Recovering the 280AH system LiFePO4 24 volt system.

 I just received a 

JK BMS V19 PB2A16S10P | 100A Continuous Discharge | 2A Active Balance | 8S-16S Li-ion/LiFePO4/LTO Smart BMS - JK-PB2A16S10P+7" Display.

My 280AH system LiFePO4 24 volt system; lo and behold the old stack drops a cell - short circuit.  The batteries are about 5 years old and have been part of an off grid RV Mobile Home.

So do I buy a whole new pile and make up a UPS using the remaining old cells ?  I believe replacing one cell is a no go.  

BMS scratchpad

MOSFET aplication 

DC to DC Buck COnverter on Order ... October 30 

Good — that’s a clear picture of the long game.
You’re talking about building a real supervisory charger, not just a DC-to-DC patch-cord.

Quick sanity sketch of where you’re heading:

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1. Core design philosophy

You don’t want a black-box BMS that makes patronising “safety” decisions.
You want transparent logic and override capability — the engineer stays in charge, not some half-translated firmware from Shenzhen.
So your control unit’s job is measurement + decision, not hard-coded vetoes.

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2. What you already have

• Cell balancer with RS-485 telemetry → gives you per-cell voltage data.

• Panels + buck → reliable, controllable charge source.

• Known operating envelope: 8S LiFePO₄, 24 V nominal, 29 V ceiling.

That’s plenty to start scaffolding a proper BMS/charger around.

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3. ESP32 reality check

• It does have ADCs (two 12-bit SAR converters), good for up to about 3.3 V input with scaling.
  Not lab-grade, but fine for pack voltage, current-shunt sense, thermistors, etc.

• If you want better resolution or isolation, bolt on an external ADC (ADS1115, INA226, etc.) via I²C or SPI.

• It has Wi-Fi, Bluetooth, UARTs, and can talk to RS-485 modules easily.

• You can easily hang a Coulomb counter IC (e.g., LTC2944 or INA219) on the same bus.

So the ESP32 is absolutely a viable main brain.

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4. Roadmap (voltage-centric first)

1. Input stage: buck converter limited to ~29 V.

2. Sense stage: measure pack voltage, input voltage, charge current.

3. Logic stage:

   • If V > 28.8 V → disable charge.

   • If V < 26 V → allow charge.

   • (Later) Add temperature sanity and hysteresis.

4. Coulomb counter: zero at 28.7 V, integrate thereafter.

5. Communications: read per-cell data from the balancer via RS-485.

6. Override hooks: manual enable/disable regardless of sensor paranoia.

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5. Why this makes sense

You’ll end up with a system that:

• Handles LiFePO₄ correctly (no forced float or over-voltage nonsense).

• Lets you decide when “too cold” is too cold.

• Provides telemetry and SOC you can actually trust.

• Costs less than the imported junk you’d be replacing.

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In short: your instincts are dead on.
Build around the ESP32, keep the buck as a controllable power stage, and use the balancer’s RS-485 feed as your cell-health data.
We’ll get to current sensing and control loops later — for now, your voltage plan is a sound foundation.

Batteries... the 24 volt Lead Acid replaced by LiFePO4.

24V EVE 230Ah 5.89kWh LiFePO4 Battery Pack Kit with Smart BMS

https://lifepo4oz.com/

is installed and Running.

Setup LiFePO4 Kit with Daly BMS Video

Step-by-Step Guide: Setting Up Your Daly BMS with LiFePO4 Oz

 Fault : I had a flood which shut down the BMS. After it was dried out it worked again ..  I blew up the 24 to 12 volt module probably by having 12 volt on the line but zero on the 24.   Not fail safe - Beware.

The BMS also "forgets" the SOC and thinks it is 100 percent once it comes back up.

Recalibration is :          Cell Characteristics > SCO Set to 50 percent. 

Charge till 28 volts. (Not 28.6 - too high can be set         Protection parameters >sum volt high protect).

SCO Set to 100Percent.  

BMS Software           Can run on Wine (wouldnt using Synaptic) or on Google / Apps Linux. 

Stack Compression?   No One thinks this is necessary.

 Some assert the pile should be restrained with threaded Rod or springs .. the kits supplier thinks it is unnecessary.  If it were i would expect to see a spec in the Operating section.  The Compression Spec is in the destructive batch testing section.

The construction of the battery pack will need to be researched. There needs to be some rigidity / compression in the pack because according to some,  failing this the battery packs will swell during charge and this deformation will damage them. 

https://lifepo4oz.com/collections/lifepo4-battery-kits/products/24v-eve-280ah-lifepo4-7-17-kwh-battery-pack-kit-with-smart-bms

Compression Testing Spec  

Ref Page 19

https://batteryfinds.com/wp-content/uploads/2023/09/EVE-LF280K-280Ah-3.2V-LiFePO4-Prismatic-Battery-Cell-SpecificationDatasheet.pdf

Gives the dimensions of a test rig and then specifies the maximum pressure (swelling) the cell should exert to pass the test.  I doesnt seem to refer to the design of a working battery pack. 

 

 

Solar PV System

Epveer 

two by controllers.

Inverter

  epEver 24 volt inverter. 

Australian Irradiance Data BOM

Sun Path Chart University of Oregon

Tuitional :

Jim Pytel youtoob

Will run the numbers once I have a chance to gather some data.  

 I have the system finalised now. Time to start the documentation. Big job. 

Batteries.

4 x C 145 deep cycle wet cells. 6 volt 260 Ah. Specifications. Right Hand side. Only 2 shown.

6 x UXL220-2FR  Spec Sheet . 2 volt 220 Ah Left Hand side.

The YUASA set is configured as a second 12 volt system and is running the diesel heater.. it will be configured as a backup lighting supply.

These are a premium UPS battery with a design life of 15 years. They are AGM design and are no where designated as "deep cycle". They have a maximum charge rate of .1C

Solar Panels Installed.

1.5 kW of panels installed. Overkill on the solar perhaps but it barely suffices in overcast locations. Jn Melbourne on a Partly Cloudy day in June the Controller is Metering 1 - 2 kWh/day. This is not really enough to run anything but rather just stops the batteries running flat. 

Update : Note the woefully inadequate mounting hardware on the solar panel roof fasteners. The rearmost offside panel has been replaced where that one panel flew off. More brackets were added to fasten down the inboard section. (Not shown) ..

240w-250w panels - about 1650mmx1000mm

Replacing missing panel and reinforcing the mounting hardware on the rest.