How to determine if a LiFePo4 Prismatic Cell is good quality or bad quality for SOLAR/Home use?

[zedconnor]

As far as I know ,

1. Cell Capacity (should be equal or higher than the Rated Ah)
2. Cell Internal Resistance at the terminals should be lower than 50mOhm
3. Cell Appearance (should be as flat as possible with no physical damage/defects)

Is this enough to decide if a cell you ordered from Alibaba or AliExpress is good or bad? Should there be other parameters that need checking without needing too much advanced knowledge, and also being accessible to the common person?

Please share your knowledge on this matter so people can at least try to deal with the shady sneaky practices of Chinese resellers.(Qr re-printing to eliminate the real identity of the cell itself and other stuffs)

 

[rodrick]

You can ask for the factory test data sheets for each cell and verify them with the QR code and I believe you can look them up on the manufacturer sites on some of the cell manufacturers I’ve read but never done it myself

basically your 3 criteria’s are pretty much what you want in solar application but I would want lower ohms mine are about 17 ohms

dealing with Alibab or Ali express can be a big risk don’t go for the cheapest and maybe make multi small orders vrs buying a large lot it may cost a little more but you can see what they send you with a smaller financial risk and it gives you time to test the smaller batch and they may be less likely to send you crap if they know your plans for multiple orders

good luck

 

[Steve_S]

1) For what we call "Grade-A" the battery should have a capacity of 5% then their AH rating. For Instance, a typical 280AH would have a Gross Capacity of 290-292 AH and a NET Capacity of 280AH from the Working Voltage Range.
2) Cell Resistance is usually 20 milliohms +/- 5. It is more important to have battery cells with Matched IR so that their resistance is identical across the working voltage range.
3) Correct -but- prismatic cell casing is like a popcan, quite soft & flexible so they are rarely "perfectly flat".

Properly Matched & Batched cells are tested through the working voltage range for their IR. These are Charge & Discharge cycled and tested typically at every 0.050 voltage step. When matched they keep the same IR be it at 3.000 or 3.400 Volts. Most legitimate companies and provide the factory cell test report. Others may do their own tests and may provide a report.

Many vendors will "Match" cells but ONLY do it at the Storage Voltage as received which is typically 3.200V (50% SOC). These ARE NOT BATCHED and you don;t get a testing report. These will not have a Cell Report from the Manufacturer.

Understand that LFP, just like all other chemistries have an "Allowable Voltage Range" which is from 2.500-3.650. This is the voltage range that causes no harm/damage to the cells. The actual "Working Voltage Range" is from 3.000-3.400 because LFP has a very flat curve, this is the voltage range that delivered the Labelled AH's.

I can comfortably recommend Luyuan Tech on Alibaba who is a well known Good Vendor who can provide properly EVE Factory Matched & Batched cells or quality B-series Voltage & IR Matched cells.

They carry Cells, Popular BMS', wires, cables, lugs & even cases.
TIP: It costs less to buy stuff from one vendor who can package all the small bits up into one box. You are then only paying for the one box + weight as there is a minimum $ per box. More boxes (regardless of weight cost more). Also Luyuan is More Competitive on things like JKBMS' than most others...

Shenzhen Luyuan Technology Co., Ltd. - Lifepo4 battery, LTO battery

Shenzhen Luyuan Technology Co., Ltd., Experts in Manufacturing and Exporting Lifepo4 battery, LTO battery and 0 more Products.

szluyuan.en.alibaba.com

BTW: The shipping guesstimator is just that. You need to open a Chat / Messenger session on Alibaba to get a proper quote from Amy.

Hope it helps & Good Luck,

 

[zedconnor]

1) For what we call "Grade-A" the battery should have a capacity of 5% then their AH rating. For Instance, a typical 280AH would have a Gross Capacity of 290-292 AH and a NET Capacity of 280AH from the Working Voltage Range.
2) Cell Resistance is usually 20 milliohms +/- 5. It is more important to have battery cells with Matched IR so that their resistance is identical across the working voltage range.
3) Correct -but- prismatic cell casing is like a popcan, quite soft & flexible so they are rarely "perfectly flat".

Properly Matched & Batched cells are tested through the working voltage range for their IR. These are Charge & Discharge cycled and tested typically at every 0.050 voltage step. When matched they keep the same IR be it at 3.000 or 3.400 Volts. Most legitimate companies and provide the factory cell test report. Others may do their own tests and may provide a report.

Many vendors will "Match" cells but ONLY do it at the Storage Voltage as received which is typically 3.200V (50% SOC). These ARE NOT BATCHED and you don;t get a testing report. These will not have a Cell Report from the Manufacturer.

Understand that LFP, just like all other chemistries have an "Allowable Voltage Range" which is from 2.500-3.650. This is the voltage range that causes no harm/damage to the cells. The actual "Working Voltage Range" is from 3.000-3.400 because LFP has a very flat curve, this is the voltage range that delivered the Labelled AH's.

I can comfortably recommend Luyuan Tech on Alibaba who is a well known Good Vendor who can provide properly EVE Factory Matched & Batched cells or quality B-series Voltage & IR Matched cells.

They carry Cells, Popular BMS', wires, cables, lugs & even cases.
TIP: It costs less to buy stuff from one vendor who can package all the small bits up into one box. You are then only paying for the one box + weight as there is a minimum $ per box. More boxes (regardless of weight cost more). Also Luyuan is More Competitive on things like JKBMS' than most others...

Shenzhen Luyuan Technology Co., Ltd. - Lifepo4 battery, LTO battery

Shenzhen Luyuan Technology Co., Ltd., Experts in Manufacturing and Exporting Lifepo4 battery, LTO battery and 0 more Products.

szluyuan.en.alibaba.com

BTW: The shipping guesstimator is just that. You need to open a Chat / Messenger session on Alibaba to get a proper quote from Amy.

Hope it helps & Good Luck,

Very informative! Thank you for taking the time to explain! And I think my next order would probably be from Luyuan as I have already tried Docan and RWT.
I have been testing the cells i ordered with 2.5-3.65 range using the ZKETECH EBC A40L tester(40 amps version).
I havent really tried the 3 to 3.4 range.

 

[Alkaline]

You can ask for the factory test data sheets for each cell and verify them with the QR code

Golden Advice everything else is a old wife's tale.