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Batteries charge/discharge cycles what's better?


EricGhost

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I'm quite incompetent about electronic&batteries, so I read here and there and understood that for ion cells the best behaviour is:

1 - Avoid high temperatures and never let go the battery to 0% 

2 - frequent charges/discharges even small 50-60-70% oup to 95% ( I've a 680Wh)

3- every about 30 cycles do a 20-30% up to full 100% charge

the above should improve the battery life, but I was wondering that there are packs of batteries  so is the electronic taking care to spread the discharge in an even way among the packs?

Are the above steps the good ones to improve your batteries life?

Anything more that you can do to improve their life cycle?

 

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40 minutes ago, EricGhost said:

3- every about 30 cycles do a 20-30% up to full 100% charge

Absolutely not - that is a hangover from NiCad days, there is no memory effect on LiIon cells.

It is all explained much better than I can here: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries.

Bottom line: the deeper the discharge the more damage you do, leaving them stored fully charged or fully discharged does some harm, better to charge just before use, and store, if not going to use the device for some weeks, at around 3.85V/cell. Operating the battery as opposed to storing it at low temperature does more harm than high temperature (within reason) I.e. 30 degrees Fahrenheit is worst than 30 degrees centigrade. Storing, at a storage voltage, is considerably improved at lower temperatures.

The reason for doing an, at least occasional, 100% charge isn't due to the batteries but the BMS. Many BMS do not keep individual cells balanced during charge/discharge, what they do is clamp each cell at 4.2V once it reaches that voltage and so the others continue charging. If you do not occasionally do a full charge, ideally leaving the charger on for an hour or two after the green light comes on, any weaker cells (and there always are some - all cells are not made equal) will slowly drop to a lower and lower voltage with each cycle until they reach low enough voltage on a long run to be permanently damaged. A full balance charge brings them all up to the same level again as long as it is done before damage has occurred.

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1 hour ago, Keith said:

 

The reason for doing an, at least occasional, 100% charge isn't due to the batteries but the BMS. Many BMS do not keep individual cells balanced during charge/discharge, what they do is clamp each cell at 4.2V once it reaches that voltage and so the others continue charging. If you do not occasionally do a full charge, ideally leaving the charger on for an hour or two after the green light comes on, any weaker cells (and there always are some - all cells are not made equal) will slowly drop to a lower and lower voltage with each cycle until they reach low enough voltage on a long run to be permanently damaged. A full balance charge brings them all up to the same level again as long as it is done before damage has occurred.

What is a good occasionally 1over 100 or 1 over 30, thanks for you answers. I have a DoD around 40-50%

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35 minutes ago, EricGhost said:

What is a good occasionally 1over 100 or 1 over 30, thanks for you answers. I have a DoD around 40-50%

It is kind of "how long is a piece of string". The better the cells were well matched in the first place, the less they may drift. There is at least one wheel (forgotten the make) that feeds the balance wires to the mainboard, that one should tilt back on the state of the lowest cell, thus making it harder to damage its pack, but I don't think many others do.

The risk of damage if some cells have got lower than others is greater the lower voltage you discharge the pack to. So my usual practice is to do a full charge + an hour or so, before going on a long run where end voltage will be lower? If i never discharged below 50% then I'd still do a full charge at least once in every 20 charges.

To give an example of how a weaker cell can behave: I usually fly my 6 cell helicopter on a 6 minute timer, cell voltage at rest is usually around 3.7V (which, off load is only about 20% capacity left) and there is never as much as 0.1V difference between the highest and lowest cells - usually nearer 0.01V) The charger always balances during charge and reports each cell voltage as it does so. Yesterday I wanted to check the behaviour of the speed controller on low voltage so I hovered the heli in the garden for around 12 minutes until the motor clearly dropped RPM. most cells were at around 3.4V but one was right down to 2.96V - too low. So you can see that another good reason for not going below 20-30% charge is weak cells voltage drop really fast as capacity gets lower.

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