Charging LiFePo4 batteries below freezing experiment

[GaryBIS]

Hi,
I ran across this video in which the person placed an LFP battery in a freezer for 48 hours, then immediately charged the battery (which has no low temperature charge protection), he then did a capacity test and the battery showed no loss in capacity. Being a bit surprised by this, he repeated the whole process again with the same result - no loss of capacity.
So, he did two charges with the battery at 2.5F with no apparent ill affects.
The cold charge experiment starts at about 7 minutes into the video. Note that the title of the video gives no hint of the cold charge test, but its there at 7 minutes.

So, what's going on here?
The cautions on not charging cold LFP batteries is just universal on the internet.
Is it not as big an issue as we think? Any data on this - that is, measurement of the damage done vs temperature, charge rate, type of LFP cell?
Any thoughts on whether one could tolerate a cold charge once in a while?

Gary

 

[45North]

Tried that link and it goes to a diy vs buy video.

Did you see my thread from a few days ago?

I'm charging my Li yard lights below freezing!

For the past 2 years - including winters - I've been using my Li yard lights despite all the warnings about not charging Li below freezing. Daytime temps here in Ottawa are consistently below freezing for weeks (months?) on end. Yet they continue to light up every night if there's been enough...

diysolarforum.com

 

[GaryBIS]

Tried that link and it goes to a diy vs buy video.

Did you see my thread from a few days ago?

I'm charging my Li yard lights below freezing!

For the past 2 years - including winters - I've been using my Li yard lights despite all the warnings about not charging Li below freezing. Daytime temps here in Ottawa are consistently below freezing for weeks (months?) on end. Yet they continue to light up every night if there's been enough...

diysolarforum.com

His video covers 2 subjects - the second one covers the cold charging test on a 100AH LFP battery.
Start at minute 7 of the video for the cold charging test - he covers all the details.
I left a comment telling him he should publish the cold charging test as a separate video with an appropriate title - I think there would be a lot of interest in it.

I did see that post on your yard lights. Its very interesting, but not sure it applies due to the differences in battery size/type and the very low charge rate?

I guess for me, what I'd like to know is if I screwup and charge the 100 AH LFP batteries in my van conversion when its really cold, will it total my batteries or just reduce their life/capacity by some minuscule amount?

Gary

 

[Bud Martin]

I ask him the question in his video since he was charging at only 15A when the battery is frozen:

Did you try charging at 50A (.5C) when the battery is frozen to see what happen?​

Jasonoid
3 days ago
I tried charging it 50 amps when it was freezing, the voltage jumps to full 14.6v and it doesn't allow it to charge. I'll be doing more testing soon, pretty interesting results.

REPLY

3 days ago
@Jasonoid Interesting, so it may be able to tolerate low C charging rate but not at high C, so may be that is when the damage occur. Looking to the repeated test result on high C rate when frozen..

 

[Bobert]

I’m no expert but here’s my opinion. According to battleborn lifepo4 batteries can be safely charged below freezing. I believe the charge cutoff point the battleborn is 23 f. At 23 it is safe to charge at its full rating. The batteries can still be charged well below 23 just at a reduced rate. I wouldn’t put much stock in the results of the experiment shown on this video
Here’s why
1 as objects get colder the rate of cooling tends to slow down therefore the exterior of the battery is not an accurate indicator of the cell temperature. The cells may have still been in the safe charge range.
2. The rate of charge was very slow it very well could have been below the rate that would damage the cells even if they had reached 2 f.

 

[GaryBIS]

I’m no expert but here’s my opinion. According to battleborn lifepo4 batteries can be safely charged below freezing. I believe the charge cutoff point the battleborn is 23 f. At 23 it is safe to charge at its full rating. The batteries can still be charged well below 23 just at a reduced rate. I wouldn’t put much stock in the results of the experiment shown on this video
Here’s why
1 as objects get colder the rate of cooling tends to slow down therefore the exterior of the battery is not an accurate indicator of the cell temperature. The cells may have still been in the safe charge range.
2. The rate of charge was very slow it very well could have been below the rate that would damage the cells even if they had reached 2 f.

Hi,
That's interesting the BattleBorn says its OK to charge down to 23F and maybe at lower temps if charging at a low rate?
Can you say where this is on the BattleBorn site?

The battery was in his freezer for 48 hours - seems likely it had a chance to cool down to nearly freezer temp. Just as a thought experiment, if you put the same size container of water in the freezer for 48 hours would it not be a solid block of ice in 48 hours? Li batteries have a specific heat that is roughly 1/4 of water, so it would take much less heat transfer out of the battery to get it cold throughout than a block of water?
How long do you think he would have to leave it in the freezer to get it down to near freezer temp?
The low temperature charge protection sensors in batteries (like the SOK for example) have their low temp charge protection temperature sensor mounted on the outside of the cells and actually closer to the case than the cell - so, they must think that the outside of the battery temp does not lag that far behind the center of cell temperature?

It would have been nice if he had discharged at a higher rate, but 15 amps is not nothing - since my conversion van only uses about 60 amp-hrs a day. I'd be happy as a clam if I was told I could safely charge at 30 amps (two batteries) when the battery is cold - only 2 hours to restore full charge.

 

[Bud Martin]

"It would have been nice if he had discharged at a higher rate, but 15 amps is not nothing "
In his video, he was charging at 15A when the battery was frozen, when he tries at 0.5C (50A) it did not behave right per his replies to me.

 

[Hedges]

I ask him the question in his video since he was charging at only 15A:

Did you try charging at 50A (.5C) when the battery is frozen to see what happen?​

Jasonoid
3 days ago
I tried charging it 50 amps when it was freezing, the voltage jumps to full 14.6v and it doesn't allow it to charge. I'll be doing more testing soon, pretty interesting results.

REPLY

3 days ago
@Jasonoid Interesting, so it may be able to tolerate low C charging rate but not at high C, so may be that is when the damage occur. Looking to the repeated test result on high C rate when frozen..

One of the regulars here did post that he tried, and battery didn't accept much current.
With voltage limited charging, starting from deeply discharged battery might have the best chance to charge at excessive rate and cause damage.

I wonder what state of charge when the 14.6V CV charge profile was applied.

 

[Bobert]

Hi,
That's interesting the BattleBorn says its OK to charge down to 23F and maybe at lower temps if charging at a low rate?
Can you say where this is on the BattleBorn site?

The battery was in his freezer for 48 hours - seems likely it had a chance to cool down to nearly freezer temp. Just as a thought experiment, if you put the same size container of water in the freezer for 48 hours would it not be a solid block of ice in 48 hours? Li batteries have a specific heat that is roughly 1/4 of water, so it would take much less heat transfer out of the battery to get it cold throughout than a block of water?
How long do you think he would have to leave it in the freezer to get it down to near freezer temp?
The low temperature charge protection sensors in batteries (like the SOK for example) have their low temp charge protection temperature sensor mounted on the outside of the cells and actually closer to the case than the cell - so, they must think that the outside of the battery temp does not lag that far behind the center of cell temperature?

It would have been nice if he had discharged at a higher rate, but 15 amps is not nothing - since my conversion van only uses about 60 amp-hrs a day. I'd be happy as a clam if I was told I could safely charge at 30 amps (two batteries) when the battery is cold - only 2 hours to restore full charge.

I didn’t get that from their web site but rather a YouTube video where charging questions were being asked of the heads of the company. The charge temp cutoff should be listed in the specs though. In answer to the temp question ice freezes at 32 but takes considerably more time to reach 2 degrees especially if it is surrounded by multiple layers fo plastic and small air gaps that could act as insulation.

 

[toms]

Just because you can’t charge a frozen cell at high C rates without reaching your high voltage setpoint - doesn’t mean you are doing any damage to that cell.

 

[GaryBIS]

Just because you can’t charge a frozen cell at high C rates without reaching your high voltage setpoint - doesn’t mean you are doing any damage to that cell.

Hi,
He did test (twice) the capacity of the battery after the cold charges and found the capacity to be the same, so, at least in that sense, there was no immediate degradation.

I guess what's bothering me is that there does not seem to be much of any data on what the actual effects of charging at low temps are. All I see are the "don't charge below 32F" statements with no explanation of what the consequences are. There are so many people using LFP batteries and a lot of us that use them at cold temps - you would think there would be more data?

Gary

 

[45North]

Good video!
And you raise an interesting question - very timely this cold January!
I understand that ev cars heat batteries before charging so it must be necessary.
So the question remains - how close can we sail to the wind?
We've been starting our cars with lead acid batteries for ages but it would be nice to take a calculated risk and upgrade to Li.

 

[Hedges]

We've been starting our cars with lead acid batteries for ages but it would be nice to take a calculated risk and upgrade to Li.

If you don't have a backup plan, you're planning to fail.
Can you push-start your car?
I have carried a backup lead-acid battery, now have a LiFePO4 jump-starter.
If you upgrade to Li, you may have the issue of battery disconnect causing electronics to blow up.

 

[Hedges]

I understand that ev cars heat batteries before charging so it must be necessary.

In particular to enable 20 minute "Supercharge"; is that at about 2C or 3C rate?

 

[Bobert]

If you don't have a backup plan, you're planning to fail.
Can you push-start your car?
I have carried a backup lead-acid battery, now have a LiFePO4 jump-starter.
If you upgrade to Li, you may have the issue of battery disconnect causing electronics to blow up.

“upgrading” to lithium for cars is presently impractical because cranking amps required to start would require a huge battery bank. The under hood temps will likely exceed the temperatures that lithium can function in without degradation Vehicle alternators are not designed for the huge amp draw that a lithium bank would need likely burning up the alternator in minutes. In short the modifications required to make standard issue lithium batteries reliable in an engine starting capacity would be prohibitively expensive and very bulky.

 

[Bud Martin]

He has " LiFePO4 jump-starter."

 

[Hedges]

I have a LiFePO4 jumpstarter suitable for modest size car engines. $89 MSRP and the size of a small lady's clutch.
Of course, it gets a rest after a few seconds operation, recharges slowly, doesn't spend its whole life under the hood.

Yes, charge regulation needs CC as well as CV or other protection so the alternator doesn't hurt itself.
Not a mindless drop-in, but with lithium costs dropping below lead, I would expect the automakers to be on board.

450 Peak Amp Portable Lithium Ion Jump Starter and Power Pack

Amazing deals on this 450A Jump Starter And Li-Ion Power Pack at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

He has " LiFePO4 jump-starter."

Yup.

 

[Bobert]

Almost all of the disadvantages of a lead acid battery are avoided by the way a engine powered car works. Almost none of the advantages of a lifepo4 battery are used in normal operation of a car. I suspect that the battery manufacturers are unlikely to spend a great deal of money reinventing lithium for cars when in 10 years electric/hybrid will likely be the norm and the market for starting batteries will be fading fast. That’s my opinion.

 

[toms]

Hi,
He did test (twice) the capacity of the battery after the cold charges and found the capacity to be the same, so, at least in that sense, there was no immediate degradation.

I guess what's bothering me is that there does not seem to be much of any data on what the actual effects of charging at low temps are. All I see are the "don't charge below 32F" statements with no explanation of what the consequences are. There are so many people using LFP batteries and a lot of us that use them at cold temps - you would think there would be more data?

Gary

There is a lot of testing going on in this area. As only low current charging takes place, and to determine degradation you need a control cell at normal temperature being charged at the same rate - none of the tests started in 2007 have been concluded yet.

There have also been vast improvements in LiFePO4 construction and chemistry since then, so i imagine it will be another 20 years before you get realistic data.

 

[jberger]

I'm not a battery engineer, but just thinking about the cell manufacturing and impacts.
The reason to worry about low temp charging is that when the electrolyte is very cold, the energy put into the cell would not be efficiently transferred across the cell. It's going to cause very localized heating and that heat promotes dendrite growth between the layers. It's the same reason you don't want to charge them when they too hot, high heat allows the layers to migrate and grow which generates the short circuits which eventually kill the cell.

High amp charging would increase the heating effect and could eventually kill the cell via the resulting shorts. Low amp charging probably doesn't promote as much damage because it can't overcome the cell and just provides a mild heating effect that gets the cell to charging acceptance faster than ambient.

What is really interesting is how the failures manifest themselves, it would seem that the shorting would cause premature failure, not just capacity loss. That's the kind of white paper I'd like to read. There is already capacity loss when the cell temp is low, but it seems like premature failure is the highest probability from low temp charging.