Dicharge Levels and LiPo Storage

[osanbob]

Hi guys and Gals,
Hopefully a simple question to show how little I really know. I have a Triton 2 EQ charger, thought it was pretty good because it costs bunch. Here is my question, I have read that I need to store my LiPo battery at a storage level (not really given) The charging/discharging instructions on the Triton has an auto cut-off at 9.0 V for 3cells when using the discharge feature. Ok but every thing I am reading on the forums say don't go below 3.6 or 3.7 or 3.8 which obviously are all over the auto-cutoff. One that I read tonight on the forum specifically said to monitor the discharge and stop it at 3.8 per cell or 11.4v total. Whose is right? I don't want to burn the house down and I don't want to pay for batteries that I ruin. For my different planes I run different batteries but I think there would be the rule of thumb to use for storage of any size battery. I have 5200mAh 4S1P 14.8v 3300mAh 3S1P 11.1 and 2200mAh 3S1P 11.1 Can someone please give up the ground truth about storing batteries for weeks until I get to fly again. Up until this week I have been flying every other day but now I must stop for a couple weeks and I believe that I need to discharge all of them to the correct level for storage. Any help is greatly appreciated.

Osanbob

 

[colorex]

Storage level is around the nominal LiPo cell voltage - which is 3.7 volts. So you can manually discharge the LiPo to 3.8 or 3.7 volts and you'll be fine.

For your 3S batteries: 11.1v - 11.4v
For your 4S batteries: 14.8v - 15.2v

 

[osanbob]

Thanks for the quick reply. I feel more comfortable knowing those number are correct. However I am a little upset at the Triton 2 EQ for not having that feature built in. For discharge it will take you directly to 3v per cell and I would have killed all my batteries. Now I can discharge and store in peace.

Osanbob

 

[colorex]

You're welcome!

 

[pgerts]

The best way to discharge is to fly ;-)

 

[earthsciteach]

Hey, I think I remember that colorex kid...

 

[colorex]

Hey, I think I remember that colorex kid...

Nah, he's just a figment of your imagination.

 

[andy_spoo]

I was wondering about this stuff myself. I presume then that Lipo's don't self discharge over time like some standard AA lithium ion batteries do then? So they won't drop extra voltage in a few months time?

What is the need to store them at a lower voltage? Is it for safety or do they suffer from some kind of memory effect like old nicads?

 

[Craftydan]

I was wondering about this stuff myself. I presume then that Lipo's don't self discharge over time like some standard AA lithium ion batteries do then? So they won't drop extra voltage in a few months time?

What is the need to store them at a lower voltage? Is it for safety or do they suffer from some kind of memory effect like old nicads?

They will, but it's pretty slow -- not more that a few percent over a month. You don't store them empty, because they'll slowly discharge below safe levels. You will want to re-sorage a long unused battery, but probably not for another 6 months or so.

As for memory, it's not a "feature" of the chemistry of lipos, however when we charge these puppies up, they are being stressed chemically, so long storage at full charge will damage them. I've noticed it in the packs after charging: a cold hard pack left overnight at ~20%, after a charge will feel noticeably more squishy. Too much of that for too long and the reactions start to go the wrong directions.

Getting below the 50% mark and staying above 20% is kind, long term, to the battery, but the typical storage charge is ~40%.

 

[tramsgar]

Of course it's important to store them balanced, and to recharge them to storage voltage if left for very long time (like during those awful winters). Cells don't self-discharge at the same rate, either.

 

[andy_spoo]

Thanks for your help Craftydan. Much appreciated.