 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion Groups General ModelsRailroadsRocketsRadio Controlled Air ModelsHelicoptersLand ModelsWater ModelsModelGeeks.com Contact UsLink To UsSearch & Site Map |
Model Forum / Radio Controlled / Air Models / June 2006LiPo Cell balancers
Are these things really necessary if one is not that bothered about getting every last watt out of a pack? Do those people with reasonable experience of LiPo cells use them? seabee > Are these things really necessary if one is not that bothered about > getting every last watt out of a pack? Do those people with reasonable > experience of LiPo cells use them? > > seabee yes. its more of safety and maintenance than pure battery performance. >> Are these things really necessary if one is not that bothered about >> getting every last watt out of a pack? Do those people with reasonable [quoted text clipped - 3 lines] > > yes. its more of safety and maintenance than pure battery performance. No, its more fashion and more expensive kit...like telling you that "Our cells are rated at 20C" - whereas more than half a dozen cycles at that rate will permanently damaged them so... "Cell balancers will protect your investment" - and help you get another half dozen cycles as above before the cells are ruined beyond redemption.. "Our cells are 20C 2100mAh type"..possibly one or the other, but not both at once., Try and get that much out of them simultaneously and they are dead after ONE cycle. "ESC is LIPO compatible" - We raised the LVC to 8.5v from 5v, so if you run into cutoff the cells will last more than ONE cycle at least. If you never use more than 70% of the rated capacity, or the rated discharge rate, and your cells will last several hundred cycles, never run into cutoff, never need balancing and give you many hours of pleasure. > Are these things really necessary if one is not that bothered about getting > every last watt out of a pack? Do those people with reasonable experience of > LiPo cells use them? > > seabee > No. If you don't over discharge either by rate or depth, packs generally stay pretty much in balance for many many cycles. Each cell gets the same mAh taken out, and the same put back in. If they start in balance they stay in balance..until one gets damaged and start to self discharge.. >> Are these things really necessary if one is not that bothered about >> getting every last watt out of a pack? Do those people with reasonable [quoted text clipped - 10 lines] > start in balance they stay in balance..until one gets damaged and start to > self discharge.. Thank you for that. It makes sense to me. It is so easy to be seduced by marketing hype. seabee > > Each cell gets the same mAh taken out, and the same put back in. If they > > start in balance they stay in balance..until one gets damaged and start to > > self discharge.. > > Thank you for that. It makes sense to me. It is so easy to be seduced by > marketing hype. Or you can be seduced by someone who doesn't know his batteries... unfortunately there is a very genuine problem with cell imbalance which is caused by the fact that no two cells have exactly the same characteristics. It's a standard problem with multi-cell batteries that are charged with a constant current/constant voltage regime such as LiPo, sealed lead-acid, wet lead acid or wet NiCad. Basically one cell reaches full charge first and denies the other cells their equal share of the limited voltage so they don't charge fully, it's a subtle process but accumulates over many cycles. In the case of wet cells the battery can be 'equalised' simply by increasing the voltage limit for a controlled time and thus gassing them then topping up the electrolyte if needed, but you can't do that with the other types so need extra hardware to balance them. Incidentally NiCad and NiMh cells don't suffer this problem as they are sealed in a steel pressure vessel and are intentionally gasses a little every time they're charged, in fact it's the gassing that produces the delta-peak that chargers use to detect they are fully charged. Of course you can debate how fast this imbalance becomes a problem, and whether a LiPo which may only have 50 cycles life the way they're getting treated by us modellers will live long enough to suffer from it 8-), but the problem is not fiction. Greg >> Thank you for that. It makes sense to me. It is so easy to be seduced by >> marketing hype. [quoted text clipped - 25 lines] > > Greg Indeed it is so. The need for cell balancing and the consequences of not doing it from time to time was explained in a recent article about electric motive power in the section about LiPo batteries. Reg >>> Thank you for that. It makes sense to me. It is so easy to be seduced by >>> marketing hype. [quoted text clipped - 28 lines] > doing it from time to time was explained in a recent article about > electric motive power in the section about LiPo batteries. Yep, and the earth is flat too. Thats why we dont fall off. In all my life, I have never seen more tosh talked about anything as an excuse to sell expensive crap to mystified punters as LIPOS..well not since the famous RF Litz gold plated loudspeaker wires at 50 quid a centimeter..and the red pens yiu had t utyy to 'reduce distort on CD's' yeah. Suckers. > Reg >>> Each cell gets the same mAh taken out, and the same put back in. If they >>> start in balance they stay in balance..until one gets damaged and start [quoted text clipped - 17 lines] > needed, but you can't do that with the other types so need extra hardware to > balance them. Actually, That's bollocks. The same current has to flow through all te ells for the same time. There is no way that one ell can deny another the same charge in mAh. As long as the cells start fully charged in approximate balance, and are not so heavily discharged that they get damaged, even if they are mismatched they will charge up to balance again - what gets take out of each cell HAS to be the same..because they are series connected. Its only when you start taking charge out by another route than the terminals, that they get out of balance. Thats self discharge due to internal damage. > Incidentally NiCad and NiMh cells don't suffer this problem as they are > sealed in a steel pressure vessel and are intentionally gasses a little [quoted text clipped - 5 lines] > treated by us modellers will live long enough to suffer from it 8-), but the > problem is not fiction. The data suggests that people who cane their cells, and use balancers get about 50 cycles. People who don't cane their cells get 200 cycles or more, even without balancers. > Greg > Actually, That's bollocks. The same current has to flow through all te > ells for the same time. There is no way that one ell can deny another > the same charge in mAh. Actually, you've shown over and over again in this group that you have very little understanding of batteries yet spout your misunderstandings as fact. In this case you're just showing your ignorance by claiming that cell imballance in batteries is "bollocks" in contradiction to the entire battery industry which has been dealing with it using equalise charging since the battery was invented!. The problem applies to any battery that is charged using the CC/CV regime and there is bound to be a lot of information about it on the web if you could be bothered to learn, sadly you've shown yet again that you can't. Greg >> Actually, That's bollocks. The same current has to flow through all te >> ells for the same time. There is no way that one ell can deny another [quoted text clipped - 9 lines] > a lot of information about it on the web if you could be bothered to > learn, sadly you've shown yet again that you can't. I am talking *specifically* about LIPOS, not about Nicad, Nimh or lead acid. The effect is there, but it only becomes significant when the batteries are damaged by abuse. The fact that the manufacturers hype their batteries, to get them abused, then sell dubious 'solutions' to fools to partially correct the abuse, and you have fallen for it, is another matter. > Greg > I am talking *specifically* about LIPOS, not about Nicad, Nimh or lead acid. Oh here we go, you claimed that everything I wrote was bollocks but when it finally dawnes on you that you're contradicting the entire battery industry you try to claim you didn't mean what you said!. > The effect is there So, contrary to what you said before you now admit it exists, so many U turns it would make a politician blush 8-). For the benefit of newcomers to this group "The Natural Philosopher" or NatsPiss as he's affectionately know by those of us who've suffered him for years, is a low grade troll who loves to give wrong and sometimes dangerous advice to the unsuspecting then keep the threads going for days, just like this. We can't kill file him because he just waits for new people to turn up and the regulars here don't like to see people given bad advice. He is at least partly responsible for this group being so quiet 8-(. Greg >> I am talking *specifically* about LIPOS, not about Nicad, Nimh or lead acid. > [quoted text clipped - 17 lines] > > Greg No greg, that's you. In a nutshell. unlike you, I have many many electric planes and LIPO batteries that I actually FLY. And monitor with things like METERS. But unlike you, I have a brain, and an education and a lifetime spent in engineering design, and enough exposure to marketing to know when not to buy a gold plated loudspeaker connector.. "The Natural Philosopher" <a@b.c> wrote : > Actually, That's bollocks. The same current has to flow through all te > ells for the same time. There is no way that one ell can deny another the [quoted text clipped - 6 lines] > when you start taking charge out by another route than the terminals, that > they get out of balance. Thats self discharge due to internal damage. It's not bollocks. The problem is that it nigh on impossible to produce cells that are identical in performance and capacity, coupled with the extreme sensitivity of the cells to damage through over-voltage and the lack of any in-built charge balancing mechanism such as is present in lead-acid, NiCd and NiMH through benign overcharging. A compounding issue is that, although leakage currents are small, they are not identical between cells and can result in significant charge imbalance. This, by the way, is one of the reasons why LiPos should not be stored fully charged for long periods. All the commonly available LiPo chargers charge the cells perilously close to the electrolyte breakdown voltage, at which point serious damage starts to occur. The voltage of a cell rises fairly rapidly as end of charge approaches. Consider three cells in series, with a single cell having a slightly lower capacity than the other two. You might think that an indicated charging voltage of, say, 11.8 volts equates to 3.93 volts per cell. In reality the individual cell voltages may range from 3.8V to over 4V. A little higher and there goes your cell. There is plenty of information about this in the (respectable) literature. I suggest you do a Google search. It would probably be true to say that the higher quality packs are less likely to cell characteristic variations that would lead to a need for regular balancing. Ironically, these are the ones that make the facility available through a balancer connector. Steve S > "The Natural Philosopher" <a@b.c> wrote : >> Actually, That's bollocks. The same current has to flow through all te [quoted text clipped - 27 lines] > cell. In reality the individual cell voltages may range from 3.8V to over > 4V. A little higher and there goes your cell. As long as they are in balance at the peak charge, they may go out of balance at less, but they will recover to balance when charged. > There is plenty of information about this in the (respectable) literature. I > suggest you do a Google search. Have done. Also have many packs. No balancers. They don't die from out of balance, they die earlier from abuse. Onlyt packs I have had go have been left switched n up trees and teh like. Tow were recovered (without balancers from zero volts to about 70% of rated capacity, the third puffed and died. With a lifetime of maybe 200 cycles being about par for the course, that isn't long enough in a an averagely busy flying career to have time to self discharge to way out of balance. Self discharge is in any case likely to be vastly increased due to micro shorts due to over discharging rate wise. For a person on a limited budget the cost of balancers and the like on small cells is greater over the pack lifetime than the cost of two packs...in the first place. If you don't charge or discharge to the hilt, the packs stay well enough i balance to get to the end of their lives without ever going far enough out pf balance..the packs I have seen that fail are being abused by people who don't even have a meter to know what is going on..one local guy was running his nominal 10v pack down to 7v.."It only seems to last about 3 months"...not surprising since I measured his discharge rate at 25C.. No doubt he has a balancer these days. If you stick to 3V or better still 3.2v-3.3v as an end point, and derate the cells to 70% of capacity, and about 70% of CLAIMED peak discharge rate, and don't squeeze the last amount of charge into them..stop at about 4.1v a cell..I can GUARANTEE that they will last longer than an "accurately balanced" pack that is run up to 4.2v, down to 2.9v, at the manufacturers 'rated discharge' rate. Balancing, or lack of balancing, is a second order effect. Its mostly negligible, and has been exploited to sell yet more gubbins to the unsophisticated. Simply because the LIPO marketing wars that have raged for over a year now, insist that the packs are capable of more than they actually really can deliver. Kokam is the worst in this respect. Balancing is like selling an engine with a needle valve in the prop itself, and then selling a heavy glove to adjust it with. The answer is to treat the cells better in the first place. > It would probably be true to say that the higher quality packs are less > likely to cell characteristic variations that would lead to a need for > regular balancing. Ironically, these are the ones that make the facility > available through a balancer connector. Cheap chinese packs ar thrown together out of any old rubbish, and are fine if you only fly occasionally. My point, once again, however,. is that *absolute abuse is what kills 99% of packs that die early*, and if they are derated they don't die from *that* cause. Chances are that they MAY have 15% more cycles left on them if balanced up at the end of their life...but ho cares..2 years down the road they are obsolete anyway. > Steve S  SignatureMy reply address does work >> "The Natural Philosopher" <a@b.c> wrote : >>> Actually, That's bollocks. The same current has to flow through all te [quoted text clipped - 51 lines] > small cells is greater over the pack lifetime than the cost of two > packs...in the first place. £24 for a 4 cell balancer is not a great expense in my book when you consider it will out last all your packs of Lipo's "The Natural Philosopher" <a@b.c> wrote :> > As long as they are in balance at the peak charge, they may go out of > balance at less, but they will recover to balance when charged. NO!!! LiPos are not peak charged in the sense that is used for NiMh and NiCd, as you should well know. They are charged by constant current/constant voltage. Constant current is used until the mean voltage/cell reaches around 4.2V. From this point constant voltage is used. Cell damage starts occurring at around 4.3V. Consider an unbalanced 3S pack. At the end of the constant current phase we may have two cells at 4.15V and the third at 4.3V. The third cell will now start to be overcharged. For NiCd and NiMH this is not so much of a problem, but a LiPo cell will now start to be irretrievably damaged. This will further reduce its capacity and exacerbate the problem at the next cycle. Steve S > "The Natural Philosopher" <a@b.c> wrote :> >> As long as they are in balance at the peak charge, they may go out of >> balance at less, but they will recover to balance when charged. > > NO!!! LiPos are not peak charged in the sense that is used for NiMh and > NiCd, as you should well know. I never for one moment said they were "in the sense that is used for NiMh and NiCd,". They are charged to a peak voltage. And thats it. If they are all 'peaked' to 4.2Yper cell, then even if they end up way different when discharged, due to different capacities, they will come back up to 4,2v per cell when recharged. >They are charged by constant current/constant > voltage. Constant current is used until the mean voltage/cell reaches around > 4.2V. From this point constant voltage is used. Grandmothers and eggs son. I have been using these things for several years, and I know exactly what the correct charge regime is. Propbably far better than you do. >Cell damage starts occurring > at around 4.3V. Consider an unbalanced 3S pack. At the end of the constant > current phase we may have two cells at 4.15V and the third at 4.3V. No. It won;t. Not if it started at 4.2v per cell. What you take out is the same ampere hours for every cell, and what you put in is the same ampere hours for every cell. IF the pack starts in balance, and there is no meaningful internal self discharge, it will stay in balance for many many cycles. Try a little basic theory like Kirchoffs law to understand why that is. What gets cells OUT of balance is damaging them, when internal self discharge through hot spots and microshorts leaves the cells at different states of charge and different capacities. I.E. typically what happens when yo run them at the CLAIMED discharge rates, or below the cutoff voltage that is sensible. At that point balancing may be required to extend th life a little, but the damage is already done, and no amount of balancing will make a damaged pack new again. The > third cell will now start to be overcharged. For NiCd and NiMH this is not > so much of a problem, but a LiPo cell will now start to be irretrievably > damaged. This will further reduce its capacity and exacerbate the problem at > the next cycle. No, you have it back to front. Its the irretrievable damage that causes the pack to go unbalanced. Of course charging a damaged pack is always an exercise of great scientific interest and if you are the sort of dickhead who flies glo engines and knows almost nothing about batteries or elctricity, then a balancer might just save your life once you have f.cked the pack into a nicely ticking time bomb. My advice is for those who understand it. Idiots can waste their money a and ignore it. > Steve S > Steve S wrote: >> "The Natural Philosopher" <a@b.c> wrote :> [quoted text clipped - 48 lines] > No, you have it back to front. Its the irretrievable damage that causes > the pack to go unbalanced. This is where you and I differ. I won't stoop to unneccessary insults like you, but merely point out the following issues that can cause packs to become unbalanced, other than by abuse/obvious damage: 1. Not all cells in a pack have the same initial capacity. This, in my view, is the number one problem. Even the better quality manufactures get it wrong sometimes. With the cheaper brands it's a real lottery. Even if a pack with such a problem starts off balanced, as soon as you discharge down to the normal cutoff voltage you have problems. 2. Unequal self-discharge rates. 3. The unbalancing effects of the unequal cell temperatures typically found in our application. [insults snipped] Steve S >1. Not all cells in a pack have the same initial capacity. This, in my view, >is the number one problem. Even the better quality manufactures get it wrong [quoted text clipped - 6 lines] > >Steve S That's a very good, very concise summary of the situation. I used to scoff at the idea of buying yet ANOTHER piece of equipment for battery charging, until I had some packs fail because of improper charging. and abusive discharging. In point of fact, a pack which is properly charged and balanced can in fact become imbalanced if left alone for a period of time. Battery packs in use do not expose all cells to exactly the same conditions, there is likely to be a significant temperature difference cell to cell in a 3 cell pack. bob > That's a very good, very concise summary of the situation. I'm not going to get into the technical details of why cell imballance occurs as it's of rather academic interest, readily available to those who are interested and only likely to feed our troll, but it's a fact of battery life. The consequences vary from minor to terminal and it's a case of yer pays yer money and takes yer choice. If I had paid lots of money for larger LiPo packs, something I'm not prepared to do because of the risk and cost but many others at my club have done, I would spend a few pounds extra to get the best life out of them, as indeed they have done Greg |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2012 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.