BMS Requirements and Cost for 200ah and larger Lifepo4 Cells

[TedH]

As I have planned and assembled my 4.8Kw battery bank, BMS amperage capacity and price has become a concern.

When I bought my first BMS, I bought one rated at 100amp, continuos, 50amp charging. When it arrived, I found the gauge of the cables suspect and am concerned that trying to push 100amps (24v BMS) continuous may be a problem. I have since decided to keep this BMS as a backup and opted for two, 320amp BMS (Ant BMS) for a total cost of about $200 for the two BMS.

My battery pack uses 16, 3.2v, 100ah CALB lifepo4 cells. Two, 4-cell packs are connected in series to generate 24volts. When my other 8 cells arrive, I will have all 16. I will connect the 8 in two packs to make 24v. Then, I will connect the two pairs in parallel to have a 24v, 200ah bank. I am using two BMS wired; both as 8S BMS.

During my research of BMS products on eBay and Amazon, I have also looked at the requirements to manage raw 200, 280, 300 and 400ah cells in 24v packs. Since I have found the BMS capacity a limiting factor, I am concerned at the availability and cost of a BMS to handle, say, a 24v, 600ah bank consisting of 16, 300ah, 3.2v cells. This would be three times the capacity of my bank or roughly 4.8*3=14.4Kw. That is a large setup capacity-wise but the footprint is about double the footprint of my 16-cell, 100ah bank.

What BMS options are available to manage the larger needs for continuous amps (600) and charging amps (150)? I suspect the BMS price rockets upward for the larger cells. Hopefully, the price comes down when I am ready to upgrade (several years).

 

[TedH]

This is the pricing that I am seeing for 4S BMS with high continuous amp discharge: https://www.ebay.com/itm/4S-12V-BIG...712989?hash=item48eaba24dd:g:9kYAAOSw7qtfLYHE

 

[TedH]

If I were going to upgrade to 8S, 24V, this is probably the direction I would go for a BMS: BMS on eBay

I would probably go 400A if assembling a pack of 200ah-300ah cells in a 24v config. I note the cabling has to be welded to the BMS; not installed.

 

[Dzl]

As I have planned and assembled my 4.8Kw battery bank, BMS amperage capacity and price has become a concern.

When I bought my first BMS, I bought one rated at 100amp, continuos, 50amp charging. When it arrived, I found the gauge of the cables suspect and am concerned that trying to push 100amps (24v BMS) continuous may be a problem. I have since decided to keep this BMS as a backup and opted for two, 320amp BMS (Ant BMS) for a total cost of about $200 for the two BMS.

My battery pack uses 16, 3.2v, 100ah CALB lifepo4 cells. Two, 4-cell packs are connected in series to generate 24volts. When my other 8 cells arrive, I will have all 16. I will connect the 8 in two packs to make 24v. Then, I will connect the two pairs in parallel to have a 24v, 200ah bank. I am using two BMS wired; both as 8S BMS.

Sounds like you are on the right path.

During my research of BMS products on eBay and Amazon, I have also looked at the requirements to manage raw 200, 280, 300 and 400ah cells in 24v packs. Since I have found the BMS capacity a limiting factor, I am concerned at the availability and cost of a BMS to handle, say, a 24v, 600ah bank consisting of 16, 300ah, 3.2v cells.

Divorce the concepts of battery bank capacity and BMS current rating in your head. They are independent of one another.

BMS should be sized based on maximum current flowing through the BMS, not maximum battery bank capacity.

What BMS options are available to manage the larger needs for continuous amps (600) and charging amps (150)? I suspect the BMS price rockets upward for the larger cells. Hopefully, the price comes down when I am ready to upgrade (several years).

It is my impression based on what I've read and heard here and elsewhere that FET based BMS' are best suited for lower current applications and are not the best option for high current applications.

For higher current applications a different BMS topology is more suitable. There are a handful of approaches but most either use external relays to control charge/discharge (and can easily handle upto 600A with the right relays and components) or control loads and charge sources directly (and thus the BMS itself is not a current bottleneck). In both cases these types of BMS are not current constrained within practical limits (600A+ is a crazy amount of power, that is 30,000 Watts @ 48V, 15,000 Watts @ 24V).

SBMS0, Chargery BMS, TinyBMS, 123smartBMS are some options

Not all of these options are expensive, some of them are. They are a bit more complicated to setup, but also more capable and flexible.

This is the pricing that I am seeing for 4S BMS with high continuous amp discharge: https://www.ebay.com/itm/4S-12V-BIG...712989?hash=item48eaba24dd:g:9kYAAOSw7qtfLYHE

If I were going to upgrade to 8S, 24V, this is probably the direction I would go for a BMS: BMS on eBay

I would probably go 400A if assembling a pack of 200ah-300ah cells in a 24v config. I note the cabling has to be welded to the BMS; not installed.

Those look like they are Daly BMS' (either rebranded or knockoffs), from what everyone says, they seem like a solid decent company as far as FET based commodity BMS' are concerned. Good build quality but very basic (this can be good or bad depending on your wants/needs). I have not personally seen any feedback or purchases of Daly BMS' above 250A.