Steve, I'm planning to build a 48v 16 to 32 cell LifePo Prismatic battery with around 10kW+ depending on the cells I get. Knowing what you know now what size cells, supplier and BMS would you suggest? PS Like your Youtube channel! -Keith
I don't have a youtube account, this site belongs to Will, I'm just a member here.
With prismatics, you ONLY want to use a max of 90%. many use 80% leaving 10% from the top & bottom to maximize the cycles.
Quicky Math: 48V LFP pack actual voltages are 40V (2.50 per cell 0% SOC) to 58.40V (3.65 per cell 100% SOC) 48.0V=3.0V per cell.
200AH X 48V = 9,600AH (-20%=7,680AH /
368.64 kWh), -16 cells
280AH X 48V = 13,440AH (-20%=10,752AH /
516.1 kWh) -16 cells
A Handy Electrical Calculator toolset to bookmark: https://www.inchcalculator.com/electrical-property-conversion-calculators/
With the Grade-A
commodity cells, which are Voltage & IR compliant "for the grade" but not fully matched & batched for Voltage & Internal Resistance (adds $ per cell) it is common to see some float & deviation, 1mv per AH is not uncommon and they do deviate more at the top & bottom. "Commodity Cells" means bought from Manufacturer, after passing grading compliance tests and without defects. Fully Matched & Batched sets can cost 2X or more. These of course are more economical to build with and with only using 80 or 90 % of the full cell capacity, that more or less negates these issues.
Some folk do get their knickers in a knot over a certain amount of minutia.
With the above stated, I feel that a good quality Active Balancing system capable of transferring High Volts from cells to Low Volt cells within an active ESS (Energy Storage System) and a good quality BMS to control & protect the battery pack is pretty important overall. NOTE on Passive Balancing: passive, is very slow, typically < 2A does little good unless the cells are Fully Matched & Bottom/Top Balanced with minimal deviation. All passive does is burn off high voltage from cells bringing them into balance with the lowest voltage cells.
My Active Balancers will be arriving this Friday 18th (so they say) and my battery systems will be completed within a week after that when I will be writing it up a bit and making observations etc. I'm doing my final powerhouse overhaul when weather cooperates.
BMS Choice depends on the application, the expected normal & maximum amps will be demanded and obviously how much charge capacity will be hitting the battery bank. For my application, I chose Chargery BMS' which will now have 300A DCC's (Solid State Bi-Directional Contactors).
CHARGING: Charging is to be determined by the total capacity of the battery bank and how long it would take to charge it on the shortest Sun Hour Days for your location if charging by solar. Most figure on 3 days full reserve, so assuming 3 days of no sun to reach 15% then you have to be able to recharge from that to 90% within the time period you can get. Alternately a Generator could be used or the grid as well with the proper equipment.
