Charging LiFePO4 at below 32F // BAD Battleborn advice

[sajjen]

We have several sheets here at work for multiple LiFePO4 batteries and virtually all of them state that the INDUSTRY STANDARD allowable charge rate at –10°C (14°F) is 0.02C. At this low current, the charge time would stretch to over 50 hours.

BUT as i stated earlier -- At 0°C (32°F), the pack appears to be charging normally, however plating of metallic lithium usually occurs on the anode during a sub-freezing charge. This is permanent and cannot be removed with cycling. Also batteries with lithium plating are more vulnerable to failure if exposed to vibration or other stressful conditions. The worse thing you can do to a very cold LiFePO4 battery is move it around or shake it …

I'm not arguing about the fact that plating will occur if you charge at too high a rate at too low a temperature. It's a known fact, and very harmful to the cells and the damage is indeed permanent.

It is not as simple as any charge below freezing = death and any charge above freezing = fine. From a basic chemistry viewpoint, the charge rate that can be accepted is a function of the temperature. Plating can occur at high temperatures if the charge rate is high enough. Plating at low temperatures can be avoided if the charge rate is low enough.

I've also seen many cell data sheets through my work. Most of them are copies of each other. None of them have very detailed testing data.

 

[Stupid Monkey]

None of them have very detailed testing data.

And you know who has done testing? Battleborn, under their engineer CEO ....

I'm still keeping mine above 10 celcius, capacity drop off is too great below that.

 

[atatistcheff]

The basic premise of challenging a CEO of a company that literally spent his entire life on the subject of battery chemistry and saying, "Nahhh, I don't believe you" is just silly.

Agree. Also, Dr. Phares didn't say everyone should set their BMS to 25 degrees, just that this is how their battery works. Of course, with all the information we've accumulated through our advanced degrees in "data sheet reading" we probably know better - right?

 

[Dzl]

The question is - if you have to have warranty work done do they pay SHIPPING in both directions?? If not - is it really a warranty or a replacement program?

Good question, it makes a big difference if they do.

 

[ghostwriter66]

Agree. Also, Dr. Phares didn't say everyone should set their BMS to 25 degrees, just that this is how their battery works. Of course, with all the information we've accumulated through our advanced degrees in "data sheet reading" we probably know better - right?

You're 100% right -- EVERYTHING a CEO says must be true !!

And YES - for some of us -- DATASHEETs are important ...

 

[Picasso]

The death of my Batteborn 24v 50ah unit was at 28f with a charge rate of 75watts. Do that over a few days and it will never wakeup again. We can't even find a BMS that does low temp cut off correct...chances of one that can trickle charge at lower temps?

 

[ghostwriter66]

The death of my Batteborn 24v 50ah unit was at 28f with a charge rate of 75watts. Do that over a few days and it will never wakeup again. We can't even find a BMS that does low temp cut off correct...chances of one that can trickle charge at lower temps?

YEP - going to say that hitting a frozen LiFePO4 battery with 75 watts is going to cause it to self destruct (probably not the technical term- LOL) ... For our batteries here the manufacturers tell us that IF we have to charge them below Freezing we need to set our chargers to charge them between a 0.02C and 0.1C CHARGE RATE - and expect to take almost 35-50 hours to do it safely.... some of the batteries we have take a normal charge at 400 WATTS -- so if they hit 32 the charger drops to 4 watts ...

In your case it 1C was 75 watts then at Freezing you would need to charge at about 01 WATT max to be safe ...

Since BattleHorn has a warranty would be interested in seeing if they replace it -- and if so -- if they charge you for shipping either or both directions ...

 

[Dzl]

The death of my Batteborn 24v 50ah unit was at 28f with a charge rate of 75watts. Do that over a few days and it will never wakeup again. We can't even find a BMS that does low temp cut off correct...chances of one that can trickle charge at lower temps?

Well there is a difference between what is available to us DIYers and what could be designed and manufactured by/for a company like BB and sold at the prices they sell at. IDK if BB BMS's do or dont have the capability to trickle charge, but it doesn't seem impossible. And its a bit of an apples to oranges comparison to compare what is available direct-from-china to DIYers to what a company with a decent R&D and engineering budget could do.

It would be interesting to learn more about this though, and the specifics of how BB bms's operate. I suppose someone with battleborn batteries (cough, cough, @Will Prowse ) could test this for the community, taking the batteries down to near freezing, freezing, and below freezing and monitoring how the charge current is affected. Could be an expensive test though if the BMS doesn't do its job though.

 

[erik.calco]

You’re...

The Y should not be capitalized as she did not begin a sentence with it.

 

[erik.calco]

I forgot which company solved this, but they send the charging current to a heater inside the battery case until temp is above an acceptable level. That makes it completely safe to apply a charge regardless of how low the temp is.

Note also that we're talking about the temp of the cells, not ambient. The cells heat up as they are charging. So, if you heat it with a heater to an acceptable level, then apply charge to the cells, there is a good chance they can maintain temp.

The BB CEO hinted they are coming out with a new battery, and I highly suspect it does the same thing.

For DIY, we don't want a temp cutoff, we want a temp A/B switch.

 

[Supervstech]

The Y should not be capitalized as she did not begin a sentence with it.

sorry, my bad.

 

[sajjen]

And you know who has done testing? Battleborn, under their engineer CEO ....

That is exactly my point. There are not relevant test data from the cell manufacturers. Anyone building a system needs to do their own testing and decide on a cold temperature strategy.

 

[Walef]

My strategy is low temperature avoidance. Although the BMS is controlled with a low temp. sensor I'm gonig to install a temp. control unit which connects three silicone heating pads located in between the cells in order to avoid low temp condition in an isolated battery box. Aim is to avoid low temp condition and BMS cut off.

 

[silgen]

In your case it 1C was 75 watts then at Freezing you would need to charge at about 01 WATT max to be safe ...

24v 50Ah is a 1200Wh battery so 75W is 0.06C

 

[orangeminnie]

My strategy is low temperature avoidance. Although the BMS is controlled with a low temp. sensor I'm gonig to install a temp. control unit which connects three silicone heating pads located in between the cells in order to avoid low temp condition in an isolated battery box. Aim is to avoid low temp condition and BMS cut off.

3 pads for 4 batteries? If the batteries do not touch each other, where would you put the pads? Underneath? Are you concerned about overheating the surface that the pads are placed against? How to you attach the pads? If it's a cold night, would the pads be on all night, or just in the hours preceding the morning solar "wake up" time.

 

[Ped]

What the guy said was the INTERNAL TEMP at 25f (not ambient) is fine at say 20A. Not at 100A. Charging lifepo4 in cold temps is not some rock solid 32f = ZERO charge.

Its a sliding scale. The colder it is, the slower the charge needs to be. 20A is considered relatively light charge current.

The reason I suspect the internt wisdom on lifepo4 in the cold is a bit over-blown is Ive used (and used to be sponsored by) shorai racing batteries for 8 years without issue and used many times in very cold temps.

 

[orangeminnie]

My current idea is to put a 12v/12w pad underneath each BB LiFePO4 battery. There is insulating hard-foam padding around all sides of my batteries except the top. A temp sensor is attached to the + terminal on the top, driving a BMV-712, which will serve as the on/off relay controller (via a slave relay). I would turn on the pads at about +2C, and off at ??.

Note: The 15w external heating pads that BB sells for $220(!), apparently wrap around 3 sides of the battery. They are on between +1.6C to +7C, but the sensor is sandwiched between the heating pad and the battery. I surmise that this is to prevent case warpage from overheating, which they warn against.

 

[Walef]

3 pads for 4 batteries? If the batteries do not touch each other, where would you put the pads? Underneath? Are you concerned about overheating the surface that the pads are placed against? How to you attach the pads? If it's a cold night, would the pads be on all night, or just in the hours preceding the morning solar "wake up" time.

Between the cells I slip small corrugated platic sheets which provides an air insulation to protect the cell housing from exessive heat transfer when battery cells heat up during high current dis-/ charge operation. I use a slot in the plastic sheets to stick the heat pattern elements. The main purpose is that the core cell material gets not under the critical temperature range. There is no need to heat up the whole battery housing. A temp sensor is placed in between the cells to monitor the heat condition.

 

[FilterGuy]

A few questions.
* I know water freezes at 0C, but what is magic about 0C in the LiFePO chemistry?
* Is there a knife edge difference between 0C and -1C?
* Do all LiFePO4 batteries have the exact same chemistry and internal structure?
* Why do the specs on some LiFePO4 cells say it is OK to charge down to -10C?
Edit: Added the following line
* Are all the other parameters For LiFePO4 cells (Besides Ah) identical between cells and manufacturers?

This is what I am getting at: Is it possible that some LiFePO4 cells actually do charge at -10C as well as others do at 'only' 0C?

 

[FilterGuy]

And YES - for some of us -- DATASHEETs are important ...

How should I read this datasheet?


Or this data sheet


Or this data sheet