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Old Oct 06, 2012, 10:52 AM
A man with too many toys
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Originally Posted by t.edwards View Post
Mine spend the winter in the "crisper" drawer in my refrigerator.
That the best temperature. Inside your house is a little too warm for mal life. Freezing won’t hurt them just don’t charge and discharge frozen batteries. They get way below that during shipping in the winter with no harm.


Most important to set at half charge (3.80 to 3.85 v/cell).



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Old Oct 06, 2012, 12:29 PM
Way to many airplanes!
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Originally Posted by tacx View Post
Do you keep your I-pad, I-phone, and all the rest of your Lipo battery operated devices in the house or in the garage? People don't realize that many of the devises we use and store in our homes have Lipo batteries in them.
What some people don't realize is the fact that there's lipos that are designed to deliver little current for a long time (weeks) and lipos that are designed to deliver a huge amount of current in a very short time (RC airplanes...).

Try to short your I-Pad or cellphone batttery and you'll find that they are relatively safe because they are not designed to deliver 40amps!!!. If you're lucky, it may puff a little (and that will likely take a long time if it ever does, but it's not likely to burst in flames). Now, do it with a battery that is designed to deliver 1000watts over a short time (any recent 3S 2.2amp will do that easily). Trust me, that will be interesting.

So, not worrying about cellphone batteries is usually ok. Not worrying enough about a bunch of lipos that could pack 10 Kilowatts or more when they are stored together is up to everybody. I believe it's better to be too safe than sorry!
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Old Oct 06, 2012, 12:43 PM
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Maybe only some Iphones. There was a young lady that had one go off in her back pocket. Burned right through the denim of her pocket and fell to the ground, but not before it gave her a bad sunburn in a bad spot. Bummer, literally!!

Thank goodness it doesn't happen often.

Gord.
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Old Oct 06, 2012, 06:02 PM
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Originally Posted by RC Man View Post
That the best temperature. Inside your house is a little too warm for mal life. Freezing won’t hurt them just don’t charge and discharge frozen batteries. They get way below that during shipping in the winter with no harm.
Well, freezing a Li cell will indeed kill it. HOWEVER, as was pointed out earlier, the freezing point of a Li cell and water are quite different.

I do not care to bother looking up the freezing point of a Li cell, but it is quite a bit down from 0°C (32°F). For example, the Nissan LEAF Li battery does not get protective heat until -20°C (-4°F).

Bill
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Old Oct 06, 2012, 08:14 PM
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WOW, 10 kilowatts.

It sounds to me like Lipos are so dangerous they should be regulated or ban by the govorrnment.
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Old Oct 06, 2012, 10:26 PM
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Originally Posted by desertstalker View Post
The freezing point of water and the freezing point of a Li Battery are not the same, needs to be quite a bit colder for a LiPo. But if you freeze them there is a good chance crystals will pierce the membrane that separates anode and cathode, then when they warm up again you have a short.

Usually nothing dangerous happens, but the lipo will be toast. AFAIK this is around -15-20C.
Sorry, still not convinced.
I have heard that one way to return dead cells back to some semblance of life is to put them in the freezer for several days, then allow then to return to ambient temps and recharge. That too needs verification. The logic is similar to what you are saying that crystals form breaking through whatever caused the internal resistance.
As far as creating a short is concerned, it can't work both ways now, can it?

Still need some reliable reference to indicate what actually happens when a LiPO cell is exposed to very low temps - that is from the range of -10 to -40 F.
How does low temps, what some are calling "freezing" create "crystals" in LiPo cells. The word "freezing" is inappropriate here, by the way.

As far as I'm concerned, this is not only a myth created through misunderstanding and reinterpretation of comments heard or read, but it also, if there is any truth to it, is something that need not be of concern because very few people will encounter temperatures in the range of this discussion, in particular, storing LiPos at those temperatures.

Still have an open mind though and would like to hear of information that is reliable and accurate that indicates permanent LiPo damage at low temperatures.
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Old Oct 06, 2012, 10:29 PM
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Originally Posted by ebill3 View Post
Well, freezing a Li cell will indeed kill it. HOWEVER, as was pointed out earlier, the freezing point of a Li cell and water are quite different.

I do not care to bother looking up the freezing point of a Li cell, but it is quite a bit down from 0°C (32°F). For example, the Nissan LEAF Li battery does not get protective heat until -20°C (-4°F).

Bill
If you have no reliable reference then dogmatically repeating this is not doing any service.

Only water "freezes", LiPos don't - but there could be changes in the cell structure - that is something that we need to know and understand and interpret with some degree of intelligence.
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Old Oct 07, 2012, 12:37 AM
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Only water "freezes", LiPos don't - but there could be changes in the cell structure - that is something that we need to know and understand and interpret with some degree of intelligence.
Freezing is the common term for a substance that is normally a liquid transitioning to a solid. Petrol can freeze, so can alcohol etc.

The electrolyte in a LiPo is a liquid. This can become a solid (freeze) if the temp is low enough, a freezer (-18C) is NOT cold enough. If you allow the electrolyte in a Li Cell to solidify you will damage the membrane separating the anode and cathode, best case a slow internal discharge, worst case you allow the anode and cathode to touch killing the cell completely.

Placing LiPos in a freezer is fine, as long as you let them warm up before charging or discharging. Keep in mind it will take a considerable amount of time for the middle of a larger pack to warm up.
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Old Oct 07, 2012, 12:54 AM
IFLYSLOW
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Lipo batteries

I charge all my lipos up to full charge, put them on a shelf in my warm hobby room and leave them there all winter. That is unless I take them out and go flying. I never store them in a cold garage or a freezer. I have NEVER had one problem at all.

I have flown the same lipos now for over five years and not one problem has ever occured.

One year I decided to discharge them down to the half way mark. That was a bad move so now I charge them up and that is the way they stay.

You can do it your way and I will do it my way. Its your call. Why would they say to keep the batteries warm before flying. There must be something to that. You like the warmth of your home so why not put the lipos where they will be warm.

Cheers,

Bob
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Old Oct 07, 2012, 03:39 AM
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Bob,

LiPo batteries will deliver more performance when they are warm so that is why You would have them preferably at room temperature or handwarm when putting them in the plane for usage. If flying in winter when using them outdoor to keep the LiPo little warm to get better performance.

But for storage their life will be prolonged a little better if they are stored cooler (like down to 0 deg Celsius /32F) and at about 50-60% if capacity. At least to storage charge LiPo when not in use is a good practice.
But as You say, we can do it our own way. I just storage charge and store them in room temperature (18-20 deg Celsius). I leave LiPo fully charge only max 1-2 days when I have planned to go flying next day (or next).

/Bo
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Old Oct 07, 2012, 04:50 AM
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All I can say is, it gets down to 0 F at times and they still work fine.
By the way, The Nissan Leaf uses li-ion batts, not lipos. different chemistry.

Gord.
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Old Oct 07, 2012, 01:53 PM
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Originally Posted by midnite View Post
Only water "freezes", LiPos don't - but there could be changes in the cell structure - that is something that we need to know and understand and interpret with some degree of intelligence.
You believe only water freezes? And you want some intelligent responses?
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Old Oct 07, 2012, 10:41 PM
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Originally Posted by desertstalker View Post
Freezing is the common term for a substance that is normally a liquid transitioning to a solid. Petrol can freeze, so can alcohol etc.

The electrolyte in a LiPo is a liquid. This can become a solid (freeze) if the temp is low enough, a freezer (-18C) is NOT cold enough. If you allow the electrolyte in a Li Cell to solidify you will damage the membrane separating the anode and cathode, best case a slow internal discharge, worst case you allow the anode and cathode to touch killing the cell completely.

Placing LiPos in a freezer is fine, as long as you let them warm up before charging or discharging. Keep in mind it will take a considerable amount of time for the middle of a larger pack to warm up.
Yes, thanks. I misspoke saying that only water freezes - what I actually meant to say was that only liquid freezes. Lithium-ion batteries may have a liquid electrolyte but LiPo batteries do not - they use a dry electrolyte polymer that resembles a thin plastic film which is laminated between the anode and cathode. That is why they call them Lithium (ion) Polymer batteries. However, apparently the batteries used for RC are a hybrid type and do contain a gell-like electrolyte and although not a "liquid" per se, I suppose that gel can solidify in extreme cold.
The gelled electrolyte allows the battery to be conductive at moderate temperatures.

Here's some info on Lithium batteries. - http://batteryuniversity.com/learn/a...stance_or_hype

The precaution telling people to not "freeze" their batteries is not providing sufficient information which is the reason for my posts on the subject. The temperatures at which that gel would actually freeze solid would be lower than most people would ever encounter - it certainly won't even happen storing batteries in the freezer. Essentially, it is a non-issue as far as I'm concerned.

So, exactly at what temperature would that gel "freeze" solid?
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Old Oct 07, 2012, 11:17 PM
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Originally Posted by midnite View Post
However, apparently the batteries used for RC are a hybrid type and do contain a gell-like electrolyte and although not a "liquid" per se, I suppose that gel can solidify in extreme cold.
The gelled electrolyte allows the battery to be conductive at moderate temperatures.
Correct, it should also be noted that modern "Li Ion" cells use the same construction, as this design is safer and provides more capacity compared to the older liquid electrolyte cells.

The temp at which the gel (highly viscous liquid) freezes is rather low, and unlikely to be reached. If I had to guess I would say -30-40C (a quick google didnt turn up much, but I have some mobile phone packs that rate storage temps down to -20C).
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Old Oct 08, 2012, 05:47 AM
A man with too many toys
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What is the freezing temperature of lithium?
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