Strange 18650 capacity test

Yi?it

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May 12, 2020
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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
 
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
 
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.
 
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
 
Yi?it said:
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
Yi?it,
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 m? 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
Wolf
 
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.
 
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.
 
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?
 
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.
 
Yi?it said:
..................can you explain 4 wire discharging method in my charger there is 2 3 4 5 6 s balance sockets..........
2 Wires for load and 2 wires for balance.

The 2 load wires will have a voltage drop on them so you will not have the proper V reading.
The 2 balance wires do not have a load on them so their actual voltage is correct.


image_icabkn.jpg

Wolf
 
Correct... you want to use a JST connection (typical balance lead) with just 2 wires on it (1s). 2 for the load, 2 for the measurement.

Its useful in multiple ways...


image_qxzybl.jpg


image_acignw.jpg
 
Overvolting wont lower the amp draw unless the controller works based on wattage.
Higher voltage also increase current due to u=i*r.

The balance leads will then act as voltage meassurement. If you use original wires for the charge/discharge port they are very thin and have resistance inside causing voltage drop. Those 4 together creates the 4 wire testing.

2 is for drawing current in or out and the 2 from the balance socket are there to meassure voltage. Suddenly you get alot better reliable results.
 
I actually learned this from daromer... and after implementing this on all my balance chargers, my termination voltages are pretty much spot on. It helps a lot.
 
?max doesn't have 1s balance lead it seems
image_saidhk.jpg


And when i measure with multimeter voltage difference is 0.05 volts max
 
Use a 2 cell plug but only use 2 of the connections and that should give you the results you need.


image_chsjon.jpg


Wolf
 
I connected the balance cables to the battery terminals with the other red and black cables.
When i open voltage meter on imax it shows voltage correct, in balance screen , but when it comes to discharge imax says no battery found.
 
I have to ask.
Are the main leads hooked up to the battery and is there an option for 1s in the setup?

Wolf
 
You can select 1s from imax but there is no balance cable for 1s, only for 2 3 4 5 and 6s balance
 
Yi?it said:
You can select 1s from imax but there is no balance cable for 1s, only for 2 3 4 5 and 6s balance

Yes you have to make your own balance cable or just use the neg and first pos from the 2s cable.
Remember most people would never "balance" a 1s so the cable is not included but for a proper V reading on a 1s you need to have that connection.


Wolf
 
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