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Active Balancing for large LiFePo packs??
#1
Looking for ideas on balancing large packs, I see a few people using Batrium, I have a lot of 1ah LiFePo4 cells. In planning phase for pack design and management. I am considering 16s80P packs, ... 8~10 packs like this. 

I want to make a large pack for an off-grid home, and a small setup for a travel trailer, that will probably just end up being some Chinese ANT BMS.
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#2
(05-19-2020, 03:40 AM)totalimpact Wrote: Looking for ideas on balancing large packs, I see a few people using Batrium, I have a lot of 1ah LiFePo4 cells. In planning phase for pack design and management. I am considering 16s80P packs, ... 8~10 packs like this. 

I want to make a large pack for an off-grid home, and a small setup for a travel trailer, that will probably just end up being some Chinese ANT BMS.
You don't mention this so forgive me if you plan this already....   First up you need to test each of these cells and group them by capacity and distribute them evenly by capacity thru the 8-10packs so all the packs are similar.   Part of this process is to test and then let sit for a couple of weeks to see if any are self-discharging.     Once you have a set of healthy packs....

Batrium is a great BMS - top of the line.   However, assuming you've built healthy packs and hooked them in parallel (before hooking in series) to balance them all out with each other - you shouldn't need a 'super strong' BMS to keep them in balance.

The main purpose BMS is to cut-off the battery from load/charge if the battery goes bad to stop the battery from damaging itself - e.g. cell/pack voltage to hi/low or temp to hi/low.   Here's an FAQ from this site on this - https://secondlifestorage.com/showthread.php?tid=6391    So you need to size it depending on the amps going in/out of the battery and how the BMS disrupts that flow when there's a bad situation.     If you're pulling <100a from the battery then you'll find many cheaper (non-visual) BMSs that will probably work for you.    Here's an active thread related to BMS choices - https://secondlifestorage.com/showthread.php?tid=9186

If you want visuals/logging/computer-monitoring, ability to control external devices, high amps (mine is 400a), ability to grow (I have 70 packs on the way to 84 packs)/larger 200p packs then Batrium is a great choice.

And as you point out - you might have smaller one for RV and larger for home.


TMI Smile
My plan is to park my RV next to my in-house battery bank and have it be 'one of the batteries' of the in-house battery bank while the RV is sitting.   So I plan for my RV battery to be same style/size one of my in-home batteries...  and of course be Batrium enabled so I can use the home Batrium to see/manage it will the RV is sitting.   The RV would have its own (maybe Batrium) for when its away from home.
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#3
Yes, I have a couple of Opus capacity testers, hoping to expand on those soon.

While I might grow in to Batrium in the end, for small scale startup I am looking at products like these-
Ennoid
DieBieMS
diyBMSv4
OpenBMS
FoxBMS
Speedict
TinyBMS
openenergymonitor
electrodacus

Some of those are for automotive, but that is an area where a lot of small modules might be in used ,which is my scenario. Any feedback on any of those products or others I would love to hear.

Core functions I need:
- ideally *active* balancing
- low/high volt cut-offs
- low/high temp cut-offs
- basic reporting/history
- easy scalability with module groups
Could be centralized or decentralized, I would not die if I had to monitor 20 modules individually instead of as a single unit if other advantages were present
(did I miss anything important)

Might integrate with something like Raspberry Pi, Arduino, or full blown PC. I worked in the construction industry for years, I have built my own solar systems, I have rebuilt my own hybrid battery packs, worked on 3 phase equipment and currently I work in IT, so working with wires and programming are in my wheelhouse, flexibility and scalability are more my goal than a turn-key product. Batrium *might* end up being my solution, but it is looking cost prohibitive to me for the amount of modules I might end up with using these tiny cells... some day I might get my hands on large AH cells to simplify... today I have lemons=make lemonade.
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#4
You might want to have a look at my setup, link below.
NO - ideally *active* balancing (passive, and just 50mA/cell. But that's proven to be enough(*1) )
YES - low/high volt cut-offs (cell level and pack level, programmable in mV steps)
YES - low/high temp cut-offs (only 2x external sensors per BMS, programmable)
YES - basic reporting/history (bluetooth connection to Android/iphone App. RaspberryPi etc possible with programming)
YES - easy scalability with module groups (now using 6x BMS in parallel, planning to reach 10x by years end!)

Cost is about $50/BMS for the 60A version, but probably wise to limit usage to 1/2 ~ 3/4 that current for extended use such as in powerwalls.

(*1) My cells get charged to only 4.08V and discharge stops at 3.4V, so leaving plenty of breathing room. Balancing is set to start at 3.90+V when cell voltages differ by +/- 15mV, in order to maximize the working time for the balancer. This works perfectly fine over time, but may cause discomfort depending on the level of your OCD.
On the plus side, self discharging cells become apparent within days as the voltage of that pack starts to drift.
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#5
chargery bms16 (cost about 110) balances at 1.2 amps per cell and lets you adjust at what voltage you want it to start balancing. It works great with lifepo4 and solar. It uses mechanical relays/contactors to stop the charge/discharge so it's capable of handling as many amps as your contactor can handle. The chargery doesn't have any tracking data, but it has a nice LCD screen that shows you the realtime cell voltage and all setting are programmable including temp sensors.

Active balancers for a 16s that actually have a decent balance amperage will cost as much as the chargery. 1.2 amps balancing is as good as most balance chargers.
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#6
Thanks for the input guys.... I am considering Chargery for my trailer setup, although I am leaning more towards electrodacus. AJW I looked at your setup, and that looks very interesting.
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