Lithium Polymer (LiPo) Battery Safety

[dangaras]

This article was shamelessly stolen from RCG (edited for 2015/2016). It is very well organized.

Treat LiPo batteries as if they were gasoline..

LiPo disposal video worth watching:

https://www.youtube.com/watch?v=E0dBCeOPw4c


Here are a few MANDATORY guidelines for charging/using LiPos (Lithium Polymer Batteries).


1. Use only a LiPo charger approved for lithium batteries. The charger may be designed for Li-Ion or Li-Poly. Both batteries are charged in exactly the same. Some older cell phone chargers may charge the batteries .1 volt too low (4.1 vs 4.2), but that will not harm the battery. However, inexpensive lithium chargers are widely available and the use of cellphone chargers is highly discouraged.

2. Make certain that the correct cell count is set on your charger. Watch the charger very closely for the first few minutes to ensure that the correct cell count continues to be displayed. If you don't know how to do that, get a charger that you do know how or don't charge the batteries.

3. Use the Taps and BALANCE CHARGE the packs as a general preference. Before you charge a new Lithium pack, check the voltage of each cell individually. Then do this after every tenth cycle there after. This is absolutely critical in that an unbalanced pack can explode while charging even if the correct cell count is chosen. If the cells are not within 0.1 volts of each other then charge each cell individually to 4.2 volts so that they are all equal. If after every discharge the pack is unbalanced you have a faulty cell and that pack must be replaced.
Taps are provided on all new lithium packs(of more than 1 cell). Taps give you the ability to check individual cell voltages and charge one cell at a time. Make sure and get the appropriate connector to go into your taps. Don't try to stick you volt meter probes in the taps to measure voltage. They could slip and short your cells. Don't try to charge more than one cell at a time from the taps. Unless you have an isolated ground charging system, you'll short your batteries out. Refer to your individual cell maker for tap pin-outs.

4. NEVER charge the batteries unattended. This is the number one reason for houses and cars being burned to a crisp by lithium fires.

5. Use a safe surface to charge your batteries on so that if they burst into flame no damage will occur. Placing them inside LiPo bags only slows down the potential exit of flammable material. Use LiPo bags in conjunction with vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, tiled floors are all good options. LiPos spit hot material and that is what causes the fire. The LiPo battery material typically lands on flammable material (couch, desk, bed, wood floor, curtains, drywall, model, liquor cabinet) and the conflagration continues from there...


6. DO NOT CHARGE AT MORE THAN 1C unless specifically authorized by the pack vendor. Many a fire in home are caused because of violating this rule. Today's highest discharge batteries can supposedly be safely charged at greater than 1C, however so far in all cases doing so shortens the life of the pack. Better to buy 3 packs than to try to charge 1 pack 3 times quickly. This may change in the future but as of Winter 2015 1C is still the recommended charge rate.

7. DO NOT puncture the cell, ever. If a cell balloons quickly place it in a fire safe place, especially if you were charging it when it ballooned. After you have let the cell sit in the fire safe place for at least 2 hours. Discharge the cell/pack slowly. This can be done by wiring a 40W light bulb of appropriate voltage (higher is voltage is ok, lower voltage is no) up to your batteries connector type and attaching the bulb to the battery or filling a plastic bucket with salt water and immersing the battery for 24 - 48 hours. Wait until the light is completely off, or 24 hours has elapsed then check the cell voltages before you throw the battery away. They are regular garbage compatible.

8. If you crash with your lithium cells they may be damaged such that they are shorted inside. The cells may look just fine. If you crash in ANY way carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. Several fires have been caused by damaged cells being thrown in the car and then the cells catch fire later and destroys the car completely.

9. Charge your batteries in a open ventilated area. If a battery does rupture or explode hazardous fumes and material will spew from the battery.

10. Keep a bucket of sand nearby when you are flying or charging batteries. This is a cost effective way to extinguish fires. This is very cheap and effective. Insurance or burning models and personal property, not so much.

11. It can happen to you, do not think to yourself that "it won't happen to me" as soon as you do that it you'll be trying to rescue your kids from your burning house or car. I'm very serious about this.

Now that we have covered that important topic let's move on to lighter matters:

2. Lithium What?
Lithium Polymer batteries are used in many electronic devices. Cell Phone, Laptops, PDA's, Hearing Aids just to name a few. Most, if not all, lithium polymer batteries are not designed for RC use, we use them in different applications than they were designed for. They are similar to Lithium Ion batteries in that they each have a nominal voltage of 3.6 volts, but dissimilar in that they do not have a hard metal casing but rather a flexible material encloses the chemicals inside. The "normal" lithium polymer batteries are thin rectangle shapes with two tabs on the top one positive one negative. The reason we use Lithium cells is that they are significantly lighter than comparable NiCad or NiMH batteries, which makes our planes fly longer and better.

3. Voltage and Cell Count:
LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.

If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.

4. 10C from 3S4P? Naming conventions explained.
How fast a battery can discharge is it's maximum current capacity. Current is generally rated in C's for the battery. C is how long it takes to discharge the battery in fractions of an hour. For instance 1 C discharges the battery in 1/1 hours or 1 hour. 2 C discharges the battery in ½ or half an hour. All RC batteries are rated in milli Amp hours. If a battery is rated at 2000 mAh and you discharge it at 2000mA (or 2 amps, 1 amp = 1000mA) it will be completely discharged in one hour. The C rating of the battery is thus based on its capacity. A 2000mAh cell discharged a 2 amps is being discharged at 1C (2000mA x 1), a 2000mAh cell discharged at 6 amps is being discharged at 3C( 2000mA x 3).

All batteries have limitations on how fast they can discharge. Because of this many LiPoly batteries are put in parallel to increase the current capacity of the battery pack. When 2 batteries are wired positive to positive and negative to negative they become like one battery with double the capacity. If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell. This 4000mAh cell has the same C rating as the original 2000mAh cells did. Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPoly batteries at higher currents than single cells could produce.

The naming convention that allows you to decipher how many cells are in parallel and how many are in series is the XSXP method. The number in front of the S represents the number of series cells in the pack so 3S means it's a 3 cell pack. The number in front of P means the number of cells in parallel. So a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P ).

5. Which battery should you buy?
With so many choices out there it is difficult to decipher what is marketing hype, what is brand
loyalty, and what is outright lies. Battery manufacturers are constantly trying to one up one another. While capitalism can drive prices down, it also can give cause to false claims about products.

One great way to find out what the best battery is, is to look at graphs of the batteries performance. Looking at how low the voltage of the cell drops at various amperages will give you a metric to compare that battery to similar size/weight batteries.

If graphs aren't your thing then simply look at what other people are using in successful setups that are similar to your application. If a lot of people are reporting long flight times and lots of power from airplane X, with power system Y, and battery Z and you do the same, then if your setup is similar the same battery will probably work well for you.

It pays to learn something about Watts, Volts, and Amps. Understanding these concepts is beyond the scope of this document, but can serve you well in not only figuring out what battery is best but also in your electric aircraft hobby.

I'm convinced that a 30C battery is better than a 10 or 20C battery. However, that all depends on your type of model and your flying style. Also, higher C = more weight!!! Sure a higher C rating means it can discharge faster. But at the same time a battery discharged at 20C continuously will be empty in 3 minutes instead of a 30C in 4 minutes while carrying extra weight, back to flying style. I love having burst power but in almost all other applications actually running a battery at or above the C rating for the model is useless. I prefer to run batteries at the C rating best suiting the model and my flying style and have a little headroom if I need it.

A final note on choosing a battery. Don't cheap out. Confirm that your batteries are capable of running that the amperage level you plan to use them at. Running a cell at a higher C rating than the battery can handle can not only damage your batteries, but it can also damage your speed control. Castle Creations has an excellent article on how using a weak battery can destroy a perfectly good speed control of any brand. Better to buy a bit better battery than you need than to destroy your electronics.

6. Dealing with temperature.
Lithium batteries like heat, but not too much. In the winter time, try to keep your batteries from the cold as much as possible. Leave them in the car while your flying, DON'T keep them in your cargo pants (NOT SO GOOD), an ammunition case with a container of warm water or chemical hand warmer is better... etc. At the same time don't let them heat up too much. Try to keep your batteries from reaching 160F after use. This will prolong the life of the cells. A good way to measure temperature is a handheld IR meter, they can be found for around $50.00 at most hobby shops.

[octagon]

Thanks for this Andre. At the pilot's meeting last night I talked about a battery discharger I purchased.It works like a charm, and now if I come home from the field with charged batteries it takes no time to put them into storage mode. It works exactly as the video say. I know it is not cheap, but as I said at the meeting, I am gunshy of LIPOs (understandably so I think you would agree), and this little device gives me peace of mind.
Here is the link:
http://www.perfectregulators.com/Universal-Lipo-Discharger-Pro

[sihinch]

It was a fabulous presentation last night, Andre. Very informative and entertaining to boot!  Thank you so much.

[eric]

I had to leave right after dinner last night so I missed Andre's talk, which seems like it was a good one. My table mates and I were talking over supper about the best way to discharge and dispose of lipos and I offered that I have submerged lipos in a pail of salt water after cutting off the wires and then disposing of the spent batteries at my local recycle centre.

After Googling this method it appears that this may be a useless way of discharging. I do have, and have used, a tail light bulb that will draw down the cells. When the light is out, the battery's flat.

What is the best way to safely discharge a lipo prior to recycling?

[dangaras]

There was a question about the smell associated with LiPos.

If you detect the same stinky sweet smell we got last night when I opened the ammo box that is the stench of the electrolyte in the packs.

It means that one or more cells have been perforated. Not enough for the water vapor in the air to penetrate and start a fire.

The batteries have got to go!! They can kill you, dead!!

Additional info:
A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated variously as LiPo, LIP, Li-poly and others), is a rechargeable battery of lithium-ion technology in a pouch format. Unlike cylindrical and prismatic cells, LiPos come in a soft package or pouch, which makes them lighter but also less rigid.

The designation "lithium polymer" has caused confusion among battery users because it can be interpreted in two ways. Originally, "lithium polymer" represented a developing technology using a polymer electrolyte instead of the more common liquid electrolyte. The result is a "plastic" cell, which theoretically could be thin, flexible, and manufactured in different shapes, without risk of electrolyte leakage. The technology has not been fully developed and commercialized[1][2] and research is ongoing.[3][4][5]

The second meaning appeared after some manufacturers applied the "polymer" designation to lithium-ion cells contained in a non-rigid pouch format. This is currently the most popular use, in which "polymer" refers more to a "polymer casing" (that is, the soft, external container) rather than a "polymer electrolyte". While the design is usually flat, and lightweight, it is not truly a polymer cell, since the electrolyte is still in liquid form, although it may be "plasticized" or "gelled" through a polymer additive.[6] These cells are sometimes designated as "LiPo"; however, from a technological point of view, they are the same as the ones marketed simply as "Li-ion", since the underlying electrochemistry is the same.[6]

This article concerns the second, more extended meaning (among the general public), while the first meaning (understood in research and academia) is discussed only in the last section.

The name "lithium polymer" (LiPo) is widespread among users of radio-controlled models, for which it may indicate a single cell or a battery pack with cells connected in series or parallel. The more general term "lithium-ion" (Li-ion) is used almost everywhere else, including consumer electronics such as mobile phones and notebook computers, and battery-powered electric vehicles.


Electrolyte details:
Although the name "lithium polymer" (LiPo) is mostly applied to lithium-ion cells in pouch format, which still contain a liquid electrolyte, there are electrochemical cells with actual polymer electrolytes, which however have not reached full commercialization and are still a topic of research. Prototype cells of this type could be considered to be between a traditional lithium-ion battery (with liquid electrolyte) and a completely plastic, solid-state lithium-ion battery.[22]

The simplest approach is to use a polymer matrix, such as polyvinylidene fluoride (PVdF) or poly(acrylonitrile) (PAN), gelled with conventional salts and solvents, such as LiPF6 in EC/DMC/DEC. Nishi mentions that Sony started research on lithium-ion cells with gelled polymer electrolytes (GPE) in 1988, before the commercialisation of the liquid-electrolyte lithium-ion cell in 1991.[23] At that time polymer batteries were promising and it seemed polymer electrolytes would become indispensable.[24] Eventually, this type of cell went into the market in 1998.[23] However, Scrosati argues that, in the strictest sense, gelled membranes cannot be classified as "true" polymer electrolytes, but rather as hybrid systems where the liquid phases are contained within the polymer matrix.[22] Although these polymer electrolytes may be dry to the touch, they can still contain 30% to 50% liquid solvent.[6] In this regard, an open question remains on how to really define what a "polymer battery" is.

Other terms used in the literature for this system include hybrid polymer electrolyte (HPE), where "hybrid" denotes the combination of the polymer matrix, the liquid solvent and the salt.[25] It was a system like this that Bellcore used to develop an early lithium-polymer cell in 1996,[26] which was called "plastic" lithium-ion cell (PLiON), and subsequently commercialised in 1999.[25]

A solid polymer electrolyte (SPE) may be, for example, a compound of lithium bis(fluorosulfonyl)imide (LiFSI) and high molecular weight poly(ethylene oxide) (PEO),[3] or a high molecular weight poly(trimethylene carbonate) (PTMC).[4]

The performance of these proposed electrolytes is usually measured in a half-cell configuration against an electrode of metallic lithium, making the system a "lithium-metal" cell, but it has also been tested with a common lithium-ion cathode material such as lithium-iron-phosphate (LiFePO4).

Other attempts to design a polymer electrolyte cell include the use of inorganic ionic liquids such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) as a plasticizer in a microporous polymer matrix like poly(vinylidene fluoride-co-hexafluoropropylene)/poly(methyl methacrylate) (PVDF-HFP/PMMA).

[Crazyflyer]

Here is a good and very scary test showing what happens with ammo boxes and lipo bags.
Thank you for the presentation Andre

https://youtu.be/CnNId0mDnBo

[dangaras]

The video is an interesting if not overdramaticcomparison of what different container failure modes occur when batteries are overcharged (no details of how they were overcharged).

It does not show more typical puncture related fires.

The test shows the best storage method by far is to store packs in ammo boxes that are kept closed and latched. Seal present or removed, still the safest!

These would also be a good container for charging.

Closed ammo boxes will contain all flames and will significantly reduce any explosion hazard. They are designed for bullets for goodness sake and a lipo has nowhere near the energy of explosives.

Keep then on a tilted out concrete board surface to avoid the heat from damaging the storage surface.

Keep a smoke detector right over the storage and charging area.

LiPos will kill you, kill you dead if you mistreat them.

Don't listen to old wives tales about them. Treat them like gasoline, they will kill you, kill you dead dead if mistreated!

[Andy Hoffer]

These photos will kill you too!  YOU COULD EVEN END UP DEAD!!

1. Simon demos the joy of lipo-free flight!
2. "Pick a pack, any pack!"
3. "They will kill you!  Dead, dead, dead!"
4. "Maybe I'll just skip the Lipos and make this a glider!"
5. "I was going to give this to my grandson, but it will be much more fun if I just fly it myself!"
6. "See how much fun this is!!"
7. "My jet is going to look so cool when I put one of those fire-breathing Lipos into the exhaust!"

[Oscar]

Thank you. It is a very informative meeting.

I do have some questions about using the ammo case for storage.

Is there a rule if thumb of how many lipo can be store in one ammo case?
Does it matter the Lipo laying horizontally and stack them up (with battery lead pointing same direction or it doesn't matter) or standing vertical with battery lead pointing upward?
I saw in princess Auto the ammo case has two sizes. Tall narrow case and wide short height case.  Does it matter what case to get (I guess it assume whether the Lipo can be stack) ?

Thank you
Oscar

[dangaras]

I think the ammo case like the one I brought to the meeting will comfortably store 6, 6S-5000 packs.

Placing them on their sides is best unless you have put some soft foam on the bottom in which case upright is ok.

If they are placed upright on the hard surface this can cause the unprotected ends of the pack to  be damaged when the ammo box is put down or if it is bouncing around in your vehicle.


On another note, I put some of my batteries into a bucket of salt water. After 3 or 4 hours I decided to see what would happen if  I punctured them while they were under water.

The following is the result:

https://youtu.be/keERLed5uuU

[sihinch]

"Double, double toil and trouble;
Fire burn and caldron bubble."

[Frank v B]

Thanks Andre for the presentation. 
As one who tried to fry his house, I welcomed the information and have acted on it.... because you said "it can kill you".

This afternoon I went to Princess Auto in Barrie... having read Oscar's post before I left.  There are two sizes of ammo boxes in the Surplus section in the back left hand corner.  The small one (clean, new) at $24.99 and large (surplus and rusty) at $37.99.  But in aisle 7 (near the front of the store, right) they have the large boxes brand new for $24.99.  So I bought two of these.

re: Simon HinchSpeare's quote from Macbeth act 4, scene 1... I just ran across a postcard I bought about 25 years ago with a drawing of Shakespeare on the front with the following words beside it  "So you think I haven't written much lately.... neither has Shakespeare! ".  Had to laugh.

Frank

[thehaze]

Lipo's

[BJROB]

HI Guys.... Heads up
For them that don't want to get killed by LiPo's
and your looking for safe storage...
Princess Auto
Has them Metal Ammo Boxes on sale
Starting Next Tuesday November 29 2016
50 Cal box 19.99 (8645012)
30 Cal box 18.88 (8145732)
Just wanting you to be safe....

[Gregor77]

Lol. I just posted this sale. Good job. I bought three.