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Home Powerwall with PCB V1.3
#11
Not sure I understand the situation fully but let me try.
Jehu boards...look like 8s boards and stacks of those running in parallel?
Okay so you also have an 8s active balancer for each stack? This covers both over and under also?
In this case I am not seeing any reason for a bms.

On the other hand if you are dumping a solar load and not actively managing each cell and you also did not pack cells matching completely across all cells or have a cell that goes out. I can assure you there will be a pack that does not match.
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#12
(01-16-2019, 04:51 PM)TrustyFly Wrote: Not sure I understand the situation fully but let me try.
Jehu boards...look like 8s boards and stacks of those running in parallel?
Okay so you also have an 8s active balancer for each stack? This covers both over and under also?
In this case I am not seeing any reason for a bms.

On the other hand if you are dumping a solar load and not actively managing each cell and you also did not pack cells matching completely across all cells or have a cell that goes out. I can assure you there will be a pack that does not match.

The boards are 7s configuration each. The pack +/- are connected in parallel with other boards in a stack, as are individual cells (balance leads). The BMS would protect in the somewhat unlikely case that an imbalance larger than the 1A balance current would be able to handle would cause some cell in the pack to exceed 4.2V or drop below 2.5V while the pack voltage was still within the pack level limits set by the charge controller/load.
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#13
Yeah I am not an expert but I do not think I understand why they would not get out of balance. Let me try drawing my idea of what would happen:
Pack 1 ++++++++ 29.6v
Pack 2 ++++++++ 29.6v
Pack 3 ++++++++ 29.6v
Pack 4 ++++++++ 29.6v
Pack 5 ++++++++ 29.6v
Pack 6 ++++++++ 29.6v
Pack 7 ++++++++ 29.6v
Pack 8 ++++++++ 29.6v
They are all balanced and everything is good but what happens if a cell goes bad.
Pack 8 ++++++-+ 25.9v
This will balance them all out to 25.9v and in a safe way to the other packs. But when you charge to 4.2v per cell or 33.6 each cell in pack 8 will have 4.8v per cell.

Maybe I am not understanding completely the setup.
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#14
(01-16-2019, 07:08 PM)TrustyFly Wrote: Yeah I am not an expert but I do not think I understand why they would not get out of balance. Let me try drawing my idea of what would happen:
Pack 1 ++++++++ 29.6v
Pack 2 ++++++++ 29.6v
Pack 3 ++++++++ 29.6v
Pack 4 ++++++++ 29.6v
Pack 5 ++++++++ 29.6v
Pack 6 ++++++++ 29.6v
Pack 7 ++++++++ 29.6v
Pack 8 ++++++++ 29.6v
They are all balanced and everything is good but what happens if a cell goes bad.
Pack 8 ++++++-+ 25.9v
This will balance them all out to 25.9v and in a safe way to the other packs. But when you charge to 4.2v per cell or 33.6 each cell in pack 8 will have 4.8v per cell.

Maybe I am not understanding completely the setup.

If any cell goes short in a pack, it should blow the cell level fuse for the bad cell and likely the board level fuse for that board from the sudden inrush of current. So that last scenario shouldn't happen.
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#15
My configuration is 14s! so 2 packs in series with 50,4V!! all 10 packs ( 5 in series and 2 parallel ) are connected to the same one 14s balancer with extern voltage-display for every seriell cell!!
if on cell going bad, then the balancer will push the other series cells more than the orher!
i have all about 70 cells parallel on ervery seriell so if one cell go bad it will not be a drama!
the other one is that every pcb bord is protected with 5 amp fuse!!
next month i will be complete with all connection and the we will se how it works?

(01-16-2019, 07:08 PM)TrustyFly Wrote: Yeah I am not an expert but I do not think I understand why they would not get out of balance. Let me try drawing my idea of what would happen:
Pack 1 ++++++++ 29.6v
Pack 2 ++++++++ 29.6v
Pack 3 ++++++++ 29.6v
Pack 4 ++++++++ 29.6v
Pack 5 ++++++++ 29.6v
Pack 6 ++++++++ 29.6v
Pack 7 ++++++++ 29.6v
Pack 8 ++++++++ 29.6v
They are all balanced and everything is good but what happens if a cell goes bad.
Pack 8 ++++++-+ 25.9v
This will balance them all out to 25.9v and in a safe way to the other packs. But when you charge to 4.2v per cell or 33.6 each cell in pack 8 will have 4.8v per cell.

Maybe I am not understanding completely the setup.

hi
yes i have 10 packs!! 2 in series also 5 packs with max 58,8v but every pack is an 14s14p configuration! so 14 cells should be go bad if this scenario would happen!!
i build ebike packs for over 5 years so a little bit knowlede i have in building this packs!
that is not other as a powerwall with 14s70p configuration!!
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#16
love the pips & the way they are housed - can't say i'm a fan of the cell pcbs - but watching closely as i bet someone soon proves me wrong and makes me like the idea for real powerwalls
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#17
So my small powerwall ist firstly ready to go!
After a few test with the PCB‘s i had a bad feeling with it to use it for a big powerwall for my house!! So i changed the idea for new LifePo4 Cells made in germany!
They are big cells with each 45Ah!!
My configuration now is only 16S2P but with more money i will do it bigger?
First test with on cell were great! i take over 120A ( nearly 3C ) and voltage drop only 50mV!!





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#18
Dont forget bms Wink you need individual voltage monitoring for the protection Wink Good works !
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#19
thank you!
now i have 16 deligreen actice balancer and viktron bmv for over-under volt protection!
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