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German Powerwall 280xLG 18650MJ1 7s40p+ 450Wp Balcony PV System and a small question
#11
(04-05-2019, 01:59 AM)Dallski Wrote: I don't know about crossflows, but I don't believe all cells will be contributing the same amount of current at any given voltage. With used cells from different brands, different IRs, different states of health, different chemistries, etc. every cell will be giving different amounts of current at different voltages. It's not a bad thing and I don't think it affects the life of a pack, it's just something to think about. For me, I've been paying a lot of attention lately to 3.6V cells vs. 3.7V. cells and trying to group them that way so they are all on the same discharge curve, but I don't know if it's that big of a deal with low current applications.

If the cells were being charged/discharged at max C, or even higher, that's when issues "could" arise. However, one thing is absolutely for certain, all cells will have the exact same voltage at any given moment for any cells that are connected in series. Sure some cells may not be able to output same current as another, but that makes no real difference in the whole pack. And if someone was designing a pack to output at 2A/cell or more, they should be using new cells to begin with as the application would require far more stability than what recycled cells can offer.

Now, because drbacke is using NEW cells, there's nothing to worry about any kind of oddities. They are new, so he could pull 2A/cell for a period of time and the packs should be able to handle it just fine. The LG MJ1 cells can do a 10A max discharge and 3.4A charge rates. But running at 40p with an estimated 30A max usage, he'll never hit the limits of the cells capabilities.
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#12
(04-05-2019, 02:21 AM)Geek Wrote: I wonder if there is a way to protect those cells that have had acid flux used on them. Even after they are cleaned if any remains. If you could stop air and moisture getting onto the surface, they wouldn't corrode. Maybe like brush on some paraffin wax or use some Lanox. Maybe someone has a better suggestion.

Personally, I would test if battery terminal protector effects the wrapper. If it doesn't, I'd use that. Given that they are new cells, and the pack is unlikely to require dismantling for service.

You are right. The acid flux contains F-SW21 which is "weak/limited corrosive", maybe this is actually a problem.
They sold it to me as electrical flux, so i didn't checked it further. My fault.
Which material is the cell wall build of?
I'm not sure if this is a real problem or can be dangerous, maybe someone else has more information?

Maybe I can use flux cleaner and the a protective resin afterwards. What about the cleaner, can it damage the plastics of the cell?
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#13
I only mentioned it because drbacke was considering adding used cells to the pack that contained the new cells and was worried about the used ones negatively affecting the new ones.

And yes, the only thing all cells share in a parallel pack is voltage.
Formerly known as Dallski
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#14
Ok I got some more Information about the "flux problem":
It seems to be Ammonium chloride which is not problematic at 20°C with most stainless steels (the cell walls are of stainless steel, but I dont know which steel exactly). It also contains little amount of Zinc chloride, which is lightly corrosive to stainless steel Sad . I will clean it up with a flux cleaning spray and afterwards put a protective resin on top.

THX for the hint, these are the little things that can get dangerous with time.
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#15
Wow, even the flux is "weak", just happens to be strong against exactly what you're working with. that sux. At least you caught it before too much damage was done. You may have even caught it before any thing happened. Just check the metal really closely and see if has any etching. But putting a protective layer over it after cleaning it off definitely won't hurt, if anything it'll help protect against humidity.
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Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#16
(04-05-2019, 12:17 PM)Korishan Wrote: Wow, even the flux is "weak", just happens to be strong against exactly what you're working with. that sux.  At least you caught it before too much damage was done. You may have even caught it before any thing happened. Just check the metal really closely and see if has any etching. But putting a protective layer over it after cleaning it off definitely won't hurt, if anything it'll help protect against humidity.

I will disassemble the system and try to get the packs clean and hope its possible without complete disassembling each battery Confused
If I'm finished, I will post you the result. THX a lot
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#17
(04-05-2019, 04:48 AM)drbacke Wrote:
(04-05-2019, 02:21 AM)Geek Wrote: I wonder if there is a way to protect those cells that have had acid flux used on them. Even after they are cleaned if any remains. If you could stop air and moisture getting onto the surface, they wouldn't corrode. Maybe like brush on some paraffin wax or use some Lanox. Maybe someone has a better suggestion.

Personally, I would test if battery terminal protector effects the wrapper. If it doesn't, I'd use that. Given that they are new cells, and the pack is unlikely to require dismantling for service.

You are right. The acid flux contains F-SW21 which is "weak/limited corrosive", maybe this is actually a problem.
They sold it to me as electrical flux, so i didn't checked it further. My fault.
Which material is the cell wall build of?
I'm not sure if this is a real problem or can be dangerous, maybe someone else has more information?

Maybe I can use flux cleaner and the a protective resin afterwards. What about the cleaner, can it damage the plastics of the cell?

F-SW21 based flux can be washed off with alcohol. I would opt for isopropyl, as metholated spirits can leave a residue.
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#18
Wow that was a *!"$= bunch of work. I cleaned every battery twice (mechanical and chemical) and had to rewrap them all.
But now I have the most colourfull Powerwall in the world i guess ^^
If you are interested in the process of 2 days stupid cleaning batteries:


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#19
What do you power with your Powerwall? How do you distribute power? Could you give me a small summary?
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#20
(04-07-2019, 10:27 AM)Maniac_Powerwall Wrote: What do you power with your Powerwall? How do you distribute power? Could you give me a small summary?

Air Conditioner (onlny in summer, not necessary here in april Wink ), TV, Light, fridge, depends on the battery state... But in the moment I dont't have to think about it, there is enough energy.
It's not connected to the grid. I build up an own electrical wire network with some extension cables, simple and effective.
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