My First 48V 6.5KWh Li-Ion Powerwall 🥰

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italianuser

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Feb 25, 2020
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Ok, time has come☺️ I'll need your help, you better know!
Having bought solar panels and offgrid inverter now it's time for the battery pack. How I said (thinking out loud, actually) in other threads I was going to get flooded AGM batteries... but I changed my mind, mainly because of the difficulty to expand a 48V lead-acid battery storage. So, cell harvesting has started, I had a bag of used notebook batteries.

Harvesting results until now are:
  • 78 cells tested and ok (after two weeks settlement), voltage over 4V;
  • 32 cell in test now;
  • 54 to test (about 70% should be good);
  • 144 cells to pull out of notebook batteries (about 70% should be good);
  • 61 discarded (49 dead cells, 6 under 80% capacity, 6 heaters).
I should end up with about 240+ cells of different capacities: i suppose 40% 2100-2200mAh; 40% 1600-1800mAh; 15% 2500-2600mAh; 5% other. And buy refurbished cells searching for a decent quality

harvesting.jpg

Setup: Most probably I'll go for a 2200mAh cell setup. My choice is 14S20P packs, each single module will be nominal 51.8V, 44Ah 2.28KWh, 280 cells, stackable. Holders 4x5 (didn't go deep on this). Cells individually fused. Busbar size (TBD).

Goal: is to have 3 modules ready for this summer (I'm slow, I know, I work two jobs + a loved wife LOL). I was thinking of using spot welder for fuses (I've seen it done real fast) but actually soldering looks a lot better to me.

Advise needed: BMS, I'd avoid cheap ones and expensive ones. Please feed me some info of what's important in BMS choice and on what's to avoid when choosing BMS.

[updates coming]:giggle:
 
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floydR

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What would be the most amps you intend on pulling. 100amps? not sure about now but it used to be taking the amp rating of most chinese Bms's and divide by 2 for usable amps too long near the top amps would damage them. so you are probably looking at a 200-250amp bms. Now if you use a bms that uses a relay (chargery up to 600A https://www.aliexpress.com/item/400...68#1000022185#1000066058#0_668#3468#15617#802 , Tiny bms 750A https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36 , and others There have been more out lately that support a relay) such as this one https://www.aliexpress.com/item/400...earchweb0_0,searchweb201602_,searchweb201603_ . I am leaving out the expensive bms's Batrium, REC, EmusBms.
Charging amps many mosfet based bmses have a 50A max charge rate. Relay based bms's don't have that limit so can charge at much higher A.
Upper and lower Voltages per cell should be settable.
Temperature settings upper temp(discharge) and lower temp (charging).
Good apps both for phone/tablet and pc. not sure if chargery has an app for pc or phone does have an external display that is used for setting it up.
Over current I know I am forgetting some things.
later floyd
 

italianuser

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Feb 25, 2020
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Those models look good, I saved them and will go and see specs (y)

Average load is 1.2-1.5KW. Maximum load won't exceed 3.3KW (I will interrupt line for loads>3.3KW for more than 5-10 seconds). Inverter's efficiency is "93% peak", let's say 90% (could be even less, I don't really know).

So load on battery pack should be maximum 63A + 10% for the inverter, total load 69.3A @51.8V (I don't know if BMS makers calculate amps on nominal 48V, I calculated using nominal volts of a 14S).

Tell me if I'm getting this right: is a BMS is mounted on each 14S20P 44Ah battery module? It does make sense to me for a right level of granularity in controlling charge/dishcharge. If I mount three 14S20P modules I would have three BMSs which divide current:unsure:

[UPDATE: bought my first 400x 2200mAh cells 90-100% capacity]
 

floydR

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I would use one bms for everything. Might have a spare bms on hand. If the battery packs start out well balanced They should stay well balanced for quite some time. Note that the links besides the one for the Tiny Bms were from searches prices vary quite alot on alliexpress.
Also you want a bms able to handle the full load. For a 69A loadmany of the mosfet based bms's would work. Daly, Ant, JBD, are a few of the ones i am familiar with. A 150A bms might work for you.
later floyd
 

italianuser

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Feb 25, 2020
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[Update 16 May 2021]
I'd like to have everthing setup before July/August , I'm waiting for all pieces to arrive from around the world and I have a question about mixed cell modules setup.

So while my current status is:
- [ORDERED] 400 cells from Holland (...sigh! sorry to say but he's not a serious business man IMHO carefull to customers requests); maybe they will arrive this month, if not I'll have to buy a stock of notebook batteries, I found them for 2€ each;
- [ORDERED] IR YT1030, due next week;
- [ORDERED] Third charger (I got Liitokala because I have another two of those);
- [ORDERED] 4x5 Cell Holders, due next week (Aliexpress this year has really done a good job on making logistics faster, well done chinese friends!);
- [CHOOSING] 4x BMS, I would actually be ok with 4x 14S 20A common port chargers; sorry to say but for now I might go for a model without monitoring (I'll add that myself, it's quite easy, but I wont be able to interact with the BMS itself, only see what it's doing); have to wait for big money to buy some serious BMSs :coffee:;
- [TBD] Enclosure; Maybe I'll adapt some metal cabinet I can buy from a local shop;
- [TBD] Structures to hold panels; this is a big point for me because mounting the 20KG/44pound 280W panels high up on three different walls of my balconies means making the holding structures, I must go an see what local dealer has as metal bars;
metal-solar-holder.jpg

And my question is this: I read on a famous book on Lithium Batteries (yes, that one) about using different capacity cells for each "P block" ( with each "P block" summing up to the same amp capacity):rolleyes:. Oh my, ok, it sounds good but I doubt it would work in a decent way because of different voltage drop when under load and I imagine BMS will always find unbalanced blocks. So in my 14S20P module I could have, standing to what the author says:

1S2S3S...
20x 2200mAh
cells = 44Ah
17x 2600mAh
cells = ~44Ah
23x 1850mAh
cells =~ 44Ah


Does it make sense? it would be good for me because I'd use all my recycled and tested cells. Or is it better to just go for cells with similar capacity (I see people use +/-500mAh cells to make packs)...
 
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italianuser

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Feb 25, 2020
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340
[Update 16 May 2021]
I'd like to have everthing setup before July/August , I'm waiting for all pieces to arrive from around the world and I have a question about mixed cell modules setup.

So while my current status is:
- [ORDERED] 400 cells from Holland (...sigh! sorry to say but he's not a serious business man IMHO he doesn't care much of communication with customers); maybe they will arrive this month, if not I'll have to buy a stock of notebook batteries, I found them for 2€ each;
- [ORDERED] IR YT1030, due next week;
- [ORDERED] Third charger (I got Liitokala because I have another two of those);
- [ORDERED] Holders, due next week (Aliexpress this year has really done a good job on making logistics faster, well done chinese friends!);
- [CHOOSING] 4x BMS, I would actually be ok with 4x 14S 20A common port chargers; sorry to say but for now I might go for a model without monitoring (I'll add that myself, it's quite easy, but I wont be able to interact with the BMS itself, only see what it's doing); have to wait for big money to buy some serious BMSs :coffee:;
- [TBD] Enclosure; Maybe I'll adapt some metal cabinet I can buy from a local shop;
- [TBD] Structures to hold panels; this is a big point for me because mounting the 20KG/44pound 280W panels high up on three different walls of my balconies means making the holding structures, I must go an see what local dealer has as metal bars;
metal-solar-holder.jpg

And my question is this: I read on a famous book on Lithium Batteries (yes, that one) about using different capacity cells for each "P block" ( with each "P block" summing up to the same amp capacity):rolleyes:. Oh my, ok, it sounds good but I doubt it would work in a decent way because of different voltage drop when under load and I imagine BMS will always find unbalanced blocks. So in my 14S20P module I could have, standing to what the author says:

1S2S3S...
20x 2200mAh
cells = 44Ah
17x 2600mAh
cells = ~44Ah
23x 1850mAh
cells =~ 44Ah


Does it make sense? it would be good for me because I'd use all my recycled and tested cells. Or is it better to just go for cells with similar capacity (I see people use +/-500mAh cells to make packs)...
 
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OffGridInTheCity

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You're table of 1s, 2s, 3s all = 44aH is on the right track but personally, I would evenly distribute the 2200, 2600, and 1850mah cells equally among the packs. For example, each pack would be something like this:
7 x 2200 = 15,400
6 x 2600 = 15,600
7 x 1850 = 12,950
--------------------
20 cells in each pack for a total of 43,950

If each pack in the series (that make up a 3s or 4s or 7s or 14s battery) has the same mix of cells and the same aH totals (and good IR) you'll get good results for balancing / general operations as each pack is very likely to have the same charge/discharge curve and stay balanced to each other more exactly.

If you're doing 20p then I'd try to be exact in the cell counts. If you're doing 100p then +/- a few cells (say 5%) is not so huge if your inventory of cells doesn't quite distribute evenly.

Further... given a single cell type such as the '2600'(s). Testing may reveal 2400, 2500, 2600, and a few 2700. You want to group these and evenly distribute on this factor as well.

And of course make sure IR is good on all cells.

To recap, the suggested technique is to group your tested cells by type and by 100mah capacity categories. Then lay out your cell holders and just round robin pick a cell from each group to fill in the cell holders.. and wa la - you'll have evenly distributed packs of cells.
 
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italianuser

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Feb 25, 2020
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(snip) To recap, the suggested technique is to group your tested cells by type and by 100mah capacity categories. Then lay out your cell holders and just round robin pick a cell from each group to fill in the cell holders.. and wa la - you'll have evenly distributed packs of cells.
Thanks @OffGridInTheCity , yes I'll be grouping similar batteries.

[UPDATE]
- My first cells order Both of my cell orders are being shipped yeah! The dutchman makes customers suffer but does send cells after all!
- Ordered 4x Daly 40A Common Port BMS (I had to choose this cheap model for now); 40A model with 20A for charging is ok. My inverter will be set at 60A charging (solar only) and distributed on 4 packs that will be 15A per pack.
 
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italianuser

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Feb 25, 2020
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Update 8th June

Received all of the products and satisfaction level is 💯:p Photos attached below.
Tomorrow morning I should receive other 400 cells from the dutchman, I've been really stressed out with the buying experience from him; if the cells are good I'll be happy with that.

Have the first 280+ cells selected to make 14S20P, they are in 14 day rest period so mounting will begin soon. Followed the flowchart shared in the forum for choosing cells, using a "4.16V / IR>80mOhm" discard threshold after two hour rest. Most cells bought from wesellcells.eu are in 40-50mOhm range.

So that will be my first 42-44Ah battery; next steps:

- Group cells in an effective way: similar IR (in a +/-10mOhm range), each series same capacity, using round-robin pick how @OffGridInTheCity says (y) keeping cells in a 300mAh range (on average, cells from 2000 to 2300mAh). Thinking about @Wolf 's methods I'll probably number the cells and use some software for grouping.

- Most probably go and search a good price for 16mm and 35mm copper bars. For the first battery I need about 6mt (20ft) of 16mm copper if I did calculations right, that's a load of metal and a load of soldering/welding to do.

Meanwhile I'll try and see if I can spot weld with my cheap Aliexpress device, as I said I had some problems in welding fuse wires.

I learnt a lot and still have a lot to learn, so it's a big thank you to you guys in the forum.

inverter.jpeg inverter-specs.jpeg
Inverter, can output more power than my actual grid, so I must trip if output>3300KW.

unsorted-cells.jpeg sorted-18650-cells.jpeg
400 cells sorted and charged, they look so good!

bms.jpeg protection.jpeg
4x Daly 14S BMS (thanks @floydR) and protection devices.

enclosure.jpeg
Ehm... this is what I'd need to put batteries in it. And another one for the inverter. A friend of mine said "when cement is still fresh you can easily rip them off" LOL :ROFLMAO:
 
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floydR

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Nice looking cabinet there. How big is one of them? about 1200- 1500mm x 420mm x 600mm? Too large to carry under your arm with ease. :)
Later floyd
edit added looks about twice the size as this one .
This is a cabinet I got when I was first at this https://secondlifestorage.com/index.php?threads/floyds-powercabinet.2502/page-2#post-19280 plans have changed several times since then and may well change again. Rather have changed yet again. going with LiFePo4 for the powerwall.
Later floyd
 
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italianuser

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Feb 25, 2020
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Yes, height and width are more or less that, I think it's about 25-30cm (10-11") wide and it's perfect for my balcony which is 1mt (3.3ft) wide. I would run fast with that on my back:D
 

Wolf

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@italianuser
Just a word of caution and advice. It looks like you have some Sony US18650GR series cells in the mix. These cells can have a very high IR when discharged and it changes drastically to a much lower value when recharging. It will throw of you pack charging /discharging parameter quite a bit if you mix them into the packs. Personally I would avoid them. Just ask @OffGridInTheCity about his experience with them. I also have stated often if the US18650GR series was all I had exclusively no problem. But mixing them would be a no no for me.
Wolf
1623151242179.png
 
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italianuser

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@italianuser
Just a word of caution and advice. It looks like you have some Sony US18650GR series cells in the mix. These cells can have a very high IR when discharged and it changes drastically to a much lower value when recharging. It will throw of you pack charging /discharging parameter quite a bit if you mix them into the packs. Personally I would avoid them. Just ask @OffGridInTheCity about his experience with them. I also have stated often if it the US18650GR series was all I had exclusively no problem. But mixing them would be a no no for me.
Wolf
View attachment 25316
Wow what an eagle eye you have, I would say a Wolf Eye :giggle:
Oh my, didn't know that. Yes they are Sony, about a third of the whole 400 cell lot are this model: US18650V3, I checked them all. During tests they had a good behaviour, not too much heating and a consistent capacity/IR.
Does this V3 series have the same problem as GR series, or maybe they are the same type of cells?
This is a closeup photo of them. The current IR of all charged cells is around 40-50mOhm. I'll try discharging a couple to see what happens to IR.

Sony Cells.jpeg
 

Wolf

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Lets just say I know my cells. In this case I spotted them quickly. I can pretty much tell you what the cell is by the wrapper and insulator color.
The V3 is definitely a different chemistry than the GR series. I would still be cautions with them as for some reason Sony cells are the odd man out.
According to the spec sheet they are a hybrid which in itself is not a showstopper and the IR is a bit low or at least according to the spec sheet.. The cathodes nickel, manganese, and cobalt combination is good for higher drain applications such as power tools etc. Just be cautious and know that these cells would be the first ones suspect if there is a balance problem. Good thing your design will include easy cell replacement if necessary. :p
Wolf
1623159512095.png1623159821506.png1623159847786.png
 

italianuser

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Ready to make the first 14s20p because the first block of cells have passed the testing phase, about two weeks, using these threshold parameters:
  • Cell voltage>4.16V
  • Cell IR<80mOhm
  • Capacity 2000-2300mAh

280cells.jpeg Battery Pack.png

What I learnt:

- Chargers may charge to different voltage levels, some more, some less;
- After nearly two weeks continuously charging cells, with summer coming, chargers need and extra fan (temperatures nearly 30°C/86°F during the day);
- It has been a lot more intense of what I expected. Last night I dreamt I had received some Tesla batteries wth:ROFLMAO:

Next steps for the weekend:

  1. Grouping cells by IR with a +/-10mOhm range; I don't know @Wolf ... I might number all cells to make grouping easier, or I might rely on my mental strength for grouping them in a correct manner...
  2. Test spot welding again using advise received here in the forum; if spot welding fails (my spot welder is a real-basic stuff) I'll go for soldering;
  3. Depending on the previous test I'll buy copper bars or not.
Ah... I still don't have a 48V charger AHH! Must resolve this today.

EDIT: open points -> ask @OffGridInTheCity about his experience with Sony cells, I have 100-150 and must understand if it makes sense to use them in this first 14s20p battery.
 

ziporah

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Can't you use your inverter to charge the packs? It looks like one of the programable chinese ones. I read the documentation and you should be able to set it at 2A, 10, 20, 30,40,50 and 60A charge current from the net or your solar panels, depending how you want to charge them.
Once you have your system online, you can use a 2S/4S charger to charge your packs at the same level, then you can balance them by connecting the 14 packs together and in the end make sure your voltages between the 14s20p packs are at the same levels and you should be able to connect them all together
 

Wolf

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Grouping cells by IR with a +/-10mOhm range;
I'm in Europe right now so it may take some time for me to answer and/or make suggestions.
IR is no so much a concern as far as sorting as is the mAh of the cells. IR should be preferably within a 15mΩ window. 80mΩ cells IDK I guess if they are good cells at least 85% SOH and the lowest cell is at least 65mΩ. I just know that a larger spread in IR between cells will stress both the lower IR and higher IR cells at different times, forcing 1 or the other to give more current at different times. Add differences in mAh results and you are building 20p packs there is not much room for error absorption.
I would look for cells that are within a 15mΩ to at most a 20mΩ spread. Then sort them by 100mAh difference. Your cell are 2000 to 2300 so you should have 4 piles. Pile 1 one of each goes into 1-14 and repeat till you run out, continue with pile 2 and so on..........................

Wolf
 

italianuser

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Can't you use your inverter to charge the packs? It looks like one of the programable chinese ones. I read the documentation and you should be able to set it at 2A, 10, 20, 30,40,50 and 60A charge current from the net or your solar panels, depending how you want to charge them.
Once you have your system online, you can use a 2S/4S charger to charge your packs at the same level, then you can balance them by connecting the 14 packs together and in the end make sure your voltages between the 14s20p packs are at the same levels and you should be able to connect them all together
@Wolf thanks for the suggestions. 45% of cells are in 35-45mOhm range, 45% in 45-55mOhm. The newer cells which I'm finishing testing are slightly lower with 50% samsungs at 30-35 and 50% sanyos at 35-45. I'm tempted to finish testing all cells to have a more homogenious distribution. That will take me another month.

@ziporah I would like to test the battery before connecting it to the inverter. And when I make the second 14s20p battery I would charge/discharge it to a voltage near to the first battery. I see many 48V chargers, icharger is quite expensive and skyrc IMAX and clones which cost less. Plus I would expect similar capacity between series and between batteries with maybe a 5% difference.
 

ziporah

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I bought this PSU a while back : ali-power-supply it claims to be able to charge LiIon, but I haven't tested it yet, to what cell capacity it can be used to charge. Perhaps someone here can shime in if they've used them. I've read trough the manual, but I didn't find yet if it is capable of bigger number of serial packs as well. There is also a 6012 version, which can push 12A instead of 6A. Otherewise there are also these available, some guys in our Belgium DIY powerwall facebook group are using them. The tested them and they are all in spec as stated by the seller.
 

italianuser

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@ziporah yes, I checked that model out, you did a good buy. What I noticed with these PSUs is that voltage written on the display isn't always accurate, my 30V PSU shows 11.5V while it's 12.2V 😅 So I always keep a precise DMM connected during usage to precisely regulate voltage.

You won't believe it, I shouldn't even say this, after spending quite a few hours searching... I bought a bunch of (extra) cheap DC step-up boards, up to 60V, and I'll try to get a 58.8V hopefully at at least 6A out of them. Cheap, yes, but they seem decent quality boards with two mosfets and big heatsinks, dunno, they might melt at first usage. Next month I'll spend some time again looking for a good charger, tell me how yours goes, it's in my wishlist.
 
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