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BMS for 24V 400A 40 x LiFePO4 cells 8S5P

molinoalto

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Hello,

I’m helping out my uncle upgrade his off grid solar system. He wants to replace his worn out lead-acid batteries (24V 2335Ah - 12 x 2V cells) with LiFePO4 cells. We have contacted Amy from Luyuan and got a quote on 40 x EVE 280Ah cells, which we plan to use in a 24V 8S5P setup.

Besides the batteries and a generator the system consists of:
  • 4,830W solar panels on a DEGER tracker
  • 1 x OutBack MATE3 System Display and Controller
  • 4 x OutBack FM60-150VDC Solar Charge Controllers
  • 3 x OutBack VFXR3024E Inverters
The change to lithium based cells will require one or more BMS. The max current load of the system is 400A. Do you have suggestions for either a single BMS that can handle all 40 cells or 5 x BMS that each will control 8 cells in series? We are looking for an affordable and reliable solution, preferably with wi-fi connectivity so the system can be monitored from a computer that isn't located in the same room as the battery cells.

Also, I had a look around Alibaba and found these 300Ah LiFePO4 cells:

https://www.alibaba.com/product-detail/100-Grade-A-3-2V-300Ah_1600092729217.html

Do you know anything about those cells? Two things come to mind. They are very cheap at only $49/piece, and the weight is much higher compared to the EVE cells, 9.5kg vs 5.3kg.

Looking forward to any comments or suggestions.

Thanks and best regards,
Søren
 
Also, I had a look around Alibaba and found these 300Ah LiFePO4 cells:

https://www.alibaba.com/product-detail/100-Grade-A-3-2V-300Ah_1600092729217.html

Do you know anything about those cells? Two things come to mind. They are very cheap at only $49/piece, and the weight is much higher compared to the EVE cells, 9.5kg vs 5.3kg.

Looking forward to any comments or suggestions.

Thanks and best regards,
Søren
Disclaimer: Newbie here.

I checked out the link and would be impressed if the specs were accurate for that price. I did notice the terminals would require something other than a bolt to attach to. Just my newbie observation. It may be irrelevant. Shipping might also be a factor in the total cost.
 
Hello,

I’m helping out my uncle upgrade his off grid solar system. He wants to replace his worn out lead-acid batteries (24V 2335Ah - 12 x 2V cells) with LiFePO4 cells. We have contacted Amy from Luyuan and got a quote on 40 x EVE 280Ah cells, which we plan to use in a 24V 8S5P setup.

Besides the batteries and a generator the system consists of:
  • 4,830W solar panels on a DEGER tracker
  • 1 x OutBack MATE3 System Display and Controller
  • 4 x OutBack FM60-150VDC Solar Charge Controllers
  • 3 x OutBack VFXR3024E Inverters
The change to lithium based cells will require one or more BMS. The max current load of the system is 400A. Do you have suggestions for either a single BMS that can handle all 40 cells or 5 x BMS that each will control 8 cells in series? We are looking for an affordable and reliable solution, preferably with wi-fi connectivity so the system can be monitored from a computer that isn't located in the same room as the battery cells.

Also, I had a look around Alibaba and found these 300Ah LiFePO4 cells:

https://www.alibaba.com/product-detail/100-Grade-A-3-2V-300Ah_1600092729217.html

Do you know anything about those cells? Two things come to mind. They are very cheap at only $49/piece, and the weight is much higher compared to the EVE cells, 9.5kg vs 5.3kg.

Looking forward to any comments or suggestions.

Thanks and best regards,
Søren

Some have mentioned the chargery BMS to be worthwhile. Search chargery on alibaba. It may interest you.
 
Do you have suggestions for either a single BMS that can handle all 40 cells or 5 x BMS that each will control 8 cells in series?
Lifepo unlike Li-Ion takes a BMS slightly differently because of the cells and their capacities.
I need some clarity here. Do you intend 5x 24V/280AH "8S" Battery packs in Parallel, or having 5 cells in parallel in one massive 8S Pack ?
If you're thinking massive single pack... not a good idea, weight alone is 204 kg/449 Lbs +/-

400A@24V=9600W because of 3 Inverters, there are several inefficiencies there but considering the age of the gear & system not surprising. It's not "bad" just more "fiddly" to deal with. Appreciate that a 24V/280AH battery built with 280AH cells can ONLY OUTPUT 280A or 1C Rate and it can ONLY be charged at a maximum of 0.5CRate which is 140A. By putting Packs in Parallel you are splitting the load & charge which lightens the "need" for a massive BMS but this places some limitations on the system. Each battery pack should be able to handle the maximum load or charge the system is expected to demand as if it is a "standalone" pack, but to do so with the info you provided will require a heavier BMS. So this calls for compromises which should be weighed & considered.

BMS' for Battery Banks get tricky.
  • The OutBack VFXR3024E Inverters can interact with each other but they cannot interact with a BMS per Outbacks manual. (at a quick glance) from what I saw here: Microsoft Word - 900-0168-01-00 REV C.docx (outbackpower.com) Does not mean there isn't a way, but an Outback Guru may know more on that.
  • 400A Capacity more or less eliminates using FET Based BMS' ! High Amp FET Based are "rare" above 250A "gross rating". This means going to a BMS with Relay/Contactor controls which handle the Hi/Lo Voltage disconnects and can handle high amperages based on the Relay/Contactor ratings.
  • Wifi / Bluetooth are common with many BMS' but range is fairly limited with most. At best you "may" be able to use a Signal Booster.
  • With multiple packs within a bank, and each pack has its own BMS keeping them independent "free agents" to do their job but there is no "coordination" between BMS' and SCCs/Inverters. This can result in packs deviating between each other to a limited extent and also hampers a few things, such as having an SCC or Inverter use "End Amps" to stop charging for example.
  • With a Distributed / Decentralised BMS each pack can be semi-independent yet coordinated & managed. "Single string that can be divided into multiple battery boxes, with fuses and cut-outs in between". See a few links below. Warning, be seated and reassure your wallet to remain calm.
Decentralized BMS':
123electric - Solutions For Green Energy Systems
BMS Battery Management by Batrium
Products catalogue | EMUS BMS

Master/Slave BMS' sub-systems:
BMS123 Smart | shop.GWL.eu
REC d.o.o. (rec-bms.com)

See Links in my Signature, there is info there you will want.
Hope it helps, Good Luck
 
Disclaimer: Newbie here.

I checked out the link and would be impressed if the specs were accurate for that price. I did notice the terminals would require something other than a bolt to attach to. Just my newbie observation. It may be irrelevant. Shipping might also be a factor in the total cost.
Yes, the price does seem very low compared to similar cells from other vendors. I have asked Amy about them, but haven’t heard back from her yet. We will go with Amy’s EVE 280Ah cells unless someone has experience with and can vouch for these dirt cheap 300Ah cells.
 
Some have mentioned the chargery BMS to be worthwhile. Search chargery on alibaba. It may interest you.
Yes, Amy mentioned the Chargery BMS as well, but seeing that Will Prowse didn’t seem to be too impressed with them, especially not how to set them up:
 
Steve,

Thanks a lot for all the input and suggestions. There’s still a lot we need to read up on, especially understanding the various types of BMS and the difference between a “decentralized” and a master/slave sub-system.

I will comment on and give answers to some of your points below:
I need some clarity here. Do you intend 5x 24V/280AH "8S" Battery packs in Parallel, or having 5 cells in parallel in one massive 8S Pack ?
If you're thinking massive single pack... not a good idea, weight alone is 204 kg/449 Lbs +/-
Either way (series-parallel or parallel-series) we’ll end up with a total of 40 cells. 204kg/449lbs is no problem. The current 12 lead-acid cells’ total weight is 1,416kg/3,122lbs.
400A@24V=9600W because of 3 Inverters,
3 inverters 3kW a piece = 9kW divided by 25.6V = 352A, therefore 400A total max load.
there are several inefficiencies there but considering the age of the gear & system not surprising.
We don’t understand what you mean by “several inefficiencies”. Our 3 inverters work as 1 master with 2 slaves. Each slave only starts when needed which increases the overall system efficiency.
The OutBack VFXR3024E Inverters can interact with each other but they cannot interact with a BMS per Outbacks manual. (at a quick glance) from what I saw here: Microsoft Word - 900-0168-01-00 REV C.docx (outbackpower.com) Does not mean there isn't a way, but an Outback Guru may know more on that.
What do you mean by interact with a BMS? From the manual you link to it says on page 11 that “The charger can be customized to charge a wide range of battery technologies including nickel, lithium-ion, and sodium-sulfur batteries.”
Wifi / Bluetooth are common with many BMS' but range is fairly limited with most. At best you "may" be able to use a Signal Booster.
A limited range shouldn’t be a problem here. There is wi-fi connectivity set up with Devolo so the batteries and the PC are on the same wi-fi network.
With multiple packs within a bank, and each pack has its own BMS keeping them independent "free agents" to do their job but there is no "coordination" between BMS' and SCCs/Inverters. This can result in packs deviating between each other to a limited extent and also hampers a few things, such as having an SCC or Inverter use "End Amps" to stop charging for example.
We don’t understand this point. Both SCCs and Inverters can be limited to min and max charge voltage (bulk/absorp/float) and can be set up with both time and current limits.
 
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Yes, Amy mentioned the Chargery BMS as well, but seeing that Will Prowse didn’t seem to be too impressed with them, especially not how to set them up:
I’d be wary, as well, but I can’t afford to be as picky as Will. My concerns are: does it do what it says it will do and does it do it well? and even if config is a little complicated (Bluetooth simplifies it now, iirc his didn’t have Bluetooth and he had to go through a series of button presses to configure). At any rate, use your due diligence. There are spec sheets and manuals available. You just have to look.
 
Inefficiencies was more in that, over time, wear & tear, reduces performance a bi with all equipment. Nothing bad, as such., opportunity to possible refresh or update the odd bitsif needed.

Interactive BMS. If a BMS system is capable of interacting with the Inverter/Charger systems, that can be used to regulate and control charging, which increases performance. Several systems use the CanBus protocols to interact, such as Victron.

The settings for Lithium is all that is really needed, that way there is "accidental" things, like doing an equalize.

Multi-packs. Example
Take 4 packs in 1 bank. all charging and your pushing 100A. They all split the charge pretty equally, it floats a little +/- 5A between then usually is normal. Quite often there is a "runner" cell, means it will reach 3.65V when the others are at 3.45V and cause an HVD (Hi volt disconnect) trip that cuts the battery off. Not unsual with commodity cells. 100A is now split with 3 packs, then another packs trips, now 2 packs are sharing 100A, click 1st pack comes back online because the hi cell settled below the threshold but 45 seconds later it trips again. This occurs when battery packs start to reach the top of their normal operating curve, which happens to be 3.000-3.400V.

Good Inverter/Chargers, standalone chargers and solar controllers can handle such fluctuations. They do NOT like when in this example all 4 packs hit cutoff and it's a hard drop. You will hear relay snaps and you may even get system resets. If there is a Genset at play doing the charging, well... let's just say, it won't appreciate it either. Inverter Gensets most especially.
note, there is more info in this response than needed, but it is a consideration for future readers who may not be so equipped.

Discharging can be to a point, where one cell reaches the cutoff threshold, most have it at 2.65-2.75, this causes an LVD (low volt disconnect) trip and cuts off the battery pack. As packs reach LVD states, the Inverter can only see the bank as "one" and will cutoff at whatever it's programmed for.

Volage Accuracy for Solar Controller & Inverter is considerably more important with any form of Lithium Based battery system than Lead.
There's a link in my signature on that.

Hope I answered your questions.
 
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