SMC Lipos 7.4 5000mah
10-16-2007, 02:06 PM
#511
REGARDING A PUNCTURE TEST:
First, there are no test standards for a puncture test. Second, there are too many variables that can affect the outcome of this test and manufacturers will tweak these variables to make their cells look good.. The failure mode is not the pouch being punctured (which does nothing more than drying out the electrolyte and killing the battery), but puncturing a cell with a conductive object basically creates a short circuit between the layers within the cell. This short circuit creates heat and once a portion of the cell reaches a certain temperature then you have a thermal runaway (usually fire) condition. For example, if puncturing with a nail, the size, the diameter, the conductivity, and the speed of the nail makes a huge impact on whether the cell goes up in flames. A large diameter nail is less likely to make the cell go up in flames since the mass acts as a heat sink and cools down the short circuit. A clean fresh conductive nail is much more likely to start thermal runaway than an old nail with a nice oxidation layer. The speed at which the nail penetrates the cell is plays a huge role as well - the faster - the worse the results. The state of charge of the battery has a significant impact too - since it's nearly impossible for a discharged battery to generate enough heat during a short circuit to cause thermal runaway. Basically, until there is one standard that all manufacturers test to, this test is useless.
First, there are no test standards for a puncture test. Second, there are too many variables that can affect the outcome of this test and manufacturers will tweak these variables to make their cells look good.. The failure mode is not the pouch being punctured (which does nothing more than drying out the electrolyte and killing the battery), but puncturing a cell with a conductive object basically creates a short circuit between the layers within the cell. This short circuit creates heat and once a portion of the cell reaches a certain temperature then you have a thermal runaway (usually fire) condition. For example, if puncturing with a nail, the size, the diameter, the conductivity, and the speed of the nail makes a huge impact on whether the cell goes up in flames. A large diameter nail is less likely to make the cell go up in flames since the mass acts as a heat sink and cools down the short circuit. A clean fresh conductive nail is much more likely to start thermal runaway than an old nail with a nice oxidation layer. The speed at which the nail penetrates the cell is plays a huge role as well - the faster - the worse the results. The state of charge of the battery has a significant impact too - since it's nearly impossible for a discharged battery to generate enough heat during a short circuit to cause thermal runaway. Basically, until there is one standard that all manufacturers test to, this test is useless.
An actual Lipo expert! 
10-16-2007, 02:16 PM
#513
The rationale for this is that Kokam changed their chemistry 1.5 years ago where the voltage was reduced and the safety levels were increased. Kokam cells actually put out more voltage 2 years ago than they do today. For them, it was a tradeoff that they accepted.
Previously, the older Kokam cells would go into thermal runaway somewhere between 12-16V. The current chemistry will withstand well over 18V/cell.
On top of that, the current chemistry of Kokam is self-extinguishing in the event of a thermal runaway condition. If you perform a massive overcharge test you will see that these cells don't create any flame.
Also, the newer Kokam cells perform better under certain conditions of a nail penetration test than their old cell.
These features may be overkill for the RC industry since Kokam took a conservative approach and it's debatable how much safety should be required.
I don't work for Kokam, but I have tested a tremendous amount of lipo cells from various manufacturers and Kokam's focus on safety is undeniable.
10-16-2007, 02:33 PM
#515
linger thanks for your info it's appreciated like I said earlier I'm no expert when it comes to Lipos but our manufacturer told me that the packs pass all the saftey requirements established for Lipos. That being said I will pass on your info to him and see what his comments are.
As far as standards of testing that I can understand that various manufacturers can peform tests to help out there cause. I have seen this to be the case with the C rate. I sent in a 25C 5000 pack to be tested and the results came back that this particular pack was a 15C at best. This is why it took us a long time to find a manufacturer who wanted to work with us on trying to create a high performance pack with a true C rate.
As far as standards of testing that I can understand that various manufacturers can peform tests to help out there cause. I have seen this to be the case with the C rate. I sent in a 25C 5000 pack to be tested and the results came back that this particular pack was a 15C at best. This is why it took us a long time to find a manufacturer who wanted to work with us on trying to create a high performance pack with a true C rate.
10-16-2007, 04:45 PM
#518
it lasts a long long long time, I can make my tc4 thermal (10 min) and then let it cool down and I can easy get another 10-15 min out of it. It is an awesome pack. Faster than the orion, It will fit into some better, and some worse. But if you have a offroad car, emaxx, traxxas, tc4 just about anything that is stick pack capable, try this pack out, you will thank me.
10-16-2007, 05:19 PM
#519
it lasts a long long long time, I can make my tc4 thermal (10 min) and then let it cool down and I can easy get another 10-15 min out of it. It is an awesome pack. Faster than the orion, It will fit into some better, and some worse. But if you have a offroad car, emaxx, traxxas, tc4 just about anything that is stick pack capable, try this pack out, you will thank me.
10-16-2007, 05:57 PM
#522
Yep...my first Platinums lasted for a couple years. One died from leaving a car on by mistake (coulda swore I turned it off...LOL), the other got "puffed" a year ago running a 7700 Mamba with the voltage cutoff turned off (...coulda sworn I wasn't an idiot) and it lasted another year after that before it finally died.
So...that's the kind of life I'm looking for if I'm going to pay 125-150 for a battery. I could give a crap about a couple tenths of a volt. I want longevity...runtime is nice as well, but aside from the "7700 incident", I've never dumped a 4800.
So...that's the kind of life I'm looking for if I'm going to pay 125-150 for a battery. I could give a crap about a couple tenths of a volt. I want longevity...runtime is nice as well, but aside from the "7700 incident", I've never dumped a 4800.
10-16-2007, 06:10 PM
#523
No matter what I say or prove some of you will never be happy with it and just want to argue. Cycle life is relative to use and abuse and I'm very confident that our packs have a high cycle life as they meet the standard that determines capacity drop at the specified C rate.
You guys just need to drop the price issue as I mentioned it before the major distributors are selling our pack 12-15 dollars cheaper than the Orion pack. Plus our pack has a higher C rate and more capacity which means a higher cost so please tell me the issue with our pricing ?
If we release a 20C pack with 4700-4800 mAH and offer it for 30 dollars less would that make you guys happy ? I doubt it as the same 4-5 guys that like to argue and comment about everything will surely find a problem with that pack as well.
You guys just need to drop the price issue as I mentioned it before the major distributors are selling our pack 12-15 dollars cheaper than the Orion pack. Plus our pack has a higher C rate and more capacity which means a higher cost so please tell me the issue with our pricing ?
If we release a 20C pack with 4700-4800 mAH and offer it for 30 dollars less would that make you guys happy ? I doubt it as the same 4-5 guys that like to argue and comment about everything will surely find a problem with that pack as well.
10-16-2007, 08:59 PM
#524
No matter what I say or prove some of you will never be happy with it and just want to argue. Cycle life is relative to use and abuse and I'm very confident that our packs have a high cycle life as they meet the standard that determines capacity drop at the specified C rate.
I abused mine and it still lasted two years before giving up the ghost. I wonder how long it would have lasted without the abuse?
The thing is that Kokam and Orion actually say how long it's supposed to last (1000+ cycles, IIRC) without losing much capacity (<20%) and I haven't heard or experienced that they were exaggerating. Two years, once or twice a week, two packs in constant use, racing, bashing...enduros, several full charges in the same day, back-to-back-to-back...
So...how long do you say yours will last?
It's not the money thing. I'd rather pay more for one I know will live. Are you going to guarantee that yours will live like the Orions? They back theirs up...and they seem to last really, really well. I haven't heard one thing that gives me a hint that your batteries are any different than any other soft Lipo pack...still no info, aside from your assurances.
10-16-2007, 10:22 PM
#525
4. For the cycle life, in Kokam's data, its cell will remain 80% of its capacity after 60 cycle times. However, Kokam discharge the cell at only 8C. Our standard is to remain 80% of the cell's capacity after 50 cycle times but with 22C discharge rate. Thus, with only 8C discharge rate, our cell can do over 60 cycle times with 80% capacity remaining.
If our packs can hold 80% of it's capacity after 50 cycles at it's rated C rate which means they would easily do more cycles at a lower C rate like Kokam uses to establish it's test result after 60 cycles then I think we can assume our packs will hold up as well as theres if they hold up under the C rate test.
I'm sure you can argue about this as well and bottom line for those who are happy and trust the Kokam/Orion pack just keep using it. Sales of our pack have been real good with positive feedback from those who use them but then again this may not be good enough for you.
If our packs can hold 80% of it's capacity after 50 cycles at it's rated C rate which means they would easily do more cycles at a lower C rate like Kokam uses to establish it's test result after 60 cycles then I think we can assume our packs will hold up as well as theres if they hold up under the C rate test.
I'm sure you can argue about this as well and bottom line for those who are happy and trust the Kokam/Orion pack just keep using it. Sales of our pack have been real good with positive feedback from those who use them but then again this may not be good enough for you.