24v Setup

FilterGuy

What, me worry?
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BUT I would also recommend a smart BMS like Will reviewed with Bluetooth so you can actually tweak & monitor your cells. Those BMS' have no internal balancing function though but that's usually OK if you have independent cell management.
I sure thought the Bluetooth ones that Will reviewed had passive balancing. Why do you say they don't?
 

BiduleOhm

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Well, with series first you have some advantages like the redundancy for example.

Also, I didn't saw many BMS (if any) who communicate with the SCC, inverter, etc... which is a big bummer because you can do really cool things to optimize energy production/usage and protect the battery/equipment. That's the main reason why I'll make DIY BMS.
 

FilterGuy

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I haven't thought a lot of this through yet, these are just my initial concerns. Am I making much ado about nothing, are these non-issues or solveable problems? or are these downsides/tradeoffs realistic?

People successfully build them both ways. If one way was not viable or had an overwhelming advantage we would hear all about it. The decision comes down to the specific requirements of the build along with the builders preferences, values, experiences and beliefs.

Series first works. People do parallel Battleborn all the time.
Parallel first works. Every Tesla on the road has it.

What is great about this forum is that you get to hear a lot of points of view and then build your own point of view.

I give my point of view but I happily accept that others have a different point of view. I will even point out when there are points of view that are different than my own.

Another thing to keep in mind: In cases like this where there is no clear consensus..... there is probably not a huge difference either way.
 

Dzl

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@FilterGuy

I sure thought the Bluetooth ones that Will reviewed had passive balancing. Why do you say they don't?

Just wanted to point out you two may not be talking about the same ones. Will has reviewed at least two bluetooth BMS' the battery hookup one, and the ebay one that was featured in his 48v 16s solar shed video.

People successfully build them both ways. If one way was not viable or had an overwhelming advantage we would hear all about it. The decision comes down to the specific requirements of the build along with the builders preferences, values, experiences and beliefs.

Which is sort of what I'm trying to think through. What are the trade-offs between one or the other system. @Steve_S thinks P then S should be a last resort, I'm not that informed on the topic, but I see lots of potential problems (or at least complexities) with S first, then P. Obviously the simplest solution would be plain ol' S and no P whatsoever, but that won't work for everyone. Battlerborns and other drop ins show that S first is viable and maybe ideal for some use cases, but they are also made to be a hands-off, self-regulating, no-user-input-or-thought-required, drop-in and forget about it battery, which is a very different situation from most DIY raw cell builds where the user bears more responsibility for managing things or at the least understanding how the system operates.

My mind is very open to changing on this subject (in fact I wouldn't even go so far as saying my mind is made up enough to need changing), as I'm just barely starting to become informed on it, so I'm hoping someone can address my concerns about S first.

Another thing to keep in mind: In cases like this where there is no clear consensus..... there is probably not a huge difference either way.

Yes, or in some cases, huge differences, but no clear better option for all use cases and skill levels.

What is great about this forum is that you get to hear a lot of points of view and then build your own point of view.

I wholeheartedly agree! There are a lot of smart and thoughtful people here.
 
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Dzl

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@BiduleOhm

Well, with series first you have some advantages like the redundancy for example.

Yes redundancy would be a big advantage for sure!

If I was skilled enough or brave enough to build one, I would try.

Also, I didn't saw many BMS (if any) who communicate with the SCC, inverter, etc... which is a big bummer because you can do really cool things to optimize energy production/usage and protect the battery/equipment. That's the main reason why I'll make DIY BMS.

The DIY BMS looks very cool, and I'm a big fan of open source hardware/software!

I'm not positive but I believe that the ChargeryBMS the TinyBMS and the ElectroDacus SBMS0 are capable of this in some way shape or form (i'm not sure how smart/granular that communication is, it may only be via relay or it may be directly if the scc or inverter supports this).
 

BiduleOhm

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The DIY BMS looks very cool, and I'm a big fan of open source hardware/software!

I'll definitely post all the info I can for others to replicate if they want, but I need to make a lot of technical choices and tests before that though.

I'm not positive but I believe that the ChargeryBMS the TinyBMS and the ElectroDacus SBMS0 are capable of this in some way shape or form (i'm not sure how smart/granular that communication is, it may only be via relay or it may be directly if the scc or inverter supports this).

Well, I plan to have ethernet com because it has a lot of advantages for what I want to do and I doubt any BMS on the market (even a 1 k$ one) has that.

Also the BMS will not control something else like the SCC, it's the something else who will get info from the BMS and decide what it wants to do (because it's not the BMS' job to do that, and I want to maintain clear isolation between components because if you don't do that you'll quickly get a big mess you can't debug, and also it's far easier to implement failsafes that way too).

But I feel like I've already wrote too much off topic, maybe I should start a thread about all of this in the right sub-forum.
 

Dzl

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But I feel like I've already wrote too much off topic, maybe I should start a thread about all of this in the right sub-forum.

You should, I haven't seen much attention paid to the DIYbms on this forum, and its a fascinating project. I also think the more discussion on how to integrate all the various components the better.

Well, I plan to have ethernet com because it has a lot of advantages for what I want to do and I doubt any BMS on the market (even a 1 k$ one) has that.

Not sure if its exactly what you are talking about but the maker of the SBMS0 (I highly suggest you learn about his projects, I suspect you will connect with his design style), recommends using Cat5 or Cat6 cable for external connections, I think this is not the same thing as what you are talking about, just the same cable. Here is a link to the manual.

Also the BMS will not control something else like the SCC, it's the something else who will get info from the BMS and decide what it wants to do (because it's not the BMS' job to do that, and I want to maintain clear isolation between components because if you don't do that you'll quickly get a big mess you can't debug, and also it's far easier to implement failsafes that way too).

I can understand wanting to maintain isolation and see the benefit of that approach. But I feel like how you define the BMS's 'job' is unnecessarily limited and absolutist. A BMS is a system of managing and protecting the battery. That means preventing overcharge, overdischarge, etc. Communicating with chargers and load side appliances (inverters, battery protects, etc), and telling them when its acceptable to charge/discharge the battery is within a BMS's scope of responsibility. Whether it communicates directly, or whether it opens/closes a relay, or handles the (dis)connection of charge sources and loads internally is a design decision. But all are methods of managing charging and discharging. Keeping each device ignorant and independent of the others as you advocate has its merits as you correctly noted, but being able to communicate with external devices has its own merits, and is in some ways might be a more elegant solution. I also want to clarify that I mentioned communicating with external devices, not controlling, which are somewhat different things.

But now it is me who is taking this thread off the rails even further, my apologies.
 

Steve_S

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There are different approaches and different use cases. Which is better overall all depends on the system, uses, needs and "wants" for it, of course.

A simple question which requires no answer, just a moment of ponderance.
Why would someone build a pack, with 16 cells paralleled internally so that only 8 can be managed / balanced ?
What do you Gain / Loose by doing so ?

Those BT model smart BMS' also have an RS module, some have USB (which can flip to ethernet) Chargery's have RS232 that can be interacted with using Modbus app.

Look here at a Smart BMS with BT & PC-UART (why noone sees the "PC UART" I don't know, likely most just don't get what it is and don't read.... such an aversion to RTFM which is easier than asking for 20 peoples "interpretation" of it.

@BiduleOhm Many BMS' (all the smart ones in any case) can be communicated with. Most have a UART option if not already enabled. "Dumb" BMS' which have no comms at all (BT or otherwise) are moot on this point. Not all Inverters or SCC's can communicate with a BMS, it's only now starting to really come into play but really, many also do not even directly support Lithium Based batteries either yet. In a perfect world hat would be different but it is far from a perfect world. Are you aware that a RaspberryPi,, Arduino and similar can be used as an intermediary, a manager, a Modbus controller... various ones can accept RS232/485 directly with a "hat" add-on or various BMS' & other devices could also route through a USRIOT device (there are others as well but USR is top notch) https://shop.usriot.com/serial-to-ethernet/serial-ethernet-converter but these can also do Serial to WIFI, CanBus and more....

BTW: I run a Midnite Classic SCC, great controller but dumb as horse manure when it comes to BMS, Lithium Based Batteries but it can be programmed around to work (kludge IMO) but it works. My Samlex Inverter on the other hand CAN talk to a BMS and has some Lithium intelligence in it's programming.
 
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