Lipo and cold

Just received this today from a friend, I thought its worth a read..

>>>Just a note to let you know of possible problem with LiPo batteries
>>> failing in the cold, if you want to forward it.
>>>
>>> Lipo's and the cold;
>>> Over the last week I an aware of 3 incidents pointing towards Lipo
>>> batteries failing in the cold, I had a 700 with total power failure last
>>> Monday, broke skids and bent boom, I did not point directly towards the
>>> battery at the time and thought switch regulator or receiver but Dave
>>> Chatburn had a similar crash at weekend using a LiPo and Align 3 in 1
>>> with a battery monitor, the monitor was showing full power at the start
>>> of the flight, machine crashed and monitor was showing red, battery would
>>>
>>> not take a charge, recovered within 24 hours of being indoors to showing
>>> full power, Dave Fisher has had a similar problem that has badly damaged
>>> a machine, battery was showing full charge before a short flight, nothing
>>>
>>> after the crash then recovered once indoors, Lipo's should be ok to use
>>> down to -5, be aware.
>>> Mark Bateman
>>> Model Flight Training
> This is an effect that is displayed by all chemistries of cell, the only
> difference is the degree of differing performance. Lithium chemistries
> appear to suffer to a greater extent than traditional NiCad/NiMh in cold
> weather but all cell types will exhibit significant voltage/capacity drop at
> the current, unusually low temperatures in the Woodford area. The cold
> causes the cell(s) to appear full and normal, however the charge and current
> delivery capabilities of the cells are significantly reduced - known safe
> flight times in warmer temperatures cannot and should not be relied upon.
> Equally, there is usually a more rapid drop in voltage at the end of the
> flight so a prompt landing is essential to avoid cell damage. LiPos can
> safely be used at much lower ambient temperatures than we have experienced
> here (they are used on high altitude ski photo shoots with AP helis in the
> Rocky Mountains for example) but the packs should be warmed before use and
> insulated against the cold once in the heli.
>
> The other important thing to be aware of is that the voltage 'drop' in cold
> weather has implications for field-charging at low temperatures. If a
> Lithium pack is fully charged or topped-up whilst cold, the peak detection
> on the charger will cut the charge at the nominal full voltage for the
> chemistry (4.2v/cell for LiPo, 3.6v for LiFePO4). If the pack is then taken
> into a warm house or workshop, the increase in temperature will cause the
> cell voltage to 'recover' and result in an over-charged state on a LiPo.
> This could damage the pack and render it useless without any immediately
> obvious cause.
>
> Steps to help:
>
> Check all your battery voltages frequently until you have an idea of the
> discharge curve for the new ambient temperature. If in doubt LAND - you can
> always take off again after a quick voltage check. If in doubt change the
> pack for a fresh one.
>
> Be aware of charging Lithium cells in the cold when recharging at the field.
> Use a 'storage charge' setting on the charger or leave the packs discharged
> before moving the pack back indoors to be safe. It goes without saying that
> the cells are fine if fully charged then used when still at the colder
> temperature, accepting the above.
>
> Don't forget your TX!!! Tx batteries are just as vulnerable to cold so keep
> an eye on those too.
>
> Tx mits really help your fingers (and Tx battery!) in this weather. Numb
> thumbs can be banished to a thing of the past! Highly recommended for snowy
> flying.
>
> Hope that lot helps,

Weird, my flight times were reduced by about a couple of mins when I was outside with my CP3 but no drastic failure for me

Sam, the guys detailed above are all using high perfomance servos in high drain aplications as RX batterys I wouldnt expect you to have the same probs with the CP just as you say slightly shorter flight times

Lipos work best when warm so keep um in your pocket untill your ready to fly, the problems above could be down to many things but lets not forget we have been in the minus` for several days now so a heli sat on the ground for a few hours at a feild then suddenly asked to pull high amps is certainly asking alot IMO

M

Heh

I have plenty of dodgy Lipo's anybody with a Heli can have them, I looks like a good way to reduce the amount of these horrible little things.

HAHAHA

So did your lipo give up or you thumbs ?

Zaidy wrote:HAHAHA

So did your lipo give up or you thumbs ?

My thumbs or brain aren't capable of heli flight, I thought it was one of yours

You would know if it was one of mine, because it will be in more bits that that..

And Dave's would be lay next to it

Can I just add a little to the discussion too.
This is an extract from an article of mine a while back. The full piece is in the RCME mag, and on the website, but you need to be a subscriber to access it, so I will just clip this bit out otherwise this thread will get rather long!

STORAGE
Lithium batteries are best stored in a dry cold environment of between 0° and 15° C. There is some evidence that storing them in the fridge, at just above freezing will considerably improve their lifespan and capacity retention but they must be protected from moisture. Fully charging them in a cold environment is not good practice, and if the temperature is lower than 10° C then charge to no more than 4.15V per cell. This is because the internal resistance of the cell reduces as it warms up and voltage then increases, so if fully charged to 4.2V when cold, and then brought into a warmer environment, the voltage will effectively rise slightly, and could get higher than 4.2V which is very bad for the cells.

Some of the more intelligent chargers now have inbuilt ambient temperature sensing, and will automatically stop charging at a reduced level when a low temperature is detected. If charging cold and planning to take the packs out into a cold winter flying session, then only charge to around 90% capacity.

Li-Po batteries in common with most cell types perform poorly when cold, and will work a lot better if their temperature is around 30° to 40° or so. Remember also that internal temperatures will rise considerably during use, especially at high discharge rates, so allow adequate cooling to ensure they don't get too hot. As with any battery, they shouldn't be left in places that are subject to high temperatures such as car dashboards or rear parcel shelves, if cell temperature is allowed to get to 70° or more, then they will probably suffer permanent damage.

I normally top up my packs at ambient temperature, just prior to leaving for the field, and then transport them in an insulated carry pouch that my wife very cleverly made from an old quilted blanket, only fitting them just prior to flight. Good quality packs, properly treated could deliver 200+ cycles, but if you always store your batteries at high room temperatures and charged to full capacity then expect to see a loss of capacity of up to 40% a year, and if abused through charging whilst still hot, and constantly pushed to maximum C rate etc, then be prepared for a lifespan of maybe only 50 - 60 cycles - if you're lucky!