dnmun
1 PW
internal resistance is only critical in charging. it makes it more difficult to make the pack balance when charging. on discharge the internal resistance does not actually reduce current flow as it does during charge.
expected battery life?
- Thread starter alsmith
- Start date
costicuta2000
1 mW
Hello and happy new year to everyone. I work in a ebike shop for almoust 5 years, and I'll share to you my experience with the ebikes batterys. They are some manufacters who put li-po cells in theirs ebikes, and the others who use 18650 cells. The batterys have almoust the same weight, but, with the years something strange is happen. The 18650 samsungs and panasonic cells last much longer than any li-po battery that others ebikes use. Now, the BH bikes, with the Nitro (45 km/h speed), use the 18650 cells. Even a 125 cc (vmoto emax 120L) who goes at 4800W use 18650 cells. (13S 26P). The scooter has almoust 3 years and 20k km and at my last test the battery still holds 50 Amps. From my experince with all those cells, li-po, lifepo4 and 18650, I can say the 18650 cells last longer than the rest. No wonder the bosch ebikes, bh, tesla use them. I think, the next pack of my scooter will be with 18650 panasonic cells. I'll set the charger to cut off at 4.1 V cell (If I'm not wrong the nissan leaf cut at 4,06V cell. He charge at 80%. A specialist of li cells told me: "never keep a li-ion cell in a hot environment and at higer voltage".He proved with a 18650 cell from a 1999 apple laptop. The cells was at 85%. He was stored at 6°C and at 20% of its capacity, charged from time to time. I think it was a sanyo cell.
Anyway, I never understood why so much endless sphere members use rc li-po battery for ebikes. They are good for rc. For me 60 km/h or 1000W is the max I'll put in a ebike. If you want to go faster just buy a electric scooter/motorcycle.
Greetins form France.
Anyway, I never understood why so much endless sphere members use rc li-po battery for ebikes. They are good for rc. For me 60 km/h or 1000W is the max I'll put in a ebike. If you want to go faster just buy a electric scooter/motorcycle.
Greetins form France.
arkmundi
10 MW
Ditto! Greetings.costicuta2000 said:
wb9k
10 kW
arkmundi said:I'm curious as I'm using A123 AMP20 prismatic cells in my battery build. I know these can sustain both a continuous and burst C-rate exceeding my current needs. A 48V 20ah 16S1P design. The data-sheet for these say:
So discharge power is 1200 watts. The MAC 10T is a 1000 watt motor, up to 1500 watts burst. So I'm good.
What's the max discharge capacity of this pack? I ask, because I bought into the MXUS 3000 watt group buy and want to explore the various limitations I might experience. Idea is to reconfigure my 4 8S1P 24V blocks into a 96V 32S1P battery pack and buying into the Infineon 18fet 4110 controller, to road test the motor. Feasible? Good idea or bad idea? Last thing I want to do is push the limits of my pack in a way that damages them. So I'm pondering the various numbers and want to do the right math/analysis. What is the max amps I can draw out of the pack? Do I need a 2P design to power this motor?
1200 Watts is for a single cell. Multiply this value by the number of cells in series; this is the max discharge power of the pack. (19,200 Watts). You are WAY below the limits of these cells. If you back out a bit and calculate 1000 Watts at 52.8 Volts (nominal for LFP in 16S), you'll see that this only equals 18.94 Amps of current from the pack. 18.94 * 3.3 = 62.5 Watts from each series cell. Hopefully this clarifies things for you if they haven't been clarified by others here already. (Easy to understand why you may have been confused---I haven't had time to look at all the links given, but the thread itself is full of half-informed opinions and arguments over semantics, which is unfortunate.)
Regarding Tesla and the 18650, the primary reason Tesla selected these cells is because they were already being produced in huge quantities, and were thus readily available in the necessary quantities (early on) without having to build the battery source from the ground up. Even at this, they have already become by far the largest consumer in the world of these batteries and are now onto building their own plant---which I've heard will build larger cells than the 18650. About time. There are advantages to having many small cells in parallel rather than just one big one--a single bad cell will cause far less disruption and may even provide several years of service before the problem becomes serious enough to require service. Cell defects are a fact of life, and this is one effective way of dealing with them in the design. However, there are limits. By using the smallest cell available, Tesla has a pack with thousands of welds--the maximum possible number of potential failure sites. Their liquid cooling method of plumbing lines right through the modules doesn't exactly pull my heartstrings either--it's a potential nightmare for service and especially when it comes time to drain stranded energy from a wrecked car. Tesla is doing some great things, but that doesn't mean their methods are always the be-all, end-all. Perhaps one day Musk will be as dismissive of this pack design approach as he is now of upfitting the Elise into an EV. I think they both were necessary compromises in the development of Tesla.
arkmundi
10 MW
Thanks for the well informed reply to my question. In part, what I'm confused by is the operative dynamics of cells configured into a battery pack. The current must flow through each & every cell placed in series, each cell contributing watts. While well below the threshold capability of these cells, there must be a real-world limit of how many cells can be placed in series. While no one here will likely approach that limit, what is it? I know that A123 is also making very large batteries for grid-storage applications. What is the largest A123 battery in current use?wb9k said:
wb9k
10 kW
arkmundi said:
The grid-storage batteries are contained in trailers like those pulled by 18-wheelers. They are mammoth, but I don't know the configuration details. The largest automotive pack I'm aware of is about 200S with a capacity of roughly 30 kW. The capacity of the grid-trailer units is 2 MW. The only "limit" I see on how many cells you can put in series is additional design safety margins to eliminate the possibility of arc flash. That, and the lack of a need for more voltage. The largest automotive packs I know of are in the neighborhood of 700 Volts when fully charged--these are mostly for buses and very large trucks.
parabellum
1 MW
Wb9k, half-informed opinions?
1)
2)
3)
1)
You forgot" with reasonable energy density"
2)
Yes, but they use them as advantages, fuse on every cell makes that pack redundant, compared to big cells.
3)
How much larger? 22700. You still believe 18650 was chosen because it was the only thing available?
999zip999
100 TW
For what it's worth. I run A123 20ah cells 24s. 80v. But If for your ebike 48v 40amp to 80 amp. with these cells for a 1500 plus cycles if made with brains. Hard to do if you don't take time to match cells plus.
The pack I made can put out 20,000 watts if lazer welded and made by wb9k or more.
Mine can only handle 8,000 watts. But my brain says 80amp max. Or 80v x80amp would be my limits. I should get 1800 cycles by using a 30amp and soon a 40amp. controller.
So don't use some maybe 2c cell. I would use a 4~5c cell and not worry if only use a C.A. and only use 15ah out the 20ah cells.
Just ask wb9kk what A123 20ah puts out safely,.17ah. Don't believe any of those bull dropping. 17ah if you want less cycle life. So on the best and safest 20ah sold cells lifepo4 from USA's 20ah cells only can live with 17ah or real life 15ah for 2,000 cycles
Answer 17ah.
Going cheap cost lots of money.
The pack I made can put out 20,000 watts if lazer welded and made by wb9k or more.
Mine can only handle 8,000 watts. But my brain says 80amp max. Or 80v x80amp would be my limits. I should get 1800 cycles by using a 30amp and soon a 40amp. controller.
So don't use some maybe 2c cell. I would use a 4~5c cell and not worry if only use a C.A. and only use 15ah out the 20ah cells.
Just ask wb9kk what A123 20ah puts out safely,.17ah. Don't believe any of those bull dropping. 17ah if you want less cycle life. So on the best and safest 20ah sold cells lifepo4 from USA's 20ah cells only can live with 17ah or real life 15ah for 2,000 cycles
Answer 17ah.
Going cheap cost lots of money.
Alan B
100 GW
18650 is just a size code, many different types of cells are put in these cans. Even A123 cells are available in them. Nothing magic about a cell size, except availability. A few years ago when Tesla was looking, what was available from multiple sources, in large quantity, that had the highest energy density?
Tesla knows their batteries burn well. At one point they had a contract that buyers had to sign to not sue Tesla over the car burning. I doubt if this is legal or that it exists today, but I know someone who knew a lawyer working for Tesla on this. They apparently were quite concerned about their liability. They know there is a risk.
Tesla's choice of these cells doesn't validate them as the best choice or even a good choice. It is a choice that was available from multiple suppliers and that can be made to work. It has been a choice that Elon has paid dearly to make work. There are many more suitable packages available that are being used by other manufacturers. They all work. It is much too early to call the winner of the packaging competition.
I don't have anything against 18650's, I use a number of them in flashlights and I'm sure they are in many of my laptops. I've even had one leak in a flashlight and corrode it, almost like an alkaline, I wonder what's up with that. But for an ebike pack they are both wonderful and awful. Wonderful how you can fit them into small spaces and get a lot of capacity per volume and weight, awful in the difficulty and number of interconnects needed to make the pack work. I'm going to make a welder sometime and make some packs, but just getting bona fide cells for a reasonable price is a real challenge. Makes ordering a few Lipo sound downright easy, and you could buy HK lipo and throw half of it in the trash and end up at about the same price.
Then there is the separate issue of chemistry. A number of fundamental chemistry combinations, and endless tweaks that make a big difference. Life, capacity, charge and discharge rates. Many tradeoffs, and differing goals for each market. Lots of R&D dollars going into this area. It will continue to evolve. But the tradeoffs are difficult. I know a battery researcher, and we talked about this. Longer life is not difficult. They can make much longer life cells right now, but there is little market for long life cells with lower capacity. Lowering the cell voltage makes a lot of life related problems go away, but the marketplace wants capacity over life. Does the industry really want a long life 20 year battery? They want a battery that lasts how long? As long as the lease or loan? Clearly they want range. And for some the power delivery is important, though that tends to come for free with big packs.
Do I want an ebike pack with a 20 year life but consumes double the volume and weight, and costs more? Might be fine in a larger vehicle, but ebikes are very sensitive to size and weight. The market needs are not constant. The wonderful batteries from the Leaf are not very compatible with bicycle frames. Do you want a pack that lasts 3 years and then plan to buy a new pack that has much greater range then? Or spend double now and get one that will last 7 years and spend the last 4 years of the declining pack wishing you had saved the extra money for one of the new packs that everyone else is enjoying by then? How long is enough?
Someone wondered why RC Lipo was often chosen for ebikes. It is amazing stuff, for a few bux you can buy a couple of small packs to start with, plug them together with the plugs that come on them, plug in the controller and your ebike creation is up and running! You can buy a few more, make a simple wiring harness and have various voltages, current capacity and range configurations, like a lego power kit. I know one fellow who reconfigures his pack for what he's doing that day. Flexibility. Cost. Small size. Availability.
People go on about safety and risk. We've all seen the fires from RC batteries, laptop 18650's, A123 battery packs, Lead-acid batteries, and even NiMH batteries. The RC batteries burn hotter, just like the laptop 18650's. But does it matter a lot how hot the match was that burned the forest? These fires have causes - shorts in the wiring, shorts internal to the cells, physical damage to cells, overcharging, overdischarging, charging damaged cells, etc. Maybe the small differences in the chemistries will prevent the fire from spreading, or maybe not. I'd hate to bet my safety on that small difference. At the end of the day the system design has a lot to do with how reliable and dangerous or safe these packs are. Cell support, protection from physical damage, fusing, insulation, chafing, heat buildup, shorts, there are many issues to get right. Any of them can turn a pack into a smoldering mess or a fireball. Some cells are a little better than others, but the best cell in a bad pack can still catch fire.
Quality Control is difficult, even the best manufacturers (Sony, Apple, HP, Dell, etc) have their lapses. Can you totally depend on brand name to guarantee quality? Really? QA involves testing the parts at both ends of the supply chain. When we construct our own packs we take a responsibility for the quality of the system, and the quality assurance. New packs need testing and a watchful eye. Weed out the bad cells. Get a good balance. A lot of work with 18650's, but ripping a pack apart after welding it is no fun. A major part of the cost of a battery pack is characterizing the cells and matching them up. Is every pack maker doing this?
One example was another fellow who kept reconfiguring his packs, going higher and higher in voltage. He was mixing different batteries, and bulk charging at very high voltages. Eventually he burned his house. He never came back and told us exactly what happened, but one way or another the QC of his technique and his pack was almost certainly a contributing factor. Would a particular chemistry have avoided this outcome? Is smoking in bed a good plan?
So what really determines the battery pack life? It is not just cycles from the datasheet, or chemistry, or cell size. Many other factors creep in, such as depth of discharge, rate of discharge, minimum capacity before the pack is no longer useful (big packs win in a lot of ways), temperature, charge regimen, storage. If a pack is just enough to do the job it will be deeply discharged each cycle which is not good for life, and it won't take much capacity loss before it will be inadequate for the task. Proper system design makes a huge difference in the pack's useful life.
In my case the main killer of batteries has been sitting idle. I can't blame a bad BMS as there was none. Just batteries or cells sitting with no load, or with light loads from the leakage of the system killed them. Those little leakage currents add up when the bike or flashlight is not in use. If you have a bunch of cells you are not using, probably best to sell them, the clock is ticking on them whether you are using them or not. Otherwise charge them to a good storage value and unplug everything. Even the best lead acid "maintenance" chargers tend to kill batteries faster than charging them periodically and disconnecting them the rest of the time. At least that's been my experience. Keep riding and they will last longer. They don't like being ignored.
What do I expect in battery life? Enough life for me to feel I got good value on my investment, and for a better battery to be out when this one is insufficient.
Tesla knows their batteries burn well. At one point they had a contract that buyers had to sign to not sue Tesla over the car burning. I doubt if this is legal or that it exists today, but I know someone who knew a lawyer working for Tesla on this. They apparently were quite concerned about their liability. They know there is a risk.
Tesla's choice of these cells doesn't validate them as the best choice or even a good choice. It is a choice that was available from multiple suppliers and that can be made to work. It has been a choice that Elon has paid dearly to make work. There are many more suitable packages available that are being used by other manufacturers. They all work. It is much too early to call the winner of the packaging competition.
I don't have anything against 18650's, I use a number of them in flashlights and I'm sure they are in many of my laptops. I've even had one leak in a flashlight and corrode it, almost like an alkaline, I wonder what's up with that. But for an ebike pack they are both wonderful and awful. Wonderful how you can fit them into small spaces and get a lot of capacity per volume and weight, awful in the difficulty and number of interconnects needed to make the pack work. I'm going to make a welder sometime and make some packs, but just getting bona fide cells for a reasonable price is a real challenge. Makes ordering a few Lipo sound downright easy, and you could buy HK lipo and throw half of it in the trash and end up at about the same price.
Then there is the separate issue of chemistry. A number of fundamental chemistry combinations, and endless tweaks that make a big difference. Life, capacity, charge and discharge rates. Many tradeoffs, and differing goals for each market. Lots of R&D dollars going into this area. It will continue to evolve. But the tradeoffs are difficult. I know a battery researcher, and we talked about this. Longer life is not difficult. They can make much longer life cells right now, but there is little market for long life cells with lower capacity. Lowering the cell voltage makes a lot of life related problems go away, but the marketplace wants capacity over life. Does the industry really want a long life 20 year battery? They want a battery that lasts how long? As long as the lease or loan? Clearly they want range. And for some the power delivery is important, though that tends to come for free with big packs.
Do I want an ebike pack with a 20 year life but consumes double the volume and weight, and costs more? Might be fine in a larger vehicle, but ebikes are very sensitive to size and weight. The market needs are not constant. The wonderful batteries from the Leaf are not very compatible with bicycle frames. Do you want a pack that lasts 3 years and then plan to buy a new pack that has much greater range then? Or spend double now and get one that will last 7 years and spend the last 4 years of the declining pack wishing you had saved the extra money for one of the new packs that everyone else is enjoying by then? How long is enough?
Someone wondered why RC Lipo was often chosen for ebikes. It is amazing stuff, for a few bux you can buy a couple of small packs to start with, plug them together with the plugs that come on them, plug in the controller and your ebike creation is up and running! You can buy a few more, make a simple wiring harness and have various voltages, current capacity and range configurations, like a lego power kit. I know one fellow who reconfigures his pack for what he's doing that day. Flexibility. Cost. Small size. Availability.
People go on about safety and risk. We've all seen the fires from RC batteries, laptop 18650's, A123 battery packs, Lead-acid batteries, and even NiMH batteries. The RC batteries burn hotter, just like the laptop 18650's. But does it matter a lot how hot the match was that burned the forest? These fires have causes - shorts in the wiring, shorts internal to the cells, physical damage to cells, overcharging, overdischarging, charging damaged cells, etc. Maybe the small differences in the chemistries will prevent the fire from spreading, or maybe not. I'd hate to bet my safety on that small difference. At the end of the day the system design has a lot to do with how reliable and dangerous or safe these packs are. Cell support, protection from physical damage, fusing, insulation, chafing, heat buildup, shorts, there are many issues to get right. Any of them can turn a pack into a smoldering mess or a fireball. Some cells are a little better than others, but the best cell in a bad pack can still catch fire.
Quality Control is difficult, even the best manufacturers (Sony, Apple, HP, Dell, etc) have their lapses. Can you totally depend on brand name to guarantee quality? Really? QA involves testing the parts at both ends of the supply chain. When we construct our own packs we take a responsibility for the quality of the system, and the quality assurance. New packs need testing and a watchful eye. Weed out the bad cells. Get a good balance. A lot of work with 18650's, but ripping a pack apart after welding it is no fun. A major part of the cost of a battery pack is characterizing the cells and matching them up. Is every pack maker doing this?
One example was another fellow who kept reconfiguring his packs, going higher and higher in voltage. He was mixing different batteries, and bulk charging at very high voltages. Eventually he burned his house. He never came back and told us exactly what happened, but one way or another the QC of his technique and his pack was almost certainly a contributing factor. Would a particular chemistry have avoided this outcome? Is smoking in bed a good plan?
So what really determines the battery pack life? It is not just cycles from the datasheet, or chemistry, or cell size. Many other factors creep in, such as depth of discharge, rate of discharge, minimum capacity before the pack is no longer useful (big packs win in a lot of ways), temperature, charge regimen, storage. If a pack is just enough to do the job it will be deeply discharged each cycle which is not good for life, and it won't take much capacity loss before it will be inadequate for the task. Proper system design makes a huge difference in the pack's useful life.
In my case the main killer of batteries has been sitting idle. I can't blame a bad BMS as there was none. Just batteries or cells sitting with no load, or with light loads from the leakage of the system killed them. Those little leakage currents add up when the bike or flashlight is not in use. If you have a bunch of cells you are not using, probably best to sell them, the clock is ticking on them whether you are using them or not. Otherwise charge them to a good storage value and unplug everything. Even the best lead acid "maintenance" chargers tend to kill batteries faster than charging them periodically and disconnecting them the rest of the time. At least that's been my experience. Keep riding and they will last longer. They don't like being ignored.
What do I expect in battery life? Enough life for me to feel I got good value on my investment, and for a better battery to be out when this one is insufficient.
NeilP
1 GW
Alan B said:
I said similar earlier that we are talking about a size and type, not a chemistry
NeilP said:
I'd pretty much agree with the rest of your 'article ' too
Alan :wink:
friendly1uk
1 MW
costicuta2000 said:
It's in the math, which I see you can't do.
arkmundi
10 MW
Tesla's team has some serious credentials, and now growing experience. Plus their partnership with Panasonic. Now that the market and potential volume for their EV's has been clarified, they will be forging a very capable cell. They announced that it'll be a new format, likely a 26700, a made to specification cell, which they can now demand. Whereas as a new entry, they could not make that demand.Alan B said:
Well yes, in EV's of any size & type - this market is huge and growing. The batteries have to have power density and long life. And now that the kind of nano-engineering that MIT/A123 invented has proliferated, we can expect more, much, much more.
Good questions, that everyone with an eBike should ask themselves before committing. I've gone on the record. I want my A123 AMP20 48V battery pack to last for 2000+ cycles, at least 5 years, and I believe I'll get that. I've made it in four 8S bricks, so I can carry either 20ah or 40ah of capacity, depending how far I'm going. On a back rack, pannier style, low center of gravity.
That everytime is promoted should be qualified and has a higher risk of catching fire and must be used with caution. I can by the way also legitimately claim that A123 nanophosphate is amazing stuff, but also safe to use on the kind of basis most people will want - use, plug in & charge and forget until ready to use again.
Uh, no, I have never seen or heard about a fire from an A123 battery. Your putting RC Lipo and A123 is the same risk category is EGREGIOUSLY WRONG!!!!!!!!!!!!!!!!!!!!!
Its why I make my battery packs with the A123 AMP20's. I avoid all that - just using a mechanical strap to connect tabs. Very easy to assemble into a battery pack. And their is significant conformity in the cells in every respect, so I have never had to do what you suggest. The cells in my packs all stay within 0.02 V of each other: discharge, charged and while charging. Its one of the amazing characteristics of these cells.
Again, it is not in my experience with the A123 packs I've made. Maybe as they age, but not now.
On that we can agree. So, paying more for my A123 battery packs, I do expect a longer life. In fact, so much longer that in the long run, the cost, per kwh consumed over its lifetime, will be less..What do I expect in battery life? Enough life for me to feel I got good value on my investment, and for a better battery to be out when this one is insufficient.
dnmun
1 PW
lifepo4 chemistry can go into thermal runaway also. it just takes a higher temperature to initiate the thermal runaway for lifepo4 than it does for lipo and the other benefit of the lifepo4 is that the oxygen is locked up in the phosphate and does not get released from the phosphate until the material reaches 600o C.
all this talk about how lipo is dangerous and blows up is all uninformed opinion.
lipo does not just suddenly catch on fire for no reason while sitting unless it is heated to high temperatures. i tried to get people to actually watch the utube video where that guy demonstrated how lipo and lifepo4 went into thermal runaway in the calorimeter under adiabatic heating. nobody watched but everybody has their own ideas and uninformed opinion.
to me, that mental laziness is offensive, but i spent decades in school too which is offensive to most of the people who think that the only criteria for intelligent opinion is how fast their bike goes. why nobody watched that video or made comments about it or the video from the professor on the parasitic reactions that eat up cycle life.
nobody ever uses real scientific data here to form opinions, just who has the fastest ebike.
lipo has to be heated rapidly with high charging current above the full voltage for long enuff to overcome the heat loss from the pack until the pack finally reaches the critical temperature to cause thermal runaway to begin.
this has never happened on any thread reported here except for the case where ian plugged her bigger battery into her smaller battery by accident and the smaller battery was overcharged and overheated but if i recall never went into thermal runaway and fully combusted and sprayed flames out of the pouches. floont is likely to have overcharged his pack because he was using the meanwell power supplies to bulk charge his lipo but even that fire may have been started by shorts, we will never know.
all this talk about how lipo is dangerous and blows up is all uninformed opinion.
lipo does not just suddenly catch on fire for no reason while sitting unless it is heated to high temperatures. i tried to get people to actually watch the utube video where that guy demonstrated how lipo and lifepo4 went into thermal runaway in the calorimeter under adiabatic heating. nobody watched but everybody has their own ideas and uninformed opinion.
to me, that mental laziness is offensive, but i spent decades in school too which is offensive to most of the people who think that the only criteria for intelligent opinion is how fast their bike goes. why nobody watched that video or made comments about it or the video from the professor on the parasitic reactions that eat up cycle life.
nobody ever uses real scientific data here to form opinions, just who has the fastest ebike.
lipo has to be heated rapidly with high charging current above the full voltage for long enuff to overcome the heat loss from the pack until the pack finally reaches the critical temperature to cause thermal runaway to begin.
this has never happened on any thread reported here except for the case where ian plugged her bigger battery into her smaller battery by accident and the smaller battery was overcharged and overheated but if i recall never went into thermal runaway and fully combusted and sprayed flames out of the pouches. floont is likely to have overcharged his pack because he was using the meanwell power supplies to bulk charge his lipo but even that fire may have been started by shorts, we will never know.
Alan B
100 GW
I've seen A123 pouch cells explode when hit with an impact. It doesn't always happen, but when it does it is quite spectacular.
I've heard that A123 based racing machines have burned up. Who knows the cause, it doesn't really matter. They can start a fire and they can burn. Easily.
LiFePO4 has advantages but it is not inherently "safe", it is somewhat like comparing alcohol to gasoline.
I've also seen videos of lipo being overcharged to make it burst into flame and it took an amazing overcharge to get it to go.
RC lipo is involved in more incidents because it is so popular for so many uses. Pouch cells are also not very protected, and the RC business is full of really inexpensive chargers that don't always work right. It is also used by a lot of people without enough understanding of the risks, though plenty of safety material comes with them these days, even from HK. But the average person may not take this seriously enough.
5 years is a reasonable life for an ebike pack. Anything over 3 years is good. But if it costs double it should last twice as long, or those interested in cost effectiveness won't find it good.
If a warning is needed, it is about taking the responsibility to make reliable safe battery packs, no matter what chemistry or physical cell configuration is being used. Know the materials and dangers involved and make a safe and reliable pack. Invest the effort into quality control, matching cells, physical protection, current limiting, proper wiring and insulation, and safe charging.
I've heard that A123 based racing machines have burned up. Who knows the cause, it doesn't really matter. They can start a fire and they can burn. Easily.
LiFePO4 has advantages but it is not inherently "safe", it is somewhat like comparing alcohol to gasoline.
I've also seen videos of lipo being overcharged to make it burst into flame and it took an amazing overcharge to get it to go.
RC lipo is involved in more incidents because it is so popular for so many uses. Pouch cells are also not very protected, and the RC business is full of really inexpensive chargers that don't always work right. It is also used by a lot of people without enough understanding of the risks, though plenty of safety material comes with them these days, even from HK. But the average person may not take this seriously enough.
5 years is a reasonable life for an ebike pack. Anything over 3 years is good. But if it costs double it should last twice as long, or those interested in cost effectiveness won't find it good.
If a warning is needed, it is about taking the responsibility to make reliable safe battery packs, no matter what chemistry or physical cell configuration is being used. Know the materials and dangers involved and make a safe and reliable pack. Invest the effort into quality control, matching cells, physical protection, current limiting, proper wiring and insulation, and safe charging.
arkmundi
10 MW
Not so and the evidence is on the ES forum for anyone to investigate for themselves, which I did, and summarized in my Cautionary tales of fires thread. Again, A123 LiFePO4 and RC Lipo are not in the same risk class. There are lot of ES members using RC Lipo, many safely, understanding the risk. But I will challenge anyone who suggests that the risk is somehow the same and therefore a moot point in making a choice of cell & chemistry.dnmun said:
Well I agree, so just wonder why you're ignoring the evidence on this question.dnmun said:
NeilP
1 GW
Lipo is un predictable...or can be,, that can be a problem...but you try and get the things to burn and they can take a lot of abuse
Here is a video I badly shot, of a single 5 amp Lipo pouch cell begin charged at 25 amps I thing and up to 8 volts...the bugger took a long time to blow ..had to hit it in the end to make it go
http://youtu.be/9FRjFxKoUYQ?list=UUN7U5PMCHSnkFbP4rinBT8g
Here is a video I badly shot, of a single 5 amp Lipo pouch cell begin charged at 25 amps I thing and up to 8 volts...the bugger took a long time to blow ..had to hit it in the end to make it go
http://youtu.be/9FRjFxKoUYQ?list=UUN7U5PMCHSnkFbP4rinBT8g
Alan B
100 GW
arkmundi said:
The transportation industry considers LiFePO4 and Lithium Cobalt Oxide in the same risk class, does it not? I haven't gone through all the new rules, but the only thing I see differentiated in the overview is lithium metal from lithium ion batteries, the classification of packs is by watt-hours.
So the question is, what third party impartial bodies recognize a hazard difference between the different lithium chemistries and packages? What substantiation is there for the differentiation?
We know there are differences in some minor details such as oxygen availability or burning temperature, but do these differences actually change the overall risk in a way that is recognizable and separable from other risks that are common to all high energy density batteries? On what basis can we assign different risk to different chemistry or packaging? Where's the actual professional data?
Let's keep this discussion at a useful professional level.
arkmundi
10 MW
There are a number of good articles at http://batteryuniversity.com if you want to look into the question..Alan B said:
Alan B
100 GW
I like LiFePO4 chemistry and A123 batteries, and I have a number of them. They are particularly good for 12 volt applications as the 4S configuration matches the voltage range well. But their cost, availability and lower energy density is a problem. Obtaining bona-fide cells has been difficult over the years, hopefully that is improving.
If you haven't seen fires from A123 batteries then you haven't looked hard enough. I've seen video of spectacular A123 pouch fires, and I've heard of others, it burns just fine. Perhaps it burns slower or at lower temperature, but that is of little consolation to the owner after the fire.
I have read Battery University but I don't think that is the quantitative data we are looking for. Battery University is a nice website, but it is one guy's (and perhaps his company's) opinion. From what I've seen the lithium sections of that site are somewhat out of date, and anytime I read the site I see errors. There is no documentation on what they mean by "safe". I'm sure a battery professional would see lots more errors than I see. It certainly isn't a scientifically precise data source, it is a training site, and an advertisement for the guy and his company. If you base your "safe" declaration on this then how do you know what it actually means?
We are looking for actual risk based differentials that substantiate the "safer" claim. If the US DOT considers them the same risk, then why would we choose differently? Both batteries should have the same warning sticker and the same warning literature for the user, legally, as I understand it.
I suspect part of the problem here is that the small differences in chemistry or packaging are eclipsed by other factors in battery pack construction. So at the end of the day chemistry or cell configuration is not sufficient to make one pack safer than another. A well constructed and QA'ed LiPo pack can be safer than a poorly constructed LiFePO4 pack.
So how can we quantify the "risk" differential? Where can we find an actual risk "difference" that matters?
Is it the chemistry? LiCoO2 is used in RC Lipo, but it is also the dominant material in all cellphones, laptops, and many portable devices.
Is it the polymer? This reduces the flammable solvents and replaces them partially with polymer materials. I've not seen much on this, it isn't really much of a change. Do A123 pouch cells use polymer?
Is it the package? Cylindrical metal cans vs mylar pouches? If the pouches are unsafe then so are the A123 pouch based cells.
Is it a particular brand? Is All RC Lipo equally poor, or is it just certain brands? Can the packs or cells be culled to filter out the "bad" ones?
Is there any real data on risk differentiation that we can use? What is the basis for this different "risk class" claim?
The sensitivity of LiPo has changed a lot over the years. The new ones are much harder to make fireball. The chemistry has been adjusted. The current production cells take a lot of punishment to make them catch fire. So the old stories of lipo that bursts into flame at 4.3V or randomly while sitting there aren't talking about the current batteries. The science of lithium batteries has progressed a lot, and much of the information we see on the internet is based on out of date and anecdotal data.
What would we regard as a "safe" pack? What tests could we require of a "safe" battery pack? Some examples:
Short the pack, what happens?
Overcharge, what happens?
Overdischarge, what happens?
Put an ignition source in the center of the pack and light it up, what happens? (this is what is done with flammable items like black and smokeless powder to determine if it is flammable or explosive).
Raise the pack to an elevated temperature, what happens at what temperature?
Subject the pack to various standard impacts and punctures, what happens?
Is any lithium battery not going to catch fire and burn energetically somewhere in this testing?
A lot of the "pack safety" comes from things external to the cells. Physical damage, overcurrent, overcharge, overdischarge, overtemperature protections. So it is not just about cells.
If you haven't seen fires from A123 batteries then you haven't looked hard enough. I've seen video of spectacular A123 pouch fires, and I've heard of others, it burns just fine. Perhaps it burns slower or at lower temperature, but that is of little consolation to the owner after the fire.
I have read Battery University but I don't think that is the quantitative data we are looking for. Battery University is a nice website, but it is one guy's (and perhaps his company's) opinion. From what I've seen the lithium sections of that site are somewhat out of date, and anytime I read the site I see errors. There is no documentation on what they mean by "safe". I'm sure a battery professional would see lots more errors than I see. It certainly isn't a scientifically precise data source, it is a training site, and an advertisement for the guy and his company. If you base your "safe" declaration on this then how do you know what it actually means?
We are looking for actual risk based differentials that substantiate the "safer" claim. If the US DOT considers them the same risk, then why would we choose differently? Both batteries should have the same warning sticker and the same warning literature for the user, legally, as I understand it.
I suspect part of the problem here is that the small differences in chemistry or packaging are eclipsed by other factors in battery pack construction. So at the end of the day chemistry or cell configuration is not sufficient to make one pack safer than another. A well constructed and QA'ed LiPo pack can be safer than a poorly constructed LiFePO4 pack.
So how can we quantify the "risk" differential? Where can we find an actual risk "difference" that matters?
Is it the chemistry? LiCoO2 is used in RC Lipo, but it is also the dominant material in all cellphones, laptops, and many portable devices.
Is it the polymer? This reduces the flammable solvents and replaces them partially with polymer materials. I've not seen much on this, it isn't really much of a change. Do A123 pouch cells use polymer?
Is it the package? Cylindrical metal cans vs mylar pouches? If the pouches are unsafe then so are the A123 pouch based cells.
Is it a particular brand? Is All RC Lipo equally poor, or is it just certain brands? Can the packs or cells be culled to filter out the "bad" ones?
Is there any real data on risk differentiation that we can use? What is the basis for this different "risk class" claim?
The sensitivity of LiPo has changed a lot over the years. The new ones are much harder to make fireball. The chemistry has been adjusted. The current production cells take a lot of punishment to make them catch fire. So the old stories of lipo that bursts into flame at 4.3V or randomly while sitting there aren't talking about the current batteries. The science of lithium batteries has progressed a lot, and much of the information we see on the internet is based on out of date and anecdotal data.
What would we regard as a "safe" pack? What tests could we require of a "safe" battery pack? Some examples:
Short the pack, what happens?
Overcharge, what happens?
Overdischarge, what happens?
Put an ignition source in the center of the pack and light it up, what happens? (this is what is done with flammable items like black and smokeless powder to determine if it is flammable or explosive).
Raise the pack to an elevated temperature, what happens at what temperature?
Subject the pack to various standard impacts and punctures, what happens?
Is any lithium battery not going to catch fire and burn energetically somewhere in this testing?
A lot of the "pack safety" comes from things external to the cells. Physical damage, overcurrent, overcharge, overdischarge, overtemperature protections. So it is not just about cells.
arkmundi
10 MW
Probably all of the above. But its Oxygen out-gasing of the polymer electrolyte of cells that lends them to inflame. So the chemistry of the polymer primarily. But the layering up process, packaging, etc. I'm sure there are some excellent academic articles researching various factors and differences between cells. Because battery research is a hot topic and well funded. Anyone making batteries for the automotive, consumer products (laptops) and the military probably has a library full of it. Someone better positioned needs to answer these questions. I'm not here to convince anyone but myself. I'm extremely happy with my choices and the performance of my battery packs. I believe I have near-zero risk of fire. Hope anyone making the choice for RC lipo, for some imaginary cost-savings, can do the same.Alan B said:
parabellum
1 MW
There are few people withot noticing A123 is dead, for some misteriouse reason, right? Just get over, kind of. Rest of manufacturers are still alife, for some misteriouse reason. :lol:
arkmundi
10 MW
Don't have a clue what you're trying to say.parabellum said:
parabellum
1 MW
Source?arkmundi said:
parabellum
1 MW
Try wikipediaarkmundi said:
wb9k
10 kW
parabellum said:
Um, I work at A123...still. It's not dead. The company continued to produce cells even during bankruptcy. Please stop reinforcing this myth. Even the mainstream press took forever to catch up to reality.
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