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DIY Lipo Discharging


Julian Murch
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4w is 4w, whether outputting a higher proportion of light (LED) or heat (incandescent) so this would take a month of Sundays to discharge any reasonable size pack. A safely located old headlight bulb or two would be simpler but surely its better not to charge batteries unless you're going to use them (if you're that bothered about storage charging - my batteries seem to last as well as anyone's and stay charged or discharged at random).

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15 minutes ago, Don Fry said:

…BUT AGAIN, if you wish to dispose of an old battery, the disposal site does not care if it’s flat or not. They have disposal systems. 


I can only speak for our local recycling centre, but they have plenty of signage now requesting all batteries are fully discharged and put only in the steel battery specific containers  - apparently fires at recycling centres caused by disposed lithium chemistry packs are now a pretty common occurrence…

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I fully discharge LiPos that are at the end of their useful life through a headlamp bulb.  I leave the battery and its load outside on a concrete yard until the lamp goes out.  I'm not sure if our local tip requires it and I'm sure they wouldn't know if I fully discharged the batteries or not but it seems the decent thing to do for very little effort.

 

Geoff

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  • 10 months later...

Referring to Simon Clarke’s post in October 2021.

 

The Vifly Storesafe discharger specification is:- discharges to 3.85+/-0.08Volts per cell. That is between 3.93v/cell and 3.77v/cell.  
 

How does the forum feel about storing Lipos at 3.9v/cell because my Vifly finishes at this; about 60%.
 

How much more detrimental would it be to store the battery at 3.9v/cell (about 60%) rather than 3.85v/cell (about 50%)?


There is so much information about this subject on the forum it’s quite overwhelming. 

 

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As long as you are not storing for lengthy periods above 4V/cell, don’t worry about it - yes the lower you go in theory the slower the degrading reactions take place, but according to the research any gains are incredibly marginal when comparing (say) 3.9V/cell to 3.7V/cell.

 

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

 

Edited by MattyB
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The very low discharge levels (<40%?) used by the manufacturers is more to reduce the energy level for bulk transport safety than it being the best for storage.

Damage resulting from storage, as long as it is below 4V/cell, tends to be insignificant compared to the damage resulting from the typical discharge rates used when flying a plane. 

The other aspect there is a range in the chemical manufacturing process used in a LiPo. Not all otherwise similar LiPo are actually equal so neither is their life even under similar usage.

We have all read about and some have actually experienced a LiPo that just goes on and on for years whereas others become of little use in a faction of that time.   

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LiPo life also depends on the storage temperature. The higher the temperature, the faster the side reactions between the chemicals in the cell that degrades the capacity/internal resistance happens. You don't necessarily need to put them in a fridge but just avoid keeping them in a boiler room or greenhouse.

Edited by Andy Stephenson
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Yes, I do keep my batteries cool. I store them in an ex-ammo box on the garage concrete floor. What I haven’t been doing is keeping them below full charge.
 

Usually flying at weekends has meant they get a weekly recycle with the occasional older battery showing signs of swelling. This year the swelling has occurred in a number of batteries some of them not being the oldest.


Possibly Covid regulations has meant the reduced weekly recycling has contributed to the problem. Plus, of course, as aforementioned in the previous post the varying chemical compositions could have a contribution.

 

That is why I’ve invested in some battery dischargers.
 


 

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2 hours ago, Mastercrashman said:

Yes, I do keep my batteries cool. I store them in an ex-ammo box on the garage concrete floor. What I haven’t been doing is keeping them below full charge.
 

Usually flying at weekends has meant they get a weekly recycle with the occasional older battery showing signs of swelling. This year the swelling has occurred in a number of batteries some of them not being the oldest.


Possibly Covid regulations has meant the reduced weekly recycling has contributed to the problem. Plus, of course, as aforementioned in the previous post the varying chemical compositions could have a contribution.

 

That is why I’ve invested in some battery dischargers.
 

 

Based on your pre-and during Covid usage patterns, I don't think the absence of a weekly discharge is the problem. The issue is that your total time spent at an elevated state of charge (e.g. >4V/cell) was always very high, which over time has led to the batteries meeting an early demise. An example from an old post that may help...

 

On 08/10/2021 at 15:21, MattyB said:

 

...Based on Nissan's experience what seems most important is the overall time a pack spends at elevated SOC (where accelerated degradation occurs due to dendrite growth etc) vs. how long it spends below the "electrochemically stressed" level (normally considered be around 4V/cell).

 

Example - A Sunday afternoon flyer who charges the night before he flies will have the battery at elevated SOC for ~19/168 hours per week; that's ~11% of the time. A pilot who flies exactly the same packs in the same model and in the same style but charges on a Sunday evening after flying will have them at elevated SOC for about 162/168 hours per week, or 96% of the time. That is an enormous difference that according to the automotive research does have a significant effect over time, especially if you are operating in warmer climbs.

 

Edited by MattyB
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This is all really interesting stuff. I need to rethink my charging strategy and charge when needed.

Manufacturing differences may also explain why a pack can be useless when one cell degrades prematurely.

I bought a new Overlander 4 cell 2200mah pack and it came with 2 cells on zero volts and internal resistances of the 2 "good" cells up around 90 milliohms. On returning the model shop said they tested it and it's fine!

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16 hours ago, Phil B said:

This is all really interesting stuff. I need to rethink my charging strategy and charge when needed.

Manufacturing differences may also explain why a pack can be useless when one cell degrades prematurely.

I bought a new Overlander 4 cell 2200mah pack and it came with 2 cells on zero volts and internal resistances of the 2 "good" cells up around 90 milliohms. On returning the model shop said they tested it and it's fine!

 

I'll wager they didn't test it in front of you when claiming that...!

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