BMFA "The Electric Page" Lipo article

[philiusm]

Anybody read the section on lipos failing over the winter in this months BMFA News?

Apparently the author has had most of his lipos go tits up over the winter. It's not something that I've noticed particularly. One bit in the article did puzzle me. He said he'd stored the lipos at 70% charge in cool conditions. I thought lipos had to be stored pretty much discharged to about 3.4v per cell, which is way lower than 70%. I also heard that they didn't like being stored in a cold place.

Maybe that's why my lipos are still going strong and his are buggered?

What I have noticed is that the lipos that I have bought most recently are far better balanced, charged and discharged, than the older ones. I guess that's because they have improved the design/manufacture process.

Regards,

Phil M

[jboweruk]

I thought they had to be stored with 'at least' a 1 third charge. But yes cool conditions don't help certainly. It hasn't mattered with mine as all indoor helis, so been flying them since I bought them.

[Blackrat]

cold weather has a huge impact on lipo's .. went flying on Saturday, first two or three packs went fine , but then after that i felt the heli had very little power at first i thought i hadnt charged my lipo's but i was sure i had. I had taken my 'ammo' box out and left it on the floor in the cold with all my packs , they couldnt have been over 2-3 degrees C , maybe even lower.

Next day i used the packs , but this time i left them in the foot well of the car and they were fine

[Sesame]

You should not let the lipos get cold when they are at 100% charge as the cold weather can make them go over charge and damage the cells, plus the cold weather affects lipos efficiency, so they will not work as well during a flight.

If your going to use them in cold weather keep them as warm as you can, on the weekend when I was bedding in my new lipos I kept them in my usual lipo case in the car and I have to say(I know bad for the enviroment) but for the time I was there I kept turning the engine on to keep the inside temperature up(I wasnt at the field long - 3 lipos dont take long to discharge).

The cellpro charger has a cold temperature circuit on it which switches in in the cold and will only charge your lipos to 90% to protect them. Also lipos should not be stored in a discharged state I have heard different opinions and they range from 50-75% of their capacity for long term storage ie a month or more, if im using them on a regular basis say weekly I keep them topped up.

one battery people at our field seem to forget is the Tx lipo upgrades they wont think twice about leaving it on the bench in the cold weather. just one to think about

[Smoothound]

FP cells normally arrive here at 3.7v per cell

[Sao]

Yeah and they are stored in a cool shed with a tin roof and single brick walls with no cavity insulation :P

[barney]

(I know bad for the enviroment) but for the time I was there I kept turning the engine on to keep the inside temperature up

Sesame...The eco friendly solution for Lipos storage at the field is nice hot water bottle wrapped in a towel in your lipo case. Obviously it makes sense to keep the lid shut!!!... and store in your motor away from any wind/draughts. Brian

[jboweruk]

Speaking of which, what about overnight? I've always stuck mine on charge, which due to the time it takes means I only use one battery of an evening, I have to hit the sack around 11 ish, so really by the time I've flown that only gives me 3 - 3.5 hours, and my batts seem to take 2 each. Net result is (until I get another charger) 1 single flight. Is it okay to leave them overnight, maybe fly 2 then charge those 2 the following evening while I'm flying the other 2? At least I'd get 10 minutes instead of 5...

[scoobycolin]

This is an extremely interesting subject since with a Lipo costing circa £170 its important to look after it. To date Ive been charging 100% the night before and then using it the following day. I avoid storing the Lipo's in the house since Im worried they might burn the house down so they live in my cold garage.

Would I be better to just charge 50% and then store in the house?

[jboweruk]

Get a nice metal box, then if they do catch, no problemo...

[Pipistrelli]

For storage Lipos should be charged to 40-50%. This is about 3.7v per cell. Lipo's should never be fully charged in cold temperatures.

The cellpro charger can manage both the above.

Cold storage will not damage Lipo's but they should never be allowed to freeze, this will damage them.

Cold lipo's will not perform very well and may become damaged if flown. It is best to keep them close to room temperature if possible for best performance and life.

[David Drew]

I understand why freezing a cell would damage it, I understand why a cold cell would not work too well - the leccy is generated by a chemical reaction and generally reactions are slowed down by cold.

But what I do not understand is - as the chemical reaction is dependent upon temperature - why a cold cell should go over- charged in storage in cold conditions. You'd think the cell would lose voltage as the reaction is slower and then go over voltage (Over-charged) as it warmed up.

There will be an expert out there somewhere......I hope

David

[jamiem]

David, as far as i know its beacuse they loose some of their capacity, and therefore a fully charged lipo (charged in the warm) will then become over-charged when the capacity drops in the cold.

I always keep mine wrapped up at the field then in the pocket of my hoodie for 15 mins before flying just to bring the temp back up a bit more

[David Drew]

David, as far as i know its beacuse they loose some of their capacity, and therefore a fully charged lipo (charged in the warm) will then become over-charged when the capacity drops in the cold.

Makes sense Thanks...so it's all about capacity rather than voltage. Colder batt, less capacity so the leccy stuffed in there is trying to occupy less space and it can't.

Like it.

David

[trebor27]

Perhaps the author of the article is lettign his batts get cold after fully charging in a warm environment. That will push them over the edge!

Cold (not freezing) is good for storage, it reduces the speed your cells deteriorate at (shelf life is a function of %charge and storage temp... Hot and fully charged is worst, cold and "low" charge is best!)
BUT.. With low charge you have to make sure that the cells will not drop too low through self discharge... As a result a good trade-off is 50% charge and store in the cool! Certainyl charge them to lower levels if your gonna check them more regularly!

Cold batteries give out less "juice" (less va-va-voom) than warmer ones! Sometimes you can see a performance increase as your batteries are used if you start with cold batts and as they warm through use!

So if you want best performance then keep em warm, but make sure you don't let them cool down too much before you start using them as a fully charge battery (warm charged) will kill it's self when cooled due to the cells going "over-voltage/over-charge"....

So...
I have 2 lipo's... I charge em in the warm... One goes in the heli one goes in my pocket.. I wander to the field (almost next door). Fly the first batt (still warm and flying keeps it warm). Then, when flat, swap batts for the one in my pocket...

Some people are shocked I keep the batts in my pocket.. But it's a risk I have considered and personally decided, for myself, to be low enough that I'm happy doing it! (If the batt starts swelling I'm sure I'll feel it, plus if a battery is in good nick, not brand new (track record) and not abused it has no reason to swell and blow when not on charge or discharge! Unless of coarse you bend/puncture it!)