Cold Weather LiPo Behavior

[Hands0n]

This morning I went out into the usual field for a spot of FPV which I';ve not done for a while.  The weekend has been dry and calm so I had both mornings out. I took the youngest lad (19) for his first FPV, he used my home-built 3in LCD monitor slaved from the FatShark googles.  It was good.

Today the temperature is quoted as being between 8c - 3c, and to be honest it felt more towards the latter as we stood out there. And the difference in battery performance between yesterday and today was also quite marked. 

I have had two different 2200mAh LiPo types with me, both from Turnigy.  I had a pair of 20-30C (blue) and a pair of 45-90C NanoTech. All were fully charged to 4.20v per cell.

Today, on the 20-30C batteries the LiPo alarm, set for 3.5v per cell, was sounding off almost immediately after lift-off until a stable hover was achieved. Then would further sound off if any significant movement was induced.  I brought the aircraft in to land so I could see what the battery voltage was and the alarm [now silent] showed 4.1v.  So, under load the voltage was dropping to or below the 3.5v that the alarm is set for.   Yesterday that wasn';t happening, but it was degrees warmer.

The NanoTech, on the other hand, rated at 45-90C performed as normal, the voltage remaining stable throughout the entire flight, returning some six minutes of fly time, exactly as they did the previous day.

What to make of all this?
Evidently, the lower C rated LiPo, while cheaper, perform suboptimally in cold conditions, experiencing voltage drop under load greater than the NanoTech units. 

Flight times with the 20-30C LiPo was about a minute less than the previous day, mostly that was me chickening out and bringing the aircraft back to land sooner as the audio alarm had become persistent, not just under load.

I feel less confident about the 20-30C in this weather and will probably pick up two more NanoTech 45-90C LiPo to use in this winter.

[guest325]

Hi Danny, yes it';s quite normal to see this sort of thing - best thing to do is keep them warm for a good couple of hours before you set off and keep them in a cool (warm) box - some of the guys at our club put them in their pockets.... not me....no way!
p.s I wouldn';t fall for the Nanotech speil it';s the C rating that matters.

[Hands0n]

Thanks.  I need to find some thermal storage for the batteries. Kept them today in the LiPo bag but it has no thermal properties.

Typically I go by the amount of time I';ve flown, coupled with the LiPo alarm just for good measure. Since adopting this strategy I';ve had no unscheduled landings ::) 

With the NanoTech I was going for the higher C rating even though I don';t typically pull too much current from my builds.  These two were on a good offer so I jumped in.  Thinking is that I';ll need to look out for better than 20-30C if I';m going to fly throughout Winter ... which I am 

[flybywire]

I went out today with 3 5000 4 cell Turnigy';s rated at 20-30c.  I always set my transmitter timer for 10 mins, and monitor the voltage onboard with the osd mini (in this case).
Now, my lipo';s are a couple of years old now, and I do notice the voltage drop increases markedly to what it did when new-ish.  Having said that, even in the cold, they all still did 10 mins easily.  After about two mins of flying, my voltage level drops to around 14 when under load, and 14.5 hovering.  Innitialy I was worried about that, but I kept flying and relied upon my Tx timer, and sure enough, all was ok.  I';m guessing (as the lipo';s are currently charging) that I sucked them out to 80%, maybe slightly more, which is fine.

As I';ve not been doing this Multi lark for too long, I';m a little unsure as to when to ';gracefully'; retire a lipo.  I';ve had one throw a duff cell (ZIppy Flightmax), but how do others know when they';re ready for the knackers yard?  Or is it obvious? i.e you go to fly one day and it just won';t lift?


Andy

[guest325]

I';m using 30-40C blues for my 450, no appreciable difference treated how I do this weather except maybe not quite as sharp when I open the tap full!
http://www.hobbyking.com/hobbyking/store/__9394__Turnigy_2200mAh_3S_30C_Lipo_Pack.html
These are 30C but 40 peak - never had any problems with them!

[fruitsalad]

i face this problem most times as i night fly a lot.....
my mad method of keeping my lipos warm,is 2 hot water bottles wrapped in towels with my lipos in between them..
keeps them lovely and warm.. ::)

[nub]

hmmm interesting maybe that';s why i never really see any difference in lipo performance in the colder weather because of the higher C rating that i usually use.

learn something new everyday

[Hands0n]

I';m using 30-40C blues for my 450, no appreciable difference treated how I do this weather except maybe not quite as sharp when I open the tap full!
http://www.hobbyking.com/hobbyking/store/__9394__Turnigy_2200mAh_3S_30C_Lipo_Pack.html
These are 30C but 40 peak - never had any problems with them!

Thats interesting - all of my Turnigy "Blues" are 20-30 unlike yours being 30-40.  Possibly explains why I got them so cheap.  Should probably look for a minimum of 30C or better