David Ashby - Moderator Posted October 28, 2008 Share Posted October 28, 2008 My apologies if this question has been asked before but I was wondering whether Li-Pos should be stored fully charged or preferably discharged down to a certain level? Thought/info would be appreciated, thanks. Quote Link to comment Share on other sites More sharing options...
Nick Rigg Posted October 28, 2008 Share Posted October 28, 2008 I thought that the optimal storage value was 3.8v per cell.Some of the better chargers have this function Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 28, 2008 Share Posted October 28, 2008 Most modern chargers have a "storage level" mode for Lithium cells. The correct level is around 3.85V per cell.The following chart gives the various charge level parameters for all common cell types. Click for bigger image. Without wishing to overcomplicate things....the following may also be useful info.The critical aspect of Lithium in respect to charge damage is due to the fact that the cell breakdown voltage of cells is only about 100mv higher than the fully charged voltage value.At ambient, normal room temperature, a cells optimum fully charged voltage is 4.2V. This optimum fully charged voltage value goes down if charged in lower temperatures - If you charge a lithium cell at below 10degC temperature the charge voltage needs to be about 4.1 volts not 4.2V.If you charge to 4.2V at this low temperature you can damage the cell due to overvoltage - at the very least you will probably reduce its overall lifetime, because when the cell is then taken to a normal temperature it will rise in voltage slightly and therefore become effectively slightly overcharged. If you charge a lithium cell to 4.2V at normal room temp and then put the cell in the fridge and take its temperature down to 10C or less you have effectively overcharged the cell because 4.2 volts at this low temperature is where cell damage is starting. This same effect could be seen by charging at normal temperature, then taking the batteries into a cold outside environment such as a winter flying session ( especially on the big rock ! ). For this reason, i usually transport my packs in a padded quilt style bag, and only fit them to the model at the last minute before flight. LiPos in common with all battery types perform much better when warm. Quote Link to comment Share on other sites More sharing options...
Always broke Posted October 28, 2008 Share Posted October 28, 2008 The FMA cellpro charger takes the ambient temperature into account when charging and will only charge to 4.1v per cell at lower temps. Clever some of these chargers. Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted October 28, 2008 Author Share Posted October 28, 2008 Ok thanks guys and Tim especially. I was playing with a dis-charger gadget and it has a default of 3.9v per cell for long term storage. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 28, 2008 Share Posted October 28, 2008 3.9 should be fine. I now routinely only ever charge to storage level, and then top off to "full" as I journey to the site, or at the site. Any decent LiPo charger that correctly detects and confirms the cell count correctly upon connecting the pack will stop charging at the correct "full" level - so worries about not topping up partly charged lipos are not a concern. Most of my models require full grunt available for a decent flight and launch. Quote Link to comment Share on other sites More sharing options...
Tim Kearsley Posted October 29, 2008 Share Posted October 29, 2008 This issue only came to my attention a week or two ago (I'm a bit slow at times!). I keep all my LiPos in a fireproof safe out in a shed and I've always stored them fully charged. This weekend, I brought them in and reduced them all to the storage charge. Like Timbo, I will only top them up when actually required for a flying session.The other question I have, which arises out of this, is - are LiPos OK at low temperatures, given they are charged to around 3.85V/cell? By low I mean typical British winter nighttime minima. I prefer to keep the batteries outside simply because my house is empty during the working day and I feel safer not leaving them unattended inside. Or am I being over-cautious?Cheers,Tim. Quote Link to comment Share on other sites More sharing options...
Nick Rigg Posted October 29, 2008 Share Posted October 29, 2008 I would think Lipos would only be dodgy during any kind of charging /discharging event. Could well be wrong of course... Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 29, 2008 Share Posted October 29, 2008 I did somewhat cover this point in my post above - the relevant bit is here again below.....At ambient, normal room temperature, a cells optimum fully charged voltage is 4.2V. This optimum fully charged voltage value goes down if charged in lower temperatures - If you charge a lithium cell at below 10degC temperature the charge voltage needs to be about 4.1 volts not 4.2V.If you charge to 4.2V at this low temperature you can damage the cell due to overvoltage - at the very least you will probably reduce its overall lifetime, because when the cell is then taken to a normal temperature it will rise in voltage slightly and therefore become effectively slightly overcharged. If you charge a lithium cell to 4.2V at normal room temp and then put the cell in the fridge and take its temperature down to 10C or less you have effectively overcharged the cell because 4.2 volts at this low temperature is where cell damage is starting. This same effect could be seen by charging at normal temperature, then taking the batteries into a cold outside environment such as a winter flying session Your actual question however seems to be whether or not the storage of them at low temperature is OK. The answer is a resounding YES - providing they are not "full" as above. Storage at low temperature - even in a fridge - is a very good way to preserve the overall life of the cells.Using them cold of course is different - they perform very poorly if cold - very noticeably in EDFS etc, where every little bit helps. I always warm them in the car or my inside pocket before fitting and flying. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 29, 2008 Share Posted October 29, 2008 Nick Rigg wrote (see)I would think Lipos would only be dodgy during any kind of charging /discharging event. Could well be wrong of course...With the exception of a cell(s) that has suffered physical damage EG in a crash etc, you are correct. Quote Link to comment Share on other sites More sharing options...
Tim Kearsley Posted October 29, 2008 Share Posted October 29, 2008 Thanks for the comments Timbo. You've confirmed what I thought to be true. I would think that the temperature in my shed last night was probably colder than my fridge!Regarding keeping them outdoors for safety, well I acknowledge that I'm being over-cautious. If keeping 'em cold in storage is potentially beneficial however, I shall continue to do so and enjoy peace of mind into the bargain!Cheers,Tim. Quote Link to comment Share on other sites More sharing options...
iawnski Posted October 31, 2008 Share Posted October 31, 2008 ok right, i havent used my lipo for 5 weeks they have been on a concrete slab in the cold garage ,when i lst used them they were fully charged ,should i have (storaged charged )them nowing i wouldnt use them for a few weeks ,how long should it be if you need to storage charge them,if i say want to use them now will they be ok /or would i just put on charger and charge normally ? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted October 31, 2008 Share Posted October 31, 2008 OK Kev, slow down mate If they were fully charged 5 weeks ago, they will still be almost full even now, and can be used straight away. Storage charge level is always a good idea, as filling them "right to the top" will always create a little more wear and tear on the overall lifespan, whereas slightly undercharging them is good for them. I now routinely always just charge to storage level when I get home, then it doesnt matter if I leave them in the cold, or the warm, and just before I want to use them, I top them off ONLY IF I know I will need every last bit of juice I can get from them - if they are only going to be in the smaller slow fly fun stuff ( like the Holy cow for instance ) then I probably wont even bother topping them up, and if its just for radio use ( I have Lipos in almost all my gliders nowadays ) - ditto I wont bother topping them up.Your latest charger is "intelligent style" and therefore IF you wanted to top them off to full just before flight then thats fine too. I also confess to occasionally getting back from a session, putting the pack / model / Tx whatever on charge to "full" level, leaving them in the cold / warm garage depending on the season, and then just leaving them for few weeks, and then... just go flying. Quote Link to comment Share on other sites More sharing options...
iawnski Posted October 31, 2008 Share Posted October 31, 2008 hail the King, -no not elvis, the welsh one from the rock ha ha. thanks for that tim you have sorted me out now, was looking at the weather for the weekend and am thinking of the junior s maybe, which takes the lipo so will put the lipo in without a charge thanks again buddy Kev Quote Link to comment Share on other sites More sharing options...
Nick Rigg Posted October 31, 2008 Share Posted October 31, 2008 I was looking at the weather for the weekend and was thinking 'feet up by the fire'.... Quote Link to comment Share on other sites More sharing options...
ericrw Posted February 10, 2011 Share Posted February 10, 2011 Honestly Timbo, I have endeavoured to find the answer to my query from other postings but not to my satisfaction. I'm quite frustrated with not only the adverse weather conditions but even more so with the weather forcasts that turn out to be completely opposite ! When the forcasters say, tomorrow is going to be a "windy" day, I don't bother charging my lipo batteries. The frustration begins when the forcast is wrong and there is just a "breeze" but because it takes nearly 1hr 30min to charge each one; I don't go flying ( I only like to fly AMs, it's an age thing !!). I discharge/ store/charge in accordence with Timbo's chart. So they are charged to approx 40% Long Term storage, over this winter. What I want to know is it OK to now charge them to say 80% Cold Storage and keep them at that percentage, then to charge them on a flying day, the additional 20%; which would cut down the charging time !! Advise please. Eric. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted February 10, 2011 Share Posted February 10, 2011 Yes...its OK to charge them to higher level Eric - the only downside is a possible reduction in total lifespan of them, and a slight reduction in maximum capacity over time.I confess to sometimes just charging to full, and then leaving them until needed. This then just requires a very quick top up to bring 'em up to full strength. As the price has dropped so dramatically ( and performance improved ) over the last few years, they are not perhaps the jewels they were, and so if mine last a little less time than they may have done if I treated them with complete tender loving care...so be it. Its quite feasible these days to just replace one of the common sized pack if it starts to diminish. Quote Link to comment Share on other sites More sharing options...
ericrw Posted February 10, 2011 Share Posted February 10, 2011 Thanks Tim. Quote Link to comment Share on other sites More sharing options...
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