Li-Po's in the cold

[G]

If you charged them in the house and then kept them very cold, they would have become overcharged (because lipos cannot hold as much charge when they're cold so they enter an overcharged state if you significantly reduce the temperature after fully charging them).   Sorry to say it sounds like they've had it. 

If you charged them in the garage, it would be interesting to let us know, because if you charged them in the day at say 10 degrees and then they went down to say 4 degrees, I would have guessed that would be slightly damaging but not enough of a temperature variation to totally ruin them in the way you describe.

[Tim Mackey]

Russell - if you check back toward the beginning of this thread, I have covered lipos and the cold in more detail.

To sum up - do NOT charge lipos above 4.15 per cell in temperatures below 10° C. 

[Reg Tyson]

I made a container for keeping lipos warm. Leaving them in a warm car is not an option as I wander off onto the moors to fly.

 I just used a  plastic food container, the type where the lid has "clamps" to hold it shut. Cheap in most supermarkets.

This was lined with polystyrene so the lipos are fully cocooned inside. The lipos are cherged in the house, put into the box and next emerge in the middle of a crisp and cold area of high moorland. 

Seems to work O.K, it was tried out today and the lipos performed very well. I normally fly electric gliders where there is a brief burst of motor use and long periods of idling. I don't fancy this in cold weather as the lipos will get cold and stay cold. I use a small electric powered model which needs the motor running all the time. This way the lipos warm up a little and stay warm untill removed.

Temperature was somewhere around 2 degrees today and the lipos performed the same as they did in warmer weather. 

Reg

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[Russell Mexome]

Thanks for the help Guys. Garry they were charged in the garage can't be sure of the temp when I charged them, but it was certainly warmer than of late, so it would appear that I have overcharged them. I did charge them in the house when I got back from flying to do a bench test. Today I did manage to put a bit more capacity in the batts by charging them at about .5 of an amp. Will give them a test run on the bench in the mornning, thanks again. 

[Russell Mexome]

Checked them out this morning yes they have had it, only 3mins run time. lesson learned  I need to be very carefull as to how I treat my Li-Po's in future

[Reg Tyson]

Hi Eric. 

I like the idea of the car bulb and a battery to power it
I have a small 12 volt sealed battery so could give it a try.

Another method I have read about, and there are many, put a small bag of rice or wheat in the microwave, heat up and use to keep the battery container warm.

This winter is shaping up to being a really cold one so keeping batteries warm is going to be necessary.

Reg

[andy harrold]

Is it ok to field charge up to full on a cold day?

i normally store my liPo's indoors but they get charged in a cold garage. is this wise? 

and finally..... i flew a leccy glider the other day , over 20 mins flight from one climb up to 600', from what i am reading that is not good practice in the cold. i guess the air temp at 600' would have been approx -2 deg c.

[G]

Yeah, charging them in the cold and then putting them in a warmer place should be fine.  It's the other way around that can be damaging. 

Letting the lipos get cold by flying high is not inherently bad, as long as they weren't fully charged in the warmth first.  You see, lipos don't mind getting cold as long as they don't enter an overcharged state.  If you charge them chock full in the warmth, and then put them in a plane and take it up to altitude where it might be minus 2 or something, they might enter an overcharged state.  Or maybe the power you used to get them up there would have taken off enough charge for them to be fine.

Apparently some research suggests that charging them half full, then keeping them in the fridge, is a way to have them last a long time.  Can't be bothered myself...

   

[Tim Mackey]

Well actually I dont agree entirely - Fully charging them in a cold environment and then bringing them into a warmer environment will potentially allow the internal resistance to reduce, and effectively the cell also then becomes overcharged. Mr FMA  himself (  Fred Marks ) advocates NOT charging a LiPo to more than 4V per cell in cold weather, as this dramatically shortens their life to as low as 10 cycles.

The following is from another post earlier in this thread...... some time back.

The following is all “recommended” treatment, from various sources.

As we mostly know, the normal maximum permissible voltage with Li-pos is 4.2 per cell.
Below 10 degrees C that falls to 4.15V - so if you charge up to 4.2 in the warm and then let the battery get cold out on the field or when stored in a cold workshop - you effectively have an overcharged battery. EG: If they lose say  .75 volt when they are cooled, then they likely will gain .75 if they are warmed. Some say that a pack charged to 100%  should not be cooled below room temperature.  Therefore if planning to take a pack out into the very cold weather, a charge to perhaps just 90% or so of capacity is advisable.  Cells at 90% or less capacity can be safely cooled below 32F (0C).

Cell temperature during use is proportional to current draw. The pack starts the flight at a particular temperature and this rises throughout the flight.

If you have  to store them for more than a month or so,  it is also advisable to discharge them to 3.7 - 3.9 volts per cell and then put them in the fridge or freezer, - protecting from moisture. Lipo capacity drops about 10% a year at room temp but only 2% a year when discharged and cold.

If you do store cold,  then do NOT store fully charged. Remember the maximum safe voltage for a lipo decreases with lower temp, so a pack fully charged at room temp, stuck into cold storage will be "overcharged" when it has cooled down.

Storage alone at low temperature does not reduce cell life, however charging at normal rates when the cell is cold can harm the cells. The FMA CellPro charger actually senses ambient temperature and adjusts the charge  to protect the cells. See link here."
http://www.fmadirect.com/detail.htm...2193&section=45

I guess really what we are saying is that for optimum performance and longevity, if you plan to move your packs from either cold to warm, or warm to cold environments, then only charge to 4.10 V or so.

As Gary says though.... many people ( including myself sometimes ) ignore all the fussy stuff and just charge 'em up and go flying !

[G]

Thanks Timbo, that's great info - I never knew exactly how much I should undercharge them at home when going to fly in the cold.  I generally just charged them to 12.3V or so (for 3S batteries) for winter flying and I've had no problems, my lipos give good performance and seem to last a great many cycles. 

[Tim Mackey]

Yeh know what you mean Gary - sometimes it all seems just too much trouble to do it "perfectly" huh Must admit ( as I have before ) many packs of mine have been charged in the cold, full to the brim, then used and recahrged whilst still quite hot, etc etc..... and I dont keep mine in the fridge either. BUT must also say, that some have lasted pretty well, and others have most definately not - I reckon now that they are getting so much cheaper, people will tend to just charge up and go irrespective of the weather  etc.

However, I do like to at least point out the right way to treat them, and then people know what they they SHOULD  do, and of course, if one has a lot of money invested in expensive large packs, then it makes sense to look after them as best you can I guess

[andy harrold]

a good excuse for me to fly on sunday then. my batteries need running down a bit!

[Jon]

A big thanks for this thread chaps

I have read it with great interest as my pennies come from a limited source !

With Lipo cycles being estimated at just 50 times but as little as 10 times as mentioned earlier...

Not fully charging or discharging to prolong its life ...

Over charging due to the variations of our wonderful British weather.

How can we ever be sure of the so called "capacity" of any LiPos we have used once or twice!  Obviously we can only estimate its capacity once used a few times ...thus charging rates will effectively be incorrect the older and more abused the battery becomes.

Maybe a rule of thumb for charging the older or abused batteries could be suggested based on the number of cycles completed and the battery owners own estimate of abuse?

also

Would I be correct in assuming that the A123System M1 batteries (which are said to be more robust) will also be effected in the same way as the now  well loved but may be ill treated common LiPo?

Jon

[Tim Mackey]

Hi Jon. The A123 cells can be treated harder, but some of the procedures still apply, such as cold weather charge and performance - they ( and LiPo ) really like to be quite hot to work well circa 120 F or so. Also it is recommended that they only drop to 2V or so, despite the claims that they can get to 1v or even lower.

They can - but this last few ounces of juice being squeezed from them is when the most heat is generated, highest cell imbalance occurs, and IR increases.

A cell never actually loses its capacity at all, no matter how old or abused - it merely loses its ability to supply it, mainly through increasing internal resistance. To say a cell has lost some of its capactiy is akin to saying the petrol tank on your car has shrunk - clogged up fuel lines, or weak pump etc, maybe but shrunk? nah !

Incidentally, hang on to the M1s until you have actually flown 'em - then see what you think. The others I have back here are 8s, and cannot be changed to 6s - they are 2 x 4s bricks in series - as made up by BRC, and are NOT genuine A123 cells....however they do work very well now after a couple of cycles.

[Jon]

Thanks Timbo....

re "hanging on to the M1s" I'll let you know once we see the results of the flight.... I'll be in touch just as soon as I can get her in the air.

Thanks also for the tips re the care of the M1s.. 

Re the Capacity of the batteries... so if I have understood this correctly, the capacity remains unchanged  as far as the charge rate calculations go but its probably worthwhile to assume the usable capacity is some 20% less.. ie: not fully charging or discharging... 

jon

[Tim Mackey]

Yes.

[G]

Allegedly the Thunder Power 2200s I have are only 2000 even when new!  Apparently a lot of manufacturers slightly exaggerate their capacities...

[Jon]

No.... They wouldnt do that would they !  now take off the 20% and what have you really!

[Simon King]

Hi there

 

As a newbie to electrics, all this talk of charging Lipo's is making me nervous!  I have just bought a 3S 3700mA Lipo and an expensive beast it was too!  Certainly it cost more than 5 gallons of decent fuel so the thought of knackering it in possibly ten charge cycles has certainly made me prick my ears up!

 

I understand the advice about how many volts to charge it too etc. but what I am not clear about is just how do I do that?  I use a Propeak Sigma charger which charges Lipos and to complement it I added a Fusion balancer which was recommended to me.  In the past, I simply connected all the cables and balance connectors, told the charger it was a 3S battery and charged at 1C- pressed the button and off it went.  When it went beep, that was that- charged!

 

Are you suggesting that to charge to 4V per cell, I sit there and watch the charger and turn it off when I see the magic number or is there some way of programming the charger to do all that for me?

 

I hadn't realised these things were so complicated!  You don't have these problems with the old Saito!

[Peter 'Ivanna Crashalot' Savage]

my dad tried flying his blade MCX out in the cold and it just would not work

[Bruce Richards]

Simon,

 

The simple answer is to charge them and store them in a warm environment unless you intend not to use them for a month or more in which case it may be worth the trouble of under charging or partial discharging. The exact voltage is not important somewhere between 3.7v and 4.0v. You should be able to hit a voltage in this range with 3-4 checks during charging.

 

Many chargers will either let you set a sop charging voltage and many more have built in dischargers which allow you to set a stop discharging voltage.

 

I must admit I do not do any of this and have had no problems in my first year of Lipo use. Maybe I am storing up problems for the future? 

[Tim Mackey]

Simon - take a look at this here. As Bruce says, it doesnt really need to be all that complex, but the advice about storage charging, and temperatures etc is all there for people who want to make especially sure that the cells are used and maintained as best as they possibly can be - Its not absolutely necessary.

Some folk service their car religiously - others hardly bother - they both still work well enough, but one will probably last a bit longer, and maybe perform a bit better.

I also covered LiPos pretty extensively in the current mag