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Using LI Po Batteries Safely

Old 10-30-2003, 12:19 AM
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Fred Marks
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Default Using LI Po Batteries Safely

In order to present as clear a picture as possible and to guide in the safe use of Li pos, no matter the manufactuerer, you will find at www.fmadirect.com under the Support section the Kokam Battery Systems Ap Note, Ap Note # 2 in pdf to download.

The following is a brief supplement to the Charging and safety sections of the Ap Note. The principal things to remember: Li Ion and Li Poly cells have Lithium in them and that is why they have five times the energy density of other chemistries. Powdered Lithium, if heated sufficiently , can ignite and burn. Understand: we can test, report, educate, add in any kind of safety device but, as long as Li is present there may be some way that it might be ignited. In the ultimate, suppose a lighning strike hits your model! The only thing to do in all this is to charge the packs in such a way that , if they do ignite, no harm is done.

Please do take time to read the following and download the information in the Ap Note.

All high energy density batteries including Ni Cd, Ni MH, Li Po, and LI Ions and the chargers used require common sense and caution. If any are overcharged or shorted, great heat and pressure result. Ni Cd and Ni Mh cells have a mechanism to vent excess gas pressure as do Li Ion cells. These cells all have in common, a thin metal can enclosure. I have experienced explosion of Ni Cd cells when the vent did not function properly. One such occurred at 1 AM in a deathly quiet shop as I worked on an Army radio system in 1984. That was behind me and about 15 ft away. You probably never saw a 55-year-old, 225 lb guy clear a 4 ft workbench flatfooted! I didn’t even bother sending the 4AH cells back to Sanyo since it was a charger malfunction that caused the event.

Li Ion cells truly can explode as they are sealed in a metal can. They too have vents. However, Lithium is a metal that, as a powered material can burn if ignited. This is true of several metals, not just Li. Magnesium burns readily even in solid form. Thermite is powdered iron that, when ignited, has been used to weld steel. Finely powered aluminum is the “fuel” for almost all solid rocket motors. Some solid rocket motors are made of extruded nitrocellulose, an organic material. Organic materials burn when ignited, just like paper. Powdered, sintered nickel takes a very high temperature to ignite.

Li Po cells also can vent if charged at too high a voltage. There is a narrow range of choice of the electrolyte for use in Lithium Ion cells. Remember that Li Po cells are a form of Li Ion; they derive their name from the fact that Li Po cells are housed in a plastic (polymer) envelope. If the envelope has a small Vee cut in the join line, that serves as a vent. The major difference with Li Po is that the envelope can swell when pressure builds to form the infamous “silver sausage”.
Any cell is ruined when pressure that causes venting is experienced.

If a Li Ion cell suffers ignition, the vent cannot act quickly enough to prevent rapid pressure build up. When this happens, the can fails instantly and catastrophically just as it can in a Ni Cd/Ni MH if the vent does not function properly. The pressure release is, therefore, explosive just like popping a balloon only with massively more force. This is why all Li Ion cells used in OEM applications such as cell phones have a protective circuit on them.

The failure mode that leads to explosion in a Li Ion leads to an event called “venting with flames” in a Li Po cell. The basic phenomenon is called thermal runaway. If, say, a Li Po cell is charged at six to seven volts, well above the nominal 4.2 V limit, the electrolyte can begin to “boil” and develop voids as temperature rises above about 180 degrees F. If this abuse continues for, say, ½ hour, the electrolyte, being organic, can eventually ignite. As we said earlier, it takes a lot of heat to igniter Lithium. In a solid rocket motor, ignition is initiated essentially by a high explosive blasting against the propellant.

If the thermal energy release of the electrolyte used is high enough, the Lithium can be ignited. In tests I have conducted, the electrolyte burns at about the intensity of burning paper when it has a heat gun blasting it. When I light the fireplace I winter, I wad up newspaper in softball size wads and put in a layer before I put wood on the grate. If I have light, dry kindling, just igniting the paper with a lighter lights the fire. Last winter was so nasty that we ran out of kindling. I found that the thermal output of the wadded paper could be increased sufficiently to ignite reasonably dry maple logs by blasting the paper with my Monokote iron. The point: Subtle but significant changes can affect ignition. Not every overcharge event causes ignition.

If the lithium ignites, it burns with an intensity and gas generation that can cause “venting with flames” that is the gasses exit the envelope with a swoosh, not a blast. If you have the pack in your airplane when this happens, your airplane is going to be damaged. If you have the pack on a highly flammable car seat, the seat is likely to catch fire.

Does this happen often? Not really; we have about a dozen such events reported in the past 18 months out of perhaps 100K cells in the field and, probably, a million or more charges. In all instances, analysis of the event has shown that the cell/pack was charged at too high a voltage and/or there was a fault in pack assembly.

Methods that are as stress-free as possible that permit one to use Li P cells in a completely safe way are outlined in Ap Note 2 located at www.fmadirect.com Open the home page, click on Support then scroll to Ap Notes to open or download the pdf file for Kokam Li Po battery Systems.

It is a simple matter to operate safely. Just as you are asked to avoid smoking while handling an open can of glow fuel, keep your hand out of the prop, don’t whittle toward yourself, and don’t fly while drinking, it is suggested that the simple warnings posted at our web site be followed. Remember, safety is a matter of discipline. Remember also, that we take care to educate the user about these things.

The safety device used by George Maiorana to change KOK 1500 4S3P and 4P packs is shown in the Ap Note. $15 spent on such a charge center is the cheapest insurance in the world. The white lining is sheet rock. I tested sheet rock by directing a propane torch flame against one side while I touched the backside with no harm. George has been handling several packs of KOK 4S4P cells with the LIPO 402 charger and his charge box for several months with no problem. Testing to date at FMA Dorect of the Kokam Safety Guard indicate that it could prevent such a charger failure from resulting in a battery fire. Very soon now, we will post a full report on Safety Guard as part of the subject Ap Note showing the various ways it can be used. A shipment of Safety Guards is being readied at this time.




George also charges the 8S4P pack used for his conversion of the 80 inch, 9 lb Great Planes Lancair, attached, that is reported to fly like a dream.


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Old 11-11-2003, 12:42 PM
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Frog
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Default RE: Using LI Po Batteries Safely

Fred Your info about safety was great.
I have been using Li-Poly batts. all summer
with no problem but I am very careful with them
I use kokam batts. the 402 charger and an army
surplus metal ammo can with small stone in it.
I have one question about winter storage they say
to have them about half charged for storage.
Why cant they be stored at full charge?
Thanks Ron from Ma.
Old 12-09-2003, 09:56 PM
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Fred Marks
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Default RE: Using LI Po Batteries Safely

Frog: I went to our true expert on the subject; JJ Hong, Pres Kokam Engrg Ltd and here is his answer: The cathode material is lithium cobalt oxide. When you apply charge current, the ionized lithium from the cathode will move to the anode. If excessive lithium ions move from the lithium cobalt oxide structure for a long time, the the structure might be damaged due to the excessive absent of lithium ion. That's why we recommand that you do not store the lithium at full charge state. Rather, less than 80% is good if you store the battery more than 6 months.
Old 12-09-2003, 10:02 PM
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Fred Marks
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Default RE: Using LI Po Batteries Safely

Safety Guard went on the web site today. The first shipment arrived a few days ago and the manual is now complete. You may access ordering information and specs at https://www.fmadirect.com/site/fma.htm?body=Store You may access the pdf file for the manual at https://www.fmadirect.com/site/fma.htm?body=Support When you reach support, scroll down to Manuals. Under Manuals, follow the instructions at the top of the Support page to save down and download the file LIPOSG Manual to your favorite computer and folder. Please study the specs and the manual to see the many ways you may use Safeguard to permit you to charge Li Pos of any make and Li Ions safely. I won't repeat all the good info in those data sources. If you have questions after you study all that, then we didn't do it thoroughly enough!

One really nice thing about Safety Guard is that it is applicable to any of the packs you now use. It doesn't have to be build in to an individual pack so you are getting beautiful protection at very little added cost. We look forward to you creative types telling us the new ways you find to use Safety Guard. Before you ask, we are working to see if it can be used on the output to Supernova. If so, that will be added to the manual. We are particularly anxious that those of you who have some of the auto detect chargers use SG on the output. This is a very inexpensive device that should help you avoid "silver sausages". I can say without fear of contradiction that SG would have prevented all but one of the few Li Po fires reported over the last 18 months. If you follow the simple guidelines of checking individual cell voltage periodically as you should for Ni Cd or Ni Mh, then Safety Guard will do the rest and protect your pack from mis-set chargers, either automatic or manual, and from charger malfunctions


JJ and I have not visited you as often of late because just about any questions about Li pos are addressed in the Kokam Battery System Applications Note in the same Support section of the web site. The Ap Note was just revised this week and has a lot of new information on it. The section on SG will be updated later this month or in early Jan. It is to your benefit to review the web site almost daily as we are introducing many new products, almost daily. Almost all are applicable to electric flight. I am sure by now that everyone of you is aware that George Maiorana and Dave Pinegar won team scale at the 2003 Scale masters flying a beautiful Russian Tu4 AEW airplane powered by Kokam 1500 cells.
If I recall correctly, we have at least 12 new products scheduled for release over the coming months leading up to the Toledo show. We are working very hard to make Li Po "plug and fly" with new pre-packaged propulsion systems as we always featured with our Ni Cds.

Some of our emphasis is shifting a bit as Kokam USA has begun a strong collaboration with major distributors around the world. In the US, Hobby Lobby, Horizon, Great planes, Dymond and a number of key dealers now have good stock of Kokam battery products.

Don't forget to e-mail us pictures of the great models you equip with Kokam products for inclusion in Li Po Gallery that you see on the home page.


Later! God bless you all and bring you a joyous holiday season. Please remember our heroes in Iraq.
Old 12-27-2003, 05:56 PM
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Default RE: Using LI Po Batteries Safely

To ALL that read this,

If you have any questions about safety issues, or questions for Fred, please use the forum for the questions or PM, email Fred directly....he is very good about answering your questions.

We need to keep this "sticky" free of questions for future updates...

Thanks to all of you for your participation and help.
Old 04-01-2004, 11:30 AM
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jerry0
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Default RE: Using LI Po Batteries Safely

From what I've read, I wouldn't use LiPos if you paid me. It isn't worth a burnd down house, or worse!
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Old 04-01-2004, 02:11 PM
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Default RE: Using LI Po Batteries Safely

Fred wrote ...
That's why we recommand that you do not store the lithium at full charge state.
Assuming you can't go and fly off the charge, what approach do you recommend to discharge a (charged) pack to the correct "storage" level? NiCd cyclers discharge to a voltage per cell level and I would assume they are probably not a good choice for this task.
And what's the break point for a period of non use that would put a battery into storage mode? Two weeks? A month?
Pretty sobering physics going on with this flavor of battery. Mine are tucked (way) inside turbine-powered models and it's almost like doing a lobotomy on an ant to get at them if I wanted to charge them outside the airframe - I don't have the luxury of an ammo box for charge protection. [sm=bananahead.gif]

Mike
Old 04-05-2004, 03:58 AM
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Default RE: Using LI Po Batteries Safely

Storage Recommendations for Lithium Ion Batteries:

Panasonic:
The batteries should be stored at room temperature, charged to about 30 to 50% of capacity.
We recommend that the batteries be charged about once per year to prevent overdischarge.

Moli Energy:
Storage temperature range is -20 to 60° C.
Recommended storage voltage range is 4.1 to 2.0 volts per cell.
For prolonged storage periods, store discharged [i.e. 2.0 to 3.0 volts per cell] and at -20° to 25° C.
Old 04-05-2004, 06:20 PM
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Default RE: Using LI Po Batteries Safely

Storage Recommendations for Lithium Ion Batteries:
OK, I got all that (from other literature) but part of the original question still remains: What technique do we employ to get a fully/almost fully charged LiPo/LiIon pack down to the appropriate storage voltage evel? The current crop of NiCd and NiMH "smart" dischargers (and chargers) don't lend them selves to that task if you want to do it automatically.

Mike
Old 11-07-2005, 11:28 AM
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Default RE: Using LI Po Batteries Safely

One of our club members had an unfortunate experience with a brand new
ElectriFly 1250 LiPo pack purchased through a local hobby shop. He charged
it through the charge connector and all was well. Then he put it in his
plane, a small 4 motored B-17 from a Gillow kit . . . smoke city! 4 motors
came on full force in reverse, 20 Amp speed controller toast.

The discharged connectors were wired in reverse at the pack terminals. Deans
Ultra that came on pack OK, red to --, black to | so he didn't suspect
anything.

Note the difference in the wires on a good pack (foreground) vs. the reversed wired pack.


Probably an isolated instance but check those new packs with your voltmeter
as soon as you get them.
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