A Battery Warmer... Really?

[Dennis Nunes]

Good evening,

Here's another article. This time it's on, of all things, a "battery warmer" for electric planes!

A battery warmer? Come on, is this a joke? Do I really need a battery warmer? Maybe, maybe not. But, you can read about why I needed one and how I built mine.

Thanks to John Thompson for posting this on their Flying Lines website at: http://flyinglines.org/nunes.battery.warmer.pdf


Enjoy,
Dennis

[John Rist]

What a great idea. Or is it cool idea!   

[realSteveSmith]

Interesting article, as always, Dennis.

I'm curious if you (or anyone else) has tested the difference in battery performance achieved by charging at the field, just prior to a flight (as apposed charging at home ahead of time). 

As a sidebar, the RC car guys preheat batteries (albeit for slightly different reasons) and there are some ready made battery warmers for sale.  I'm not sure if they would fit your flight packs as the 'standard' rc car pack is a 2s of approximately 6000mah capacity.  Link below:

https://drcproshop.com/expandable-heated-lipo-sleeve/?gQT=1

[Dennis Nunes]

I'm curious if you (or anyone else) has tested the difference in battery performance achieved by charging at the field, just prior to a flight (as apposed charging at home ahead of time). 

As a sidebar, the RC car guys preheat batteries (albeit for slightly different reasons) and there are some ready made battery warmers for sale.  I'm not sure if they would fit your flight packs as the 'standard' rc car pack is a 2s of approximately 6000mah capacity.

I have not tried charging at the field. Mainly because we don't have any power source other than my car battery. And I really don't like using my car battery as a power source.

The other thing that might come into play in charging at the field, especially on cold weather days (below 45°F), some chargers will not work if the temperatures drop below 55°F.

The R/C car battery warmer would be great if I could fit 10 Li-Ion batteries in the pouch!   

Dennis

[dave siegler]

I would not use a heater without being able to measure the core temperature of the battery   

I am working in that space (BMS and safety) and would say the effect you see is true, but you did not consider cycle life or safety.   

You give up cycle life. faster than you than capacity. without thermal monitoring, you could very easily overheat the pack and go into thermal runaway.

Heat is the enemy of batteries.  One discharge may take an hour or more to cool the pack internals.
Model airplanes bury a pack in the airplane and don't provide cooling to store them hot in an enclosed space. 

In industry, heaters are used only to charge in sub-freezing conditions.   The rest of the time cooling is the issue. 
We also have the pack instruments and have active thermal management,

So a slightly higher capacity pack is the answer. 

The RC car guys are limited on the pack rating by rule, this is dumb and not safe IMHO
The way to get the most out of a pack is to run the pack near the thermal limit.  Almost burn it down each discharge cycle.
It's far too easy to get a pack in thermal runaway. 

[Dennis Nunes]

I would not use a heater without being able to measure the core temperature of the battery   

I am working in that space (BMS and safety) and would say the effect you see is true, but you did not consider cycle life or safety.   

You give up cycle life. faster than you than capacity. without thermal monitoring, you could very easily overheat the pack and go into thermal runaway.

How would one go about measuring the core temperature of the battery or thermal monitoring in the battery packs we use?

Dennis

[Ken Culbertson]

I would not use a heater without being able to measure the core temperature of the battery   

I am working in that space (BMS and safety) and would say the effect you see is true, but you did not consider cycle life or safety.   

You give up cycle life. faster than you than capacity. without thermal monitoring, you could very easily overheat the pack and go into thermal runaway.

Heat is the enemy of batteries.  One discharge may take an hour or more to cool the pack internals.
Model airplanes bury a pack in the airplane and don't provide cooling to store them hot in an enclosed space. 

In industry, heaters are used only to charge in sub-freezing conditions.   The rest of the time cooling is the issue. 
We also have the pack instruments and have active thermal management,

So a slightly higher capacity pack is the answer. 

The RC car guys are limited on the pack rating by rule, this is dumb and not safe IMHO
The way to get the most out of a pack is to run the pack near the thermal limit.  Almost burn it down each discharge cycle.
It's far too easy to get a pack in thermal runaway. 

Dave:
What I know about battery life could fit on the head of a pin with or without dancing Angles.  I use them and I understand capacity and voltage issues just fine, but I rely totally on what I read here when it comes to how to treat them.  For years I have been storing LIPO batteries at about 35% in my refrigerator and LI-Ion charged unless I don't plan to fly for a week or so.  I recently read on an RC forum that the refrigerator is a bad idea and that a hot battery was a bad thing.  Your post implies that storing them cool (not even close to freezing) and letting them get hot in use may not be the bad thing after all.  Am I missing something?

Ken

[Paul Smith]

I have not tried charging at the field. Mainly because we don't have any power source other than my car battery. And I really don't like using my car battery as a power source.

Dennis

I have noticed a row of expensive cars with the hoods up charging Lipos at the field.  The smart electric flyer spends $100 for a dedicated lead acid charging battery and does not risk his ride to charge his toys.

[Lauri Malila]

In many classes where battery size limits the performance, LiPo-heaters have been a standard thing for years. That way you can squeeze more juice out of the battery.
They are heated to 40-50°C, not more. L

[Brett Buck]

I would not use a heater without being able to measure the core temperature of the battery   

I am working in that space (BMS and safety) and would say the effect you see is true, but you did not consider cycle life or safety.   

You give up cycle life. faster than you than capacity. without thermal monitoring, you could very easily overheat the pack and go into thermal runaway.

Heat is the enemy of batteries.  One discharge may take an hour or more to cool the pack internals.
Model airplanes bury a pack in the airplane and don't provide cooling to store them hot in an enclosed space. 

In industry, heaters are used only to charge in sub-freezing conditions.   The rest of the time cooling is the issue. 
We also have the pack instruments and have active thermal management,

So a slightly higher capacity pack is the answer. 

  I think you are missing the point a bit - the idea is to squeeze the (obscenely heavy) battery weight down to a minimum, which means running it as low as you dare, and as hot as you dare, and if it affects the durability, then so be it, they'll make more of them. Consistent operation is also a goal, you want the same (or more) capacity at 8 in the morning as you get at 3:30 in the afternoon, and the temperature might go from 50 degrees to 105 degrees.

    Dennis might be able to go to a 2.6 amp-hour battery instead of 2.8, that's an important gain.

   Its the same with a lot of things - people are also looking at how small a wire gauge you can use, to save half an ounce here or there, and technically it probably boils down to the melting point of the insulation. So, what is better, a 18 gauge Kynar wire or a 14 gauge PVC wire?

   It's a competition, people are going to push things to the breaking point (and sometimes beyond) to gain an advantage, and are willing to risk the consequences.

       Brett

[dave siegler]

  I think you are missing the point a bit - the idea is to squeeze the (obscenely heavy) battery weight down to a minimum, which means running it as low as you dare, and as hot as you dare, and if it affects the durability, then so be it, they'll make more of them. Consistent operation is also a goal, you want the same (or more) capacity at 8 in the morning as you get at 3:30 in the afternoon, and the temperature might go from 50 degrees to 105 degrees.

    Dennis might be able to go to a 2.6 amp-hour battery instead of 2.8, that's an important gain.

   Its the same with a lot of things - people are also looking at how small a wire gauge you can use, to save half an ounce here or there, and technically it probably boils down to the melting point of the insulation. So, what is better, a 18 gauge Kynar wire or a 14 gauge PVC wire?

   It's a competition, people are going to push things to the breaking point (and sometimes beyond) to gain an advantage, and are willing to risk the consequences.

       Brett

Ok sure,  but not for me. 

In a high performance situation, I would be worried about temperature cutoff.  They warm up nicely on their own. We see that all the time in power tools, they cut out for temperature before SOC limit.

In 40 years of working in power electronics, I have seen too many failures and fires.  My advice always is to use the correct wire size, use a bigger battery.  Many more safe ways to save weight. Like there is a lot of unnecessary metal on most motors.

I've seen too many stunt planes that are lightly built, slathered with paint, and a large, heavy decompressed motor on it.  Seems confusing to me. 


You can heat the pack up to 122F, you can run an even smaller pack.  Your run time and life will be way down but your capacity will be way up. 


 

[Brett Buck]

I have noticed a row of expensive cars with the hoods up charging Lipos at the field.  The smart electric flyer spends $100 for a dedicated lead acid charging battery and does not risk his ride to charge his toys.

   I note that you will run down a single car battery with a few recharges. Charging from the car lets you charge the car battery back up. Also, my charger also allows "regenerative discharge" - that is, discharging your LiPo batteries back into your car battery so you can charge it back up.

   There is a lot more power going in and out than you might think.

      Brett

[Brett Buck]

I've seen too many stunt planes that are lightly built, slathered with paint, and a large, heavy decompressed motor on it.  Seems confusing to me. 

    I am not sure where you are getting those ideas. As an example, my paint job was about 6 ounces and has a large, highly compressed motor on it. Other people have even more lightly built, and even larger and more highly compressed motors. Usually running 15 or 20% nitro.

     If you would like to understand why stunt planes are built and powered how they are - after 70+ years of experimentation by thousands of very sharp people - then you are probably in the right place.

   I have no idea if Dennis' battery heater is going to be a net positive or not. But it is at least an interesting idea, and worth a try. If it doesn't work out, then at least we have learned something.

     Brett

[Howard Rush]

They warm up nicely on their own.

I see that the Molicel P30Bs (and maybe other LiIon cells) have a voltage drop and a considerable internal resistance rise toward the end of the run.  This makes for a lot of cell heating toward the end of the run.  If I preheat the batteries, can I reduce the heat from excessive discharge and come out ahead on cell life?  Seems ironic.

Dennis, I, too, have learned stuff from Randy, although it takes longer to sink in in my case.  Hey, I have a bunch of Peltier-effect doodads, a lot of 18650 cells, and some extra coolers.  I oughta be able to make a heck of a battery warmer that's also a cooler.   

[Howard Rush]

Behold: https://www.amazon.com/Ivation-Electric-Portable-Thermoelectric-Adapter/dp/B08CX45PKD/ref=sr_1_15_sspa?crid=36CBHFKT2O59G&dib=eyJ2IjoiMSJ9.69kScP_LzpKrpeC79W2Slc-o9EkmGOuAsDQpXTh9kOcliP18Y0Y15V20eE1TDBBjboeaQDf55xZXWZa0tSTeCoMThrEfXtexYRLuXVaY2na6aRULRexdbFEv5gzfroUTqL5e7gotaN9lMifR6J8RcaEBRm3mRU24CQ-9sbb9ChAOc0FD_e9RMDfH0MI8kdi-qV5GHiGnK8ZwiWi0H_3tkCVS_fzez6VtWgrgt2_vov3SAoH2XDTN0PmCoQPSLns-CzFX2UGIdBheZf1oBaHK5bskpqEnBxk9h4PkwVmC-4s.MvJH74ZZnz9QTg7QUpT4dTVPM7NWq0VIwEXmbp-pEtE&dib_tag=se&keywords=portable+heater+and+cooler+combo+for+food+car&qid=1740729765&sprefix=car+heater-cooler%2Caps%2C182&sr=8-15-spons&ufe=app_do%3Aamzn1.fos.9fe8cbfa-bf43-43d1-a707-3f4e65a4b666&sp_csd=d2lkZ2V0TmFtZT1zcF9tdGY&psc=1#productDetails

[William DeMauro]

I've hesitated to reply here for a while now to see how this would play out. I've tested  many lipos and Lion batteries over the last few years. I've also talked to others here and compared my results with theirs. I have a test stand where I measure loads and simulate full flights loads where I can see the results in real time. I also take the temperature of the batteries both before and after and during. Just to toss some very simple results out here. I don't want to write a book and I want to keep on topic here I will say that both too cold and too hot are bad. Simply put if you start out at room temperature 70-85 degrees and have a fully charged battery 4.20 (Most chargers short charge the battery on default setting 4.17-4.19) and if you don't overload it to the point where it exceeds the manufacturers max temp in flight it will work fine. I and everyone else who are using Lion batteries have already proved this. I am mostly referring to 6 cell packs, which is what Dennis is talking about. (Yes P30B do run cooler and have a lower IR and a little more capacity than previously available and recommended Lion batteries)  For most of us a small cooler will work fine to keep them warm enough. That same cooler will also keep them from getting too hot in the summer. I don't know why anyone brings their batteries on the field in a metal ammo can, Put one out in the sun for a few hours and see how hot they get. Put a blanket or a piece of foam on top of the batteries to keep them warm. A simple hand warmer in the cooler will also keep them warm enough, they make rechargeable ones if you don't want to get the disposable ones. both can be found on the usual web sites. Thank you Dennis for the very informative article.

[spare_parts]

Lets say 6S*4V*2.5Ah = 60Wh
60Wh / 12V = 5Ah from your car battery per charge.
You should easily get 4-6 charges, unless you have a compact with a tiny battery. For my lighter needs I recently bought a 40Ah LIFe 12V, something like 13lb.

Be aware that most charging systems limit battery current to about 20A or so. 4 charges will take an hour of runtime in the car to get that 12V battery full. You'll pay for it with car battery life.

The RC car crowd has been heating batteries for a long time. They banned thermal heating so racers got smart and use high current charge/discharge cycles to heat from the inside out. There's talk of hitting 8Ah LiPo with 40A prior to the race.

[Page Peterson]

Dennis,

Thanks for the idea. I got the same bottle warmer and put in cooler with a portable USB power supply.  It was mu first time out this spring as the temps got to mid and upper 40s. Putting the used LiIon batteries in was a great use of the heat they give off.

I charged batteries right before going out and the voltage when pulled out of the cooler dropped vs freshly charged voltage, but it was less than I remember from the fall. I put back in 150 less mah than records from the October. I also ended up cutting the run time down a little for later flights since it was first day back and my arm and back appreciated the reduction.

Page

[Bill Schluckbier]

I have been flying electric for a long time, generally, in the fall, my cutoff outside temperature is about 45 degrees.  Cooler than that and my fingers start to get numb which hinders flying.  This is for R/C.  For C/L, since you are pretty much walking all of the time, my cutoff is about 40 degrees if sunny and not windy. 

When getting ready to fly in cooler weather I will bring the batteries up from the basement and let them warm up in the main living area of the house (still stored in a steel box). Overnight that brings them up to room temperature, probably around 65 degrees.  While at the field, I will lay the batteries on top of the dash hopefully exposed to the sun with the car closed up. On a sunny day, the interior of the car will be nice and comfortable and that is how I keep the batteries warm.  When getting ready for a flight I simply walk up to the car, grab a pack and go fly. I have been doing this years and it works well enough.  I fly R/C pattern as well (2x5S packs, 4000-4500 mah) and it works well for the larger packs as well.  If I do any field charging, I use my pattern packs which have been retired; they can still deliver enough power to charge the smaller C/L packs.  My charger allows for a 24v input, so I normally connect two 5S packs in parallel to power it.  Out of this, I can normally get a 6S, 2200 mah pack four times.

I try to balance battery use I to try to use the newer packs more frequently than the older ones; that means that the new packs get flown first and potentially get re-charged at the field for the last flights.  A good day of flying is generally about 8 flights; after that I really start to get sloppy.