10kWh LifePO4 DIY Battery Addition..... Here is my write up.

That seems to be just the solis as only reports I have seen. Since moving to sofar hybrid mine works flawlessly with Seplos. Reaches 100% without any errors and ready to discharge straight away or if not sits idle until needed.

So is it -dare I say - plug and play now with a new seplos bms and a 16s2p setup of catl cells

What do you mean by "apply the parameters.xml to match your cells", can you elaborate?

Sorry for the questions, I am just about to buy a few hundred AH of catl cells and the seplos BMS and want to make sure I can make it work with my solis.

can you charge one of these 10kwh batteries in 3 hours without damaging the battery (beyond what is normal charge discharge)?

2 living here, wfh, oil, we only use about 2600kwh PA

Looking at the price on the previous page for a DIY 15kwh battery and pinergys 7c between 2am and 5am, pay for a 10kwh battery in a couple of years even without solar. We went over 10kwh a day 23 times last year.

Does that sound feasible?

I have done the firmware update of my Seplos as above. It has made a difference I think at discharging as the battery goes below 20%. However I am getting an error code on my 6kw Solis - 1052 OV-ILLC when the Solis turns off charging at 100% which requires restarting the Solis. I am thinking that I need to change a few settings on the Solis so it goes into float at a voltage lower that the Seplos cut off. Any advice would be appreciated. Not sure if this should be in the Solis or Seplos threads.

So I'm toying with the idea of doing a DIY build to add to my existing 8.2Kwhr Givenergy battery. I'm not too worried about the tech side of things, such as building a box, BMS hookups, balancing, etc all that is fine and plenty of research material out there, or wise people on this very forum to help there if needed.

What does make me stop and pause though is the whole cell procurement. Compared to Amazon it's the wild west on Alibaba if you ask me! :-) Has been for a decade or more and I generally avoid alibaba where I can. Yeah, yeah.....I know 99% of the time if you open a dispute you'll get your money back, but it's a "faff on" that you could just do without.

What's the general consensus on the "best" battery store to go with? Looking for 16x 300-310aH cells but would also consider 280aH if they were reliable. Happy to spend a little more if they are reliable cell and don't **** themselves when you pull 50-100 amps out of it (voltage dropping like a brick etc)

Pwod on Aliexpress, Docan on Alibaba, Nkon.nl and Fogstar in the UK

Please do. I also am tending towards nkon.nl site. 30-40% more expensive than the others, but it if helps reduce cell variability in performance, that's money well spend. I'd be ok if the other sites just called a spade a spade. i.e. here's some 280ah batteries and they are only 220ah but the price is excellent. At least then you know, but it's the one cell in 16 that buggers you.

Did you go for the grade a/grade b cells ?

I’m also very much interested in how the Nkon.nl cells work out for you too please. I’d love to make one for my folks. I‘d rather do it once, ‘set and forgot’ and it just works. I personally don’t want a ‘hobby’ that keeps breaking or getting into debate with some Chinese company of cell capacity. It’s hobby enough for me to learn it once only. And then start to save money the next day and forever more.

Not knocking those who buy direct from China. They are likely more aware of the DIY setup than me. 

First off, I presume you tested to manufacturer's spec at the appropriate discharge current and with very thick, short, low resistance cables and all the way down from 3.65V to 2.5V? (I never bothered to capacity test my cells myself - I'm too lazy and it would take too long and it would cost me money if the system was off line or had lowered capacity)

And I don't get the maths here? Did you not get any refund for the OYear cells that were below 150Ah? If you did, you need to deduct that from the total money you spent. I have had numerous disputes with AliExpress sellers and AliExpress has ruled in my favour and given me a refund every single time.

So that left you with the extra cells you ordered from PWOD at a 150Ah battery then, not 120Ah?

Also - this is beside the point a bit - I am always a strong advocate in getting the most bang for your buck. I always advise people to get the cheapest PV panels as in EUR per watt. But in this case I don't mind spending a bit of extra to get the extremely sturdy and safe CALB type cells rather than the aluminium EVE type cells that will bloat, even if compressed

I got PWOD cells that I am very very happy with. They tested 238ah/280ah. Failed with my dispute for a partial refund as they said my tester wasn’t the correct one.

I plan to get my second 16 at the end of the year. Still not decided who I go with and definitely won’t rule out PWOD. As I have said on here before, I wish the Chinese sellers would be upfront with the specs as the value is excellent. I paid 1950e and I see the price is still the same.

I was only starting out when I got the cells from OYear so missed the dispute window, capacity tester and had some cells down as low as 114. Did the full range test at 10a with very short cables.... When I started running the pack at 120 after a few weeks I ended up with two cells voltage swinging massively vs current so replaced the 4 worst ones with the PWOD 4. Still running the pack at 120 as some of the original Oyear cells will only support that, Seplos jumping frrom 25% capacity to 15%, or 85% to 100% etc unless SOC down at 120ah.

That's a great video from Andy. I like his work, very entertaining and always informative. I'd be in the same boat with respects to capacity. 270-275ah out of 280ah cell. Yeah, come on..... it doesn't really matter. 260ah similarly....but if you start getting into the 240's or 220's, or lower.... then your not really getting what you paid for. And while Andy didn't come across any/much deviation, empirical evidence from this thread says that it does happen. Natrually I can't speak 1st hand here, but knowing China.....lots of shenanigans goes on there :-)

What would more interest me/worry me is the voltage of the cells under duress (load) rather than the capacity. Take this video from Sun Fun Kits (who Andy likes and endorses btw and how I found them)

(328) The Final Word On Grade B - Lifepo4 cells Grade A vs Grade B - SFK - YouTube

So drawing 50-60amps (250-300w) per cell isn't a crazy test either. You'd expect/hope that most of them could do that. The problem is if you have an aggressive BMS if your pack voltage dropped you could get cut offs, even if the capacity was generally ok at lower draw downs.

It's a tough one. There seems to be a lot of differencing of opinions out there. Hard to know for sure and 1-2 dodgy cells could wreck your head.

That's not to endorse the buying of Grade A's over Grade B's. I reckon dodgy cells happen everywhere.

Not sure if you watched the video as it was pretty long, but that was sort of the whole point. He was testing cells in there that when he was drawing 60A he was barely seeing a flicker on the voltage. 0.05v drop in voltage that sort of range when drawing 60A. Good solid cells. Then other cells where he was seeing it go from 3.3v -> 2.65V drawing the same current. Crap "B grade junk" I think he called it. The reason why 60A is a good test, is that you could regularly see that kind of current from a battery via a ME3000 drawing 3kw to satisfy a kettle and house load etc. so it's not a useless test.

Now if you had a BMS seeing a pack voltage drop of that significance, you could see it cutting off the battery, even though you have substantial capacity left. It's a hard one to know. I do think that Off Grid Garage is right, really in terms of capacity I'd say they are all much to a muchness barring the odd dodgy supplier taking cells which may have already had 4000-5000 cycles on them and floggin them as new. Hopefully these shisters are few and far between, but we all know they're out there. :-(

I do like Andy's final thoughts, "We want people to use batteries filling them with solar and good energy and just USING them". Like that kind of positive vibe.