30 Pcks 13S10P 30Ah Need Help for BMS

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Bib60

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Hi everybody
For my solar system i have 30 packs about 13S10 30Ah each.
My charger will produce 5000W 48V maximum to charge my battery.
I have a problem to select how i will manage theses packs with BMS system.
I wanted to add 1 BMS 15A per packs from China and use my packs in parallele mode but all the sellers says to me that if my charger will produce 80A and if BMS will get more that 15A it will burn !!!
So now i'm asking me if i need to put all my 30 Packs in parallele mode like this i will have a big pack like 13S300P and i will use BMS 300A to be safe.
Do you think i'm in the right way ???
Thanks a lot for yours answers.
Laurent
 

OffGridInTheCity

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If you have 30 packs in parallel and you apply 80a - it will be 80a/30packs = 2.7a/pack... so a 15a BMS will be fine.

In your case - with 30packs in parallel, with each BMS at 15a, then many (20+ of them) of them would have to trip to overload the remaining ones.

The downside of 30 separate packs/BMSs - you won't know if up to (aprox) 20packs have tripped as the overall battery will continue to run at 80a on just 10 of them active.

I use aprox (20 and 10) to illustrate my point because BMSs don't always operate to the advertised specs so I wouldn't count on a full 15a per BMS. :)
 
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Bib60

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Hi
It's this the problem, at the end of charge, for example, 29 packs will be protected by BMS, high voltage protection, the last BMS will get 80A of charge and will burn no ?
Thanks
 

OffGridInTheCity

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Earlier you wrote "13S10" and "48v" and "....30 Packs in parallels mode like this i will have a big pack like 13S300P...." Yes, that would effectively 13s300p.... and still 48v. When packs are in parallel the voltage of each pack will be the same (that's how parallel acts / forces this to happen) so the current is evenly distributed. There is no 'last pack'
 

Bib60

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I mean if i keep packs separatly with one bms on each pack.
If it's not working i will make with my 30 packs only one big pack.
 

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Bib60

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Finaly, it will be better to attach all my pack in parallel mode and use only one BMS.

I will use 200A BMS and 4 active Equilibrer.

20210410_115834.jpg20210410_115850.jpg

I will need your help for to know if i will do the right thing :)

I want to connect together my 30 pack with copper wire like you can see on picture, is it too much or can i use a small wire to do this ?

In third picture, it will be the easier solution to connect all pack but i will have a problem to attach pack behind, after i make one face it will be very heavy to move the pack to connect the other face !!!

Inked20210410_115910_LI.jpg

With the last picture, i can prepare each pack to be connect, after i put all my pack on the wall i can attach each cell with long copper wire and sold it, what do you think about this solution ?

Inked20210410_121500_LI.jpg

Thanks for your help.
 

OffGridInTheCity

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It looks like you're connecting the packs (in parallel) to a 'buss-bar' running across the 30 packs. This buss-bar needs to be able to carry the max amps of your design... 200a? (if I read it correctly above). For 200a - you'll need a much thicker bus-bar than I'm seeing in the pics. More on the order of 1 or 1/0 AWG ....

Here's a wire chart I use - https://www.powerstream.com/Wire_Size.htm Notice 1 and 1/0 lines - more in line with 200a....
1618069282808.png
 

Bib60

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200A is for total of 30 packs because of BMS specification.
I think you are wrong, this copper wire i want to use is only here to connect 30 group of 10 first cells between them and for to equilibrate voltage between them, Amp Power is passing trough the all pack, not by this small copper wire.
Each pack will "produce" 6.6A max. (6.6*30=200A)
Each pack can produce 70A max because of cells specifications so 2100A maximum 😱 for 30 packs.
But i only need 105A because of my solar inverter who produce/accept only 5000W (5000/48V)
Look the picture you will understand i hope
20210410_181330.jpg
 
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OffGridInTheCity

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In my post, I was talking about the black wires in the picture above. The pack interconnecting wires that serialize the packs for sure need to carry the full load on all wires.

The red wires.... If they were BMS sense leads, they don't need to carry the full load as but these are not BMS sense leads.... they actually parallelize the packs and my guess is they should be able to carry the full load. In my own setup, I wired mine to carry the full load
BUT I can be wrong about the red wires :)

There are actual experts on this forum - perhaps one of them will comment.
 

Bib60

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The full load don't pass through the red wire !!!
The only load who is passing through the red wire is when the groups of cells haven't got the same voltage and want to equilibrate between them.20210411_002911.jpg
 

floydR

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My feeling is that the single wire between packs would carry no amps because it is a single wire and not completing the circuit paralleling each 10p pack. This is from your drawings, i only see a single wire. Will there be a + and a - wire paralleling each pack to the other packs in parallel?
i am very far from an expert.
Later floyd
 
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Bib60

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Yes, you are right
The red wire between packs will carry only the neccessary amp to equilibrate each cells packs between themself.
 

grundholm

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This is the same way JEHU designed his PCB's - then all the BMS wires is connected to the red wires. The main thing is that your cells (parallel between the red wires) is balanced and have the same voltage, otherwise you end up with high current running through your red wires when cells try to equalize. Say one of your cells go bad, then current (from the good cells) will try to equalize the bad cell and you end up getting hot or broken red wires - that's why people add a fuse on each cell and a BMS to stop the potential firework.
 

Bib60

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Hi grundholm
I understand what you mean.
Before to connect the red wire i will take care that all cells have the same voltage to don't have high current during equilibrate.
I can use fuse wire to connect them but wich value ?
The maximum Amp for one cell is 7A, for one cell pack i will have max 70A, it will be the maximum in case of one full charged block of cells will try to equibrate one full discharged block of cells.
Do you think 70A fuse wire will be a good idea to connect my block of cells ?
Where can i find fuse wire that i can sold ?
Thanks
 
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grundholm

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I would say that a fuse on the red wires should be small, like milliamps - because you only want to allow a small current for equalizing. I don't know this exactly. This is the boards I was talking about:

In this video he shows his trace-fuses. The cells are in series and he has a SMD fuse (5A) on the positive side of the series-string and a wire (like your red) between each cell and before the connector (to the BMS or other boards) he has the small trace-fuses.
 

Bib60

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As you can see in my pack, each block is made with 10 cells, no protection for theses 10 cells in parallele mode in each block.
I can't change this setting, it will be for me too expensive and too long to add one fuse on each cell, i have 3900 cells ;-)
All cells are the same with same specification.
 
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grundholm

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Look at the 4th page - it's from the book 'DIY Lithium Batteries' by Micah Toll - It's a very good book!

ok, so - don't think about the amps when you make something parallel - amps will be 'sucked' through your series string, parallel will make your 10cell packs equal in Voltage - and if they are already balanced, then the flow of amps will on the red wires will only be milliamps, if any at all. Say String 1 pack 1 is 3,2 Volt and String 2 pack 1 is 3,5 Volt - it's around 10% difference, then pack 1 will try to suck those 10% from pack 2 (through your red wire) - and because the packs are 10A then it would be equal to something like 1A.

I'm not an expert in this, so someone please correct me if i'm wrong.
 

Bib60

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Hi
I've made a test between one 10 cells pack at 2,75V and the second at 4,20V, when i connect them together in parallele mode, i have 10A between the 2 pack, the highter is charging the lower until the two packs will have the same voltage, so my copper wire will be enough to carry the max amp equilibration in case of.
 
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