|Jan 28, 2003, 01:18 PM|
Something Very Strange about Charging Kokams
Jan 27, 2003
I hate to admit it but this is something that I thought could never
happen to me, since it has never happened to me before in my
many years of flying RC models and charging batteries.
I've been using my Ginzel Spectra charger to charge Li-ion cells.
I've charged them over a 100 times in the last year with no problems.
I've also been using it to charge the Li-poly cells. I decided to try a
test and charge a Li-poly pack at 3C. It was a 2s pack of kokam 1020ma
cells. I set the Ginzel charger for 2 cells and 3 amps and watched as the
charger initialized and started charging. All was ok.
I checked it about every 10 minutes to make sure it was charging ok.
At about the 40 minute mark I noticed the charge rate was down to
100ma and the cells were at 8.37 volts, so I decided to stay and
take the cells off charger as soon as the rate went below 100ma. I
pulled over a chair and sat down and rechecked the charger display.
WHAT the HECK?? The charger display was now showing 9 amps
and 10.5 volts. I was astonished at the numbers, but stood there
watching what was happening because I couldn't believe the display.
In about 20 seconds the charge rate went down to 8, 6, then 4 amps
but the voltage was still 10.5 volts. I looked at the lipo pack and it was
starting to swell, so I quickly disconnected the pack and took it out
into a 5°F garage and set the pack on the cold cement floor. The pack
however was not hot, so a temperature probe would not have helped.
I have absolutely no idea what happened as to why the charger changed
to the different charge settings. I did not touch either the charger or the
cells while watching them, there were no brownouts or a/c power
flickering, there were no static sparks, I was using the same power
supply I've been using for 2 years, and all the connections were still tight.
I'll repeat that it has charged many Li-ion cells with no problems.
What is really weird about this is that the charger isn't rated to charge
ANYthing at a 9 amp rate. There isn't any way you can even set it to 9 amps.
The lipo cells were fairly new with less than 6 cycles on them but they had
not been performing well. When discharged at 3 amps or 3C, the voltage
on the pack would quickly drop to 6.6 volts which was much more of a
voltage drop than others have reported. I thought that a 3C charge, which
was approved by the manufacturer, may boost them up a little, but the cells
are now completely ruined.
I guess I am fortunate that I am not yet another member to report a
fire occurring when charging lipos, which could have happened had I not
been watching them. If you think that this would not have occurred when
using a dedicated 2 cell charger, (so the charger could not change the
parameters) then you should read this thread, which shows that even a
dedicated 2 cell charger can cause problems with lipos and start a fire.
I have been an R/C flyer for more than 40 years and I am very familiar with
charging batteries. This is the first pack that has ever been destroyed and
I really don't know why it happened. The question I have is....was it a charger
problem or is there something very unusual going on inside the kokam cells?
If it's a charger problem, why did it not occur when charging the dangerous Li-Ion cells?
Be very careful when charging kokam cells, the house you save could be your own!!
If you haven't read it yet, you may want to go to kokam's web
site and read the Precautions under the Safety selection.
Check the last sentence in those precautions.
|Jan 28, 2003, 04:16 PM|
Joined Oct 2001
To me, it's very obvious that it's a charger problem. When you set the charger for 2 cells and 3 Amps, that's the MAXIMUM limit, not a vague suggestion. Under no circumstances should the charger exceed those parameters. The charger shouldn't say, "Well, I'm set for 2 cells at 3 Amps, so I think I'll randomly switch to charging 3 cells at 9 Amps."
Now, you said there were no brownouts, etc.. Are you running your charger off a filtered power supply? You can't see a brownout that only lasts a few milliseconds, but the charger can. You can't see a power surge, but the charger can. Not saying you're wrong, but a lot can happen that you can't necessarily see.
|Jan 28, 2003, 05:08 PM|
I've also seen the problem with my Ginzel but never let it get above 8.5 for the two cell packs. I observed it reach 8.5 on the display and aborted the charge. I then read the cell on the same charger under the voltage display a few minutes later and it only showed 8.2 volts.
Look at the thread below. He's using a dedicated lion/lipo charger and had some packs "balloon up" on him. Now the only way to balloon up a cell would be to apply too much voltage to it correct? This is a dedicated charger with settings for one two three cells. Shouldn't it too be limiting the voltage?
Maybe the Kokams can't be charged with the same algorithms as the lipo's. Maybe the Kokams change and don't charge correctly when cells are going bad?
By the way, I've been charging lion's 1200,830,600 for around a year with this charger and have never seen this problem before. Whats changed in this equation?
Anyone else having problems with other chargers?...
|Jan 28, 2003, 07:00 PM|
"By the way, I've been charging lion's 1200,830,600 for around a year with this charger and have never seen this problem before. Whats changed in this equation?"
Same situation as mine. Never a problem with many Li-ion charges, now suddenly I puff up a pack of lipos. Very strange. I was suspecting it to be a charger problem, but now I'm not so sure. I'm using a regulated, filtered, switching power supply of 12.6v at 8 amps made by Cherokee International. Both it and the charger have performed flawlessly together for about a year.
The charger routinely checks the status of the cells it's charging and can adjust the settings to fit the cells. But as mentioned above, it should never go Over the values that you set manually, and it never has on any of the other cells I've ever charged on it. So how it got to 9 amp and 10.5 v settings, I have no clue. I feel like running the same test again, since the cells are already shot, and touching a quick short across the output leads just to see what happens, because something made the charger change its settings. It could have been an electrical glitch, and I'll never know, but I sure don't want it to happen again.
I asked JJ in another thread what the maximum voltage the lipos could take before the cells incurred damage and this was his reply. So if your charger is showing 8.5 volts, you should be ok, but I would still measure the voltage at the cells with a DVM just to make sure.
"I can say that 4.3volt will not demage the cell but more than 4.5 volt will demage the cell remarkably."
And I'll agree that the other thread you mentioned, telling of cells being ballooned on a 3 cell charger that can't go any higher in voltage, is also unusual.
|Jan 28, 2003, 07:16 PM|
I've seen the ginzel do this, but not on any of my Li-Poly packs (yet). I've seen it happen on differing types of packs. I traced it back to poor connections to the battery. The Microprocessor inside doesn't like to have anything but PERFECT connections to the batteries. Anything else and it goes haywire sometime. I'd check to make sure your bannana plugs are still contacting well, and that all solder joints are good. There also might be some coldish joints inside the spectra. I built one of my spectras and had to pay VERY close attention to cold solder joints. Take it apart and go over the board carefully.
The fault of blowing the packs up certainly lies in the charger, a Kokam cell cannot reprogram your microprocessor (unless Mr. Hong is a very very smart man.... but all sabotage/revenge conspiracy theories aside).
The only fault the battery might have played is in it's contacts which may not be perfect. You said that you weren't getting good performance, perhaps the solder joint to the leads is poor and not allowing much current. Certainly worth a check/resolder.
|Jan 28, 2003, 07:58 PM|
I think what we have here is a combination of thing. No one ever dreamed of charging a Li cell at 3C so the charger probably was not tested at that amperage for the Li's.
You pushed things into charging "lo-lo land" and anything can happen. The charger you are using was probably built before anyone heard of LiPo's let alone 3C charging.
As far as I know, no cell can take a 3C charge without shorting it's life.
When you get way out in left feild, Sh__ happens, but it is nice to know the limits.
|Jan 28, 2003, 08:55 PM|
Gaithersburg, MD, USA
Joined Jun 2000
DNA Et Al: You are cautioned in the Ap Note and in the instruction sheet that comes with the Kokam cells that the charge should be at 1C and that the charge algorithm must be as shown in the Ap note. If you do other than that, you are told that you are at your own risk.
We got a lot of posts wanting to be able to charge at >1C, so Kokam ran tests of the cells at > 1C. The report of that testing was presented in my post in the Kokam Lithium Polymer Battery thread on Jan 17 as copied below. ( You may want to review the entire post with the curves attached) Please note that only the charge current was escalated; never the charge voltage. The 10.5 V the Ginzel applied will definitely ruin the cells. The reason the current started to fall is that the electrolye began to vaporize and the flow of electrrons was inhibited as the pack went into overchage.
Quote from Electroman from Pg 74 of Kokam Lithium Polymer Battery thread on jan 17: "I recently promised to publish the data Kokam provided me from lab tests. The attachment below ( in the post being quoted) contains three figures. The first figure shows that the cells can be brought to 90 % of full charge in the shortened time period indicated. If you want 100 % charge, you still have to wait a bit as current tapers down as the cell approaches 4.2V. The impact of this is that you can charge at 2 or even 3C in the field between flights and lose only a max of 10% of the flying time. For example, if you are making 25 minute flights, and you must wait for 25 minutes to get the pin again, you can fly all day with one pack. I would certainly stick with charge at 1C when in the shop. Remember that liPo does not self discharge so it is hot-to-go any time you are ready to go to the field."
The chemistry for Kokam Li Pos, other Li Pos, and Li Ion are the same and charging is the same. I observe the following with regard to the difficulty DNA encountered with the Ginzel:
1) Have you ever tried to charge a Li Ion at 3C with it? I am not suggesting that you do that as it would be extremely dangerous.
2) the only thing that will make a Li Poly or Li Ion swell or overpressure is if the charge voltage gets too high.
3) the battery is essentially a "dumb resistor" and can respond only to higher charge voltage than it is supposed to see.
4) It takes quite a bit of overvoltage for some time to make a cell swell as shown in the curves of overcharge that were presented in the above thread
5) The issue to be examined is why and how is the cell overvoltaged?
6) You received a Kokam charger as a gift from Mr Hong and Kokam USA. Have you charged the cells in question using it? This gives us a baseline as we know that it charges precisely with the algorithm specified. If you had no probelm charging with the LIPO 402, then that seems to indicate that there is a problem with the Ginzel. See Jube Cornpone's report on the LIPO 402 in that thread. In addition, one post a bit earlier has indicated unexpected changes in charge parametrs using the Ginzel. he bright light is, if it does it to your liPo, you have a silver sausage, not a hole in your shop wall.
7) In the applications notes, I have stated that the specifications for charge, discharge, and handling the Kokam cells ensure that they perform as specified. If one elects to do something differently, the results can vary.
8) The two incidents that I have seen reported in the forum have
all involved microprocessor controlled chargers. The Orbit Microlader can and will change setting to select NiCd if power is lost. I have checked the Maha and find that , in the event of power loss, it defaults to shut down, displays an "ERROR" message, and can not be reactivated until the pack is disconnected and reconnected. I know little of the Ginzel.
9) The only things required of a charger for li Po is that they have a current regulator adn a voltage regulator. These are passive events with no interaction with the LiPo cell and should require nothing on the part of the charger related to the cell itself.
10) The one action that the microprocesssor takes as an active function , if it is a feature, is measuring when current falls to C/10 to cut off charge.
11) It is well to remember that the Ginzel was designed to charge Li Ion, al most certainly at not more than C1. So, it is difficult to tell what it is doing.
12) Guidance: a) Until further notice, I would be very cautious about using any microprocessor-controlled charger to charge Li Ion or Li Poly at charge rates higher than 1C. I would never, ever charge a li Ion at >1C b) I would not charge a li poly at 3C to full charge. Please note what I wrote above: It is OK for "refill" in the field. At home, there is no good reason to fast charge any battery unless you have some time-urgent need. (DNA; I understand that you just wanted to try it to see if it would work. I appreciate the good effort. Now that DNA has found that the Ginzel has some difficulty with that, the rest are forewarned.) c) I will ask Mr Hong to comment on the tests that were run that I reported in the above quoted post. I assume for now that the charging was done with a regulated power supply in order to get the high rates and the deliberate hig voltage. d) Strange as it may seem, the simplest chargers may be best; i.e., the ones that use a voltage and a current regulator and no dependency on a microprocessorsuch as the LIPO 402. d) from my knowledge of Li Ion chemistry, there is no way that the cell can react to anything other than voltage higher than the specified voltage. While working on the adapter for Supernova, I did find that the cells will swell if you leave them on overcharge at over 4.235 V/cell for very long.
One final thing: Any of our cells , NiCds, NiMH, etc will be damaged, certainly will swell or vent, and (in the case of li ion) may explode if overcharged. The types other than Lithium self regulate when charge rate is C/10. At much higher than that, they go into overcharge unless a very precide control is used to cut off charge. Every charger is subject to potential failures that can cause overcharge. Timed chargers are the very worst.
|Jan 28, 2003, 09:02 PM|
Walled Lake, MI, USA
Joined Feb 2000
Good grief, DNA, did I put a jinx on you by what I said in that other thread? For those who didn't see it, DNA had mentioned in another thread about several charging incidents involving LiPo cells. I made the comment that we really didn't know what had happened in those cases because no one actually witnessed what had happened since the chargers were unattended.
What are the odds that less than 24 hours later, DNA would be sitting in front of his charger witnessing this!
But even with a knowledgeable witness, we still have a mystery on our hands. We have a full description of the charger's behavior and what it did to the cells. The question is, what caused it to happen? As Chuck points out, even though the cells have been tested at a 3C charge rate, they haven't been tested on every charger at that rate. At the very least, we know that there is not enough benefit in 3C over 2C to make it worth taking the risk of destroying cells.
The important thing to all of us is that we learn as much factual information as possible as quickly as possible. This is no time for a rush to judgment against a certain type of charger, a certain type of cell or the interaction between certain chargers and certain cells at different settings. We're still in the experimental stage of using this type of cell for e-flight, and there are still unknowns. Perhaps early e-flight implementers of NiCd and NiMH recall a similar learning curve.
|Jan 28, 2003, 09:08 PM|
Li-ion cells have been around for a while now and charge the same as
Li-poly cells. The Spectra is capable of charging either type up to 12
cells or up to 6 amps. It can also be updated by plugging in a newly
programmed eprom chip for new cell types and new features.
The ceo of kokam said the cells could be charged at 3C, so I thought
I would try it.
Thanks for the suggestions, but I'm pretty handy with a soldering iron
and haven't had a bad or cold solder connection in any of my electronic
projects in over 40 years. I also use gold plated banana plugs for the
connections. I did recheck the pack and everything is soldered solid.
After working fine for about a year, I doubt if the charger has any bad
solder connections, but I will check it, now that I've had a problem with it.
|Jan 28, 2003, 09:09 PM|
Joined Dec 2002
something very strange thing happened around DNA
Charging current 3amps(3C CHARGING!)...40minute pack 8.37v....
It is abnormal very rapid charging.(2s max voltage shall be 8.4v)assume that each cell has 90% capacity=0.9x2=1.8A
suddenly the display shows 9amp.10.5 v....?
and doubt kokam cell and charger.......?
This is very simple calculation.If you doubt cell,
.Suddenly 3.0amp current increased to 9amps.That means kokam cell generates 6amp current to the charger from the 1.8A capacity.
IT is a great discovery that during the charging the cell generated the power to the energy source!!
Something very strange thing happened around DNA. After reading all your thread about kokam, i realized you don't like kokam lipo. I kindly ASKED FRED TO SEND KOKAM LIPO 402 CHARGER TO YOU.DID YOU RECEIVED OR NOT? IF NOT,IT WILL BE UNDER WAY.I am a fortune teller for longtime.
However I appreciate for your notice of safety.kokam cell is very very safe battery if you use right charger with right set up.
If you are kind,pls send swelled samples to FMA.They will send it back to kokam to analize the gas inside(we have fart engineer like your job) and electrode analysis.we can clearly determine the reason what happened.
|Jan 28, 2003, 09:15 PM|
Like I said, this same thing happened to me at .8c (800ma) on a 1020 pack. So the rate is not the total issue here, unless .8c is too fast also. The pack was at 7.8 volts to start and rose to 8.5 before I stopped it.
|Jan 28, 2003, 09:44 PM|
My Ginzel is doing well with my Kokams (so far). I do notice that it is very static sensitive. Several times I have touched the charger or cells being charged by it and the display will go blank or have strange characters on it. Of course, I am there doing the touching so I reset the charger. Don't knbow what it is doing to the battery when this happens. I also noticed the rapid voltage increase if there is a bad connection to the battery. I reset my charger before reconnecting. Wonder if the current goes up after
the connection becomes good again?
|Jan 29, 2003, 12:17 AM|
This is a statement from my first post.
"At about the 40 minute mark I noticed the charge rate was down to
100ma and the cells were at 8.37 volts"
The charger acted normally just as it always has when charging Li-ions,
by decreasing the charge current while maintaining the voltage at 8.3 volts.
The charge may have started at 3 amps (3C) but at 40 minutes was down to
0.1amp (100ma is not 3C) and I was getting ready to remove the cells from
the charger since they were nearly finished, when the charger settings changed
for no reason that I know of. To say I was shocked to the see the new settings
would be an understatement. I thought that maybe the display numbers had
frozen, which is why I didn't disconnect the cells. Then I saw the lipos starting
to swell and immediately unplugged them.
It may very well be a charger glitch, but it has been a very reliable charger
for quite a while now. It's just that this has never happened before on any of
the many other cells that I have used it with, and I still don't know what may
have caused the glitch this time.
No, I have never tried to charge a Li-ion pack at 3C because I have never read
that it was safe. I have read comments on Ezone about safely charging the
kokams at 3C to shorten the charging time.
I have charged other 1020 kokam cells on the same charger at least 25 times
at rates of 1C to 2C and have never experienced any problems with those cells.
It was only the two cells that were not performing well that I had a problem with.
The cells had been discharged to 5.9 volts. After sitting for about 5 minutes, I
measured the voltage on each cell separately and found 3.17 v and 3.19 v.
So I put them on to charge at 3 amps and everything went fine for the first 40
minutes, with the 3 amps gradually decreasing to the 100ma mentioned above.
The pack only swelled about 1/8" when it was disconnected and taken outside
to a cold garage floor. It is slowly returning to normal with the swelling receding.
No, I have not received a kokam 402 charger, but another ezone member who
wasn't expecting to receive one was surprised when he did. Maybe you sent it
to the wrong person.
JJ, I never said I didn't like kokam cells and I have bought several of them to
compare to my Li-ion cells. I may disagree with some of the posts being presented
about them, but that's my job, to smell out the bad farts and make them smellable
to others, so they don't get the wrong impression. If you would like me to send the
cells in for additional fart analysis, just let me know when and where.
|Jan 29, 2003, 08:45 AM|
Joined Jan 2002
"It may very well be a charger glitch, but it has been a very reliable charger for quite a while now. It's just that this has never happened before on any of the many other cells that I have used it with, and I still don't know what may have caused the glitch this time." - DNA
Having been reliable for a period of time leads one to believe a device remains reliable, but the opposite MAY (I emphasize, may - it's pure speculation on my part, absent evidence) be true.
It is known that vital components in a wide range of products sometimes fail short of their usuful life expectancy. For example, automobiles are often recalled after being on the road for a period of years, when latent defects show up.
Why not send the cells to JJ, and the charger to Ginzel?
There is a reason, or reasons, for the failure, and the respective manufacturers are in the best position to figure it out.
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