Slow Cell Charging


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Sonic01

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Sep 19, 2017
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125
Hi Guys,

In my cell testing I've noticed something odd with a few cells, I'm using the Opus and I've realised a standard charge cycle on a healthycell from 3v to 4.2vis about 3h.

With some cells I'm getting really long charge times, between 7h-24h.

The cells do indeed charge, and their discharged ma matches the other cells from the same pack, they just seem to trickle charge (approx 50ma) for AGES to reach 4.2v.

Should these go to the bin?
 

daromer

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Oct 8, 2016
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5,662
If you let those cells sit for a week or 4 you will see that they selfdischarge. So basically they wont work that well in your pack and yes Bin them or atleast dont use them in conjunction with other cells.

I get that every now and then and i throw them in the bin.
 

Geek

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Aug 15, 2017
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920
Make sure the cell has good contact. Opus can be notorious for poor connection.
 

DarkRaven

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Sep 2, 2017
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This is the reason why manufacturers usually tell you in the datasheet how long a standard charge will take. One might think it isn't important, but it sure can be. Some chargers also have a built-in and preset cutoff timer at 3h because of that, most 18650s are specced for 2.5h to 3h. Any lithium cell (or lithium cell based battery) charged at 1C should be charged within this time. If it isn't then something is wrong. Or you have a big battery and can't charge at 1C, obviously then it will take longer and the timer needs to be deactivated (or you have to start a 2nd charge).
 

Sonic01

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Joined
Sep 19, 2017
Messages
125
DarkRaven said:
This is the reason why manufacturers usually tell you in the datasheet how long a standard charge will take. One might think it isn't important, but it sure can be. Some chargers also have a built-in and preset cutoff timer at 3h because of that, most 18650s are specced for 2.5h to 3h. Any lithium cell (or lithium cell based battery) charged at 1C should be charged within this time. If it isn't then something is wrong. Or you have a big battery and can't charge at 1C, obviously then it will take longer and the timer needs to be deactivated (or you have to start a 2nd charge).

when i set to 1A charge a lot of my cells take 3.5-4h... is this still reasonable? most of my cells are 2200-2800.
 

Korishan

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Jan 7, 2017
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It's not just overall time that effects them. You need to check to make sure the charger isn't shutting off due to overheating during the capacity test. If it shuts off for 5 mins every 15 mins or so because the resistors get hot, then it could add a lot of time overall.
 

Sonic01

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Sep 19, 2017
Messages
125
Korishan said:
It's not just overall time that effects them. You need to check to make sure the charger isn't shutting off due to overheating during the capacity test. If it shuts off for 5 mins every 15 mins or so because the resistors get hot, then it could add a lot of time overall.

does the opus do that? how would i know if it has?

ambient temp is also pretty low where im charging as well, between 4c and 13c at the moment so i imagine that would help with cooling.
 

daromer

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Oct 8, 2016
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Korishan: it was the charge that took the time :)

At 1A a 2.8Ah cell will take atleast 2.8h. With that said you can not fill the battery 100% with 1A constant current since it will closer to the end go into CV where the current goes down. So 3-4hours for that type of cell is normal.
 

Sonic01

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Joined
Sep 19, 2017
Messages
125
daromer said:
Korishan: it was the charge that took the time :)

At 1A a 2.8Ah cell will take atleast 2.8h. With that said you can not fill the battery 100% with 1A constant current since it will closer to the end go into CV where the current goes down. So 3-4hours for that type of cell is normal.

yup, thats what i was thinking. thanks for confirming.

so if i have anything that takes over 4h i should bin it right? bearing in mind my highest cell is 2.8Ah
 

daromer

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Oct 8, 2016
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In general it should not take over 4 hours no. If you want to bin it its up to you. I would most likely put it aside. Most of my cells taking that time have been self discharging ALOT.... :) = bin
 

Korishan

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Jan 7, 2017
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Yeah, I forgot about the CV mode where the amps taper off. So, yeah, that would increase the time needed to fully charge the cell. :)
 
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