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Old Sep 14, 2003, 07:20 AM
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LiPo pack balancing poll

There have been multiple reports of Lithium Polymer cells eventually varying in voltage when connected in series (i.e., in packs). This imbalance results in ruination of the relatively high-voltage cell(s) and, sometimes, a fire, during charging.

Do you think pack manufacturers should build means to check individual cell voltages into their packs?

- R.D.
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Old Sep 14, 2003, 08:00 AM
Luis Bustamante
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Absolutely. I will make it a part of my routine to check each cell in a pack before charging.
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Old Sep 14, 2003, 08:06 AM
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Sal C has shown one way to do it, without increasing the pack dimensions: http://www.rcgroups.com/forums/showt...hreadid=120946
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Old Sep 14, 2003, 08:32 AM
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With out a doubt they should be built in such a way that you have access to each cell to check for imbalance these cells are far to volitile to just seal them up and call it good. Sal C had a very good idea with his setup and it would be very easy for pack makers to add this safty feature.
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Old Sep 15, 2003, 10:23 PM
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Premade Pack Cell Balancing

HOw do you go about checking individual cells in dealer made packs?
Thanks
Stuka
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Old Sep 16, 2003, 12:06 AM
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Good question Stuka. The answer in my case is not to buy dealer made packs.
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Old Sep 16, 2003, 01:08 AM
DNA
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The extra wires might be fine for experienced users, but how do you get people to actually use them? I've seen knowledgable users post reports about swelling up packs of lipos because they didn't push the correct buttons on their charger.

What about the novice lipo user who buys a pack from Tower along with a Triton charger. There are lots of instructions to read about charging lipos. Do you think they're going to understand what they're doing when being new to this technology? If there were extra wires on the pack, would they read the instructions and check the pack and know why they were checking it? Some of them may not even own a Dvm, as has been seen in some posts.

There have been threads on Ezone with titles like..."I've bought some lipos, what do I do with them now." Are the extra wires going to help this person. Some vendors are still selling bare cells with a pc board soldered to them with no instructions for how to wire the cells for use, and no safety or charging instructions. There have also been several recent threads saying that the 2s packs they've received are less than 6 volts when New, and that includes both popular brands of cells. Why is That happening? It shouldn't! Are the cells defective in some way when assembled? With the extensive testing we've heard they go through, they should not be below 6 volts when new. Why are they?

It's time to face reality gentlemen. The ONLY way lipos are going to be safe for all RC users is if they are put into consumer packages just like the cell phone and camcorder packs we see in use now, inside a plastic container with protection circuits in place. Those packs are in much wider use than RC packs, but you seldom hear of one of those packs exploding or causing a fire. Let's face it, there are people out there using lipos who should not be using them in their present form.

I'm charging my lithium camcorder batteries as I type, with no worry whatsoever. I'm planning to use the camcorder to record a video of a lipo being overcharged to show the results. I'm really surprised that none of the vendors have bothered to tape a video of a lipo exploding from an overcharge. I guess they're more interested in profits than safety.
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Old Sep 16, 2003, 07:13 AM
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I agree with DNA's assessment, with the exception of the last line. I believe there was an honest under-estimation of the dangers of using Li-poly cells for R/C use without the inclusion of safety circuits. We know that the manufacturer and distributor representatives of all the major brands of Li-poly cells used in R/C have posted messages here about making safety circuit boards available. Strong consideration should be given to making these safety circuit boards mandatory on all R/C packs. Simply adding additional wires to check voltage will not help the least knowledgeable Li-poly users who need the most help.
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Old Sep 16, 2003, 07:37 AM
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50 different charger 8 to 10 different companys selling batterys
with different chimestry ( max and min carge levels) Level of elec
experance is very low You can tell by how many fires , Puffed cells
There has being enough data for chargeing and dichargeing to sink a battleship. But like the Ion's i ran them and got super results but one friend said he charged them to 4.4volts and the third time he kill them only Real lucky Almost no way to inpress
on people of the results of what they do. Even the LapTops with
all there saftey stuff Human nature won't let one perdon do it ok
then the X one not acepting the facts as they are or any reanionning So they have to add 3oz's for saftey. and charge $30
more for the pack. CU
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Old Sep 16, 2003, 08:22 AM
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Dave Hederich's assessment is very good.

Regarding its last sentence: I would add that I am honestly afraid that LiPos could disappear from the modeling scene, if the safety issue is not addressed by charger and battery manufactures by means of built-in safety hardware.

When you look at the extensive LiPo marketing to modelers, it is not exclusively a market for experts. It is a consumer market, and will eventually be held to the product safety standards now applied to other consumer products in the US.

- RD
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Old Sep 16, 2003, 09:10 AM
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Speaking for myself, I will say here that I understood the risks and accepted personal responsibility for the consequences when I began three years ago to experiment with charging CR2 primary lithium cells. I maintained that attitude throughout my experimentation with rechargeable Tadiran lithium metal cells, surplus Li-ion cells and surplus Li-poly cells. In retrospect, I didn't take adequate safety precautions with all of my experiments. I was fortunate that I experienced no catastrophic failures. But if I had, it would have been 100 percent my fault.

Even though the current Li-poly cells being sold for R/C use are more mainstream, I still consider them to be experimental. With each new Li-poly incident reported here, I've reviewed and tightened up my safety precautions regarding all cells. I try to evaluate the rewards and risks of everything I do in life, and do what I believe is right for me.

Personally, I find cell experimentation to be interesting and rewarding, and would continue to do it even if all R/C lithium cells were removed from the market. I am concerned when I see people attracted to the performance of lithium cells without fully comprehending the risks. But this is true for many things in life beyond lithium cells.

Life is risky. That's part of what makes life interesting. I do not want all risk removed from my life because evaluating risk and overcoming it is one of life's great rewards. I'll adapt to whatever comes out of this, and continue to do what's best for me regardless of what someone else may think is best for everyone. There is no one thing that's best for everyone because everyone's different.
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Old Sep 16, 2003, 12:50 PM
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"I've seen knowledgable users post reports about swelling up packs of lipos because they didn't push the correct buttons on their charger. "

Hey, I represent that remark

"It is a consumer market, and will eventually be held to the product safety standards now applied to other consumer products in the US."

Someday, only Outlaws will use LiPo's

Seriously, I agree 100%. I'm a tinkerer. If someone says it won't work, and can't explain to my satisfaction, why, then I'll try it myself, and succeed or fail, but at least I'll know why.

I enjoy the 'silk purse from a sow's ear' we get when we find a cheap surplus item like the Johnson 250 motors or the Qualcom LiIons. Heck, they've come and gone here over a couple years, and they still work good today! There have been other, not-so-good items we've tried, and there will be more.

When something catches fire when you know you are abusing it, it's one thing, but when it happens in your parked car while you think it is safe, it's another! I haven't heard the deffinate answer on what caused these fires, but it has my attention.
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Old Sep 16, 2003, 01:39 PM
luc
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Personally, I think there is more danger of ruining a pack by building it rather than buying an already built one.
The cells with these alu tabs are a pain in...and a not so good solder joint will result in bad or poor contact, threatening the imbalance of cells.
I know what I am talking about, as it happened twice, despite alu solder-it paste,....
So I really think built packs are better for the user, even if we can't have access to each cell individually, which I regret.
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Old Sep 16, 2003, 02:28 PM
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"So I really think built packs are better for the user, even if we can't have access to each cell individually, which I regret."

Luc, I can't see any reason why a manufacturer wouldn't be able to build us a pack like Sal C's, can you?

Regards,

- RD
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