6mm if you can buy with the welded in place terminals of a larger size they will likely be better in the long haul.
I have not stripped any but you do have to be more careful with the M6 6mm diameter set screws.
 
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