Martin Harris - Moderator Posted March 3 Share Posted March 3 I received some unexpected low battery warnings when flying my scaled down IC powered Ohmen the other day. Due to the long nose (designed for EP) it was necessary to locate the receiver battery as far back as possible, so I fitted a soft cased 2S LiFe pack to be as much “fit and forget” as possible. Some charge/discharge testing revealed the pack was well down on capacity so I decided to change it - not as easy as expected as it had swollen badly making it difficult to remove! It came as a bit of a surprise to see this swelling - I thought this was only a LiPo problem so now I’m wondering about the common advice that they’re safe to charge in situ - perhaps this should only apply to metal cased ones? Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 3 Share Posted March 3 As you suspect Martin I think the soft pouch variants need almost the same caution as Lipos - the metal cased A123s are the bulletproof ones. It seems not well known that you can also get genuine A123s in 18650 size as well as the 'standard' 26650 cell. My cells (hundreds!) were taken from Dewalt drill packs in 2007 (18 years!) and have been thoroughly abused in EV projects, and though I've lost a few due to over-discharging (my fault), most still perform well. I've never had a soft-pouch LiFePo4 so no experience of those 😉 Would 2x 18650 cells fit Martin? Quote Link to comment Share on other sites More sharing options...
Nigel R Posted March 3 Share Posted March 3 Looks rather battle worn at this point! Phil, I thought it was the LiFe chemistry that was "less prone" to inflating. Maybe this pack had an internal fault that caused the swelling? Although it looks like both cells have swollen. Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted March 3 Share Posted March 3 I accidentally charged a LiFe pack on a NiCd charge and all it did was puff up, no flame or smoke. LiFe is much safer to abuse than LiPo. 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 3 Author Share Posted March 3 They were my cells of choice a few years ago but I thought they’d stopped making A123 18650s as I couldn’t find any when I looked a while back - I’d be delighted to find a source! I know there are a number of similar ones on the market but haven’t found any confirmation of quality. The shabby appearance was mostly due to balsa dust shaken up during enthusiastic flying… Quote Link to comment Share on other sites More sharing options...
Mark Hewett Posted March 4 Share Posted March 4 I've been fitting LiFe receiver packs to all new models in preference to NiMH, all soft cased and of various brands. I don't balance charge them - maybe that's naughty, but I searched the forums without finding evidence of problems and an experienced prolific flyer in our club said he's been doing that for years with no issues. I had two packs (both the same brand, but I can't remember what - something 'racing' I think) that puffed up after not much use. Still seemed to work okay and tested okay for capacity, but I discarded them. The others have all been fine. Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted March 4 Share Posted March 4 Out of curiosity, why don't you balance charge them? My own (limited) experience has been poor - although both packs came in used models; all other aspects of the models showed good care and maintenance, so I had no reason to doubt them. They both refused to balance, making me distrust them. Quote Link to comment Share on other sites More sharing options...
John Lee Posted March 4 Share Posted March 4 Last year I saw a similar LiFe Rx pack that had swollen a bit more than Martin's. It was being used in an RC yacht at a local boat club and the owner asked for opinions as to whether it was OK to use. I commented at the time that I had never seen one that had swollen before but that it was relatively common with LiPos. Of course I gave suitable disposal advice. So not unknown, but rare. It made me wonder as to the exact chemistry of these packs and whether they are true LiFe's? Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 4 Share Posted March 4 The only time I've had a LiFe cell swell like that was when I accidentally left a transmitter switched on, and flattened it completely. They are generally regarded as much safer than LiPos, and I have some that must be 15 years old by now, and still going strong. Having said that, nothing made by man is ever perfect, and the odd faulty one will always slip through quality control. That's just the way things are! As Phil has said, get decent ones and they do seem to last well. -- Pete Quote Link to comment Share on other sites More sharing options...
Mark Hewett Posted March 4 Share Posted March 4 2 hours ago, GrumpyGnome said: Out of curiosity, why don't you balance charge them? I don't balance charge LiFe receiver packs, just because I charge them in the models, mostly through external switches with a charge port, some packs are inaccessible, and using a separate balance lead would be a hassle. I'm not recommending it or saying this is good practice though, just that I couldn't find evidence of a problem. What does everyone else do? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 4 Author Share Posted March 4 The puffed pack has always been balance charged via an extended balance lead. Although puffed and dramatically down on capacity, cell IRs were closely matched. I don’t recall it ever being over discharged or charged wrongly. Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted March 4 Share Posted March 4 1 hour ago, John Lee said: ...It made me wonder as to the exact chemistry of these packs and whether they are true LiFe's? This LiFe chemistry is a true "Li-ion" type where the Lithium is not held in metallic form. Instead of nickel or cobalt, it uses iron phosphate FePO4 which makes the cell much less prone to fires when abused. The trade-off is that it has a lower voltage and energy density, although it has a better self-discharge rate and superior cycle life. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted March 4 Share Posted March 4 7 hours ago, John Lee said: It made me wonder as to the exact chemistry of these packs and whether they are true LiFe's? I think LiFe is a single specific chemistry. The terminal voltage is different to the typical LiPo cell that we use, so they're "easy" to tell apart, I guess. LiPo is more a construction method. Can include many variations of lithium chemistry, gel makeup, polymer, and cathode material. Both degrade with heat and extreme of charge/discharge, which includes developing the gas build up / puffing problem. 6 hours ago, Martin Harris - Moderator said: The puffed pack has always been balance charged via an extended balance lead. Although puffed and dramatically down on capacity, cell IRs were closely matched. I don’t recall it ever being over discharged or charged wrongly. Slow or fast charge? Just wondering if there has been a heat build-up issue, where the pack was buried inside a model during charging; fast charge might well exacerbate that. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 4 Author Share Posted March 4 It’s certainly worth considering but I’m not sure that much heat is generated during charging. I will try a test with one in an enclosure. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 5 Author Share Posted March 5 …which I’ve done. A bit of serendipity produced a small wooden box from my workshop in which a 700mAh 4S pack, made from two packs identical to (and the same age as) the puffed pack fitted almost perfectly. It also had holes already made in it which allowed the lid to close and a temperature probe to lie alongside the pack. If I’d have designed it from scratch, it couldn’t have been any better! I charged at 1C and the temperature rose to a maximum of 4 degrees above ambient. Discharging the pack at a slightly higher than average rate in service of 400mA raised the temperature to 6 degrees above ambient. Bearing in mind that this enclosure has much thicker walls, less free space and twice the energy capacity of the model’s, I’m pretty reassured that the battery’s position wasn’t a contributory factor in its demise. 1 Quote Link to comment Share on other sites More sharing options...
Tim Flyer Posted March 5 Share Posted March 5 I have been using LIFE batteries both in transmitter and receivers for about 10 years now and they have been very reliable. They are in all the 9 planes I fly regularly. I have once had a battery puff up when it was accidentally left on for days, and one of two batteries retire a bit early but have not had any real problems . I balance charge at 0.5c and do not get any heat issues . I use a balance lead extender from Component Shop where charging access is difficult. I certainly prefer LIFe batteries to The others for receiver and transmitter power. Quote Link to comment Share on other sites More sharing options...
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