Li-Ion FAQ & Safety

Hi cpfers,
Seeing a lot of interest in rechargeable Lithium Ion going in cpf, I've decided to write up faq/infomation thread on the characteristic, usage and danger. I hope this thread will be useful and protect members so no one will be making news on the papers.

This post will focus on the safety of you and your rechargeable Lithium Ion cells. If you are new and interested in using rechargeable Lithium Ion technology please do have a read. If you are knowledgeable and find some error in my post, please correct my mistake. Please suggest some, I will continue to maintain. Below FAQ is based on a Li-Ion cell without any protection circuit.

Li-Ion Characteristic
=====================
Voltage per cell – High 4.2v : Low 3.6v
Life Cycle – 200 to 500 depending on usage
Shelf Life – 3 to 5 years
Type - Available in all sorts of sizes
Power – High power to weight ratio


Li-Ion – Lithium Ion
NiCd – Nickel Cadmium
NiMh – Nickel Metal Hydride


Li-Ion Charging
=================
i) Can I charge my Lithium Ion batteries with a NiCd or NiMh charger?
No, NiCd/Mh charger is not compatible with the charging characteristic of Li-Ion. Do not wire up your NiCd/Mh charger to charge Li-Ion it will not work. Please use a charger designed for rechargeable Li-Ion.

ii) My Li-Ion cell does not warm up during charging why is that?
Unlike NiCd/Mh, most Li-Ion will take a charge of 1C happily and will be cool through the charging process. Some Li-Ion are non standard and can only accept slow charging current please check with the manufacturer.

iii) My grandpa said batteries should be discharged completely before recharging if not they will lose their memory. Is it true?
Yes your grandpa is right. Memory lost exists in NiCd technology. Some manufacturer also claims that memory exists in NiMh. These cells are designed for complete cycle (discharge and charge) to work properly.
Li-Ion is NOT subjected to memory lost. So you can recharge it whenever you like.

iv) I like to have my Li-Ion cell full capacity at all times. I want to have a fully charged cell when I need. Can I leave the cell in the charger to maintain the charge?
Li-Ion does not like to be overcharged. If you have an intelligent charger it will be fine. Overcharging is dangerous for you and your cell. Li-Ion has good low self discharge so you won't find yourself picking up a half discharged cell.

v) My Li-Ion cell(s) fits nicely in to my rechargeable surefire, it's brighter than my neighbor's HID. Can I also recharge the Li-Ion cell with the surefire charger?
Current surefire rechargeable flashlights charger is not compatible with Li-Ion. So do not try to recharge with a surefire charger. However, it may change in the future.
First of all, you need to make sure that the battery chemistry is correct and matches your Li-Ion cell(s). Secondly, identify the voltage of the battery pack. If all matches, you should be safe.

vi) I manage to find some Li-Ion cells from a laptop battery, are they useful?
Start with some simple diagnostic. Separate the cells and check the voltage of each cell. If the cell measures some voltage above 0.1 volts you are in luck. Li-Ion cell below 3.0 volts requires a slow charge. Apply a small current of 0.01C until the cell voltage reaches 3.0 volts. Then a charge current of 1.0C can be applied. Some Li-Ion are non standard and can only accept slow charging current please check with the manufacturer.

vii) I keep reading 1.0C? 0.01C? What is it?
C = Capacity of a given cell.

C is used as a measurement of charge and discharge current to the battery capacity.

If a cell has a mAh rating of 2100 then C equals to 2100.
e.g. Sanyo NiMH 2100mAh
----------------------------------
1.0C = 2100mAh x 1.0C
= 2100ma

0.01C = 2100mAh x 0.01C
= 21ma

Li-Ion Usage
============
i) Can I use rechargeable Li-Ion instead of CR123A Lithium cells?
Depending on the equipment you have. Li-Ion has a voltage of 3.6 volts per cell. CR123A Lithium and other non-rechargeable Lithium batteries are available in 1.5volts and 3.0 volts. The electronics in your equipment may or may not malfunction if it does not have voltage toleration. Check with the manufacturer.

ii) If a Li-Ion is 3.6v per cell, can I use it as a replacement of 3xAA 3.6v NiCd/Mh(1.2v per cell)?
Yes, in terms of voltage it is fine. However, you should not over discharge Li-Ion. Safe discharge voltage of Li-Ion is 3.2 volts. Do not try to discharge the cell to 3.0 volts. It is not safe as the voltage drops rapidly as the cell depletes.

iii) I acquired some used Li-Ion cells from laptop battery packs. I've used them for sometime but they are leaking liquid. What should I do?
Even though they are old, the chemical from the battery can be quite reactive. Clean up with dry paper towel. It's also a time to bin the cell.

iv) The Li-Ion cells from the laptop battery have shallow tab/nipple. How can I use it?
Some members have success with magnets in order to raise the tabs. *** Need mode info ***

v) I love to throw my lights on the floor to demonstrate the tough construction of my lights. Will the battery survive the impact?
If your light is strong to survive the impact, then the battery should also survive. Cell manufacturer are forced to put more density in to a smaller size. This means Li-Ion cells have thin walls. They can be crushed in an impact.
Some battery manufactures warn users not to disassemble batteries. Lithium is a dangerous chemical, it reacts violently in water. The chemical in your Li-Ion is not quite the same as bare Lithium but it should be treated with respect. If the cell leaks, please bin it appropriately. Most countries support battery recycling facilities please check with your town council.

vi) I like to short circuit cells to watch sparks flying in my dark closet. I heard that Li-Ion has superior power. I want more sparks. Can I play with them?
If you read warning on any of the batteries that you have, you should see 'Do Not Short Circuit'.

vii) My Li-Ion just exploded and killed my dog. What can I do?
Either you are not doing this correctly or you are having a bad luck. It's your responsibility for the risk of use.

Li-Ion Storage
==============
i) Some people keep cells in fridge to prolong life. Should I do that?
If you wish to store your Li-Ion cells, you can put them in to the fridge but make sure it is dry. Humidity will cause harm.

ii) I found a source of cheap Li-Ion cells, I want to buy a whole lot and bury them in my underground cellar.
The chemical in Li-Ion cells starts to degrade once it leaves the factory. Buy appropriate amount so you can always get fresh cells when you run out. Share the source with other cpf members. That's what cpf for.

iii) Is it safe to leave Li-Ion in my car?
This question is like " Is it safe to leave my 8 months old baby in the car? " You get the idea...

Depending on the cabin max temperature of your car. It can reach 80c in some parts of this world. Some laptops have high operating temperature that kills the Li-Ion cells quickly.
Li-Ion batteries will probably survive very low temperature.

Finally, I am not responsible for your use of Li-Ion and also the correctness of the information here. Treat your Li-Ion with respect as though they are like explosive material.

Vince.

For magnets there are many suppliers.
The one that has the thinnest magnets and good stock is K&J Magnetics. http://www.kjmagnetics.com/discs.html
On the discs page above, I use the 1/4" diameter magnets to make nipples.
Notice they have 1/32", 1/16", and 1/8" thick magnets.
I have a selection of these and use the one that is the smallest that still works.

Thanks Floating Spots for the magnet info.

I just solder a blob onto the nipple.

I thought excessive heat on Li-Ion and Li cells was a BAD thing. Otherwise, a solder blob would be perfect!

[ QUOTE ]
JSWrightOC said:
I thought excessive heat on Li-Ion and Li cells was a BAD thing. Otherwise, a solder blob would be perfect!

[/ QUOTE ]
It would be, but the method (cleaned, fluxed, hot and hurry) used is so quick, that the heat is only superficial, and does not have time to penetrate deeper than the terminal plate into the battery itself.

At least, that's what I used to do, but if you can use magnets, so much the better. /ubbthreads/images/graemlins/cool.gif

I can be quick with soldering, there's just always the fear of it blowing up in your face. How conductive are the magnets?

[ QUOTE ]
JSWrightOC said:
I can be quick with soldering, there's just always the fear of it blowing up in your face. How conductive are the magnets?

[/ QUOTE ]
The surface prep. combined with the high heat (100W gun) did such a good job of confining the heat that the cell itself (1/4" below the plate) was only just barely warm.

The little disc magnets seem to conduct very well. I used some of the 1/4" thin ones that come with those magnetic "rave" blinking body lights like they sell on ebay.

Ever have problems with the magnet sticking to the battery contact instead of the battery itself when you remove the battery/magnet from use? /ubbthreads/images/graemlins/tongue.gif

(I have seen a few ferrous battery contacts in my lifetime)

[ QUOTE ]
JSWrightOC said:
Ever have problems with the magnet sticking to the battery contact instead of the battery itself when you remove the battery/magnet from use? /ubbthreads/images/graemlins/tongue.gif
(I have seen a few ferrous battery contacts in my lifetime)

[/ QUOTE ]
I hate it when that happens, so I use an even stronger stick magnet to remove 'em. 8>)

About soldering the battery terminal.. I have tried it on a 14500, and one of them start to leak at the + terminal. I am pretty sure a good cell won't leak. /ubbthreads/images/graemlins/frown.gif

To add to Koalas great Li-Ion post I got the OK from Jim McPherson from the RCgroups board to crosspost his ultimate guide to Lithium Polymer batteries (which are quite similar to Li-Ions)

Klaus

Ultimate Guide to Lithium Polymer Batteries

After seeing the many many posts on LiPoly's and answering similar questions time after time I've decided to put up a guide for using LiPoly batteries. Please post any suggestions you have here and I'll add them to the guide.

Lithium cell technology, both lithium polymer (Li-poly or LiPo) and lithium ion (Li-ion), is quite different from the more commonly used NiCd and NiMH. There are many things to consider before using lithium cells for e-flight. But none is more important than safety. While all cells must be treated with respect due to the energy they contain when fully charged, lithium cells have the highest energy density. They also have some unique qualities that require special safety considerations. Before discussing other aspects of lithium cells, it's important to first understand these special safety considerations. (Thanks Dave Hendrich)

1. Charging/Saftey IMPORTANT!
If you are new to flying DO NOT use lithium polymer batteries. NO EXCEPTIONS Read on to find out why.
Now for the other important info:
Lithium cells must be charged very differently than NiCad or NiMH. They require a special charger specifically designed to charge lithium cells. In general any charger that can charge lithium ion can charge lithium Polymer assuming that the cell count is correct. You must NEVER charge lithium cells with a NiCador NiMH only battery charger. This is dangerous. Charging cells is the most hazardous part of using lithium batteries. EXTREME care must be taken when charging them. It is important to set your charger to the correct voltage or cell count. Failure to do this can cause the battery to spew violent flames. There have been many fires directly caused by lithium batteries. PLEASE BE RESPONSIBLE when charging lithium batteries. Here are a few MANDATORY guidelines for charging/using LiPos.

Mr. Fred Marks made a good statement: "Saftey is a matter of discipline"...please don't forget that.

1.Use only a charger approved for lithium batteries.
2.Make certain that the correct cell count is set on your charger. If you don't know how to do that, get a charger that you do know how or don't charge the batteries.
3.NEVER charge the batteries unattended. This is the number one reason for houses and cars being burned to a crisp by lithium fires.
4.Use a safe surface to charge your batteries on so that if they burst into flame no damage will occur. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces are all good options.
5.DO NOT CHARGE AT MORE THAN 1C. I have personally had a fire in my home because of violating this rule.
6. If a cell balloons while charging DO NOT puncture the cell while it is still hot. Put the cell/pack in salt water and wait until the cell has cooled. Once it is cool gently puncture the pack's outer casing and put it back in the salt water. After this the cell is safe to throw in the garbage.
7.VERY IMPORTANT: 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 airplane 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 burns the car completly.
8. Charge your batteries in a open ventilated area. If a battery does rupture or explode hazardous fumes and material will spew from the battery.
9. 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 absolutly necessary.
10.Realize that these batteries are dangerous, do not think to yourself that "it won't happen to me" as soon as you do that it will happen to you and 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. Doing either can harm the battery. It is important to set the low voltage cut off on your electronic speed control so that it stops your lithium polymer packs from going below 3.0 volts per cell.
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 cells of the "round"(thanks Derrik) 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 Lithium Polymers, 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?
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).
Currently LiPoly technology does not allow currents as high as NiCad or NiMH batteries do. 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 4x 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. General usage tips.
1.Lithium batteries don't work well in cold air. If you are flying in the winter keep the batteries in your car for best performance.
2.Don't let the batteries overheat. Try and keep them under 140-160 degrees F. This will prolong your battery life.
3.Don't push the batteries past their rated maximum C rating. This will damage the battery and the apparent capacity of the batteries will drop. If when you recharge you are only putting ½ to ¾ of the rated capacity back into the batteries you are probably pushing them too hard.
4.Monitor the voltage of individual cells. Keeping all cells in the pack at exactly the same voltage is important for both the safety and long life of your batteries.
5.If your building your own cells then put spacing between each cell in the pack to help cooling of the pack. This is most important when building packs larger than 2 cells.
6.Some LiPoly cells use aluminum tabs that you must solder to. Normal soldering procedures will not work on aluminum. You'll need to purchase aluminum soldering paste. The vendor where you purchased your aluminum tab cells should stock this paste.

If you have any suggestions for future sections or additions to the current document let me know and I'll add the information requested...if I know the answer!

-Jim

Pic miss-treated LiPoly/LiIons

Holy-moly!! What a mess!!

[ QUOTE ]
Kevin Tan said:
Holy-moly!! What a mess!!

[/ QUOTE ]
That photo is a still from an interesting video of a Li-poly cell subjected to some serious charging abuse. The testing was done by one of the enthusiasts on the RC groups forum. The account of the testing is an interesting read. It, and a link to the video can be found with a bit of searching on the RC groups battery forum. Here is a link to a good starting point:
RC Groups battery forum

On reading the account you will see that it took a lot of abuse to get the cell to burst into flames. Do not be overly complacent about this. Reportedly Li-poly are much less sensitive to abuse than the regular Li-ions that some of us are using for lighting.

Klaus,

Sobering.

"word to the wise" type stuff that saves heartache (if heeded). Thanks.

Doug Owen

Could a moderator stick this to the top, please?

Here's a link to the battery explosion thread.

Yikes!!!

And here's the video:
LipoFire.mpg
LipoFire.wmv

[ QUOTE ]
Kevin Tan said:
Could a moderator stick this to the top, please?

[/ QUOTE ]

Second that

Klaus

Just updated the faq, Sorry I am not a very good technical writer but I hope it's useful.

cheers
Vince.

Wow, this is the third forumn that I've seen that Lipo fire video in. Yes, if you crank a ton of current into a battery when it's already charged, you'll upset it. If you put it on styrofoam, it'll burn really well.

If you're charging packs, use the recommended charger. If you're dealing with raw cells, you are responsible to charge them properly. Keep in mind that even if you do everything properly, accidents happen--clips fall off, wires short, etc. So, don't charge your cells on a flamable surface--especially something extremely flamable like styrofoam. Horribly abused Li cells can explode and spray hot chemicals and throw fragments of case a long distance. Please be careful, everyone.