Kokam Lithium Polymer Batteries! - Page 78 - RC Groups
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Feb 02, 2003, 04:40 PM
The blade numbers go up to 11
stumax's Avatar
JJ and Fred, Yesterday I charged up a 2S pack of 3270 cells using my lab power supply – set the voltage to 8.46V and limited the current to 3A, it took about 45 minutes for the charge current to drop to 500 mA which is when I took them off. I then connected the pack to my model which has a Hacker B2012L driving a Vasa55 ducted fan. To measure the current I used a LEM current clamp and a Fluke digital mulitmeter for voltage.
Hot off the charger I couldn’t reach full throttle because the current draw was to high, let it get up to 18A for about 10 secs just to measure thrust and volts (14 oz thrust! 6.65V) I then back the throttle off to 13A (about 10oz thrust, 6.8V) and ran it for a minute, after which the curent dropped to 12.5A. I then opened the throttle further to see if I could get full throttle at less than 18A, still not able to, so I backed off to 13A for 30sec, then 10A, then 8A then 6A, each for 30sec. At the last setting I noticed the cells looking “different” so I cut the power.
I felt the temperature of the cells, slightly warm, around body temp. The body of each cell has lost it’s “vacuum sealed” look – they’re not puffed up, but the outer layer isn’t sucked against the rest of the cell. Have I just killed my cells in one go? The cells still seemed to give excellent power, but as they are sealed it is obvious that some form of gas has been released. I haven't run them again, or recharged them, and won't do so until I get further advice. The pack voltage is now 7.62V. Any advice? Thanks, Stu.
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Feb 02, 2003, 05:46 PM
Registered User
I never intended to be a posted boy for safety and have thought about this long and hard before saying anything. BUT, if someone can learn from what happened to me then I'm doing the right thing. I don't want to get in the middle of a poop storm on this topic.

Anyway we came back from our first session of dog obedience class. We had a 7 month old miniature Schnauzer. The first one is without the dog - Darby. Anyway we drove down our cul-de-sac street returning from the class only to see smoke pouring out of our house, a fire truck and neighbors all standing around. I was out of the car before the car stopped - my wife was driving. I ran into to the house to see three firefighters in our smoke filled house. On the tile bar counter between the kitchen and family room there was a molten blob. Where I had been charging 1020 Ma Kokams in a GWS Tiger Moth . it burned down along with a Direct 280 with a Astro 010 the 98% done that was next to the Moth. Poor Darby was in her cage 6~8 feet from the fire epic center. She was ok because the smoke level was only 3.5 feet down from the ceiling.

The firefighters said our house was 5 to 10 minutes from going up in flames. A wooden chair was burning and a aerosol adhesive can was burning off like a roman torch. Luckily we have a monitored alarm. It went off and they called the fire department. The fireman told us that 99% of the time it's a false alarm, but not this time.

Anyway all we really had was smoke damage, but burnt foam and epoxy is nasty stuff. All the rooms in the house are being repainted and they have to rip some drywall down to get rid of the smoke smell in the insulation. I figure the total bill for the insurance company will be 30K. We aren't living in our house because of the work being done to repair the house.

I don't know for SURE what cause the fire because I wasn't there to see it happen. I was using a C777 charger, which wasn't harmed in the fire because it was on another counter with jumpers going to the battery. I have been using it since without any problems. I have used this charger for four months now and have NEVER felt any of the Kokams get above room temperature while charging. NiCad’s and such tend to get very hot while charging, but not Kokams with the C777. I should have put the temp sensor on the batteries while I was charging the Tiger Moth, but I had a false sense of security I guess.

My long winded point to all this is to make people aware NOT to charge their batteries unattended. It's very wise to charge any battery on a fireproof surface and/or enclosure. Also, keep anything that is flammable away from that battery area. I had some epoxy, aerosol can, another plane and tape that burned as well, adding to the fire damage. The bottom line is I think Kokams are great and I continue to use them, but with a lot more caution.
Feb 02, 2003, 05:46 PM
Registered User
More pics........
Feb 02, 2003, 05:47 PM
Registered User
Last one..........
Feb 02, 2003, 06:09 PM
My cat up close
bipeflyer's Avatar
Geez....if that was me,my wife would have killed me for sure,wow!
Sorry to hear of that,hope you get things sorted soon 30k? Ouch!

Any idea at all why this happened? A short perhaps? Scary stuff!

I will never leave a charging battery un attended again..
Thanks for the warning.

Feb 02, 2003, 06:22 PM
Registered User
poobs's Avatar

Thanks for sharing

Was that a Maha charger????
Feb 02, 2003, 06:34 PM
Registered User

very sorry zoomzoom !!

I am very sorry to your family no matter what .I appology for that.
we will have a safety meeting internally how to solve this matter technically and commercially.worst case we will stop selling until we find reasonable solutions.

I will ask FMA to investigate the fire.

again very sorry.
Feb 02, 2003, 06:51 PM
Registered User

safety notice to kokam users !!

Dear Sirs,

There was 3 reports of catching fire.one was from other vendors'
and two were from kokam cell.though those cells are UL approved,no lithium batteries are perfect against overcharging.
we don't want to toss this safety problem to the charger only.basically kokam shall notice followings safety instruction.

1) pls don't leave battery in charging unattended.
2)pls don't use unproven chargers
3) more than 1 C charging is not recommended.

pls give a special notice until kokam find reasonable solutions.

Sorry for unconvenience.
Feb 02, 2003, 07:11 PM
Registered User
Mr. Hong,

The problem is I don't know what caused it. Please don't stop selling them that is not my intent of writing about what happened. I personally feel that FMA and Kokam are doing the RC hobby a big service in general. No one needs to apologize. I thought about it for weeks before saying anything. It's embarrassing for me to talk about it. I’m 44 years old and have been in the Aerospace engineering field for 16 years until recently.

I did a dumb thing by charging the batteries in the plane and not having the temp sensor installed. But, like I said I have never felt the batteries get the least bit hot while charging with the Maha C777 in the past.

The few facts I do have about the situation and fire are as follows. They were 2 Kokam 1020's wired in series with the FMA PC board terminals already installed. I originally charged them separately to bring them up to full charge before hooking them up in series. I had flown two or three times with them in the Tiger Moth and had no problems. I'm guessing they had about 4 full charges on them since new. The motor in the Tiger Moth was a GWS dual IPS A geared motor. It flew great with this setup. I had been very careful NOT to totally run the batteries all the way down. The only power source on the counter when the fire started were the jumpers going from the charger to the battery plug sticking out the bottom of the Tiger Moth's wing. There was nothing else in the counter area that could have ignited a fire. I do wish I knew what the cause of the fire was.

I have faith in your product(s). And I'm currently charging a single Kokam 1020.................. just outside on the patio away from anything that can burn while charging .......

FYI - The insurance company has been very good about taking care of everything. They have been asking about info on the batteries so far I have been stalling them and I’m not going to give them any specifics.
Feb 02, 2003, 07:17 PM
registered user
DNA's Avatar
"2)pls don't use unproven chargers "

He said he had been using the charger with no problems for
4 months.

How long does it take before a charger is a "proven" charger?

In the case of my Ginzel that puffed up a pack of kokams, and
luckily no fire was involved, the charger has been working fine
for over a year on li-ion cells. Is it a proven charger?
Last edited by DNA; Feb 02, 2003 at 07:52 PM.
Feb 02, 2003, 07:24 PM
Registered User
Bipeflyer and Poobs,

Yup, it was a Maha charger. I have two and they both work fine.

Yes, the wife was a little ticked a me, but she is a good sport and got over it. Another thing that got her to raise an eyebrow was when I had to haul stuff out of the house for the cleaning crews. Currently just about everything is boxed up or shoved in the garage. Anyway I had been stashing airplane kits around the house. My method of madness was to spread them out so she couldn't tell who many I had. Well my day of reckoning was when I had to pile them all up in the garage. Hummmmm, there 49 inbuilt kits plied up that she could see anyway................. Her only real comment was what concerns me is I see more that one of the same model. I quickly changed the subject........................... gee honey is it going to rain today...........
Feb 02, 2003, 07:29 PM
Registered User
poobs's Avatar

not the Kokam's fault


Sorry you got caught However, I'm glad you still have a roof over your head.

Back when I was looking for a charger. I did a search under Maha and remember reading some scary stuff. I think someone else had a near fire using more conventional batteries.
Feb 02, 2003, 08:53 PM
Registered User
ZOOMZOOM: I appreciate more than you can know the intelligent and kind way you address the event. Today, we all are mourning because we lost seven wonderful people yesterday to an "event". Such things can only be resolved with a careful and structured examination of facts and piecing together what happened. I remember over 40 years ago doing such an investigation into the loss of a very expensive "model airplane"; a 12,500 lb Mach 0.85 drone after it had gone in from 23,000 ft. It made a nice hole in the desert near Yuma.

As with the shuttle, we had only the telemetry data and the stuff dug out of the hole in the ground and flown back to Hagerstown. The Project Engineer and I, as an A.P.E., personally took on the investigation. Our company was "under the gun" to find out what happened. The responsibility was great. his was an $85 million program. It took three days of going through every piece there down in a hangar in August heat. That fiberglass and sand ate us alive. Finally, I found the little Vickers swash-plate hydraulic pump, the same as used in every aerial bucket truck you see. The little pistons, barely a quarter inch in diameter, were blued like a gun barrel from heat. We had the culprit. The telemetry data showed fluctuation and then loss of hydraulic pressure. Incredibly, I imagine that swash plate pumps provide hydraulic pressure for the shuttle.

But why? This was a pump used in many, many airplanes, and hundreds of industrial uses. You search the records as NASA is doing now. It did not take long to find that the pump was designed for a 125 hr life as it was for use in a drone in an experimantal program and was not yet MIL SPEC. In other words, that pump was to be changed when it had 125 hrs on it. Turns out that lab and pre-launch running , and the like had accumulated 185 hrs on it and no one caught that.

I have told you about the work on the F14 in 1980 in which we were trying to explain why we lost six airplanes to spin-stall. It took six months and a hundred people of the hihghest caliber, including Sir Framk Whittle to sort that one out. The F 14 is a much better airplane today and continues to serve us all well. It wil be called upon to do a tremendous job in the coming weeks. Some 40 years after I assisted the Navy in it's design and development. I have the original artist's rendering of the conceptual airplane, then known as VFAX (Navy Fighter Attack Experimental) hanging on my ofice wall. Bob Kress, Bob Aberle, Tom Hunt, et al had some level of involvement. Why do I tell you this? Is it because I am nostalgic? No. It is important that you know how I approach such things. Very methodically as an engineer.

I had mentioned a day or two ago that I was concerned about using microprocessors for control of charging. When I just tried to send a long e-mail with attachments earlier and the machine locked up on me and I can only bring it back by ending the task, I am reminded. I am sure you have all gotten the e-mail in the past week re Bill Gates snide comment about GM cars and their very clever answer. Software is a bitch!

I believe the thing for Kokam to do right now as a temporary measure is to state that microprocessor chargers are not approved for charging Kokam cells. (DNA, that is what JJ was saying, although he said proved. You have to give a little on differences in language and not nit-pick every word) We can only make that statement as a directive from Kokam regarding Kokam cells. However, in my opinion, any charger that can change settings, etc, without your specific command should not be used to charge batteries. Any batteries. I don't care if you have charged li ions for two years without incidence. It only takes that one- in - a- million quirk to bite you.

I personally checked the Maha for one specific condition: i.e., I unplugged the AC adapter and observed that, when plugged back in, it went to a no-charge default, issued an Error display, and would not recommence charge until I unplugged the pack and reconnected. Can any other condition cause it to change? I don't know for sure. Perhaps a power surge (vs drop out) or some noise spike could reprogram it. I have had people ask me why their Futaba (et al) microprocessor radio suddenly reversesd ailerons in flight. WOW!

Kokam runs tests every day to verify in a representative sample, that the cells neiher explode nor burn when overcharged. We are at a loss to know until further investigation why these cells might have ignited. Today is a holiday in Korea. They all come back to work tomorrow and JJ has already started an investigation to see if such a happening can be duplicated in any way. I the meantime, we have confidence in the LIPO 402 and those chargers that have manual setting of the number of cells and charge rate.
Feb 02, 2003, 09:40 PM
Registered User

sorry zoomzoom!

Pls don't misunderstand what DNA yelling me.my concern is to avoid any possible problem can happen.surely we want to investigate this fire no matter what's problem.

could you tell me where do you live to my e-mail; jjhong@kokam.com

again sorry for the problem that caused by kokam.
Feb 02, 2003, 10:10 PM
Registered User


Technology like people can fail, have quirks and can be upredicatable after being solid for ages. The moral of the story is dont leave your batteries untended while charging. And get a fire extinguisher. I'm gonna. I think the concept of voltage spikes and restting the charger makes sense, but who knows for sure. Dedicated chargers without microprocessors should be the most secure, but......Watch em. Sorry about the loss. YOur wife is a saint!

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