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Independent modules
#1
Hello,

I'd like to set up a modular system. Each module should have its own Monitoring IC, Balancing IC and Charger IC. Since they are used cells, I would not like to connect the modules in parallel. A master board is also planned for controlling and monitoring the modules. What would be the possibilities to connect the modules without a direct connection? I thought about adding a DC/DC converter to each module output, so each module would be completely independent. But I don't know if this makes sense.

Many thanks for the answers.
Vincent
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#2
I am having trouble following your idea.
What would a module look like?
What voltages would different sections run at?
How many cells would you use?
How would you connect cells/modules together in your system?
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#3
If I interpenetrated that correctly the term you are looking for is strings.

If you are going to have separate strings of batteries. Example for a 24v system 2P(7S80P) then the 2P (2 Strings 7 Series 80 Parallel) would be connected at their positive an negative ends. You would have 14 separate (80P) packs to balance. However there is no isolation between the two strings as a whole.*(See note) Only for each 80P pack. There are advantages to building a system in this fashion, one being that if you need to disconnect one string for maintenance.

However, if you are looking to completely isolate the two strings, there is no simple or cost effective way to do so. The only sensible solution I can see, would be completely separate chargers and inverters. This could only be achieved if you use inverters that can be used in parallel. This could have advantages, in that if one system goes down you have some level of redundancy. I cannot really see this being cost effective, unless you are building a system large enough that two inverters would make sense in the first place.

Even if you had a device to isolate the two strings, you would still need multiple inverters and charge controllers. The only other possibility would be some kind of bi-directional buck/boost converters. Even then I cannot imagine a system where that would be practical.

* (Note) Some systems use two separate strings to mix battery chemistries. This is not advisable unless you have a sound knowledge of electronics and battery chemistries. However, Daromer does run a string of LiIon in parallel with a string of LiFe. I imagine this could also be done with lead acid, but would not be nearly as effective, as the discharge characteristics of the two chemistries are too dissimilar.
100kwh-hunter likes this post
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#4
You might want to have a look at my system. I have one master busbar to which several chargers, inverters and batteries are connected. Each battery is separately monitored by its own BMS.
It's a modular design that has slowly been expanded, and at the moment I have 2x chargers, 3x inverters, 3x batteries (each 14s100p).

I think something like this does most of what you want, except that you need to match the voltage before (re-)connecting a battery.
OffGridInTheCity likes this post
Modular PowerShelf using 3D printed packs.  30kWh and growing.
https://secondlifestorage.com/t-AJW22-s-...PowerShelf
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