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Diy Active balancer
#11
Self discharge or just other ir. No matter what it will happen on diy packs and is the most common issue.

So you need to consider to be able to balance the full string and not part of the string. So 14s with 2x8s modules will not work im afraid Smile

Your desing is nice and i like the approach and hope you find a suitable sollution to go above 8s.
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#12
Ideally there needs to be a way to balance between boards, particularly if you want the system to be almost infinitely expandable.

With larger systems, say 22s that we use for 48V LTO packs, this would mean 3 boards, cells at the start and end of the pack charge before cells in the middle, requiring balancing to even out the charge levels.

Without a balance interconnect between boards, the middle 8 cells would stay low and the end cells would stay high.
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#13
If people are curious, each balancer board will keep track of how many amps of balancing goes into each pack
So bad packs will be spotted by analyzing that data

(04-22-2020, 08:16 PM)daromer Wrote: Self discharge or just other ir. No matter what it will happen on diy packs and is the most common issue.

So you need to consider to be able to balance the full string and not part of the string. So 14s with 2x8s modules will not work im afraid Smile 

Your desing is nice and i like the approach and hope you find a suitable sollution to go above 8s.
I dont see where it would not work.
With 2 8s modules you can balance out the entire pack.   there will be a slight difference between the first and second balancer, but thats customizable by future software upgrades
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#14
(04-22-2020, 10:57 PM)BaronVonChickenPants Wrote: Ideally there needs to be a way to balance between boards, particularly if you want the system to be almost infinitely expandable.

With larger systems, say 22s that we use for 48V LTO packs, this would mean 3 boards, cells at the start and end of the pack charge before cells in the middle, requiring balancing to even out the charge levels.

Without a balance interconnect between boards, the middle 8 cells would stay low and the end cells would stay high.

I think you and Daromer are missing that when using the 8s system on a >8s pack, there would be at least 1 overlapping cell between the low 8s and high set, thus with even 1 overlapping cell, that low grouping would always show as an imbalanced "cell" to the upper grouping, and the 2nd balancer would transfer capacity between the overlapped cell and the rest of the 8s group. Here's a picture illustrating it for a 15s system:


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#15
If you overlap thats fine but then the system must be set Up so isolation exist..without overlap this system Will not work. Its basically like not having any balancer Smile

Problem with overlap is that the software must compensate where the teansfered energy comes from
If you dont do that you cant report back transferera energy and or that middle cell will have a higher transfer rate. This is correctable in software.
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#16
Yeah, that'll work, a nice way of keeping it simple.

Just make sure all of your documentation and marketing material make the overlap clear, I think a lot of people will get caught out with this as it is not "normal" for stacking systems.
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#17
(04-24-2020, 07:19 PM)daromer Wrote: If you overlap thats fine but then the system must be set Up so isolation exist..without overlap this system Will not work. Its basically like not having any balancer Smile

Problem with overlap is that the software must compensate where the teansfered energy comes from
If you dont do that you cant report back transferera energy and or that middle cell will have a higher transfer rate. This is correctable in software.

In the software I keep track of every cell received balance Ah.
And what do you mean with isolation ?
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#18
Overlap causes to have different grounds. So need isolated signals.


The overlapped cell allso need to have different calculations since it gets energy from 2 places or taken energy from 2. So you need to interpolate and send that data between Them to offset it.
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#19
The communication bus is completely isolated. So there won't be any issues with that.
There will be some software difficulty in keeping track of that overlap cell. Since it can receive energy from 2 ways. That is something I will have to dig in and try to find a solution.
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#20
Cool
Then ur om track Smile looking forward how tonsolve it. I did some rough calculations some years back on that topic and it takes some time for sure.
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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