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Strange 18650 capacity test
#1
I got myself the imax b6 and when i discharge a a cell from laptop battery at 1 amp, voltage drops to 4.05 as usual so this means IR is not bad, but after that voltage drops fast until somewhere around 3 volts and stays there. However when i tried to discharge it with 0.5 amp it discharges normally and gives out 2000 mAh. Whats the problem
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#2
No one knows the problem
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#3
I dont think we understand

How long time does it take to drop to 3V at 1A vs 0.5A to what voltage?

What capacity at 1A?

You have left alot of factors so its impossible to give you an answer more than guessing wildly
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#4
For accurate IR you have to use a tester. I use the yr1030 tester that way I don't have to guess if the IR is good. With the tester you can compare it to what the battery specs are since all battery manufactures use the same methods to test the IR on their batteries.

If the IR is 60 milliohms or below it's probably good for laptop batteries. I think in your situation there is probably something wrong with your charger that it won't discharge at 1 amp.
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#5
Cell drops to 3 volts in 30 minutes and stays there. Imax is pulling near 1 amp at 3 volts but when i discharge with 0.5 amps test ends at 3 volts and test lasts around 4 hours capacity at 1 amp is around 1500 and at 0.5 amp 2000 and i dont think my charger is faulty other cells i tested at 1 amp discharged normally
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#6
(05-13-2020, 08:29 AM)Yiğit Wrote: Cell drops to 3 volts in 30 minutes and stays there. Imax is pulling near 1 amp at 3 volts but when i discharge with 0.5 amps test ends at 3 volts and test lasts around 4 hours capacity at 1 amp is around 1500 and at 0.5 amp 2000 and i dont think my charger is faulty other cells i tested at 1 amp discharged normally
Yiğit,
Are you putting the balance leads on?
If you are discharging just 1 cell you still need to put the balance leads on as the voltage drop from the discharge across the load wires will give you an erroneous V reading. Also what is the original capacity of the cell?
If its a 3000mAh cell and at 1 amp you get 1500mAh then you got a bad cell. Also what is the mΩ of the cell. Tested with a proper 4 wire 1 kHz Ac IR tester. Also just for a side note it would be nice to know what the cell manufacturer and model number is it is always easier to give answers when all the information is on the table.
That way when we try to give you an answer we are not shooting in the dark.
Additionally any pictures are always welcome and sometimes very informative
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#7
I thank you for trying to help me but i think that cell is no good anymore. And im not a big recycler i only need 150 cells for low power e bike so its not reasonable for me to buy the internal resistance tester. Anyways thanks again.
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#8
If you plan to draw anything above 1A per cell you need a decent IR tester. The Imax can do this but as sad you MUST have the balance lead connected. If you dont do that you have results that arent rellevant in terms of higher current.
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#9
Does not seem strange to me... some cells are just not able to deal with higher discharge rates. Many laptop cells are like this, and if this is the case, you have to be extra careful when building for something like an ebike. In high drain applications IR measurements are a must.

It doesn't matter if you are doing a big or small project. If you want to do it right, you have to make the investment into the tools.

Also, make sure your testing procedure is not flawed. If you are using an RC charger for testing at higher currents, then using a 4 wire measurements (with balance leads) will provide you much better results.

You should also look at the datasheet for the cells to make sure you are not applying them incorrectly. How many cells in parallel are you going to have in the ebike pack and what are you max loads?
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#10
I was thinking about 14s9p and 500w 48v motor. A bit overvolting will drop the amp draw, am i right? And can you explain 4 wire discharging method in my charger there is 2 3 4 5 6 s balance sockets.
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