# Frozen LiFePO4 Cells and Charging



## Guest (Dec 28, 2011)

Frozen LiFePO4 cells and charging. 

It is said among the manufacturers not to charge the cells below 32 F. 
Why? Is it another hold over from the Lead Acid issues of the past? 

So far no one has tested this issue. Why? 

So what do you all think? Or know?

Pete


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## ElectriCar (Jun 15, 2008)

Surely you don't think the OEM's put that info out there without knowing for sure if there was an issue do you? I can't imagine that. Probably something to do with shortened cycle life or such, IDK.


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## Guest (Dec 28, 2011)

But none of them mention the issue. Can't imagine that they would not do that either. Actually I can see that they would just put information because that is what they heard. The issue with self discharge is a hold over from lead acid. As the LiFePO4 cells really have no self discharge. Yes, I can see. 

So besides that what do you think would happen? 

Pete


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## MN Driver (Sep 29, 2009)

With Lithium Cobalt cells, charging them while they are below 0c (32f) can cause lithium plating. I actually had it happen to a cell phone of mine, it was out in the car when it was -10f overnight and I brought it in and plugged it into the charger without thinking about it. The next time I used it, the battery lasted about 10 minutes before it was dead. I pulled it out and it was swollen. I've tested it and it still has its rated capacity at a very low discharge and charge rate but the voltage sag is terrible. Internal resistance(or ESR, choose your name, I don't care) has clearly spiked through the roof with this cell.

It seems that LiFePO4 is clearly more resilient than Lithium Cobalt or we would have heard someone with a horror story already. Then again charging rates are generally very low and not many people pay attention to measuring internal resistance or voltage sag anyway so its hard to say if anyone has done any damage without noticing. :shrug: Time will tell or eventually there will be testing or a manufacturer will give us an answer.


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## Tesseract (Sep 27, 2008)

gottdi said:


> It is said among the manufacturers not to charge the cells below 32 F.


The solvent which the electrolyte (a lithium salt) is dissolved in is composed of two or more carbonate esters with freezing points that vary from as high as ~35C (ethyl carbonate) to as low as ~3C (dimethyl carbonate). Needless to say, once the solvent freezes the lithium salt comes out of solution and the cell won't accept charge.

EDIT - note that just like adding salt to water lowers its freezing point, same with adding LiPF6 (the usual electrolyte for LFP cells) lowers the freezing point of the ester solvents. When I tested discharge performance on TS-200Ah cells two years ago the equivalent series resistance of the cell exactly doubled when put in a freezer at -11C overnight.


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## Guest (Dec 28, 2011)

> When I tested discharge performance on TS-200Ah cells two years ago the equivalent series resistance of the cell exactly doubled when put in a freezer at -11C overnight


For how long. I am just testing charge and discharge function when freezing a LiFePO4 cell in a block of ice at 5F in our chest freezer. So far charging is just fine. Just wish I had a way to monitor internal temps of the cell while encased in ice and charging.


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## Guest (Dec 28, 2011)

So far the temps increased plenty to melt the ice around the cell and I can measure terminal temps and they rose above 40 F rather quickly and have remained rather stable but it does melt so the internal temps are well above the initial 5 F when starting out. Still they are cold cold. It's not too likely that any cell would remain encased in ice for long since the internal temps would rise fast enough to keep the cells safe.


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## Guest (Dec 28, 2011)

The plastic case is rather insulating and would help keep outside temps from being a real issue and if they were it would not be an issue for long. So far my Leaf has been just fine in our cold area. Not crazy cold but the pack is well within the safe limits of charging no matter how cold it is outside. 

The car performs rather well in the cold too.


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## Guest (Dec 29, 2011)

Found a problem with my setup. The block of ice was not fully frozen. I will need to leave it in the freezer for much longer to be sure that the water and battery are fully frozen. It is a test and cell sacrifice. It is a test to see if there is a problem or not. So far from our test yesterday there is no problem showing. Both were done cold but not cold enough. We will attempt again. I will leave the cell in the freeze for a few days before trying the test again. That way there is no doubt that the cell is frozen and that the water is frozen solid. 

So until then the tests I have done the past two days just confirm a base for charge and discharge rates and a base to be consistent in the testing. 

It matters not if the cell is destroyed or not and it matters not what the outcome will be but there will be an outcome. I am not the only one on board with no damage to the cell. Batteries have been used in the cold for decades. What's changed? Nothing. So lets see what these will do or not do. 

Pete


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## Tesseract (Sep 27, 2008)

How long did the internal resistance remain elevated after leaving the cells in a freezer at -11C overnight? I didn't really pay attention. The cells I was testing were not "disposable" so as soon as I saw that the cell voltage sagged twice as much I limited the amount of time the cells spent at high current.

Note that the proper way to determine the resistance of a cell is to measure its voltage at two different currents and divide the difference in voltage by the difference in current.

For example, according to my notes the terminal voltage of one 200Ah cell at -11C was 2.890V at 100A load and 2.621V at 300A load; the difference in voltage is 0.269V and the difference in current is 200A so the effective "internal resistance" of the cell is 0.269V/200 = 1.345 milliohms.

And yes, the higher internal resistance means more heat will be produced (via our old friend (enemy?) I²R) which will "thaw" the solvent and reduce the resistance, etc... Indeed, every LFP cell I have tested will deliver substantially more current for a given voltage drop once heated up (and by this I mean heated up to 60-65C).


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## JRoque (Mar 9, 2010)

Hey Pete, thanks for testing this out.

Some question I would have are:

- Does it swell on it's own just by being frozen or does it swell only while being charged?
- If swelling only when being charged while frozen, what was the charging rate?
- Can a slow charge (ie: C/10) raise the temp above freezing point?
- If possible, can you charge the cell while it's in the freezer? ie: will this charge current flow keep it from freezing/damaging?

I understand LifePO4 cells don't heat up much when charged but any bit temp rise might put it over the freezing point and save them.

JR


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## Guest (Dec 29, 2011)

2008 Hi-Power 100ah cell. Cell resting at 2.5 volts for a few months was chosen for the test. It is a known good cell being what it is and being it is an early LiFePO4 cell of lesser quality than the more current cells. But still decent. 

I took the cell and placed it out in the open during the evening to bring the temp of the cell down to the current temp of the evening air which was 28 degrees. I was hoping for lower and it had been lower a few nights before. I figured this would get me to a cold point well below the freezing point. Success but it was short lived. Once we started the charge procedure the temps rose but not by much but above the freezing point. I decided to place the cell on a block of ice and place another on top to keep the cell as cool as possible. 

My technique for charging was to charge at 15 amps but really needed to start it at 19 amps and let it taper to 15 amps. The technique is consistent and works quite well. Once the cell reached 3.65 volts I turned down the amperage to 10 amps then to 5 amps and each time allowed to reach 3.65 again. Once it reached 3.65 @ 5amps we terminated the charge. 

I did this on two consecutive days. The second day what changed was the medium I used to keep the cell cold. I placed the cell in a bucket of water and placed that bucket in our chest freezer and let it freeze overnight. In the morning I pulled the bucket out with the frozen water and cell imbedded within. The temp of the freezer was 5 degrees F when I pulled it out. I began charging again using the same technique. 

We logged sort of every 10 to 20 minutes or so until the charge cycle was complete. Exactly the same both days. 

The problem today was I found that the bucket of water was not fully frozen and therefore was not as cold as expected. I did check the terminal temps and never saw over 50 degrees. 

As for the discharge I used my old Starter/Generator for our discharge medium. This allowed a discharge current of 25 amps at the start and on the first day we reached 30 amps at the end of the charge when we terminated at 2.5 volts. Todays discharge resulted in an amperage of 40 amps at the end of the discharge cycle and the same 2.5 volts. 

I logged that as well and have two graphs overlapping. I have the numbers on both tests so you can see that the results were nearly the same each time. 

Both the Charge and discharge times were quite close. 

I currently have the cell once again in the freezer and we will let it remain for a few days if not a week. That will be a good long time to be sure it's cold. Our freezer will reach 0 degrees F. It will in fact go below 0 degrees F by a few degrees. It's nice and cold. 

Attached is my PDF with graphs and log numbers. 

Pete 

PS. No swelling of the cells what so ever during these tests. Cold or Hot. 

We always charge below max and end before max. 
No need to play in the danger zone.


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## Guest (Dec 29, 2011)

I am going to try to charge the cells in the freezer. Should be no real issue except I need my charge cables to reach which may be a problem. That is why I want to use the block of ice. Might insulate the block of ice. I can do that. I have a nice large styrofoam container that would work for that. I will do that instead.


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## Guest (Dec 29, 2011)

I have a good base line for my technique for the charge/discharge so that I can be consistent with our test. I have shown I can be consistent enough to do a good test. The next one will be added into the base results to see if there is any real difference. 

First charge was 5 hr, second was 4:40 minutes
First discharge was 2:57 minutes, second was 2:48 minutes or something like that. I think its a 12 minute difference time wise. 

Close. The Second test was better controlled than the first. We now have our base technique. It works.


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## JRoque (Mar 9, 2010)

Hello Pete. Well, if it survives that, it'll survive anything. Perhaps the temperature limits listed by manufacturers is so it can meet the rating but not necessarily because it would outright fail.

One thing's for sure, dipped in a block of ice there won't be any chance for a temperature rise during charging. But that's a good way of torturing it to extremes.

Great work!

JR


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## Guest (Dec 29, 2011)

Extremes are exactly whats needed. That way you know if your not at the extreme you are still good to go. Love to torture the components. It's the beta tester in me that does this you know. I just gotta bust it if I can. Mostly I just have to know if I really need to insulate my cells. I am making the most worst case I can for around here. If it survives this it will be great. If not it will still be great. At least we will know. 

Pete 

I will update when I do the next test.


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## Tesseract (Sep 27, 2008)

Pete - the problem with charging the cells when they are very cold is that they might not accept any charge. The only way I see of getting useful results here is to measure the Ah going in then turn around and discharge the cell to measure the Ah delivered. Supposedly, cells below freezing will accept less charge which will show up as a loss of capacity during discharge.

So, discharge a known number of Ah from your 100Ah cell then place it in a freezer overnight with charger cables connected but don't begin charging until the next day. Replace the same number of Ah as you had previously discharged then discharge once again. Note any difference in Ah delivered before reaching the same endpoint voltage.

Repeat as necessary with different cells to get a statistically meaningful sample size


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## Guest (Dec 29, 2011)

Tesseract said:


> Pete - the problem with charging the cells when they are very cold is that they might not accept any charge. The only way I see of getting useful results here is to measure the Ah going in then turn around and discharge the cell to measure the Ah delivered. Supposedly, cells below freezing will accept less charge which will show up as a loss of capacity during discharge.
> 
> So, discharge a known number of Ah from your 100Ah cell then place it in a freezer overnight with charger cables connected but don't begin charging until the next day. Replace the same number of Ah as you had previously discharged then discharge once again. Note any difference in Ah delivered before reaching the same endpoint voltage.
> 
> Repeat as necessary with different cells to get a statistically meaningful sample size



I can't measure a known AH in or out. I don't have the tools. 

If a super cold cell refuses to take a charge you will see it in the discharge because you will only be able to discharge for a sorter time than expected. 

My first two have become my base which is what is needed anyway for how I can do this experiment. 

So when I do the test again the cell will be much colder and if there is a loss of acceptance then the discharge time will be less. 

I can't do it on multiple cells because I am only wanting to sacrifice one. I have other cells but they are either being used, going to be used or damaged already. 

I guess I could do some base tests on some damaged ones to get a general idea of capacity and then do a super cold test to see if it damages them further or if just the cold not allowing the charge to take place and just get a shorter run time. Who knows. 

For now it is one cell. It is however an older style and of lesser quality and I figure if it holds up to this then others will fair much better. Or at the least no worse.

If you have a way for me to measure AH in and out I'd love to do that. 

I can't control my charge as well as I'd like but at least I have a technique that is consistent as well as the discharge. Using a motor is not ideal because it does not allow me to control the amperage output. It will just be what it is. 

But since it is consistent it will do for a time frame reference. If it does not match it will show up on the graph. 

If I can put a something around a wire and have it measure AH in and out even with the inconsistency that would be super. 

Got an idea on how I could do that before I pull the cell out of the deep freeze again?


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## Guest (Dec 29, 2011)

> the problem with charging the cells when they are very cold is that they might not accept any charge.


Well we are trying to find out if the will or won't. That is the issue. The key in this statement is *might*. That's right, they *might* not but then again they just *might* do fine. 

Either way will will eliminate the *might* issue. We want to remove any doubt.
We want to remove as much as we can to prevent speculation. 

Wish I could do better but I do feel it will show without a doubt one way or another.


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## Tesseract (Sep 27, 2008)

gottdi said:


> ...
> Either way will will eliminate the *might* issue. We want to remove any doubt.
> We want to remove as much as we can to prevent speculation. ...


I agree with your general premise, however I don't think you'll be able to resolve the question of whether charge acceptance is reduced when the cells are below freezing unless you can control and measure both charge and discharge currents accurately. You might be able to discern a gross difference in capacity by winging it, so to speak, but you won't catch a small loss in capacity nor will you be able to tell if the loss is just temporary - ie, only present below a certain temp - or permanent, since you don't know the original capacity with any certainty.

By all means do as many tests as you want, just be wary of making an absolute conclusion from imprecise data.

I wrote "might" above because I, personally, have not done the charge/discharge tests, nor do I intend to. I don't get paid to do this sort of testing and, unfortunately, none of the bills I pay every month will accept LFP testing data in lieu of cash...


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## steven4601 (Nov 11, 2010)

The question on what happens with low temperature charging is rather intriguing to me. 

I have/had a shipping box full (about 90 still in) of about 2 year old ANR26650 which are possibly rejects or 'repurposed' cells. Sadly I have no use for them yet. Perhaps great for all sorts of tests. Also a few Headways hw38120/hw38140's And possibly if I ask nicely also a few S.E. 130Ah's from 2008/9. 

To count the Amp-hours going in /out I can use a hobby R.C. charger which can do 30Amp in both directions. Changes due to temperature are only relative no absolute Amp-Hour accuracy is needed. 

Now what is left is finding the time to actually do these tests/experiments


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## Guest (Jan 1, 2012)

Well I busted out the Glacier in a bucket to take a photo this evening. I will be refreezing the cell but I will be keeping it cold till tomorrow. The bucket was the weak link here this time. Did a quick video too and posted on my blog. I was surprised the the bucket busted but the pressure of the frozen water was just too much. This will be a very serious deep freeze and charge test and should be done on Wed or Thursday. More like Wed as we are expecting rain on Thursday. 

Pete


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## roger (Jan 24, 2010)

Hello all,

following this thread I´m able to report you my experiences with my Thundersky/Winston battery pack equipped to my car for daily usage over the last 1,5 years. I have nearly 30000 kilometers in electric mode on this car now with those pack, I think around 5 to 6 hundred charges until now and it´s the second winter season in use. I have no insulated battery boxes, no additional heating equipment and I was always able to charge and use the car. Deepest overnight temperatures while charging outside were minus 12 degrees Celsius a few times last winter. I can´t report any damage or steady capacity losses until now. At cold temperatures capacity is a little decreasing for sure, but remains at warmer conditions. 
There is also a remarkable decrease in voltage sag after driving them a little bit, they warm up internally a bit. Best way to get in the most energy is to charge the car immediately after a drive. But it´s also possible to charge them cold. 
To prevent an undercharge with the most used CC/CV curve with the charger I´m using a CC1/CC2 curve leaving at a specified voltage at a very low charging current of 1/50 of capacity. This is a little tricky because charging voltage sag in first CC phase is higher at cold temperatures. Best way would be a little temperature compensation to the charging end voltage to get a full charge.

Best Regards

Roger


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## JRoque (Mar 9, 2010)

Hello Roger,

Thank you for sharing your experience with cold cells. Not that it matters much to me based on my location but I'm glad to see you showing these cells work in cold weather just fine. It's getting clearer that manufacturers print the temperature limits just so their cells meet the written specs but they still perform acceptably, and do not sustain permanent damage, when somewhat outside these parameters.



roger said:


> ...This is a little tricky because charging voltage sag in first CC phase is higher at cold temperatures. Best way would be a little temperature compensation to the charging end voltage to get a full charge.
> 
> 
> > Could you please elaborate on that? I would think that a cold cell is not able to accept as much current so your voltage would rise, not sag. Since the charger will also limit the voltage, your charging time should be slightly longer while the cells come into operating temps.
> ...


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## Guest (Jan 3, 2012)

The voltage is showing just fine. The first set is CC for charging. I can set the amperage to start around 19 amps. It will then taper off till it balances and settles in at 15 amps. It is irrespective to voltage. It should charge up just fine. Since we have a base to compare to we will know if the charge takes longer. We will also know if the discharge takes longer which will also show that not as much energy was absorbed. But we will charge until done. Then discharge. Should be doing the full Arctic Glacier Charge Test on Thursday. It will be filmed. The cell has been sitting at 1 degree below zero f for a week. We had to refreeze the cell in water because of a busted bucket. But the cell has been kept on ice. It is about the worst case you will encounter. I suspect it will be just fine and charge just fine as the internal cell will warm up straight away. Not hot but enough to charge fine. If I check and find I have no voltage when we do the test I know damage has happened to the cell. So far it is showing proper voltage as expected. Voltage is steady. 

Pete


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## palmer_md (Jul 22, 2011)

I'm confused. Are you testing cells at -1F or 31F? Are you testing a cell that is encased in ice? Ice is an excellent insulator. Ever been inside an Igloo? Toasty warm inside when it is way below zero outside.

If you are really testing these cells for cold charging, I hope your keeping the ice off of them while they are held in a cold environment and then charged while remaining in that environment.


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## MN Driver (Sep 29, 2009)

"It will be filmed." Thank you Pete! It feels like I just got a New Years gift because this is a video I've been waiting for someone to make. Wish I had my hands on some cells, I feel like buying 2 70Ah or 100Ah cells from Cali's CALIB just to have some toys to torture test. Safe and controlled environment, I like the outside, it would be great to be outside in case the carbon stacks of my 500 amp load tester decided to let out the white smoke. Usually in January we get one night where it is -20f and about ten days worth of -10f nightly lows. Winter 2010 we had a -25f nightly low. I'd love to go out in the winter cold and play with real world factors like battery warmup methods(through high amp voltage sag) of cells in the cold where such a warmup method would be battled by extreme outdoor cold and wind directly. I'm thinking voltage sag to 2.25v or 2.5v for very brief periods with a short rest between amp draws would warm them up briskly, hard part would be whether or not its hot-spotting in the cell too much. Charging is weird with CC, CV cold enough and the voltage would go almost straight to the chargers constant voltage and sit at CV at a low amp rate because the cells aren't sucking in the current well. I'm very familiar with the effect from NiCd, NiMh, and Sanyo Lithium Cobalt 18650's. It would be great to see these.


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## Guest (Jan 3, 2012)

Figured someone was going to mention that. Well the plastic case is just as much an insulator as the ice. The ice is to keep the cell cold during the charge. I can't charge while in the freezer. So encased in ice and starting at -1F I will put the whole thing in a very thick styrofoam box to keep it cold while charging. I will be checking the temps during the charge but it is the only way to keep it cold. No matter what condition your charging in the plastic case will act as an insulator and hold in heat. I do not expect the cell to remain at 
-1F at all. I just wanted to keep the cell as cold a possible during the 5 hour charge time. No cell will ever be encased in ice but they are all encased in plastic. Not to worry. It is a test and if I had a way to bring all my charging equipment to the freezer and make it work and keep the freezer top closed I would do that. But it is not to be. It is what it is. 

Your ideas on how it will perform? I do know that snow is a super insulator. Ice not so good. So the ice will keep the environment quite cold but it will not remain at -1F we will record all information possible and try to keep the environment cold. I do not live in the arctic.


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## roger (Jan 24, 2010)

JRoque said:


> Hello Roger,
> 
> Thank you for sharing your experience with cold cells. Not that it matters much to me based on my location but I'm glad to see you showing these cells work in cold weather just fine. It's getting clearer that manufacturers print the temperature limits just so their cells meet the written specs but they still perform acceptably, and do not sustain permanent damage, when somewhat outside these parameters.
> 
> ...


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## JRoque (Mar 9, 2010)

Hi. I've never been inside an igloo but I believe the reason they stay "toasty" inside is because the body heat is contained within the confined area with a layer of air insulator between the body and the ice.

The way Pete is working his experiment, the ice will behave as a heat dissipator because it's in direct contact with the cell. There isn't a layer of air to insulate and retain heat so any bit of temperature rise that the cell might have will be removed by the surrounding ice. That's all theory of mine, of course, we'll have to wait for Pete's conclusion to see.

JR


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## palmer_md (Jul 22, 2011)

JRoque said:


> The way Pete is working his experiment, the ice will behave as a heat dissipator because it's in direct contact with the cell. There isn't a layer of air to insulate and retain heat so any bit of temperature rise that the cell might have will be removed by the surrounding ice. That's all theory of mine, of course, we'll have to wait for Pete's conclusion to see.
> 
> JR



I agree, and it will be interesting, but not sure how valuable the information is because there are not too many people who will have a pack of batteries that are encased in ice. The experiment would be better if the batteries were just placed in a cold environment like a freezer and then charged and/or discharged while remaining in that environment. The ice encased battery introduces variables that are not present in the real world. But to reiterate, I do think that if you have a temp sensor on the battery terminal while you are charging you will get some information which will be interesting.

Pete, why can't you run the cables into the freezer? You explained earlier that you could not charge them while inside, but I did not fully gather why you could not do it.


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## dladd (Jun 1, 2011)

I thought the damage from charging at sub-freezing temps was a slow degradation of performance, not a sudden failure. I'm not sure what a few cycle tests will show you. Everything may look fine during the test, but how do you know if any 'plating' occurred? Long term life may still be affected, you won't know from these tests, right?


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## Guest (Jan 3, 2012)

dladd said:


> I thought the damage from charging at sub-freezing temps was a slow degradation of performance, not a sudden failure. I'm not sure what a few cycle tests will show you. Everything may look fine during the test, but how do you know if any 'plating' occurred? Long term life may still be affected, you won't know from these tests, right?


Well no one has actually said for sure. The manufacturer says no. That means we will do it. If it is long term damage I won't care. If its short term I will if there is nothing that is great. Will we know for sure? NO. I guess I could take a perfectly good cell and dissect it and put it under an electron microscope and check the condition of the medium and do a serious freeze test then do the same thing and see if there is any visible damage. With an electron microscope you would see plating. 

But since we do not have that level of testing we do this kind of testing. I feel that there is going to be no issues recordable and doubt that any long term effects will really matter. Now if I did this daily for the next few years then there may be some issues. But once and awhile I see no issues. But we won't know unless its done. It is a more real life test vs I think test. Thinking does nothing. Doing does. I think so I take it to the next level. It is what I can do and since no one else has done it I guess it's up to me. I am doing this to determine if I really need to deal with insulating the battery boxes. The worst we see here is 20F and that is for a very short time. My Leaf handled that no problem and it has no insulated boxes or at least heaters. 

Pete 

Where did you hear that they would plate if charged cold?


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## Guest (Jan 3, 2012)

> I'm not sure what a few cycle tests will show you.


Maybe it won't show anything. Want to keep guessing? Like I said. I don't think its an issue either. It will make a good video and it will be the impact of a cell in ice you know. The Arctic Glacier thing. It will be very very cold. I'd love to go to -20 or more but this is all I can do. 

Pete


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## MN Driver (Sep 29, 2009)

The ice surrounding the cell will build an air pocket as soon as it melts any water, once it does that there is a thin insulating gap. It doesn't take much because double pane windows come with a thin gap, I think as thin as 1/4", but I think most are 3/8" or a 1/2" but it doesn't take much gap to have an insulating air pocket where the cell isn't under direct compression. My thought would be to add some salt water, which has a lower freezing temp to the thin layer and that way you have water thermally conducting directly with the plastic shell.


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## Guest (Jan 3, 2012)

I am aware of that issue. I am still trying to see if I can do this while remaining in the freezer. I am also aware in real situations the cell will heat up and even if not in cold water they will get warmer than the surrounding area. It is a natural sequence of events. That is exactly what I want. I will put the block in the cooler. I may actually go get some dry ice to help keep it cold. I can't stop the warming process no matter what.


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## GizmoEV (Nov 28, 2009)

gottdi said:


> Well no one has actually said for sure. The manufacturer says no.
> [snip]
> Where did you hear that they would plate if charged cold?


From this article titled "Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries" by Kang Xu from the Electrochemistry Branch, Sensor and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland 20783-1197 published in the Chem. Rev. 2004, 104, pp4303-4417.

"Thus, at temperatures lower than the liquidus temperature (usually above -20 °C for most electrolyte compositions),50e,159,160 EC precipitates and drastically reduces the conductivity of lithium ions both in the bulk electrolyte and through the interfacial films in the system. During discharge, this increase of cell impedance at low temperature leads to lower capacity utilization, which is normally recoverable when the temperature rises. However, permanent damage occurs if the cell is being charged at low temperatures because lithium deposition occurs, caused by the high interfacial impedance, and results in irreversible loss of lithium ions. An even worse possibility is the safety hazard if the lithium deposition continues to accumulate on the carbonaceous surface.

"At temperatures higher than 60 °C, various decompositions occur among the electrolyte components, electrode materials, and SEI or surface layers, while LiPF6 acts as a major initiator or catalyst for most of these reactions.152,310,332,333 The damage caused by high-temperature operation is permanent. Because gaseous products accumulate, a safety hazard is also likely. Therefore, the specified temperature range for the normal operation of most commercial lithium ion cells is -20 °C to +50 °C. While sufficient for most consumer purposes, the above range severely restricts the applications of lithium ion technology for special areas such as military, space, and vehicle traction uses."

Here is the author's bio, _"Kang Xu was born in Chengdu, China, and received his B.S. degree in Chemistry from Southwest Normal University in Chongqing, China, in 1985 and M.S. in Polymer Chemistry from Lanzhou Institute of Chemical Physics, Academy of Sciences, in 1988. After working on polymer electrolyte materials from 1988 to 1992 at Chengdu Institute of Organic Chemistry, Academy of Sciences, he went to Arizona State University and received a Ph.D. degree in Chemistry in 1996 under the tutelage of C. Austen Angell. From 1997 to 2002, he was awarded the National Research Council Research Associate Fellowship and the American Society for Engineer Education Postdoctoral Fellowship, respectively, and he served during the tenures as a guest researcher at U.S. Army Research Laboratory with T. Richard Jow as academic advisor. He was employed by the U.S. Army Research Laboratory in 2002. His research interests concern materials development for electrochemical energy storage applications, which include lithium or lithium ion batteries and electrochemical capacitors. He won R&D Achievement Awards from the Department of the Army in 1999, 2001, and 2002 for his work on electrolyte materials. He authored over 60 research publications and 11 patents and is a member of the Electrochemical Society."_

This paper has been the most definitive I've found on what happens when the temperature is low and a battery is charged. There doesn't seem to be an issue during discharge, however. It appears that the 0°C charge cutoff isn't a hard and fast temperature but given the mix of things in the electrolyte it may be that there is a higher probability of lithium ions plating out when charging below 0°C. Remember that temperature is just the average kinetic energy of the atoms and molecules not that every one is at that temperature. This means there are going to be parts of the battery at the molecular level which will be below 0°C for moments in time. Maybe if a lithium ion is trying to intercalate at that moment it may plate instead. If this is true then the lower the temperature the higher the probability of ions plating out.

Last winter I found that the case temperature of my cells was always above 0°C after a 3 mile drive up my hill. I have 3/4" of hard insulation around my box which is nearly sealed shut.

On ice temperatures...0°C is when water freezes. There is 0°C water and 0°C ice. Once heat of fusion is removed the water is then solid and can continue to drop in temperature so Pete's block of ice is likely starting out at -17°C if it has been in his freezer long enough. Given the info from the article referenced above, I doubt you will see much if any noticeable capacity loss charging at this temperature with only a few cycles. I wish we could take them to -40°(C or F) and test them out.


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## Guest (Jan 3, 2012)

Good article. Not specific to LiFePO4 but good. I am sure that most will never see even close to this kind of abuse. For sure none of use here where we live. So if it is fine then I am quite sure it will be fine to not have to worry about super insulated boxes or even heating the boxes. But in areas where you do see -F temps you might want to have some sort of heating or warming. Warming will be enough. 

Pete


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## GizmoEV (Nov 28, 2009)

gottdi said:


> Good article. Not specific to LiFePO4 but good.


No, but LiFePO4 was part of the discussion and that LiPF6 was a common electrolyte used in LiFePO4 cells. The article is about electrolyte research and results so that is why all Li cells were included. At least there is one authoritative source on what happens when charging very cold Li batteries and also why discharge at those temperatures doesn't hurt them. It sure beats just believing a factory spec sheet when they provide no reason and just seem to copy everyone else.

I agree that warming will likely be enough. Yesterday I did a nearly 70% discharge on my 200Ah pack in a span of about 3 hours followed by a 55A charge rate. The case temp started at 9°C and ended at 27°C. I then did a 50% discharge in about an hour and the temperature only rose to 30.6°C. When I wasn't climbing a hill or waiting for traffic or a light the discharge was a relatively steady 135A on the last discharge. I have an insulated box so not all of the small temp increase at the end can be attributed to higher heat loss to the air. I see this pattern quite a bit. Less heat gain at higher temperatures.

I look forward to your results.


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## NabilAhmad (Feb 26, 2011)

Keep up the good work, Pete. I look forward to your shared experience! 

Indeed, this is not a laboratory grade test, but certainly could give rise to serious concern if you are able to detect significant losses.

For what it's worth, if you do have a thawing of ice immediately surrounding the cell, I'm confident the liquid water will still produce conditions significantly severe. After all, this is an isolated cell - not in the middle of the pack. So then this gives rise to the applicability of any findings on real packs. The outer edges would recieve the least benefit from internal heating, but what is the threshold? An inch in? Two inches in? There are a myriad tangents to persue, but to what end? Regardless of your findings, I doubt it would be a bad idea to integrate warmers for charging in extended cold conditions. 

Looking forward to your next installments!


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## Guest (Jan 4, 2012)

I had to change up the testing. Had a problem with the cell in the bucket of water. I first put a shallow layer of water in the bucket and let it freeze solid. I then put the cell on top of that slab of ice and then filled the bucket up with water to freeze. I did that to keep the cell on top of the ice and have the rest surround the battery except the top. Well all went fine but today I went to go check the cell in the freezer and found that the cell had been pushed nearly out of the water by the expanding freezing water. The water had gotten under the cell and as it freezes it expands. The sides of the bucket keep it all contained and since the sides were well frozen the only place the water could go was up. But since the battery was still sitting in the water the expansion of the water could literally push the cell out of the block of ice which it did. It was not fully out and I found it was not fully frozen either. The temp of the cell was only 20F this morning but the sides of the freezer we're below zero. So I decided to go ahead and remove the cell from the block and bust up the ice and put the ice in the portable cooler along with 15lbs of dry ice. Well maybe about 10 lbs now. The cooler is very thick and will maintain the cold within quite well if I have dry ice in the cooler as well as the regular ice. The cell is not directly on the dry ice as that could be a bad thing. I don't want to try putting it directly on dry ice. The dry ice measures -20F so quite cold. I now have it cooling and I hope it will work as expected. I will check later and go fetch more dry ice if needed soon. I hope to make this a go either today or tomorrow for the test. The cell will not be encased at all. Just the plastic case protects the insides from the cold. So the outside temps will be very cold. Dry ice to keep it cold. Charging will take a good 4 1/2 to 5 hours at the amperage I am charging the cell. 

That is the change up but we are still continuing the test. It will still be arctic glacial conditions except not encased in insulating ice.


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## Guest (Jan 5, 2012)

UpDate: 

Started the charge of the frozen battery. Our static information at the start of the test is as follows.

2:51 pm
3.162 volts static
-2.9 F
---------------------

3.920 volts...........zero time...........20 amps.........-2F
3.808 volts...........:47 sec..............15 amps.........-2F
3.697 volts...........1:26 min............10 amps.........-2F
3.548 volts...........3:00 min............5 amps..........-2F
3.540 volts...........4:52 min............5 amps..........-2F
3.631 volts...........29:03 min..........5 amps..........-10F
3.630 volts...........44:20 min..........5 amps..........16F
3.650 volts...........50:15 min..........5 amps.........-16F
3.429 volts...........53:00 min..........2 amps.........-16F
3.410 volts...........56:28 min..........2 amps.........-18F
3.432 volts...........1:26:40 min.......2 amps.........-20F

So very cold temps will require being warmed so they can actually take a good charge. At this rate it will be well into tomorrow before the cell is charged enough. So an unprotected cell will require insulation and a warmer to keep it just above freezing so it can take a charge. According to the information here anyone with an Elcon won't be able to charge a pack because the pack will spike up higher than the cut off voltage and when the charger sees the voltage up that high it will shut off thinking its full. Ooooops. 

So the cold forces the voltage to spike at normal amperage to above the recommended voltage of 3.65 volts. In keeping with our recommended charge algorithm it will be impossible for the elcon to charge unless the cell is above freezing. My two graphs show at a temp that is cold but above freezing. 

The dry ice is keeping the cell from warming up and since the amperage is so low it does not have much chance to warm up. At least not until the dry ice is gone or the cell removed from the cold environment. 

Any ideas about charging above the recommended voltages to force feed the cold cell? Think that might damage the cell? What we need to know is if I can like go to 4.6 volts and then taper off until I reach like 5 amps? Mmmmmm. 

Pete 

This is an ongoing test but once the dry ice is gone the test is done as I won't spend the money again for more ice. It does a bang up job keeping the cell very very cold.


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## EVfun (Mar 14, 2010)

If you take the voltage high and the cell proves to be damaged you will have no way to know if it was the cold or the high voltage (also known to cause plating.)


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## bjfreeman (Dec 7, 2011)

that is the reason I use cold plates between cells. also for max charging cooling.
the 1/4 in additional per cell is worth in extremes.


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## Guest (Jan 5, 2012)

I am just going to do my normal routine for charging and keep it within normal parameters. Working on video right now. Not much to see. Block of ice was an interesting idea but that dry ice did the trick. Damn cold in that cooler. 

Pete


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## Guest (Jan 5, 2012)

You don't want it too cold but wicking away excess heat would be good if you live in a very hot climate. So far my batteries have been fine at the high temps I have put them through. None above the max recommended by the manufacturer. If it ever gets that hot I will move to a cooler location as I would be out of my comfort zone. 

Pete 

No warming the cells would be what I would want if it ever got cold enough. Single cell warmers would need to be found as I plan on putting cells under my VW Bus. So some insulation and something to warm them. I am not needing them to be hot but warm, meaning at or above freezing.


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## GizmoEV (Nov 28, 2009)

gottdi said:


> UpDate:
> 
> Started the charge of the frozen battery. Our static information at the start of the test is as follows.
> 
> ...


Celsius temperatures added to make comparisons to the spec sheets easier. Remember that the article I referenced earlier talked about -20°C being the lowest to go before plating would definitely occur. It looks like there is a practical reason beyond cell damage to not charge at such low temperatures.

Your results explain why when my cells are below 10°C that the charger never gets to the point where it stops charging until the timer shuts it off. The current tapers back until, in my case, the pack reaches 69.3V but when the pack was at ~10°C on my last balance check the voltage never quite got there. The charger kept pumping in about 350mA. I'm only charging to 3.465vpc so I don't know what would happen if I charged a bit higher up the curve.

The Zivan seems to charge very similar to how the Elcon chargers do so I'd be in the same boat if my pack got really cold. I guess that if you are in "danger" of having your pack much below 0°C that you could just be sure to charge it immediately after a drive regardless of DOD.


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## Guest (Jan 5, 2012)

Voltage is climbing ever so slowly at 2 amps but it is at least 3.440 volts now but at -37 degrees. Damn it's cold and sooooo slow charging. 

I guess I'd be a bit slow at -37 degrees too.


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## GizmoEV (Nov 28, 2009)

gottdi said:


> I guess I'd be a bit slow at -37 degrees too.


I'd be a little stiff too!

I sometimes ask people if they know how to make a trip shorter. Answer, "Drive from here (Kelso, WA) straight through to Orlando, FL non-stop except for fuel." After that, every trip is a short trip.

Now I can ask people how to make charging quicker. Just charge when the batteries are at -40°! After that, every charge is fast.


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## Guest (Jan 5, 2012)

LOL. Thanks. Made my day


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## Guest (Jan 5, 2012)

Looks like the cell is no longer accepting a charge at -37 degrees and 2 amps. It's still chugging away but the voltage has stalled and even looks to be going in reverse a touch. I will check again in an hour. Damn thing is getting colder by the hour. I was not wanting to go quite this cold but it is showing some interesting results. At some point it will be just to damn cold to charge. Maybe that is the whole thing about cold. It just slows down so much it can't do anything. It goes into hibernation mode. Once warmed it should fire right back up. We shall see. I will do a charge later when I take it out of the deep freeze and see if it bounces back to normal. So keeping the voltage below the cutoff point of 3.65 the amperage has dropped to two to three amps and has stalled. At some point I am sure it will go backwards. I will graph it when done. I am quite sure I won't be fully charging this cell at this temp. 

Pete


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## Guest (Jan 5, 2012)

3.64 volts 5hr 7 min 2 amps -34

So it _has_ come up a bit. Time to turn down the amperage again.


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## GizmoEV (Nov 28, 2009)

Are you keeping a spreadsheet with your data so you can see a running total of the Ah being put into the cell? It won't be perfect but it will give you an idea of how much attempted charge was put into the cell.


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## rwaudio (May 22, 2008)

gottdi said:


> 3.64 volts 5hr 7 min 2 amps -34
> 
> So it _has_ come up a bit. Time to turn down the amperage again.


What was the SOC when you started? Are you going to do a discharge test when it's done to see what you were actually able to put in??

Although it was 61F today (crazy for a January day here) I'm interested in your cold weather testing. Although it would be out of the norm to try charging when it's that cold, it's nice to know how the pack would behave if I tried.


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## Guest (Jan 5, 2012)

I am writing every thing down I can. Not sure if I can come up with AH information from this but I am writing it all down to make a graph and gather what I can. 

The Cell was fully charged and discharged to 2.5 volts at a 40 amp load. At which point we terminated the discharge as the cell would not provide much from that point on and I did not want to go further. It represents what I do when I charge and discharge under normal driving conditions. So in that light the cell was considered discharged. I could have gone a bit further because of the load being placed upon the cell. However if the cell was at 2.5 and only like a 25 amp load then it would have been a bit emptier. But it was nearly depleted for a normal drive condition. 

It is a bit on the extreme side of things but it is good to know. Yes, I can do a discharge test first before I go back to doing a warm charge and discharge. 

I wish I had a meter to tell me the AH in and out. 

Anyone want to donate one? 

Pete


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## Guest (Jan 5, 2012)

> Although it was 61F today (crazy for a January day here)


Not crazy, we get that too. Granted your further north but not crazy. Heck it was in the low 70's here today. Winter? Ha!


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## rwaudio (May 22, 2008)

gottdi said:


> Not crazy, we get that too. Granted your further north but not crazy. Heck it was in the low 70's here today. Winter? Ha!


Today's temp broke a 90 year record, so I would say crazy (for here).
Other than the 100km/h winds it sure beats the usual temps. Makes it a lot easier to warm up the garage and work on the EV


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## Guest (Jan 5, 2012)

Cool 

New info: 

3.73 volts 5 hr 52 min 2 amps -38 F
3.550 volts 5 hr 57 minutes .2 amps -38 F

So I have dropped the amperage again and it is now down to .2 amp. It will crawl like nothing now. Time to let it go up once again to 3.65. I did not watch close and it went to 3.73 volts. Ouch. Well it was only for a brief time. I am sure no harm because the highest these are rated by the factory is 3.8 volts. So I remained below that. 

The graph will look kinda funky. Going to go graph right now. So nearly 6 hours into this and the cell would have normally been fully charged by now. 

Pete 

Graph coming.


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## GizmoEV (Nov 28, 2009)

Attached is a Ah calculation spreadsheet with your initial data filled in. There are two versions, OpenOffice.org and .xls. You can fill in the rest of your data to see how many Ah have been pumped into the cell. It is not perfect but gives a decent estimate.


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## Guest (Jan 5, 2012)

Thanks.

That shows I only put in 14.7 AH into the cells after 6 hours. Ouch.


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## Guest (Jan 5, 2012)

The spread sheet will help me a bunch to figure out general AH in or AH out. I guess I can do this in reverse right? Or not? But at least I can now check AH into the cell. I can see if i am close to normal. 

Pete


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## GizmoEV (Nov 28, 2009)

gottdi said:


> The spread sheet will help me a bunch to figure out general AH in or AH out. I guess I can do this in reverse right? Or not? But at least I can now check AH into the cell. I can see if i am close to normal.
> 
> Pete


It should if you put in negative current. It just averages the current on a given line with the one above and assumes the current (and voltage) was constant for that time interval.


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## Guest (Jan 5, 2012)

It's plenty good enough for the type of testing I am doing. Good enough to show results that can be used. 

Thanks again.

Pete 

Time to go get more info.


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## Guest (Jan 5, 2012)

Well I am going to call it full at 7 hours and 4 minutes and .2 amps and 3.65 volts. I just can't adjust my amperage any lower and be able to record it. It is still sitting at -37 degree F. So at this temp you get about 15 or so AH's put in and that is about it. So at this point the cells go into hibernation and just don't do a damn thing. So I am going to leave it for the evening and let it freeze more. I am sure it will remain nearly at that level until tomorrow. I will check in the am to see what is happening. It will be interesting to see how well the cell puts out power at that temp. I will hook it up tomorrow to see. Should burn off the power fast. Might go longer than expected once the internal cell has warmed up. 

Pete 

Not much to see.


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## Guest (Jan 5, 2012)

Here is a clip from my video showing the cell in a block of ice. I took it out this morning. Kinda fun. Glad I went with dry ice.


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## Guest (Jan 5, 2012)

And another view of the cell on dry ice all frosted up. There is regular ice mixed in with the dry ice too. 

Pete


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## barron (Dec 10, 2011)

Can charging cells below 50F actually destroy them never mind at freezing temperatures?

http://www.wattflyer.com/forums/showthread.php?t=40769

I found myself looking at this link and others due to a recent bad experience.
I have a 72V nominal 60AH pack of 20AH LiFePo4 grey market pouch cells of a certain well known manufacturer.

I live in Phoenix, Arizona which does not have a particularly cold climate but last winter I saw a step reduction in capacity and increase in cell IR after a cold snap, then this winter the pack performance suddenly (over two days) tanked. I am getting > 20V drop at 3C discharge and about 1/4 of the original range.
I use a BMS, never over or under volt (min 2.1, max 3.6), discharge at 3C max and 1C typical. Charge at 1/6th C. I have the equivalent of about 70 cycles on the pack but typically don't discharge pack below 50%.
The performance tanking this winter correlated exactly with a couple of cold days where I was charging at night in temperatures of around 40F.
It seemed too much of a coincidence not to be related, so I started looking round the internet and found, to my horror, a few references, like the link above that talked about not charging below 50F. I read some other info that talked about lithium power tools not allowing themselves to be charged below 50F.

Can this be true?!!! A single charge below 50F can destroy cells?!!! If it is true, it doesn't seem to appear on manufacturers data sheets and there seem to be a lot of lithium products out there that don't guard against this condition, which makes me question the validity of the 50F limit...?


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## Guest (Jan 5, 2012)

I have not had much trouble with my Nissan Leaf in the cold weather and we have had plenty of low 20 degree F evenings. I know I never charged at those temps yet but the cells can discharge reasonably well in the cold. Most charging is not recommended below zero degrees C. I have been doing this today at as low as -37 F. Could not charge much. Yes, if its too cold you could have trouble getting a full charge even though the charger thinks its full. The voltage the charger sees will he higher as the temps drop. So yes you could see those partly filled cells and reduced distances. I would not think that 50 F would be any trouble. I can see below freezing. Usually cells are recharged right after you get back from a drive so the cells are internally warm enough to properly charge. If you let them get too cold before you charge you can have trouble. If you don't and charge them warm you should have no trouble even if they get cold because they will warm quickly and you can take out nearly what you put in. 

But don't bother charging when it's 30 below and you don't have a way to warm your cells. 

They hibernate in real cold weather so you can't charge normally. 

Pete


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## Guest (Jan 5, 2012)

Also depends upon the type of lithium cell your charging. Some may in fact have trouble at those temps. We also don't charge our cells much past 3.65 volts per cell. 4.2 volts per cell in any lithium cell is too high in my book. Just because it says you can does not mean you should. That is the upper most limit under ideal conditions. Don't. Go less and if cold even less. 

Pete


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## barron (Dec 10, 2011)

gottdi said:


> Also depends upon the type of lithium cell your charging. Some may in fact have trouble at those temps. We also don't charge our cells much past 3.65 volts per cell. 4.2 volts per cell in any lithium cell is too high in my book. Just because it says you can does not mean you should. That is the upper most limit under ideal conditions. Don't. Go less and if cold even less.
> 
> Pete


Thanks for the info. If the maximum voltage needs to be lower at lower temperatures it seems like this information should be on manufacturers datasheets otherwise we have to guess how much lower if any (although of course I still need to determine with certainty that was the root cause in my case). I haven't seen temperature/ versus max charging voltage on any manufacturers datasheet so far, just minimum operating and storage temperatures.


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## Guest (Jan 5, 2012)

Went to have a look at my cell and it is happily hibernating at 3.3 volts. The inside temp is beyond what my meter can check and that is -58 F. The terminal and upper part of the cell is at -57 F. So the cell is sufficiently cold. To say you need to warm your cells and to have insulation to protect from this sort of cold weather is a confirmed no brainer. This is an extreme test. 

Now for the discharge test this morning. 

Pete 

This is just beyond cold.


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## Guest (Jan 5, 2012)

Checked the cell at -57 degrees and connected it to the motor. Well, it would not run the motor. I could not even get it to spark when shorting the cell. The voltage dropped into the millivolt range when shorting it out. So NO power to give at -57 degrees. 

We have the cell out to thaw and try to get it to move the motor. 

Pete


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## Guest (Jan 5, 2012)

Now that the cell is above zero at about 11 degrees the cell is allowing some voltage to be released. Once warmed up to above freezing we will do a complete charge discharge on the cell and graph it. The graph on this test is pretty much useless. The cold will put the cell into hibernation and nothing really happens at below zero temps. All that time last evening really did nothing. 

Pete


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## GizmoEV (Nov 28, 2009)

barron said:


> Can charging cells below 50F actually destroy them never mind at freezing temperatures?
> 
> http://www.wattflyer.com/forums/showthread.php?t=40769


That link is talking about LiPoly cells. They may behave differently at cooler temperatures. The reading I've done about this all agree with what I quoted earlier in the thread, that plating happens down around -20°C not at 10°C (50°F). I have several charges on my TS pack when it was below 10°C but all at or above 0°C. My pack has delivered in excess of 24,500Ah (200Ah pack) over the past 2 years and just a couple of days ago I did a 70% discharge and it didn't behave any differently than it always has. I suspect that there is something else going on with your pack.

For the first 6000Ah I charged to 4.00vpc but after that I started charging to only 3.465vpc. I'm not sure that ending voltage needs to change so much based on pack temperature but ending current does depend on ending voltage. Are you charging your pack to 3.6vpc and letting the current taper down to well below 0.05C? If so you may have been murdering them by overcharging on every charge.


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## barron (Dec 10, 2011)

I only occasionally charge the whole pack to 3.6V (although I did charge the whole pack to 3.6V during that cold spell I mentioned). Usually I just cut charge off when BMS goes into balance mode which is when first cell reaches about 3.4V. 

In balance mode, the current is tapering down to between 3.4V and 3.6V and by the time the first cell reaches 3.6V, the BMS balance current is at most 250mA (which on my 60AH pack is therefore a 0.004C charge rate), BUT that current will all be going through bleed resistors for cells at 3.6V so the cells won't even be seeing as much as 0.004C by the time they are at 3.6V, in fact they are probably seeing effectively 0C. 




GizmoEV said:


> That link is talking about LiPoly cells. They may behave differently at cooler temperatures. The reading I've done about this all agree with what I quoted earlier in the thread, that plating happens down around -20°C not at 10°C (50°F). I have several charges on my TS pack when it was below 10°C but all at or above 0°C. My pack has delivered in excess of 24,500Ah (200Ah pack) over the past 2 years and just a couple of days ago I did a 70% discharge and it didn't behave any differently than it always has. I suspect that there is something else going on with your pack.
> 
> For the first 6000Ah I charged to 4.00vpc but after that I started charging to only 3.465vpc. I'm not sure that ending voltage needs to change so much based on pack temperature but ending current does depend on ending voltage. Are you charging your pack to 3.6vpc and letting the current taper down to well below 0.05C? If so you may have been murdering them by overcharging on every charge.


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## mizlplix (May 1, 2011)

A wide array of heat/cold tests were done to batteries of all types at JPL for NASA. Unfortunately access to their results is restricted. But it included immersion in liquid nitrogen, then thawing. Most lithium based cells survived and acted normally. No data was given on actual operation during the extremes.

It would be nice if someone could sift through this and similar information for us.

Miz


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## Guest (Jan 16, 2012)

Well the results are if the cell is around zero degrees it will allow very little in the way of charging ability and will allow about the same out. Very little. At 20 below it is nearly asleep. At 58 below it is fully in hibernation mode. The plastic case survived well and when the battery thawed it woke up and began working again. Sluggish when cold. But the internals of the battery need to be at these temps to act this way. If you keep the core above zero and better above freezing you will find that they work just fine. That is the reason for keeping them warm. It is not because it will kill them. Its that cold puts them to sleep. These are like living creatures. When cold they hibernate. No doubt you would want to as well. 

Pete


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## mizlplix (May 1, 2011)

And it seems that the lithium/iron/polymer batteries being used lately are more able to function at elevated temps than even say...the Lithium/cobalt type used in our cell phones (they are really picky as to the plus end of the scale). 

The polymer cathode matrix seems to receive and transfer the lithium faster than most other kinds...so far. I am sure that will change with time.

Miz


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## Ziggythewiz (May 16, 2010)

Sinopoly claims: 
Operation temperature (charging)0℃～70℃ 
Operation temperature (discharging)-20℃～70℃

This doesn't seem to fit well with your test, can any differences in the formulation have that much of an impact?


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## Guest (Jan 31, 2012)

Ziggythewiz said:


> Sinopoly claims:
> Operation temperature (charging)0℃～70℃
> Operation temperature (discharging)-20℃～70℃
> 
> This doesn't seem to fit well with your test, can any differences in the formulation have that much of an impact?


My testing was very extreme and a company will be very much likely to be very very conservative to remain in the safe zone. 

At -4 F the cells will discharge but they will be sluggish. No doubt about that. but at -20F they just don't do much. They will squeak a motor a touch. Much below that they do absolutely nothing. 

Charging the cells at 32 F is no problem but at zero it begins to be a problem where the colder it gets the more amperage needed to put in power. So if your cell is truly at zero degrees you will not be able to fill it completely if you use your normal charge algorithm. The voltage will rise far above the max limit even if empty. 

So the manufacturers data is fine and in the safe zone. So you can charge your cells if the cells are truly sitting at 32 F. You can still fully charge them even at 15 F. But get to zero and you are having problems. 


Pete 

The A123 cells seem to handle the cold better. 

We shall see. One day I may test one of these in extreme cold too.


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