I was out early this morning 7am to get some air time in before the family got up and running. It was about 2 degrees at the field so pretty chilly. I was quickly up and running and the first 2 batteries were fine (I assume as they came straight out of my flightbox). But while flying these 2 batteries my others were sitting on a bench in the cold. Well from the third battery on I was in trouble. Not one of the four batteries I had left to fly with had any punch in them at all. Last weekend, in warmer conditions, I was hovering with them after 5 or 6 minutes in the air, this week they wouldn't hold a hover at all, even straight off the take off, with the plane slowly tailsliding down.

I don't remember anything like this last winter. Though I wasn't really doing much 3D'ing then. I read some threads and the guys in the northern hemisphere are are using warming pads, hot watter bottles, etc to keep packs warm before flying. Has anyone got knowledge/experience with this? And if so what sort of performance drops are you noticing and are you pre-warming your packs??

Yeahh... I got the same problem too.... I was flying my Spitfire with my 2450MAH Battery with 35C Burst... But the battery just do not provide enough kicks.... sAD.... I love speed....

Common problem. Solutions range from warming pads to keeping them in your pockets. I was advised that it wasn't a good idea to have loose change or keys in there with them though.

el cheapo food/drink warmer. $29 from DSE, plugged into your car. I use mine to preheat 6S5000 & 4S 5000 packs for boats.

http://www.dse.com.au/cgi-bin/dse.st...uct/View/M4500

You beat me too it Ozzy, I have noticed if i keep mine in my inside pockets close to my body they have a lot more punch. I have a pocket system now, left pocket freshly charged, inside pocket next flight and right pocket discharged.

If you want the best performance you should get your packs to above 30 degrees and preferably up to 50 degrees. There is a lot of info on this in the high performance forum, these guys are running up to 8 kilowatts in hotliners so they know how to get the best performance from their packs! Personally I leave my car running for about 10 minutes before I fly, line up my packs along the dash vents and blast them with the heater.

Older packs would self warm because they had high internal resistance, newer packs are very low IR and hold voltage much better but don't self warm as readily unless you are pulling massive amps.

Lithium Polymer cells have a recommended sitting temperature of 25 to 30 degrees C. When their temp drops below 20 degrees they start to suffer from voltage sag, under 15 degrees it gets worse, under 10 degrees and you can damage them if you try to put them under a decent load. This is the basic factory spec on the cell structure and has been conveyed to me by a few different factories.

Basically you will kill your packs if you operate them under 10 degrees regularly and try to push them.

Another problem with high discharge rated cells is they never get a decent temp rise in many setups because they are not being run hard enough, this exacerbates the problems at very low temps.

Does this mean its good to run your cells hard enough to get them nice and warm? Will this make them last longer? I guess it's like trying to putt around in a F1 car, eventually its going to break down because its made to go hard.

No its more like dont run them below 10 degrees or they wont last very long. Basically you MUST warm them up before use if they are really cold, they perform better at the optimum temp of 25 degrees (this is purely the factory optimum temp ratings) and are supposedly safe to use as normal down to 15 degrees.

Is it the same for charging? I have found the past cupple of nights it has taken longer to charge?
PEZ

Originally Posted by BulletMaster

el cheapo food/drink warmer. $29 from DSE, plugged into your car. I use mine to preheat 6S5000 & 4S 5000 packs for boats.

http://www.dse.com.au/cgi-bin/dse.st...uct/View/M4500

Well BulletMaster thanks for the advice. I got one of these yesterday afternoon and this morning my toasty warm batteries were as punchy as ever!

Still learning

Of course, you could just move to the Gold Coast Mr K. I don't seem to have that problem very often, maybe 3 weeks out of the year

Clovus

Could you imagine that conversation....
Husband - "we should move to the Gold Coast"
Wife and kids- "Why? "
Husband- " So when i go flying my lipo's will be warm"

Ha!!! I managed to con her that my new station wagon was because the kids were getting bigger. Little does she know kids is code for planes.

Nice work!!