LIFEPO4 Battery discussion thread

cavedog said:
So when the solar boom started were these pylontech batteries cheap or something? 2nd hand market is flooded with them now. Crazy. Didn't know they used those pouch cells. Thought they had prismatic cells.

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They where the oldest in the msrket if i am not wrong. That is why every bloody battery has a pylon protocol with inverters they kinda started it all
 
cavedog said:
Unrelated to the batteries but as mentioned in the Solar in rain and cloudy weather thread when my inverter is connected to the grid the ac transformer max is 4kW the rest offloads to grid. If I cut power to it then that artificial limit goes away and I can push 5.2kW easy on the ac transformer without overload alarm.

I don't know why it does that and there is no setting for it so looks like for most part I will just run in offgrid mode. I even checked the temps and they are not affected by it. The only thing it doesn't like temp wise is the 3kW geyser element.

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Can you use a narrower scale with grid frequency? It only operates in the 49-51 range.
 
cavedog said:
I'm also thinking of getting one of those CFE rack batteries. R5000 or R4500 if I can find a seller willing isn't a bad deal depending on the state of it.
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Would be really interesting to see whats inside and swap the bms out with a JK bms
 
wingnut771 said:
I guess R5k is worth risking it for the biscuit.
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DTBA said:
Would be really interesting to see whats inside and swap the bms out with a JK bms
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Yeah I'm really keen to see the build quality and see what cells look like and capacity also. I will probably get one this comming week as I need to go to the office so I can meet one of these JHb sellers as they are the lowest priced ones. The PTA ones still want around R6500. If I can get it for R5k or lower I think it will be worth it.
 
cavedog said:
Yeah I'm really keen to see the build quality and see what cells look like and capacity also. I will probably get one this comming week as I need to go to the office so I can meet one of these JHb sellers as they are the lowest priced ones. The PTA ones still want around R6500. If I can get it for R5k or lower I think it will be worth it.
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Lets hope we get access to BMS.
 
At R5,000, a CFE 5.12kWh lithium battery is an absolute bargain, but you need to proceed with extreme caution. Secondhand or refurbished CFE-5100S units do pop up around this price point, but there is a major technical reason why these specific models are being dumped so cheaply on the South African market. [1, 2, 3]

The Catch: Why Are CFEs Selling for R5k?​

The older generation CFE-5100S modules are infamous in South African solar communities like the Power Forum for severe firmware and hardware flaws: [4]

  • BMS Thermal Runaway & Fires: Early batches suffered from catastrophic Battery Management System (BMS) failures. A notable number of units actually caught fire or melted down due to faulty internal balancing, prompting a massive wave of warranty returns (RMAs).
  • Firmware Communication Glitches: These units frequently lose communication with popular inverters (like Deye, Sunsynk, and Luxpower), causing the system to unexpectedly trip into low-voltage protection modes.
  • Mass Refurbishing: Many of the R5,000 units are repaired or refurbished stock that distributors couldn't sell as new. [1, 3, 4]

Critical Checks If You Still Want to Buy It​

If you decide the R5,000 price tag is worth the gamble, protect yourself by verifying the following before handing over cash:

  1. Check the Serial Number: Ask the seller for the manufacture date. Avoid anything built between 2022 and early 2024, as these represent the highly problematic batches.
  2. Firmware Version: Ensure the battery has been flashed with the absolute latest CFE firmware patch, which was released to address the charging cut-off and inverter communication drops.
  3. Physical Inspection: Open the casing if possible or inspect the casing seams carefully. Look for any bulging, warping, or a chemical/burnt smell, which points to compromised cells.
  4. App Verification: CFE units have a built-in Wi-Fi module. Force the seller to connect it to the CFE App in front of you so you can read the true State of Health (SoH) and actual cycle history. [5]

The Verdict​

At R5,000, it is incredibly cheap for a 5kWh bank. If you are using it for a basic, low-draw backup system (like a small inverter just running lights and Wi-Fi), it might be worth the risk. However, if you are planning to hook it up to a high-demand hybrid solar system, it is highly recommended to skip it and pay a bit more for a safer brand.
 
Yes, you absolutely can replace the factory CFE BMS with a JK BMS, and it is actually a highly popular "revival" project in South African DIY solar communities. [1]
By tossing out the problematic native CFE management board and installing a premium JK Smart Inverter BMS (such as the PB2A16S10P or PB2A16S15P), you bypass all of CFE's notorious firmware, thermal balancing, and shutdown issues. You turn a risky, unstable R5,000 battery into a highly reliable, robust 5.12kWh powerhouse.
The practical steps, requirements, and caveats for this conversion include:

1. Match the Technical Profile
  • Cell Layout: The CFE-5100S is a 51.2V 100Ah pack consisting of a standard 16S (16 cells in series) LiFePO4 chemistry configuration.
  • BMS Selection: You need to purchase a 16S JK Inverter BMS rated for at least 100A to 150A continuous discharge. Make sure you purchase the specific "Inverter" version (PB series) rather than the standard DIY hobby version, as the inverter model includes native CAN bus and RS485 communication protocols required to talk to brands like Deye or Sunsynk. [1, 2, 3]

2. The Conversion Process
  • Open the Casing: Disconnect the battery completely. Remove the top lid of the CFE mental housing.
  • Strip the Old Logic: Safely disconnect and label the original CFE balancing wires, temperature sensors, and the main positive/negative power leads attached to the factory BMS.
  • Wire the Balance Leads: You must completely replace the factory balance wiring harness with the new wires provided by JK. Wire them sequentially from Cell 1 (Negative) all the way up to Cell 16 (Positive).
  • Mounting: The internal layout of the CFE battery is relatively standard. The compact form factor of a 100A JK BMS generally fits neatly into the front compartment where the old board sat, though you may need to drill alternative mounting holes into the mounting plate. [1]

3. Key Benefits of Making This Upgrade
  • Active Balancing (The Biggest Upgrade): The factory CFE BMS relies on weak passive balancing (wasting tiny amounts of excess cell energy as heat). The JK BMS features built-in 1A or 2A active cell balancing, which actively pumps energy from high cells into low cells. This will perfectly re-balance and "heal" any mismatched cells inside the used CFE pack.
  • Flawless Closed-Loop Communication: The JK Inverter BMS has highly reliable, pre-programmed protocols that simulate Pylontech, Growatt, or Deye battery communications seamlessly, ending the sudden communication drops. [1, 2]

4. Important Trade-Offs to Consider
  • The "Cost Catch": A quality JK Inverter BMS with active balancing costs roughly R1,800 to R2,500 in South Africa. If you buy the battery for R5,000, your total investment rises to around R7,000–R7,500 plus your manual assembly time.
  • Loss of Native WiFi App: You will no longer use the standard "CF Energy" app. Instead, you will monitor the battery natively via the vastly superior JK BMS Bluetooth App, which gives you precise, cell-by-cell voltage data and telemetry. [1]
If you have basic electrical DIY confidence and a decent soldering iron or crimping tool, this is the single best way to utilize a cheap CFE battery without inheriting its factory flaws.
 
To connect a new JK BMS balance harness to cells with welded terminals, you must never solder directly onto the cell tops or weld with the BMS wires attached, as the extreme heat will permanently destroy the internal lithium chemistry or fry the BMS.
Instead, use one of the three established DIY methods to create a secure, safe mechanical connection.

Method 1: The Ring Terminal & Self-Tapping Screw (Most Common)
If the cells are joined by thick, flat aluminum or copper laser-welded busbars, you can secure the JK balance wires mechanically by drilling into the center of the existing busbar.
  1. Prepare the Balance Wires: Crimp a small M3 or M4 copper ring terminal onto the end of each JK balance wire.
  2. Drill the Busbar: Use a small drill bit (e.g., 2.5mm) to carefully drill a shallow pilot hole directly into the center of the welded busbar. Work slowly so metal shavings do not fall between the cells.
  3. Secure the Connection: Screw a short stainless steel self-tapping screw through the ring terminal and into the pilot hole. Use plastic washers to ensure the screw cannot vibrate loose.

Method 2: The Solder-to-Busbar Method (Safest for Cells)
If you prefer soldering over drilling, you must do it before the busbar is attached to the cell, or use extreme speed and heat sinking to protect the cell terminal. Since your terminals are already welded, follow this strict heat-sink protocol:
  1. Pre-Tin the Wire: Strip and tin the tip of the JK balance wire with solder.
  2. Prep the Busbar Surface: Lightly sand a tiny spot on top of the welded busbar (not the cell terminal itself) and apply a drop of high-quality soldering flux.
  3. Use a Heat Sink: Place a damp cloth or a heavy piece of metal directly on the cell terminal next to your target spot to absorb stray heat.
  4. Flash Solder: Using a high-wattage soldering iron (60W–100W), touch the iron to the busbar for no more than 2 seconds to pool a small amount of solder, then instantly press the pre-tinned JK wire into it. Remove heat immediately and cool it down.

Method 3: Spot-Welded Nickel Tabs (For Dedicated Spot Welders)
If you have access to a battery spot welder, you can weld a clean mechanical point onto the existing terminals.
  1. Spot Weld a Tab: Take a small strip of pure nickel tab and spot-weld it directly onto the existing welded terminal or busbar.
  2. Solder Safely: Because the nickel tab is thin and juts out away from the battery, you can safely solder the JK balance wire to the far tip of this tab without transferring dangerous heat down into the cell.


⚠️ Critical Safety Rules for the Conversion
  • Disconnect the Harness First: Never have the balance wire harness plugged into the JK BMS while you are attaching the wires to the cells. One accidental short will instantly incinerate the BMS logic board.
  • The "B-" Main Power Cable: Before doing any balance wiring, the main thick blue B- cable from the JK BMS must be solidly connected to the main negative terminal of the entire cell pack.
  • Verify Volts Before Plugging In: Once all 17 balance wires (B0 to B16) are secured, use a digital multimeter to test the harness plug pins sequentially. Pin 1 to Pin 2 should read ~3.2V, Pin 1 to Pin 3 should read ~6.4V, and so on. Only plug the harness into the JK BMS once the voltages step up perfectly without any reverse polarity.
 
AI. Can't really take what is says as gospel. It told me to remove battery 3 from my setup immediately as it poses an extreme high risk of fire or catastrophic failure.

I need to immediately switch off the bms switch and breaker and transport the faulty unit to an approved battery repairer to rebuild the battery with new cells. :cautious:
 
cavedog said:
AI. Can't really take what is says as gospel. It told me to remove battery 3 from my setup immediately as it poses an extreme high risk of fire or catastrophic failure.

I need to immediately switch off the bms switch and breaker and transport the faulty unit to an approved battery repairer to rebuild the battery with new cells. :cautious:
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Indeed. Just wanted to see if it would agree with me :P

I pictured drilling holes into the busbar to tap new JK balance wires to replace dodgy cfe bms. Just not sure about the main negative if its an easy swop or is there desoldering and crimping lugs required. AI didn't help me there.
 
LFP technology is really moving fast now. Seems like cycle life is pointless now. 8000+ cycles...

They should rather focus on refining the BMS as it seems the cell technology is so good already.

Screenshot 2026-05-24 071438.png
 
cavedog said:
LFP technology is really moving fast now. Seems like cycle life is pointless now. 8000+ cycles...

They should rather focus on refining the BMS as it seems the cell technology is so good already.

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I’ve been saying cycle life is meaningless. It’s about the calendar aging.

They already have. It’s called JK BMS.

Only possible with DIY battery.
 
wingnut771 said:
I’ve been saying cycle life is meaningless. It’s about the calendar aging.

They already have. It’s called JK BMS.

Only possible with DIY battery.
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Yeah the Jk seems like the best in the business. For my DIY project I might actually get a JK and replace the CFE battery pack with it. Will see how the enclosure is for it. Might be tight if they have a trash bms.
 
cavedog said:
Yeah the Jk seems like the best in the business. For my DIY project I might actually get a JK and replace the CFE battery pack with it. Will see how the enclosure is for it. Might be tight if they have a trash bms.
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JK is quite compact when compared to other BMSs.
 
Yeah cell08 is low again. I think cell08 is cooked. The OVP was set at 3.7v so wonder if it got any damage. There is like 2800 ovp in the bms logs so yeah might have gotten some damage and has less capacity now compared to the others.

Screenshot 2026-05-24 080424.png
 
cavedog said:
Yeah cell08 is low again. I think cell08 is cooked. The OVP was set at 3.7v so wonder if it got any damage. There is like 2800 ovp in the bms logs so yeah might have gotten some damage and has less capacity now compared to the others.

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I wont say that till the battery is balanced.

Reason be it ran 350 cycles with really bad balance settings.

You will be have to keep it going for month or so with slowly increasing charge voltage.

The reason why I say cell 8 is not toast is because its not the same cell the went it to OVP

That is why I ask last time what cell went in ovp


So lets say cell 8 is only getting charge to 88AH max. getting the balancer to balance the 12ah into that cell is going take a while at 200mah.
 
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