Mechanisms that decrease the Lifespan of Lithium-Ion batteries and how to avoid them

[Living Large]

{snip}As for bad cells in my experience and all others are it will happen within the first 5 to 10 cycles if it is going to happen. So if you are worried about a over charge, do what I am doing. Set the Orion to turn off power to the charger if any cell goes to 4.1 to 4.2 volts. Hook a relay up to the CC Panel Input and short out the panels.

OK, now I have what I was looking for. Perseverance can be a good quality, or a bad one - depending on the circumstance. I'll add this puppy to the file. THANKS!

[Mike90250]

Great, we can't edit profanity :

Sure you can. So F**k**f.

[SunEagle]

Sorry guys, problems are still there but intermittent PHP scrip errors. We are going to a new dedicated server for SPT and are in the process of looking to hire a programmer to look after the transition and bring us up to the latest version of the forum software.

Ahh crap, pete here, accidentally posted as jason again

P.S all editing functions are working normally for me, at the moment

The edit functions come and go for me. Maybe because I use two computers to access the forum. Right now I am on my work computer running windows 7 business OS. My home computer runs windows 7 home OS. I use Mozilla Firefox as my web browser for both computers.

And I can edit on my work computer but could not last night on my home computer. Strange.

[Jason]

Sorry for the ___________________. Forum is broke and I cannot edit or insert spaces or paragraph breaks.

Sorry guys, problems are still there but intermittent PHP scrip errors. We are going to a new dedicated server for SPT and are in the process of looking to hire a programmer to look after the transition and bring us up to the latest version of the forum software.

Ahh crap, pete here, accidentally posted as jason again

P.S all editing functions are working normally for me, at the moment

[Sunking]

Sorry for the ___________________. Forum is broke and I cannot edit or insert spaces or paragraph breaks.

[Sunking]

I appreciate all these suggestions, and will put them on file. I do realize the voltage point I used in the example is not what I would use in real life. I saw the PowerLab used in a YouTube video to balance a battery bank in an EV - very impressive, but the guy had 54 cells or something like that. 16 should be a cake walk.

It is a piece of cake. __________________________________________________ __________________________________________________ __________________________________________________ ___________________________I stand by what I told you several months ago. Use something like an Orion Jr and do not use the 150 ma Balance feature. Just use it as a Cell Level Monitor and program it to do what you want. That is what I am doing. The most useful feature is buy you a Shunt and use the Coulomb Counter. In just a glance you know exactly where you are in SOC. __________________________________________________ __________________________________________________ __________________________________________________ ___________________________You will not be able to charge like I do, fast charge. Instead just use CC/CV set to 54 volts. That is roughly 80 to 90% SOC. Set Bulk = Absorb = Float = 54 volts. Once your batteries charge up to 3.4 vpc they will saturate and hold 80-90% SOC. Any power after that comes from the panels until the sun goes down then you start using battery power. If you use the Orion Jr it only has a 3 digit accuracy, and you are not going to see much of any difference in voltage when charged up. My weakest cell voltage is the highest at 3.389 volts on the Fluke, and the strongest cell has the lowest voltage of 3.380. That is less than .01 volts from low to high. If I take the batteries all the way down to LVD of 46.4 volts, the voltage is dead Flat 2.900 vpc __________________________________________________ __________________________________________________ __________________________________________________ _________________________As for bad cells in my experience and all others are it will happen within the first 5 to 10 cycles if it is going to happen. So if you are worried about a over charge, do what I am doing. Set the Orion to turn off power to the charger if any cell goes to 4.1 to 4.2 volts. Hook a relay up to the CC Panel Input and short out the panels.

[Living Large]

Stop and think about what you just said. What is the difference between 16S and 100S of an EV? That was a point Davide was making when describing Delta Voltages. At no time should there ever be more than .1 volts difference between the lowest and highest cell voltages.

I know the difference should be 10's of mV at most, and that balance will typically not be lost quickly. What I am not understanding as a newbie is if there is a failure mechanism where the difference could "run-away" in a few days, before the user could intervene, causing a hazardous situation while the user is sipping a beer or otherwise enjoying life and not tending his PV system.

So in a 16S say you have 15 cells at 3.5 and 1 at 3.6 Your pack voltage is at 56.1 and a set point of 57.6 volts. You are still in Constant Current mode pumping maximum current from whatever charge source. Your Delta is 57.6 - 56.1 = 1.5 volts. What happens on a 100S with 99 cells at 3.5 and 1 at 3.6?? You have a pack voltage of 350.1 volts. set point of 360 volts and a Delta of 9.5 volts.

Good point, which I missed. I am still wondering if one bad cell in 16S could "shoot" to 10V, while the other fifteen are 3V, and still be charging.

That tells me 4s and 8S is no problem, 16S border line, and 100S you need a cell monitor.

"borderline" there could be a catastrophic event?

But keep in mind you are not going to 3.6 vpc Glory Land or 57.6 volts. You are shooting for 54 volts of 3.375 vpc Float. That puts you within a 3.3 to 3.4 vpc operating range at full charge.So LL get a Cell Monitor. Secondly get yourself a Powerlabs 8 or 2 of them and use as your monitor. A Powerlabs 8 will do anything you want with any battery. Bottom Balance is real easy with a Powerlab 8, or even Top Balance. When you get the cells, connect them all in parallel, set PL8 to 2.5 vpc and 30 amps discharge, and walk away for a day and night. Nxt morning you have perfectly BB cells. Wanna change your mind and Top Balance. Hook up 8 cells in series and use the PL 8 to charge them. Then do the next 8 cells. Want to re-balance at the bottom next year. Turn off the panels and let the system fully discharge and LVD operates. Find the high cell or cells and discharge them. Wanna see what the cells are doing. Download the discharge curves from the Power 8. My best tip is use a Coulomb Counter so you can see what goes in and what goes out. Lastly if you wait another 6 months to a year there will be at least 2 more commercial BB BMS systems on the market. Davide at Ethlion and Jack at EVTV are both coming out with one and EV West already has one on the market.

I appreciate all these suggestions, and will put them on file. I do realize the voltage point I used in the example is not what I would use in real life. I saw the PowerLab used in a YouTube video to balance a battery bank in an EV - very impressive, but the guy had 54 cells or something like that. 16 should be a cake walk.

[Sunking]

The scenario I was trying to set up is relative to the issue brought up in the video and I thought with a similar example but for 16S instead of 100S, for the purpose of addressing safety.

Stop and think about what you just said. What is the difference between 16S and 100S of an EV? That was a point Davide was making when describing Delta Voltages. At no time should there ever be more than .1 volts difference between the lowest and highest cell voltages. So in a 16S say you have 15 cells at 3.5 and 1 at 3.6 Your pack voltage is at 56.1 and a set point of 57.6 volts. You are still in Constant Current mode pumping maximum current from whatever charge source. Your Delta is 57.6 - 56.1 = 1.5 volts. What happens on a 100S with 99 cells at 3.5 and 1 at 3.6?? You have a pack voltage of 350.1 volts. set point of 360 volts and a Delta of 9.5 volts. That tells me 4s and 8S is no problem, 16S border line, and 100S you need a cell monitor. But keep in mind you are not going to 3.6 vpc Glory Land or 57.6 volts. You are shooting for 54 volts of 3.375 vpc Float. That puts you within a 3.3 to 3.4 vpc operating range at full charge.So LL get a Cell Monitor. Secondly get yourself a Powerlabs 8 or 2 of them and use as your monitor. A Powerlabs 8 will do anything you want with any battery. Bottom Balance is real easy with a Powerlab 8, or even Top Balance. When you get the cells, connect them all in parallel, set PL8 to 2.5 vpc and 30 amps discharge, and walk away for a day and night. Nxt morning you have perfectly BB cells. Wanna change your mind and Top Balance. Hook up 8 cells in series and use the PL 8 to charge them. Then do the next 8 cells. Want to re-balance at the bottom next year. Turn off the panels and let the system fully discharge and LVD operates. Find the high cell or cells and discharge them. Wanna see what the cells are doing. Download the discharge curves from the Power 8. My best tip is use a Coulomb Counter so you can see what goes in and what goes out. Lastly if you wait another 6 months to a year there will be at least 2 more commercial BB BMS systems on the market. Davide at Ethlion and Jack at EVTV are both coming out with one and EV West already has one on the market.

[Living Large]

How would you get into that situation? Under charge 3.3 vpc is on the order of 50% SOC and just one battery at 100%? Yes it would have to be a bad cell and most likely an open cell with very little current flowing.

My question is sparked by the discussion of LFP and safety here recently - but I was hoping to avoid mentioning shunts or balance boards.

The scenario I was trying to set up is relative to the issue brought up in the video and I thought with a similar example but for 16S instead of 100S, for the purpose of addressing safety. Remember I don't have any equipment or experience - and am still pushing papers around. I am trying to determine if I should have cell level detection in case a cell goes batty quickly, before a human being catches it. Not having any experience - maybe a cell can't go bad that quickly?

I would be monitoring the cell voltages on a regular basis. Is it your opinion that between loss of capacity and one cell voltage going out of whack that I should notice the imbalance developing long before I am at risk of burning the house down because one cell went bad and I overcharge it?

[Sunking]

Dereck, I watched the videos (thanks for the link and tip) - and I have a question. For a 16S bottom balanced battery bank, let's say the target is 16 * 3.6 = 57.6V. 15 cells are at 3.3V, or 49.5V, and an outlier is at 7V and still charging (V = 56.5V). Is 7V not near being catastrophic, and not something to be concerned about? Can this be viewed as not a danger, but rather just a bad cell that will need to be replaced once the capacity loss is recognized? Or would this be cause to have individual cell monitors? I was initially thinking of monitoring individual cells and triggering a cutoff under certain conditions - this would seem to be one unless it is overkill.I hadn't put any thought into failure mechanisms, until people started pointing out that code may require certain kinds of fire protection. This current conversation has my interest.

How would you get into that situation? Under charge 3.3 vpc is on the order of 50% SOC and just one battery at 100%? Yes it would have to be a bad cell and most likely an open cell with very little current flowing. LL by all means use a cell monitor, and Orion Jr is a good one and made for 16S. I don't have a problem with cell monitors, I take issue with Balance Boards. There is no way to use Balance Boards with any Solar Charge a point that appears to be missed by everyone. You cannot signal any Charge Controller to cutback its current to the value of the Balance Boards bypass value of say .5 amp or 1 amp. Not even the one and only lithium Charge Controller out there made by Genasun can do that. All you can do is install a Contactor between the Panels and Charge Controller and use a Cell Monitor to operate the Contactor to either disconnect or short out the panels.

[PNjunction]

I am hoping that if I go with LFP, all this falls into place... starting with the right plan and equipment is a must

That makes all the difference. Again for lurkers, where this thread seems to cover all lithium chemistries in existence, one of the reasons that we choose LiFePo4 is that iron phosphate is one greedy little molecule, and does not like to give up oxygen, even under abuse. This is FAR different than other lithium chemstries that come from the likes of laptop-pulls, crashed Nissan Leafs, etc.

No need to rehash the whole thing here, and the reason John B Goodenough came up with Lifepo4 from a safety standpoint in the first place is easy to find. A123 mentions it in their whitepaper, and although they concentrate on "nanophosphate", you can just as easily use the term iron-phosphate:

http://www.a123systems.com/prismatic-cell-amp20.htm

Just trying to remind people to concentrate on the right version of lithium for the job and application at hand.

[Living Large]

LFP batteries are dangerous on the charge side. Not so much on discharge side. It is very common knowledge that a Bottom Balanced Pack cannot be over discharged to destruction, and this is basis of Bottom Balancing. Above 8S Delta could approach 1 volt or more. Is is charging where the danger comes in, not discharging Discharging only becomes dangerous when you Top Balance. Then it is possible for one cell to go flat, and have the other cells with charge remaining to drive the flat cell into reversal and over heat. Lithium is the only battery chemistry that still works with a dead cell, just lower voltage. With Bottom Balanced cells it is impossible to drive any adjacent cells into reversal and over heating.

Dereck, I watched the videos (thanks for the link and tip) - and I have a question. For a 16S bottom balanced battery bank, let's say the target is 16 * 3.6 = 57.6V. 15 cells are at 3.3V, or 49.5V, and an outlier is at 7V and still charging (V = 56.5V). Is 7V not near being catastrophic, and not something to be concerned about? Can this be viewed as not a danger, but rather just a bad cell that will need to be replaced once the capacity loss is recognized? Or would this be cause to have individual cell monitors? I was initially thinking of monitoring individual cells and triggering a cutoff under certain conditions - this would seem to be one unless it is overkill.

I hadn't put any thought into failure mechanisms, until people started pointing out that code may require certain kinds of fire protection. This current conversation has my interest.

[Sunking]

OK, this is good, but the last statement assumes that cells never fail. This is not a safe assumption. Why can you not accept that the possibility of cell failure is real?

Why do you assume I do not consider the possibility of cell failure when in fact I have. A BMS wil not prevent that from happening. Especially one with Bleeder Boards which is what I object too. LFP batteries are dangerous on the charge side. Not so much on discharge side. It is very common knowledge that a Bottom Balanced Pack cannot be over discharged to destruction, and this is basis of Bottom Balancing. Do you know Davide Andrea the owner of Elithion and author of BMS. I know him well, even was offered a job by him to lead up product development on his BMS line-up. Even played golf with him over the 4th. We have had numerous discussions on Bottom Balance. He has no problem with BB, and fully acknowledges it is a better protection from Over Discharge because it is Passively Safe and requires no automation whatsoever. Cut Offs using pack voltages is more than adequate and really not even needed. The only problem Davide has is with charging cells over a cell count of 8S due to Delta differences that could present itself during a Charge Cycle. Above 8S Delta could approach 1 volt or more. Is is charging where the danger comes in, not discharging Discharging only becomes dangerous when you Top Balance. Then it is possible for one cell to go flat, and have the other cells with charge remaining to drive the flat cell into reversal and over heat. Lithium is the only battery chemistry that still works with a dead cell, just lower voltage. With Bottom Balanced cells it is impossible to drive any adjacent cells into reversal and over heating.Go to Davide Website and see what he says about BB. As you would expect he is pro BMS because he is a BMS manufacture, but he acknowledges BB is a valid and safe method. Just not one he prefers. If you listen closely he tells you why he prefers Top Balance. Nothing to do with safety, it has to do with ignorant operators. He acknowledges BB will extend battery life, only requiring occasional re-balancing once in a while, and perfectly safe. I even used one of his techniques to monitor SOC, a Coulomb Counter Gas Guage. I am not ignorant, I know what I am doing, and I do not need a BMS. When you have automated systems, people tend to become complacent and rely on them. Not me. http://liionbms.com/php/tutorials.php

[Living Large]

{large snip}
Thing is, with solar and the desire for autonomy, we are basically in what is called the "Sub-C" niche, that is most of the time we'll never be exceeding more than 0.5C, usually much less, and while EV concerns may be valid, they aren't at the forefront for us, although obviously still there to some extent. Also, while designing for an 80% DOD may be an exciting proposition we STILL don't really want to cut it that close (if we can afford it) because we can't count on the sun's availability at any given time. So for a stationary solar bank, they will be pampered if one does their power-budget right - but like any battery chemistry, common sense protections like LVC and so forth are necessary.

Individual cell monitoring is nice, but for me is not needed *in a sub-c application*. Provided that you use quality cells like A123, GBS, Winston, etc they are generally pretty well matched out of the box for our usage and once checked and reasonably balanced for sanity tend to stay that way. {large snip}

So that's kind of where I'm at. I haven't gone to 48 volts, but I have been able to maintain good quality cells with a touch of conservatism, and reasonable monitoring provided I start out sanely. I've done the top vs bottom balance thing, and both work because our "sub-c" application isn't so demanding. Not hands-off, but not an unreasonable task-master either. Education without having to go over the top works.

This is all consistent with what I learned here over 6 months of asking questions, and watching discussions between people who have used different balancing techniques.

1. Start with matched cells from reputable supplier
2. Balance them
3. Cells will tend to stay in balance over time (at least months, from reports I have seen)
4. Stay away from the knees - I am planning for 80% DOD to 90% SOC
4. Incorporate LVD and HVD, either through CC/Inverter or add-ons if needed or as a backup safeguard
5. EV and solar are different applications, and different techniques (balancing) may apply, based on the application
6. For solar, users are using various balancing techniques successfully

I am hoping that if I go with LFP, all this falls into place... starting with the right plan and equipment is a must

[PNjunction]

Wb9k - yep we're on the same page.

I actually was familiar with C/20 "end current" from the Pb world, and found it interesting that they match, but that is just a coincidence for this value being the same. I noticed it in the manufacturer's literature, and also from peers in the marine world on another forum who are in the low-voltage niche (compared to ev that is). Of course there are exceptions like high-end pure-lead agm's (which I LOVE) but we won't go there at this time.

I didn't immediately jump on a 289 because I wasn't sure it would be fast enough to watch pwm pulses - but I want one anyway. Maybe if I'm good to my cells this year, Santa will bring me one.

Clarity and identifying your application and user-skill set is vital when dealing with lifepo4 issues, something I'm always harping on. Without it, a forum needs continual server upgrades just to handle a single thread that takes every application for lithium into account.

Thing is, with solar and the desire for autonomy, we are basically in what is called the "Sub-C" niche, that is most of the time we'll never be exceeding more than 0.5C, usually much less, and while EV concerns may be valid, they aren't at the forefront for us, although obviously still there to some extent. Also, while designing for an 80% DOD may be an exciting proposition we STILL don't really want to cut it that close (if we can afford it) because we can't count on the sun's availability at any given time. So for a stationary solar bank, they will be pampered if one does their power-budget right - but like any battery chemistry, common sense protections like LVC and so forth are necessary.

Individual cell monitoring is nice, but for me is not needed *in a sub-c application*. Provided that you use quality cells like A123, GBS, Winston, etc they are generally pretty well matched out of the box for our usage and once checked and reasonably balanced for sanity tend to stay that way. At least in my experience. Go gray-market, used, hacked cells, high-performance EV, well then you BETTER have those safeguards in place. Even the A123's when purposely unbalanced a little bit did tend to "drift" back together over many cycles (no bleeder boards either) when using the pwm charge controllers. Not practical for a first-time setup of course, but an interesting observations. The cells that were unidentifiable from other batteries just did not play nice. Subsequent checking with a hobby charger revealed bad capacity and internal resistance specs on the junk cells. The A123's were ALWAYS reliable out of the box, although maybe not matched enough for a space-station project.

Improvements do happen over time too. In the prismatic world, the old Thunderskys had an issue of using dissimilar metals on the interior anode/cathode clamps. Winston fixed that (supposedly, I haven't cut one open) among a number of other improvements. So lurkers beware - forum data can become stale. Gotta' keep up. Here too, the user's exterior connections when using dissimilar metals demands clean, snug connections, and perhaps a light coating on no-alox, penetrox etc to keep resistance down.

That is what I found interesting with my experimental banks with no bleeder boards at sub-c. Provided I started out sanely, and use GOOD products like A123, GBS etc, they play together nicely. Use trash, reject gray market used cells and the like, (easily spotted with previous tack-welds) and one better have a life-support system on each and every cell, even in a sub-c environment.

So that's kind of where I'm at. I haven't gone to 48 volts, but I have been able to maintain good quality cells with a touch of conservatism, and reasonable monitoring provided I start out sanely. I've done the top vs bottom balance thing, and both work because our "sub-c" application isn't so demanding. Not hands-off, but not an unreasonable task-master either. Education without having to go over the top works.