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Battery Capacity calculation


Mars
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I deal with Voltronic Axpert a lot but never used monitoring ( i even dont have a PC )

But now i have almost 800 big Lifepo4 cells in The Netherlands ( They are 60Ah and on sale by the way )

and i want to test capacity of them before selling.

 

I have the old cheap version Voltronic KS 24V PWM 2.400W only USB A or B port on it

If i find a PC and install software ( Watchpower i believe ) can i learn capacity from software after charge or discharge?

@Coulomb

 

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6 hours ago, Mars said:

If i find a PC and install software ( Watchpower i believe ) can i learn capacity from software after charge or discharge?

You probably could, but I think you will be far better off getting yourself a dedicated cell charger/discharger. You could sell it at the end of the testing.

One big problem is that the Axpert doesn't directly measure the battery current, and infers it using an estimate of inverter efficiency. So the accuracy would be poor.

But I think the biggest problem is that you'll have to test the cells 8 at a time with the 24 V inverter, and you'll be wanting to drain them to fairly low levels. it sounds like they're from different origins, so some will have higher capacity than others, so you'll risk some getting under-voltaged unless you have a BMS as well. Then the BMS has to talk to the inverter to tell it to stop discharging when the first cell voltage goes low (under say 2.5 V). Then how do you test the other cells in that string?

Testing 800 60 Ah cells is going to take a lot of time. Good luck with your testing and sales.

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What accurancy is poor for you ? For example we are selling 67Ah Lifepo4 cells of A123 but  we sell as 60Ah to avoid liability. So %10 deviation from 67Ah is ok for us.

Dedicated charger tester any example you have ? Because 60Ah can be tested at 30A but can also discharged up to 200A.

Cells are brand new ,  Specifications and Photos  are here if you want to see. ( We are mostly selling 60AH. We also have 20AH but very expensive )

You gave me a good idea to use BMS with Shunt like SBMS of Electrodacus. 

Then the question is if SBMS can give me capacity info for individual cells or only for total 8 cells as well. Any idea about SBMS ?

 

After talking with you I guess i will not test 800 of them. I basicly can not manage it. When we are selling we sell with Guarantee to take back returns and refund. So it is more logical to use people for testing :)  Not only time but when we test we need to open protection tape of Tab. Then people can think them as second hand if tape is open , tabs are damaged etc. So if i can test 80 of them it is enough.

 

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3 hours ago, Mars said:

What accurancy is poor for you ? 

I was thinking that if you give each cell a capacity rating, you'd want it to be within about 5%, and you might struggle to get that accuracy from an inverter without a direct current shunt.

3 hours ago, Mars said:

Dedicated charger tester any example you have ?

No, this isn't my area of expertise; I think there is something commonly used in the remote controlled plane industry that is well regarded and moderately priced. "Cell log 8" comes to mind.

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Cells are brand new ,  

Oh! I got the impression that these were surplus, hence the need for testing.

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Then the question is if SBMS can give me capacity info for individual cells or only for total 8 cells as well. Any idea about SBMS ?

Again, not my area of expertise, sorry.

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