Li Ion batteries weights and performance - Page 1
Forum section: electronics / projects

author: akis
author_rank: Frequent Contributor
timestamp: April 04, 2017, 09:10:46 pm
content: I have long been using hobby batteries for my device which draws around 1.3A @ 22.2V (nominal) . Those batteries are 6S and are listed as 3600mAh or 3700mAh, as can be seen in this link:https://hobbyking.com/en_us/turnigy-3600mah-6s-30c-lipo-pack.htmlThe above is just an example of the battery packs I have been using.Invariably, these battery packs develop "weak" cells, and many times "dead" cells. Sometimes after just two or three charges. Others last longer. Others develop "weak" cells but can still be charged and discharged, albeit at less capacity.In order to avoid cell damage, I have stop discharging at 3.67V per cell.These battery packs are made of 6 cells in series. The cells are rectangular "slices" packed on top of each other and therefore extremely compact. The weight of the 6S 3000mAh-3600mAh is around 550g-580g.Recently I also bought a dozen 18650 at 3000mAh - good makes, efest IMR and EBL. These weigh between 44-47g each. 6 of them would weigh around 266g, which is less than half the battery packs above.The battery packs are "naked" have no electronics/protection modules, the 18650s have a protection circuit (thus more excess weight).Now I wonder, on paper they are more or less the same energy, yet the 18650s are half the weight.Since the hobbyking battery packs are really bad quality, it means they are not really 3000-3600mAh as advertised. To be sure I re-charge them at best at 2300mAh having taken them down to 3.67V.How then can the branded 18650s also show same or better mAh at less than half the weight? I have not tried discharging them yet to see what I can get out of them, but I believe them to be true, because they are good makes.

author: Audioguru
author_rank: Super Contributor
timestamp: April 04, 2017, 10:16:48 pm
content: The large Hobby King Li-PO batteries are not too bad, but the little ones are cheap garbage. There are much better but more expensive batteries out there.

author: ovnr
author_rank: Frequent Contributor
timestamp: April 04, 2017, 10:22:46 pm
content: Quote from: akis on April 04, 2017, 09:10:46 pmIf you only take them down to 3.67 volts, you haven't really emptied them completely.Also, these are 30C batteries, thus rated for something like 90 amps. Try finding a 3Ah 18650 that will spit out 90A.

author: thm_w
author_rank: Super Contributor
timestamp: April 04, 2017, 10:52:43 pm
content: How is hobbykings warranty for these? and what voltage/charger/rate are you charging them to?I would be a bit surprised if Turnigy didn't meet the 3,600mAh spec. So thats a 20% increase in capacity.As ovnr points out at 30C this would be 108A continuous discharge, compared to the 20A continuous of the IMR 18650.46g * 6 * 1.2 = 330gSo about an additional 75% weight (from thicker copper foil and?), for 5x greater discharge rate.

author: amyk
author_rank: Super Contributor
timestamp: April 05, 2017, 02:47:36 am
content: In summary, the weight difference is because those Turnigy cells are designed for current, while those 18650s are designed for capacity.

author: Dago
author_rank: Frequent Contributor
timestamp: April 05, 2017, 03:39:28 am
content: How are you charging the batteries? Are properly balancing them instead of just charging? If you are not balancing them then one cell will usually die pretty fast.These Turnigy batteries have an "ok" reputation in the RC world and can seemingly last 100-200 cycles at LEAST of "heavy" (compared to your use) RC use.

author: akis
author_rank: Frequent Contributor
timestamp: April 05, 2017, 05:42:55 am
content: I charge using balanced charger at 1.5A. I typically put in around 2000-2400 mAh.I stop the discharge at 3.67V because if I carry on any longer then one cell suddenly collapses down to 3.0V or less. This happens with all those turnigy or zippy batteries. It is also the reason why the packs become useless sometimes only after a few charges. One of their cells cannot hold its charge no longer and cannot stay above 3.8V or so while the rest of the cells go up to 4.1V - 4.2V

author: senso
author_rank: Frequent Contributor
timestamp: April 05, 2017, 06:23:42 am
content: Efest is not a reputable brand..Grab some real brand name Samsung, Lg or Sony's from Nkon.nl...

author: akis
author_rank: Frequent Contributor
timestamp: April 05, 2017, 02:39:46 pm
content: I have been conducting some tests.With fully charged batteries, I managed to draw 1400mAh from the EBL "3000mAh" batteries and 2050mAh from the efest "3000mAh" batteries.I drew down to 3.45V and did not want to go any lower.I am not sure how low one is supposed to drain the Li-Ion batteries before they become damaged?

author: danmcb
author_rank: Regular Contributor
timestamp: April 05, 2017, 03:07:53 pm
content: li-on does not have as flat a discharge curve as LiPo4. Also lower peak current. But they are really small and light for the power. Attached is the datasheet for some Panasonics which are supposed to be very good. You can take them down to 2.5V according to Panasonic - but I would be happier with about 3.0V - depending really on how fast the discharge was.

author: akis
author_rank: Frequent Contributor
timestamp: April 05, 2017, 04:12:48 pm
content: "You can take them down to 2.5V according to Panasonic"My own personal experience with two dozen turnigys and zippys is that anything below 3.5V and a cell will most likely die/become very weak. Actually after a few discharges to 3.67V, one or two cells become very weak.I would say an acceptable battery range should be between 3.2V and 4.2V, equidistant from the 3.7V midline and a change of over 30%.I am testing another EBL 18650 and will draw it down to 2.5V.

author: danmcb
author_rank: Regular Contributor
timestamp: April 05, 2017, 04:45:38 pm
content: do Zippy etc do Li-on? I thought either LifePo4 or LiPo. it's a different chemistry and a totally different animal. These Panasonics are the kind of thing the emergency services and so on like - at least according to the guy I bought them off ;-)That said, I am now thinking of how to put the pack I have here through as many cycles as I can until it shows signs of dying. Need to set up a test system. Could build it around a phidgets card I have lying around.

author: akis
author_rank: Frequent Contributor
timestamp: April 05, 2017, 09:04:35 pm
content: This is the performance of the efest 3000mAh vs the EBL 3000mAh - all discharged at around 1.2A-0.8A. Forgot to mention, at the end of the chart we have drawn 2000mAh.The top chart is the efest and the bottom two charts are the EBL ones. Clearly the efest is much better than the ebl batteries.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 06:27:04 pm
content: Quote from: danmcb on April 05, 2017, 04:45:38 pmNope. Lipo is purely a meaningless marketing word, only describing the form factor. They are all li-ion. Most modern high-capacity cells today are NCA/graphite chemistry.Zippys, Hobbykings etc. are random shit, and the actual products can randomly change, so it's quite meaningless to make a lot of conclusions based on Hobbykings."totally different animal" only in the sense of quality control. The chemistry is basically the same, but of course Panasonic etc. have the newest tricks (and good safety).Proper cells are OK with complete discharge.I have never seen a cell, even a low-quality brandless, go bad due to full discharge down to datasheet value (such as 2.5 or 2.8V). Maybe the issue is that some people are not looking at the cell voltages at all, but the pack voltage divided by the number of cells? If yes, then they need to say so! So when you are stopping at 3.5V, some lower-capacity cell in the series pack is already at 2.5V. So you are not discharging the cell to the voltage you think you are discharging it to. The answer is to either closely match the capacities, or use a cell-level BMS.The best modern commercial off-the-shelf cells are getting very close to 300 Wh/kg in gravimetric energy density now. Some random hobbyking cells are naturally much lower; both because they are high-power cells, a tradeoff increasing power density but decreasing energy density; but also because the smaller no-name Chinese manufacturers have less money to spend on R&D to find the newest tricks.

author: danmcb
author_rank: Regular Contributor
timestamp: April 06, 2017, 06:31:47 pm
content: Li-on, Lifepo4 and Lipo are all the same thing? Hmmm. What's your source for that information? They have quite different charge and discharge characteristics and voltages, for a start. I have actually done discharge tests on Lifepo4 and Li-on and observed that myself. Lifepo4 is much flatter.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 06:38:01 pm
content: Quote from: danmcb on April 06, 2017, 06:31:47 pm"Li-on" is nothing."Lipo" means practically nothing. We call them pouch cells. Marketing wants to call them lipo. There was (in the late 1990's IIRC) this idea of a solid electrolyte, but it wasn't commercially realized, but the name stuck, and was reapplied to pouch cells (aluminium-plastic laminate; the plastic is the "polymer" so yeah, it's ok!)LiFePO4, also called LFP, is one cathode material, it's a subset of lithium ion. Others include: LCO (the classic), LMO, NCA, NCM, etc. They are all li-ion.Most li-ion cells today are either LCO or NCA. LFP serves some niche purposes. LFP indeed has very different voltage curve compared to the others, naturally due to the lower voltage, but as you say, it's also flatter. Anode material affects the curve (the flatness), too. Some NCA cells are flatter than others.Source is me.But yeah, to reanswer the original question more clearly, why the 18650's from Panasonic etc. are so much better in energy density:* They use never tech, they have the money for R&D. Li-ion is all about complex chemical and manufacturing process tricks! So the cheap nobrand Chinese cells use tech that can be described as 10-year old* These high-energy-density cells offer lot less power density. It's a tradeoff. They are brilliant in 2-hour discharge applications, but cannot supply currents like 5*C. High power cells require more reactive surface area, so there is less room for the bulk material to store the energy, so to speak.

author: akis
author_rank: Frequent Contributor
timestamp: April 06, 2017, 06:57:26 pm
content: I have tried another Efest IMR 18650 "3000mAh". I drained it down to 2.5V and it gave me 3013 mAh just as advertised. I drained it at around 1.3A dropping to 0.77A towards the end (fixed load of 3R).Suffice to say this is why this battery is regarded very highly amongst vapers. Now, vapers discharge them at very high currents, even as much as 30A with sub-ohm coils. My coil is 0.2R and I use it at 35W therefore around 13A for around 1.5 second "puffs".Going forward. I am running these tests because I want to move away from using Hobbyking's "random" batteries for another device I have been using, totally unrelated to vaping. My device uses two 6S battery packs therefore 24V + 24V at 1.3A. My device stops working at 20V therefore I do not drain the cells below 3.45V (at 1.3A). I then recharge the packs at 1.5A. After a few cycles one, or more cells in a 6S pack, and usually the "outer" ones (ie cell 1 or cell 6), fail to hold a charge over 3.8V. This has been verified on over 24 battery packs and of different makes, Zippy, Turnigy of various sub models.On another thread we came to the conclusion that the reason for the consistent failure of the outer cells must be the fact that they have soldered some very seriously thick leads to cells 1 and 6 and the heat has traveled and has compromised the outer cells. It is a good theory.Therefore I decided to use industry standard 18650s or 26650s whereby I could depend on a serious manufacturer for consistent performance.My tests with 3000mAh Efest IMR show that I would get around 1 hour - 1 hour 30 use at 1.3A constant draw, which is quite low , I am aiming at around 2 hours min.So now I have purchased good brands (according to vapers forums) 5200mAh and 4500mAh 26650s and will run some extra tests. Here is a discharge chart of the Efest IMR - hope you like it

author: danmcb
author_rank: Regular Contributor
timestamp: April 06, 2017, 06:57:52 pm
content: OK, thanks for the explanation - Li-on was a typo on my part.By the way - this is something I came across recently, maybe you already saw it. Looks interesting. Glass batteries :http://spectrum.ieee.org/energywise/energy/renewables/does-new-glass-battery-accelerate-the-end-of-oil

author: akis
author_rank: Frequent Contributor
timestamp: April 06, 2017, 07:09:39 pm
content: Quote from: Siwastaja on April 06, 2017, 06:27:04 pmI discharge cells to around 3.4V and yes due to balancing some may drop lower but never as low as < 3.0V. When the charger is attached it shows one or two cells have now become "lazy" and they do not hold their charge anymore, nothing over 3.8V (give or take) whereas the other cells reach 4.15V-4.2V (or as near as). It is always cells 1 and cells 6 that fail. This is a very common fault with hobbyking's batteries judging from over 24 packs I have tried.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 07:41:24 pm
content: Quote from: akis on April 06, 2017, 07:09:39 pmHow are you measuring this? Do you actually measure each and every cellduringthe discharge? This is what cell-level bms's are for, but they are still uncommon in the RC land.

author: amyk
author_rank: Super Contributor
timestamp: April 07, 2017, 03:09:45 am
content: Quote from: akis on April 06, 2017, 06:57:26 pmWhich other thread? My theory is that the outer cells are the ones getting bent/damaged (partial delamination, maybe even small shorts due to the corners getting pinched together) during assembly/packaging. If you carefully disassemble into individual cells you may notice this. The ones in the middle stay flat.

author: gmb42
author_rank: Frequent Contributor
timestamp: April 07, 2017, 12:05:25 pm
content: Quote from: Siwastaja on April 06, 2017, 07:41:24 pmCell level monitors have been available (and cheap) in the RC world for a number of years, e.g.this. Balancing chargers\dischargers for even longer.I have a number of relatively cheap (including Zippy\Turnigy) batteries that have have around a hundred flights each with no sign of issues. The batteries are discharged at around 10C average, so 6 minute flights and then balance charged at around 5C (initially, until the CV phase) to 4.15V\cell. The last 0.05V takes forever at very low currents so I don't bother. The ESC in the plane is set to cut power at 3.5V\cell under load although I don't intentionally fly to that point as it's pucker inducing, and on landing and checking the cells usually show around 3.6V. After the session has finished all batteries are charged\discharged to a nominal 3.7V\cell for "storage".I've retired batteries due to reduced capacity (easily spotted on the charger display) but can't remember the last time I had a dead cell.Like all hobby related items there are very expensive batteries available for those with excess cash, but they have generally shown to be only marginally better than the cheaper stuff on both capacity, output and longevity.If there were manufacturers with new high-tech capabilities that could make lightweight high discharge rate cells that retain capacity over many charge\discharge cycles they would make a lot of money in the RC world but that doesn't seem to be the case.

author: akis
author_rank: Frequent Contributor
timestamp: April 07, 2017, 02:06:33 pm
content: Here is a discharge chart of the Turnigy 6S 3600mAh pack (just discharging one cell).As you can see the cell does indeed deliver 3600mAh but then the voltage drops very abruptly and suddenly and alarmingly even. I am not sure if this cell is completely destroyed now, I am charging it up slowly.I believe that "sudden" death happens at different levels and not necessarily just below the 3.5V as this cell did.Which I further assert is the reason for so many turnigy and zippy packs going "bad" when one or more of their cells abruptly die not even a few charges in.

author: akis
author_rank: Frequent Contributor
timestamp: April 07, 2017, 02:12:34 pm
content: Quote from: amyk on April 07, 2017, 03:09:45 amThere was another discussion where I opened up a pack and showed the shoddy soldering - very dangerous indeed.There is no physical damage to the cells, I have examined a fair number, what is constant is the very thick leads soldered onto the outer cells and I believe this excessive heat has compromised the outer cells and has caused them to become weak only after a few charges.The second and most serious issue is the sudden cell collapse as the chart shows above, and at 3.5V-3.28V -

author: akis
author_rank: Frequent Contributor
timestamp: April 07, 2017, 02:21:46 pm
content: This is the typical display from two chargers showing the "weak" outer cell, it's always the same one regardless how many packs I have tried in the past 12-18 months (over 24 packs).

author: amyk
author_rank: Super Contributor
timestamp: April 08, 2017, 12:43:26 am
content: Quote from: akis on April 07, 2017, 02:06:33 pmYou pulledover 4000mAhfrom a cell rated at 3600, ending its discharge at just slightly above 1V. That is definitely overdischarging!Otherwise, the shape of the discharge curve looks completely normal --- but you should've stopped at slightly past 3600, when it started to reach the knee of the curve. In general, as the discharge current is decreased, the curve becomes flatter and the knee at the end becomes sharper --- and this is a cell designed for high current. If the scale at the bottom (please always supply units on a graph...) is hh:mm, then you discharged a 3600mAh cell at C/3.See the graph here and elsewhere, your cell is behaving normally:http://electronics.stackexchange.com/questions/32321/lipoly-battery-when-to-stop-draining

author: Audioguru
author_rank: Super Contributor
timestamp: April 08, 2017, 12:58:30 am
content: In the radio controlled airplanes world, Hobby King Turnigy batteries have no quality control. Some cells are good and some are bad. That is why they are cheap. They do not sell the bad ones to another cheap battery distributor. You might be lucky and get a battery with all good cells or one with all bad cells. But most batteries are in between.

author: HKJ
author_rank: Super Contributor
timestamp: April 08, 2017, 08:54:25 am
content: For extensive test of 18650 and other round cells, check my website:Compare the cells here:http://lygte-info.dk/review/batteries2012/Common18650comparator.phpThere is also a review for each cell, the full list is here with the newest at the top:http://lygte-info.dk/review/batteries2012/Common18650IndividualTest%20UK.html