LIPO and cold

[dimon]

Hi, i want to fly in about 9 degree F temperature, so, i think to cower battery with those flexible hand hitters, or to make for it some tempProofe cover, and wondering if it's gonna work, any other suggestions ?:confused:

[Pinecone]

Over on RCG I have seen poeple who made a cover out of thin foam. The opack, once it starts working makes its own heat, so you just want to keep from loosing too much of that heat.

Keep them in your car or pocket until you hook them up to use.

[tkilwein]

In -4F they only put out ~1/3 capacity once in the air and cooled down.
I keep them in my shirt pocket inside the coat.
Have a RAYDIO Warmer for the fingers.

[agjell]

Interesting thread! I have no idea if this would work; but you could isolate the heat inside aluminum foil and newspaper. I guess I would use the foil in contact with the battery, as this will reflect the heat back, and then isolate around with newspaper. Maybe a last layer of foil on the outside of the isolation as well? Please post results if you try!

[istandalone]

i've found that if you just fold the lipo up in a few layers of newsprint, it'll keep it's warmth and you can fly just about as long as you would in 70f weather.

[CAMOMAN]

I tried my lipos for the first time in 45 degree weather this weekend and they didn't perform very well.....The esc kept going into low voltage shutoff whenever I gave it throttle.......I put one in my pocket and warmed it up and it worked well until I did some loops and fast climbs..............I guess cold and lipos don't mix to well..........It was my first experience with this and a good learning experience........I just hovered around and couldn't really get into it for it would go into low voltage cutoff.........had fun anyway..............

[Pinecone]

BTW according to the instruction sheet with my CellPor 4S that I rencetly got, you should not let fully charged packs go much below room temp. The Cellro reduces the max voltage to 4.1 volts per cell when the temp is lower than 55 degrees.

[MrMel]

BTW according to the instruction sheet with my CellPor 4S that I rencetly got, you should not let fully charged packs go much below room temp. The Cellro reduces the max voltage to 4.1 volts per cell when the temp is lower than 55 degrees.

The problem isnt taking a fully charged lipo into the cold, the problem is if you CHARGE it during the cold, thats VERY dangerous since when the pack heats up (if you move it to room temp) the voltage raises and you get over-voltage/firebomb.

Thats why you have that safety feature on the Cellpro.

[Pinecone]

Actually they have a warning about cooling a fully charged pack also.

The max safe voltage for a lipo goes down with temp.

[hamslice]

so if i keep my lipos warm until right before i fly (60 secs from truck to air) then i am fine?

i have been flying all winter last year and so far this year and have not had any issues with doing this.

the lipos stay warm until flying and keeping themselves warm. avg outside temp around 28 to 30 deg

[Pinecone]

Yes.

[Steve Rogers]

I use something like this only a little larger. So far it has worked GREAT in not only keeping packs warm but warming them up when there cold.

http://www.stacksandstacks.com/html/119963_portable-12-volt-cooler-warmer-5-liter.htm

[istandalone]

you should not let fully charged packs go much below room temp

straight from the kong power website, store a fully charged (charged at room temp i'm sure) lipo in the freezer. take out of freezer and let warm to room temp before using. so, reading that, i doubt the cold is really bad for the lipo, just don't charge/discharge in cold or really hot temps.

[Pinecone]

Realize, Kong Power and Air Thunder packs are different than other packs. That's why you can discharge them lower than other packs.

In general you don't want to store lipos fully charged. Many reports here and on other boards, of people seeing seriously degraded performance from leaving packs fully charged for extended time.

From FMA CellPro instructions:

n In Cold Weather Balancing Mode, charging automatically stops at 4.10V/cell when temperature is below 55°F to prevent cell damage.

As I understand it, at lower temps the max safe voltage is lower than when warmer. So a fully charged pack, when cooled becomes overcharged due to the change in pack characteristics.

[MrMel]

As I understand it, at lower temps the max safe voltage is lower than when warmer. So a fully charged pack, when cooled becomes overcharged due to the change in pack characteristics.

Incorrect,

A fully charged pack becomes "not full" when cooled down
I fly daily, charged in room temp, going outside (at the moment at 20F).

Its the other way around that is dangerous since you then charge to 4.2v which will raise when heated up.

However, going into the cold: A) voltage will be lower, B) Capacity will be lower
Lower the flight-time and lower the pitch is what I do during winter.

To keep it to minimum though, pre-heat the packs, I use a beach (isolated) bag + heated bottles of water among my packs.

And: Bringing back lipos from the cold (long time storage in the cold), dont run them at full first cycle, keep it "light".

Btw, AT/KP is good in the cold since you can overdischarge them, however, they are not firesafe cells so same rules apply to overvoltage as any other lipo.

[Pinecone]

Have you measured voltages going from warm to cold?

Its 40F here already, so I can't test myself. :)

I am trying to find the reference on cold and lipos. IIRC it was on the Kokam site. But there was info on one of the manufacturer sites about not allowing the cells to be cooled after charging to 4.2 volts per cell while wamer.

I did find some other interesting things.

Recommended storage temp is 40F - 70F (NOT freezing).

Discharging only 70 - 80% of capacity increase cycle life SEVERAL FOLD.

['arry 'eadspeed]

I agree with MrMel about lower temp affecting voltage and capacity .. in theory.
However, as I fly my TRex600 in the Canadian cold (a balmy +3 degC today tho) I am not seeing any noticeable reduction in flt time.
I have one of Pete Kirby's Low Volt alarms on the 600 and always fly until it starts to light up so, unless it is temp sensitive itself, my "land now" voltage is a consistent 20v.
Anyway, the recharge, after 7 or 8 mins flying around (no 3D) is still typically 3800 mAh into a TP 6s 5000 pack.

I surmise that this unreduced performance is because the 2 batts I have don't get cold in my car and they self-heat during flt. I also think, since the cold air provides more lift, that the machine needs a little less power to fly.

I will be interested to see what happens when it gets much colder ... if I fly then!

[MrMel]

If you have you packs "pre-heated" you will see less "average loss", specially if you run a governor who can mask up for lower voltage.
But peaks and how fast the batteries recover from it will be very much affected.

This starts already at temps below 70ish F and gets worse the lower you go.

Thats why I preheat my pack and lower the pitch during winter, that way flight-time stays the same.

In larger machines I fly bigger packs then friends in warmer countries, and I suspect we have about the same performance..

Pinecone, I have cells laying around, gonna measure it now and put it outside and check tomorrow morning.

[Pinecone]

Here is the statement from FMA that I was looking for:

Packs charged to 100% should not be cooled below room temperature. Cells at 90% or less capacity can be cooled below 32ºF (0ºC).

And this is the same as I saw before on the Kokam site.

IMO, the safe thing is to NOT cool fully charged packs. Your choice though, and your lipos. :)

[MrMel]

Packs charged to 100% should not be cooled below room temperature


Lol, its about 3 times a year we have above room temp outside here :rolling
So we are screwed.

[MrMel]

Checked the cell I put outside yesterday, it went from 4.035 to 4.027 when going from room temp to 30ish F.

[Pinecone]

Or just charge to 90% rather than 100%.

Many chargers have a "fast charge" option, that cuts off the charge early.

[MrMel]

Always use Fastcharge regardless, and 80% rule, preheated pack during winter.

I have 10s lipos with 285+ cycles on them now, still going as strong as new voltage wise, did a capacity check they had lost less then 9%.

And I fly all year around, my lower limit is around 15F.

[SilverFoxCPF]

Hello Terry,

I was also interested in this. I happened to be in some 8 F weather with my GPS. I brought the unit inside and measured the voltage of the Li-Ion battery. It went from 3.77 volts when cold to 4.01 volts when it warmed up to room temperature.

So, If I had charged the cell in the cold, then brought it into the warm, I would be set for a "rapid venting with flame" issue.

I am not sure if there is any issue with taking a cell charged to 4.2 volts into the cold.

Tom

[Pinecone]

Like I said, there is the warning in the Cell Pro docs, and last spring I found some stuff on the Kokam webpage about this, which said don't fully charge and then cool. I don't remember if I posted quotes here or on RCG from the Kokam site on cold and lipos.