Tim Kearsley Posted May 18, 2008 Share Posted May 18, 2008 Hi all,Been out flying the Ripmax Spitfire this morning (absolutely beautiful flyer). I'm using either 3200 or 3300 mAh batteries and am getting 10-minute flights without any problem (a lot of half-throttle flying though).My charger reports on the cumulative mAh put back in to battery and I wonder how this relates to how discharged the battery is? For example, the first battery used this morning (a 3200 mAh Kokam) took 2175 mAh of charge. Any idea how this relates to the state of discharge? Obviously if you take 2000 mAh of charge out of a battery you would expect to put more than 2000 mAh back in to restore full-charge as it can't be a 100% efficient process.Anyone know what the situation is with this?Cheers,Tim. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 18, 2008 Share Posted May 18, 2008 Well of course there are variable factors at work here, such as how accurate the meter on the charger actually is . Simplisticly ( I like simple if it suffices, and for me it usually does ) in order to put back in the full capacity of the battery ( or cells ) it must have given up all of its capacity in the first place, and unless you are running your cells right down to completely "flat" that simply doesn't happen. LiPos as you know, should never be completely emptied. Also, the age of the battery /cell will also affect how much charge it can take back in, and as they age, and the chemistry wears out a little it simply won't accept as much charge back in. Putting 2000+ m/a back into a 3200 ma pack seems OK to me, and suggests you are ( correctly ) stopping the drain well before the pack is depleted - this should help increase its life, and if your flight times are acceptable, then rejoice ! Quote Link to comment Share on other sites More sharing options...
Tim Kearsley Posted May 18, 2008 Author Share Posted May 18, 2008 Makes sense, as always, Timbo. Yes, I certainly don't want to drain the batteries to the point even that the LVC in the ESC cuts in. I'm very happy with the flight times with the Spit. The Eagle Tree data logger last weekend recorded peak current draw of a little over 45A with full throttle but only around 12A for half-throttle, which is where much of my flying takes place. So I've set the countdown timer on the Tx to 10 minutes and can be fairly secure in the knowledge that I'm neither draining the battery too low nor drawing current at much more than 4 or 5C on average.Tim. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted May 19, 2008 Share Posted May 19, 2008 Would it not be just as easy to measure the voltage of pack or the single cells, to know the charge state?Why does it matter how many milli amps it takes to get to a full charge? Just a little puzzled.Erfolg Quote Link to comment Share on other sites More sharing options...
Tim Kearsley Posted May 19, 2008 Author Share Posted May 19, 2008 I think you're quite right Erfolg and I did make a note of the battery voltage as well. I was just interested in how the amount of charge that's put back in relates to the amount taken out, that's all. The practical point is that I want to ensure that I don't cane the battery to try and get as long a life out of them as possible.Cheers,Tim. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted May 20, 2008 Share Posted May 20, 2008 I think the life time performance is potentially of interest.Most manufactures who post relevant data seem to be claiming about 5000 (if I remember correctly)cycles to 80%. Yet modellers seem to be quoting values that are very low. It could be that the your logged discharge rates may help establish if operating within the C discharge rating, ensures a longer life, circa the manufactures claims. Or tend to indicate the manufactures are quoting figures based on very low C discharges.It could be that you are entering into an experimental that previously been the exclusive realm of Timbo (to my knowledge) on this site. Power to you.ErfolgErfolg Quote Link to comment Share on other sites More sharing options...
Guest Posted May 20, 2008 Share Posted May 20, 2008 wouldn't be surprised if it was also based on low charge rates - ie well below 1CJohn Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 20, 2008 Share Posted May 20, 2008 Some LiPo figures |I have seen suggest that if you regualrly discharge above 50% of maximum claimed C rate, then expect a life cylce of mo more than 20 - 30 before deterioation sets in. That is certainly one big benefit that the Li-Ion cells have over LiPo.....there life expectancy is many hundreds of cycles even at high discharge rates.Trouble is thety are a lot more expensive ( at present ) and heavier with slightly lower voltage - they can however also be fast charged at up to 3C Quote Link to comment Share on other sites More sharing options...
Erfolg Posted May 20, 2008 Share Posted May 20, 2008 John I have posted a thread to try and establish the basis of sub 1C charging. To date I have had no replies. I am sending a query to a couple of manufactures to see if they can shead some light on the subject, the why and how less is useful.Many years ago I corresponded with "Saft" on memory affect to NiCads, for work. They were quite catagoric, it does not exsist if used normally. Yet many say and said otherwise.For me low C charging is of passing interest, I guess it is not that important, but then again, who knows?Erfolg Quote Link to comment Share on other sites More sharing options...
Former Member Posted May 21, 2008 Share Posted May 21, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 21, 2008 Share Posted May 21, 2008 True, but then how many of us bother to set the slow charge rate when we get home after a session at the field, at least doing it slowly some of the time will help a little.... ooo errrr misssus ! Quote Link to comment Share on other sites More sharing options...
Former Member Posted May 21, 2008 Share Posted May 21, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Leon King Posted May 21, 2008 Share Posted May 21, 2008 Radio aeromodelling must be the greatest hobby ever, but it's certainly not easy for non-techies to master all about Li-po's ! Quote Link to comment Share on other sites More sharing options...
Erfolg Posted May 23, 2008 Share Posted May 23, 2008 I am still puzzled to where the slow charge idea comes from, is it due to oxidation of cell materials?I have read that that the depth of discharge is important in determining cell life, no less than 40%. Is this true?There appears to be questions than deffinative answers, very little evidence, most of what I do appears to be based on rumour.The few things I believe to be true, due to examples or manufactures advice areneed a Lipo chargercharge at a rate of 1C max.Cell balancing is a good practiceFast discharging can damage or limit life of cells, dependant on cell rating.charge batteries at ambient conditions not when hotLipos do not like it cold?the rest are yet to be demonstrated or measured evidence to put into perspective slow charge at less than 1Coperation under cold conditions kills liposdeep discharges shorten life, less than 40%I am not really sure that all I believe to be true is based on hard fact.RegrdsErfolg Quote Link to comment Share on other sites More sharing options...
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