n3eg
Newly Enlightened
Is it dangerous or detrimental to terminate LiIon charge the wrong way, i.e. tapering current and floating at 4.1 volts per cell for a short time like 8 hours?
Terminating LiIon (Co) charge the WRONG way - question
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lightfooted
Flashlight Enthusiast
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Yes.
Katherine Alicia
Enlightened
that`s a good question and I don`t the answer to it either, because other than tapering the current, it`s no different from charging it and putting it in parallel with other charged cells just like in a powerbank. And if tapering current were dangerous I`d like to know why as well.
lightfooted
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WalkIntoTheLight
Flashlight Enthusiast
I think you misspelled the word, "No."
DIWdiver
Flashlight Enthusiast
I'm not sure what you mean by tapering the current. To do that deliberately would be pretty strange, but not necessarily dangerous. To do it as a byproduct of a proper charge is completely normal.
A normal charge cycle would be a limited current at the beginning, which is the CC or Constant Current phase of the cycle. During this phase the current is held constant and the voltage increases. When the voltage reaches the maximum charge voltage (which varies from about 3.9 to 4.25V, depending on your priorities) the charger won't let the voltage go any higher and we enter the CV or Constant Voltage phase. This switchover happens naturally as the charger won't let the voltage go any higher. In this phase the voltage is held constant and the current tapers off naturally as a byproduct of the battery chemistry settling down.
Depending on how discharged the battery was and how hard you charge it, the CC portion can take anywhere from zero to several hours. If you have a big battery on an underpowered charger, it could take even longer. The CV phase typically lasts several hours. If the discharge was shallow, you could start partway into the CV phase, and it could be pretty short.
The link provided by lightfooted says you can't terminate charge based on voltage. Taken in the proper context, this is correct. However, it would be much more clear to say that if you respect the maximum charge voltage, you CAN terminate on voltage, but you SHOULDN'T. If you stopped when you reached the maximum voltage, you would not have a full charge, as you'd be skipping the whole CV phase of charging. This isn't dangerous, just wasteful of the battery's capacity, and you would only do it if charging fast was more important than charging full, say for a 30-minute charge of a power tool battery.
The "best" way to terminate the charge is when the current in the CV phase has fallen to a certain fraction of the battery's C rate. Commonly, fractions around 1/10 are used. Another way is to terminate after a certain time in CV phase, say 3 hours. I think this is generally considered not as good. To stay in the CV phase for longer (say your 8-hour 'float') isn't dangerous, but it isn't good for the life of the battery. The higher the voltage and the longer the 'float' the harder it is on the battery.
The current and voltage limits contribute significantly to the lifespan you will get from the battery. In general, higher currents and higher voltages will give you faster charge and higher capacity, but shorter life. The reverse is also true. The 4.1V you mentioned is fairly conservative. You'd sacrifice a few percent of the capacity you could get at higher voltages, but you could get significantly longer life if the battery was otherwise treated well.
So I would say I wouldn't disagree with any of the previous posters. Incorrect charge termination is not good for the battery life. But a few hours of float at 4.1V is likely to go unnoticed in the grand scheme of things.
The things that are dangerous are charging a compromised battery (that's another subject to itself), charging outside the allowed temperature range, or exceeding the max current or voltage. The max voltage limitation is particularly important when charging cells in series, as the limit can be exceeded on a single cell before the whole battery reaches it's max.
A normal charge cycle would be a limited current at the beginning, which is the CC or Constant Current phase of the cycle. During this phase the current is held constant and the voltage increases. When the voltage reaches the maximum charge voltage (which varies from about 3.9 to 4.25V, depending on your priorities) the charger won't let the voltage go any higher and we enter the CV or Constant Voltage phase. This switchover happens naturally as the charger won't let the voltage go any higher. In this phase the voltage is held constant and the current tapers off naturally as a byproduct of the battery chemistry settling down.
Depending on how discharged the battery was and how hard you charge it, the CC portion can take anywhere from zero to several hours. If you have a big battery on an underpowered charger, it could take even longer. The CV phase typically lasts several hours. If the discharge was shallow, you could start partway into the CV phase, and it could be pretty short.
The link provided by lightfooted says you can't terminate charge based on voltage. Taken in the proper context, this is correct. However, it would be much more clear to say that if you respect the maximum charge voltage, you CAN terminate on voltage, but you SHOULDN'T. If you stopped when you reached the maximum voltage, you would not have a full charge, as you'd be skipping the whole CV phase of charging. This isn't dangerous, just wasteful of the battery's capacity, and you would only do it if charging fast was more important than charging full, say for a 30-minute charge of a power tool battery.
The "best" way to terminate the charge is when the current in the CV phase has fallen to a certain fraction of the battery's C rate. Commonly, fractions around 1/10 are used. Another way is to terminate after a certain time in CV phase, say 3 hours. I think this is generally considered not as good. To stay in the CV phase for longer (say your 8-hour 'float') isn't dangerous, but it isn't good for the life of the battery. The higher the voltage and the longer the 'float' the harder it is on the battery.
The current and voltage limits contribute significantly to the lifespan you will get from the battery. In general, higher currents and higher voltages will give you faster charge and higher capacity, but shorter life. The reverse is also true. The 4.1V you mentioned is fairly conservative. You'd sacrifice a few percent of the capacity you could get at higher voltages, but you could get significantly longer life if the battery was otherwise treated well.
So I would say I wouldn't disagree with any of the previous posters. Incorrect charge termination is not good for the battery life. But a few hours of float at 4.1V is likely to go unnoticed in the grand scheme of things.
The things that are dangerous are charging a compromised battery (that's another subject to itself), charging outside the allowed temperature range, or exceeding the max current or voltage. The max voltage limitation is particularly important when charging cells in series, as the limit can be exceeded on a single cell before the whole battery reaches it's max.
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