Originally Posted by hard line

I don't know how the results compare to a purpose-built bag but I fill three plastic soda bottles with hot (140F) tap water and lay them in the bottom of a small (6-pack) foam cooler. Then fold in a towel and carry the batteries on top of that in a couple ziplocks.. Seems to keep them warm, but not hot.

good lotech setup

but don't worry about heating hot as you like, up to the point you can't handle them no problem

and especially beneficial for longevity despite fast charge rates.

Opposite for storage, cooler the better

I prefer to cook my batteries sous vide.



=P

Originally Posted by prototype3a

I prefer to cook my batteries sous vide.



=P

True confession...... When I was testing my batteries resistance @ specific temps -- I double vacuum sealed them and used the sous vide to establish their temps. Worked fantastic and gave me precise control over their temps.

Thank God for Google, I wasn't sure if "sous vide" meant you's guys had fallen off the deep end

Joe

Really? Sous vide controllers have been very widely used for a long time now, and not just for cooking.

A very cost-effective method of providing steady-state temps via hydronics for all kinds of DIY stuff.

I assumed all battery testing would use at least something similar, given that so many reactions vary widely with changes in temperature.

Originally Posted by scott page

True confession...... When I was testing my batteries resistance @ specific temps -- I double vacuum sealed them and used the sous vide to establish their temps. Worked fantastic and gave me precise control over their temps.

I have to admit that I was sitting here wondering how well a sous vide unit, a foam cooler and some ziplock bags would work to keep packs warm in cold weather.

Originally Posted by prototype3a

I have to admit that I was sitting here wondering how well a sous vide unit, a foam cooler and some ziplock bags would work to keep packs warm in cold weather.

Foam box (cooler) and bottles of hot (~130 - 140 F) water (like coke bottles) would probably give you the best thermal inertia.

However I'm pretty nervous about water and batteries (even in bottles) so I use HotSnapz reusable hand warmers. They are basically just a heavy duty bag of supersaturated solution of Sodium Acetate with a metal activator disk. When you snap the metal activator disk the solution has a seed crystal so has an exothermic crystallization change of state. Temps of the warmer stay below 130F so are perfect for use with Lipos. To "recharge" the hotsnapz you just put them in boiling water for 15 to 20 minutes - the crystals change back to supersaturated state and you allow to cool prior to re-use.

I'll put a link to those I use -- it's not an affiliate link - just so you can see more information. https://www.amazon.com/gp/product/B004CUZQT4

Originally Posted by MCSGUY

Heating packs not only can improve life expectancy it adds flight time (+10% 95F vs. 59F):
https://www.rcgroups.com/forums/show...&postcount=198

Yep, just bought a couple of these: https://hobbyking.com/en_us/turnigy-...ag-12v-dc.html
Who says you can't teach an old dog new tricks?

Joe

I am a regular and enthusiastic reader of this thread, but never actually write anything. But maybe I can contribute something constructive as an exception.
I live in Switzerland and the warm season in this country is unfortunately very short.
Some ambitious RC pilots in my environment have built themselves a "Heatbox" for the LiPO's of their electric models.

The electronic components for such a "Heatbox" can be bought at Hadi-RC (a German company) and as far as I know, they also ship worldwide:
http://www.hadi-rc.de/epages/es12512...2FAkkuZubehoer

A great, picture-rich example for the diy construction of such a heating case can be seen under this link:
https://www.mgthun.ch/Projekte/LiPoH...fer/index.html


Since the flying season is coming to an end in many parts of the world and the building season has begun, one or the other could consider to build a "Heatbox" to support the well-being of their LiPo's and extend their flying season.....

Mike

Impressive!

Originally Posted by hard line

I don't know how the results compare to a purpose-built bag but I fill three plastic soda bottles with hot (140F) tap water and lay them in the bottom of a small (6-pack) foam cooler. Then fold in a towel and carry the batteries on top of that in a couple ziplocks.. Seems to keep them warm, but not hot.

Originally Posted by John61CT

good lotech setup

Yeah, but I didn't see it as high tech vs low tech. I thought of it as being free. I've got the cooler and ziplocks, and the bottles would have been trash.

Free for something that works is right-priced. And yes...I'm cheap.

Thanks Mike! I have to agree with JamesK, that’s impressive.

Joe

Originally Posted by scott page

Foam box (cooler) and bottles of hot (~130 - 140 F) water (like coke bottles) would probably give you the best thermal inertia.

However I'm pretty nervous about water and batteries (even in bottles) so I use HotSnapz reusable hand warmers. They are basically just a heavy duty bag of supersaturated solution of Sodium Acetate with a metal activator disk. When you snap the metal activator disk the solution has a seed crystal so has an exothermic crystallization change of state. Temps of the warmer stay below 130F so are perfect for use with Lipos. To "recharge" the hotsnapz you just put them in boiling water for 15 to 20 minutes - the crystals change back to supersaturated state and you allow to cool prior to re-use.

I'll put a link to those I use -- it's not an affiliate link - just so you can see more information. https://www.amazon.com/gp/product/B004CUZQT4

I work with 6s22k packs a lot so I was thinking that the higher thermal conductivity of having the packs essentially in direct contact with the water would speed the process for the massive packs. For smaller packs, I'm sure air works fine as long as there is a fan in there to move the air a bit.

A few years ago, I had a project that required flying in cold temps and we kept the packs in a cooler with some sort of "hand warmers" and then we added some foam boxes to the aircraft to help the packs stay warm once installed. In our application, the heat from discharge was enough to keep the packs warm in flight with the thin insulation boxes.

About the significance of flying with warm batteries vs cold batteries. Seems clear that it affects IR, max outputs and maybe flight duration. Those things may be more critical on some planes than others.

If I'm going out on a cold morning with an easy flier...expect to use a lot of light throttle...and don't really care to get every last minute out of the battery -- then how important is pre-warming to me?

If I heat up my battery and use the extra mAh that it provides and then allow my batts to cool without charging will there be bad effects? I charge my pack relatively quick so for me this is mostly theoretical.
Ex:
5000mAh pack at 60 degrees and depleted to 3.7V using 3600mAh. Then, allowed to sit for a day and volts climb to 3.8.
compared to:
5000mAh pack heated to 95 degrees and depleted to 3.7V using 4000mAh. Then, allowed to sit and cool for a day and volts do what?
My numbers are just off the top of my head, but the question i am asking is obvious, does temp change effect voltage, specifically voltage recovery.

I don't believe it does for any practical amount. If it did, we would be reporting voltage change dew to storage temp. Also, the mAh difference is actually used in the batt at discharged as heat do to higher internal resistance because of starting temp. So both packs used the same mAh in total, one just used 400mAh more as heat. I just want to confirm my suspicions.

A similar, but not identical, question could be asked about possible energy in at charging do to temp.

Thanks,
Scott

Originally Posted by hard line

Seems clear that it affects IR, max outputs and maybe flight duration. Those things may be more critical on some planes than others.



If I'm going out on a cold morning with an easy flier...expect to use a lot of light throttle...and don't really care to get every last minute out of the battery -- then how important is pre-warming to me?

How long is a piece of string?

Like saying the C-rate " ismore critical on some planes than others"

If you can fly at 20% of your usual current rate. . .

Depends how cold, but it is not a subtle change.