My First 48V 6.5KWh Li-Ion Powerwall 🥰

italianuser

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Joined
Feb 25, 2020
Messages
148
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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Aug 23, 2017
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1,066
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
Messages
148
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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Aug 23, 2017
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1,066
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
Messages
148
[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); 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)...
 

italianuser

Active member
Joined
Feb 25, 2020
Messages
148
[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); 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)...
 

OffGridInTheCity

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Joined
Dec 15, 2018
Messages
1,530
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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