Off the wall crazy question

Johndobbs

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The final design of my battery pack will consist of parallel and series wiring it is 16 cells four sets of four at 12 volts each pak 100 amps.
I saw an interesting photo on the internet I was curious if this is possible when it comes to the wiring of a BMS or if this might be dangerous?
The packs would you all be wired red to red black to Black to increase amperage I believe the photo speaks for itself when it comes to the BMS wiring.
BMS Wiring~4.jpg

of course the positive and negative on the center pack would be reversed if this does work and my setup would have four packs instead of three.

Also does anybody happen to know if a BMS will work if not all the battery lines are connected I plan on starting with 4 cells then ad another set when I can.
Of course I can use for separate be a message if I have to.
Thank you for your time
 

SCClockDr

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I'm seeing 3 batteries in parallel. (We'll not quite, the center battery is reverse polarity.) The way you have them arranged will require a BMS for each 4s string. Each sense wire needs to differ by 3.7v from its neighbors. I'm seeing 3.7, 7.4, 11.1, 13.8, 3.7, 7.4, 11.1, 13.8, 3.7, 7.4, 11.1, 13.8. A sure fire way to release the magic smoke from the BMS.
If you rearrange to 3p4s vs 4s3p you can get by with one 4s BMS.
 

Johndobbs

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I figured it'd be something about it that didn't work.
Also forgot that the drawing was made by somebody else.
Using a separate BMS for each 4-pack was my next option.
Thank you
 

Supervstech

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I see three 12v batteries wired in series resulting in a 36v battery, with thick cables shorting out battery 3 and battery 2...

Bad things will happen if this diagram is followed...
 

Supervstech

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I understand the OP knows this... but others could misread or simply follow the picture.
 

Supervstech

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Also, if you use individual BMS boards for the setup, they should communicate with each other, or be designed to operate with multiple strings.
 

Johndobbs

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Thank you for the replies.
I am most likely going with individual BMS is for each pack anyhow remember correctly the one I choose is about rated at 100 amps and one for each of the four packs would be 400 amps and I wouldn't even use half of that which would account for any inconsistency with the specs
 

April

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of course the positive and negative on the center pack would be reversed if this does work and my setup would have four packs instead of three
Its using a 12s BMS . Most of them will do 4S if the 4th black wire in is connected to negative .
Using the next set of 4 sense circuitry seems like it should be possible on the middle battery and then the following 4 on the last.
Certainly if you have 4 batteries you are going to be 4 wires short and need a 16s.
I once thought I could make 2 of 4s BMSs work on an 8s battery but never got a way to connect them worked out .

Its easier to just buy what you need and keep the others for later .
 

SCClockDr

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Thank you for the replies.
I am most likely going with individual BMS is for each pack anyhow remember correctly the one I choose is about rated at 100 amps and one for each of the four packs would be 400 amps and I wouldn't even use half of that which would account for any inconsistency with the specs
So you've decided to go 4 in packs parallel @ 12 volts? Otherwise you are still @ 100 amps. (The same 100 amps travel all the way around.)
 

Johndobbs

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Can't remember if it's parallel or series but basically black to black red to Red across all the packs I believe that increases the amperage availibility if I remember correctly and maintains the 12 volts.
Running 12 volts because I have a bunch of stuff running direct DC off the batteries.
Down the line I'll probably end up getting it inverter for AC stuff if I need
 

Supervstech

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Yes, that is 12v
You need one, or several 4s BMS devices...
 

Buzzard Bait

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I do so . One on each string. I prefer to ensure a bad cell is picked up straight away before it damages others.
Thank You April. I already have them coming, but I may have misunderstood something from another post, and was afraid I had over spent again. Thanks again for the info.
 

FilterGuy

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You can wire the cells two ways: Parallel-then-series or Series-then-parallel Serries-parallel.jpg

In both cases you get 12 volts and if the cells are 100 Ahrs you get 400 AHr.
  • With Parallel-series you can get away with one 4 cell BMS, but it has to work harder to balance and it will be harder to detect a bad cell.

  • With Series-Parallel you need four 4 cell BMS' but each one does not have to work as hard to balance and it will be easier to detect a bad cell. Also, if one of the 4 BMS shuts down due to an over or under voltage on a cell, the other 3 will try to take over.

I would lean toward saying Series-parallel is better, but I would be interested in hearing what other folks think.
 

April

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You give the balance feature too much prominence . It does next to nothing in the big picture.It does not balance the pack . Thats a misunderstanding.
 

FilterGuy

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You give the balance feature too much prominence . It does next to nothing in the big picture.It does not balance the pack . Thats a misunderstanding.
OK.... that makes the difference between the two wiring scheemes even less.
 

Johndobbs

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Suggestion thank you for the suggestion filterguy.
Actually don't have the money to buy all 400 amps worth at once I was planning on buying for the time 12 volts and hundred amps a BMS for each one at a minimum of 150 amps.
And by the hundred amp packs one of the time till I get the total amprage I want.
Plus mutch of the bluetooth bms units i find don't test well eith the rated amprage so i plan on getting one rated for 150A or 200A that way the actual amprage draw won't be a wory.
Also with my lack of experience with these cells I don't like putting more than one of them in a Cell just in case something happens even if they are properly balanced the matched just a personal preference.
Thank you for your post
 

Buzzard Bait

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I do so . One on each string. I prefer to ensure a bad cell is picked up straight away before it damages others.
Hi April as I said I have a BMS for each of my BYD batteries. What I didn't say is all four are 150 amp BMSs with a separate charging port. I have watched a video of Will's in which he said if I try to parallel over two sets of batteries that I might be asking for trouble. So now I am wondering if there is a preferred method to combine the batteries. You were kind enough to reassure me on having a BMS for each battery, and I hoped you might help me out again. I was just going to buss all the batteries together in parallel on the positive posts. Then connect each of the BMSs B- leads to neg on each battery negative post. Then buss all the BMSs P- negative leads to a common load, and after that I had planned to join all of C- leads to a buss going to the Solar Charge Control. Well that was the plan before I saw the video, but now I have invested a good chunk of change in something that might be a problem. I would like to use all the resources I have, but I may need a little advice. Thank you in advance.
 
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