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Old 11-08-2007, 05:35 PM   #31
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Linger's post just proves the more things change, the more they stay the same.
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Old 11-08-2007, 05:45 PM   #32
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Default overcharging lipo's

One good thing about lipos is that it is very easy to tell if you are overcharging it, simply hook up a voltmeter to the lipo. If it is over 8.4v, you are banned.

See, easy.

Linger, STOP teaching people how to endanger everyone. If an idiot overcharges a lipo and lights himself on fire, oh well. If he does it to me, we have a problem.

I want to thank Linger again for his knowledge and insights. Linger, you are an awesome reference on LIPO's, and an asset to rctech.
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Old 11-08-2007, 05:51 PM   #33
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Quote:
Originally Posted by billjacobs View Post
Linger, STOP teaching people how to endanger everyone. If an idiot overcharges a lipo and lights himself on fire, oh well. If he does it to me, we have a problem.
Eh, that's probably my fault, I get the impression linger was reluctant to say anything. There's been a few posts on here from people that are talking about experimenting with this stuff, as well as talk of a charger with some kind of variable setting, perhaps the one linger mentioned. I was going to dig them up, but ling swooped in to save me. :-)

Regardless, that practice should be outlawed with rules. If I owned a club, I'd be tempted to hit someone with a lifetime ban if they endangered public safety with irresponsible charging practices. It may be a tech headache, but some headaches are worth it.
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Old 11-08-2007, 06:34 PM   #34
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Quote:
Originally Posted by linger View Post
billjacobs - overcharging lipos is a pandora's box waiting to be opened.
Yes - overcharging will give better discharge performance.
It is also extremely unsafe. Repeated slight overcharges will make a safe cell unsafe as well as killing the cycle life tremendously.
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Old 11-08-2007, 06:34 PM   #35
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linger,I am not following you. Cheat will allways be possible.

You know in Athletics problably the records of the last 20 years are a lie, for what I hear after Balco's scandal.

You can aply your thinking to other type of batteries, can not? For example you can try to charge one of Nimh directly from the maim socket at home, you will destroy some of them but have the chance that one at least will end with a hell of a voltage. With that pack you will win the race.

Cheat will be allways present. In fact what is the Zap process if not make some harm to the cells so that they are able to deliver more voltage that what they were meant for?

The problem of what you are saying is that if you let the lipos voltage go above 4,2v you will not end will a pack to win the race but with a pack to throw away because it will be rubish.
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Old 11-09-2007, 04:35 AM   #36
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PDM,

Sure, cheating will always be possible. But if i got this correct, the difference between the best lipo pack and a flame thrower is just a few mv. Where are you going to draw the line?

If linger's info is correct (and i trust his informative info) i think there should be control over the voltage (ie. one random car is voltage checked at the start of the race: if the battery is above 8.4 the driver should be disqualified from the event).

Expecting comon sense from rc racers is not, in my opinion, a good idea
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Old 11-09-2007, 05:24 AM   #37
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Itchy, lets put it this way, it is not easy to change the values of a charger.

It is even harder to put a lipo on fire. I deal, for some years now, with lipo in model airplanes. Most of the chargers will make impossible to put a lipo on fire during the charge. The good brands of lipo cells do not catch fire even in abuse of charging.

The fires in lipo can occur in a case of a short circuit (I am not sure the word, but if you make a conection between the + and -) or if the cell get punctured, but even in this cases it is not 100% sure you will have a fire.

The problems that happened with lipos during charging were mainly because of non equalized cells inside the same pack but a long, long ago. At the beguining of lipos packs were sold without equalization conections, but now all of them have.

People must understand that lipo chemistry work in a completly diferent way that Nicad and NiMh do.

If you overcharge a lipo or let it go above 4,23v/cell you will not end with a fantastic power for racing, you will end with a pack that will deliver nothing and must be thrown to the recycle bin. So what is the point of trying to make the voltage go higher unless you want to throw the pack away?

Possibly people want to make the voltage go higher but in the charger of oponent pilots, so that when they start the race they will discover they do not have power in the pack and will loose the race
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Old 11-09-2007, 05:50 AM   #38
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Responses/reaction in general to previous statements:
-I'ld bet you guys if Lipo would became main-stream for racing and be used on a large scale, here also problems (hopefully no big accidents) will occur.
We all would be ignorand if we'ld say that wouldn't enhance the chance of "problems". (s currently with Nimhs)

-Where-ever developments for race purposes are made, manufacturers go to the max, although step-by-step...

-Racers allways will try to create an "edge" so, prople will find a way (or several) for abusing Lipo's in time (or as stated allready have).

Responsability:
I doubt the solution is in Nimh vs Lipo, or clubowners being charge-police or something. It would take all the fun out of running a club because of liabiltyshit and so on.
At first the racers should also have some sense of responsabilty to start with.
Although we all know racers sometimes need to be protected against their own "drive".

As for other involved parties, manufacturers, clubs, governing bodies, matchers, etc... they also should think about this one and make a united statement ruling/stand in this one.

Discussions, opinions and goals:
I do not have a cut and dry answer or a decent suggestion myself yet....

Guys I'm all for discussing serious topics but try to honor each others opinions and think we're all going for the same goal here...safe, fast and fun racing solutions...
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Old 11-09-2007, 07:37 AM   #39
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Linger, I have been thinking about what you wrote, I looked your other writings.

I do not want to be rude, so I will put this as a joke that we have here.

The joke speaks about the diference of diferent knowledges the Theoretical and the Practice

The Theoretical is when someone knows everything but nothing is working;

The Paractice is when someone can put everything working but doesn't know why

In your case the Theoretical and the Practice are together, because nothing is Working and nobody knows why.

You may know a lot of theory of lipo but sure you never tryied what you say.

Overcharge a lipo in NiMh mode in the charger, c'mon you are joking aren't you? Maybe you can put it on fire but overcharge it in the way that you say with a slightly higher voltage in a way that you can put it in your car or plane after that i would like to see.
how do you make to stop the voltage at those 8,6v in the nimh mode. Everybody that knows lipo know that when the pack reach 8,4v it is not charged yet. In the some situation you can make the pack reach 8,6v but at that time it is not cahrged yet and so far away of beeing overcharged.

Of course I am ready to apologise if you show me I am wrong.
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Old 11-09-2007, 08:39 AM   #40
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At the moment LiPo (most of them) are still considered more dangerous as they can explode due to a crash rather than just during charging. There is a reason why only one make of LiPo is even allowed to be transported by plane and it isn't because the other LiPo manufactors have a good safety record...

For the reported NiHm problems, these are primarily (almost exclusively) incidents during charging. Those that think this is due to high amp charging are only half right. The problems have occured at lower charge rates too. Also, in the past with even 1200 Mah NiCads the same charge rates have been used. I even charged a 1200 Mah pack at 10A (idiot, I know) with only peak detection technology (no temp shutoff) and nothing bad happened. The problem with todays batteries is that battery companies have sacrificed (some will argue: compromised) safety for performance. They have made the walls of the cells thinner to make more room inside to help increase capacity and voltage. They made internal changes that have reduced the cels ability to prevent pressure from building up inside the cels and it would the pressure valves on the cels don't work as well as with older generations. All this combined make these cels much more dangerous during charging than older cels despite the fact that we have much better and safer charging technology at our disposal than we had 20 years ago.

The key thing here is that even when abused to some extent the pressure valve should allow the cel to vent instead of explode. Right now that does not seem to be the case.
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Old 11-09-2007, 08:58 AM   #41
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Why not just run a123 cells? A 2s pack will easily get you through a 6 minute main w/ a wicked hot motor, they won't dump, they charge in 15 minutes, they don't explode if you crash, if they short out or get over charged they have vents that will release pressure, they are rated at a 30c constant discharge rate so you are looking at a cell that can discharge at 69 amps of continous current and even larger bursts. If you want to question their safety then take a look at what major auto manufacturer is working on an all new electric line of car that will use these cells.
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Old 11-09-2007, 09:03 AM   #42
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Quote:
Originally Posted by party_wagon View Post
Why not just run a123 cells? A 2s pack will easily get you through a 6 minute main w/ a wicked hot motor, they won't dump, they charge in 15 minutes, they don't explode if you crash, if they short out or get over charged they have vents that will release pressure, they are rated at a 30c constant discharge rate so you are looking at a cell that can discharge at 69 amps of continous current and even larger bursts. If you want to question their safety then take a look at what major auto manufacturer is working on an all new electric line of car that will use these cells.

You just have ot figure out how to fit them in existing cars.
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Old 11-09-2007, 09:48 AM   #43
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I read here a lot of people is thinking that what is happening with cells exploding is a problem of a batch of bad IB4200.

I can be wrong but I deeply believe the case is because people are using high discharge rates as never before and we have reached the cells limits.

This happened allready with electric pylon racing planes. They discharge the cells so fast that they can use them only once. If they try to use a second time the result is the same we are experiencing now.

A lot of people is now using very fast motor with levels of power not allowed before in the time of 12T brushed. Even with more powerful brushed motors they were so ineficcient and get so hot that power level were naturally limited.

After that, with brushless motors, were the esc beeing so fragile that once again power levels were again limited, but now the esc are powerful enought motors are very strong, in some cases people had changed to 5 cells racing (making it even worst) and the power is asked to the batteries. They are just saying they can not hold no more those amounts of power, or better, they can, but at that cost.

It is quite simple to me, quite simple. People have to go back in one of the things or forget NiMh. Or try to use only new batteries.

I believe that any Pro is experiencing this problem as they can allways have fresh cells from the sponsors.
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Old 11-10-2007, 03:56 AM   #44
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I don't think it is a bad batch, I consider it a faulty design. As I stated before, most problems occur during charging using charging strategies that have been used for over 20 years. It has not been until the introduction of the 4000+ Mah batteries that cel explosions have become more than a very very rare event.
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Old 11-10-2007, 05:42 AM   #45
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Default IB 4200 cell

I had a my first battery incident this past weekend with an IB 4200 svh pack.

I am not a hardcore racer and had not been out for six months. I had cycled this pack once and then put it on charge at 1.5amps. I attempted at 5 but was false peaking due to the battery being dormant for so long.

Pack seemingly ran strong, I ran the car hard. When I noticed my car slow I just assumed my pack was done. Little surprised that the car was pulsing forward when in neutral and then promptly filled with smoke.

It didn't result in a huge explosion, but obviously the pack was compromised.

I didn't abuse the battery, but I am thinking that it's condition of non-use had contributed to the failure. It was not hot when I put it in the car.
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