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Old 04-05-2007, 02:27 PM   #241
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Quote:
Originally Posted by r0adrunn3r
Mr Black - if a LiPo cell is torn apart - What happens?

From the videos I have seen, the explosion and fire is a result of overcharging the packs. I haven't heard if an explosion if the cell is ripped apart...

Tearing it apart should not more ill effects then the nail test shows.

We ground a corner off of one and it actually did nothing so results may very but we have yet to have any smoky explosions or fire on any of our Platinum or Carbon packs to this date and they have both been out for about 2 years now.
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Old 05-17-2007, 12:04 PM   #242
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good info concerning cycle life of cells from various manufacturers.
helps if someone can read german.


http://www.slowflyer.ch/000000972c0e...290e/index.php
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Old 05-17-2007, 12:59 PM   #243
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Originally Posted by linger
good info concerning cycle life of cells from various manufacturers.
helps if someone can read german.


http://www.slowflyer.ch/000000972c0e...290e/index.php
This may help:

http://babelfish.altavista.com/babel...0e%2Findex.php
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Old 07-06-2007, 09:00 AM   #244
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ok guys I've got a question about C ratings. I understand how you use it with the capacity to get your constant amp draw but help me with this scenario....

Lipo A - 15C 5000
Lipo B - 20C 5000

Lets say we run a stock motor so either of these should handle the situation just fine. Generally I would think the higher the C rating the better the cell (lets also assume a both packs from a quality company like Kokam). What will the 20C do better than the 15C? Hold voltage under load better? More efficient? More runtime? Anything?
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Old 07-06-2007, 09:17 AM   #245
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Originally Posted by padailey View Post
ok guys I've got a question about C ratings. I understand how you use it with the capacity to get your constant amp draw but help me with this scenario....

Lipo A - 15C 5000
Lipo B - 20C 5000

Lets say we run a stock motor so either of these should handle the situation just fine. Generally I would think the higher the C rating the better the cell (lets also assume a both packs from a quality company like Kokam). What will the 20C do better than the 15C? Hold voltage under load better? More efficient? More runtime? Anything?
The higher C-rating will make the battery able to withstand a higher amp load. Running a 5000mAh with a stock motor it will be difficult if even possible to reach the limit of either so you will more then likely not be able to notice any difference.

But if you had a 3000mAh @ 15C or 20C then you would feel better performance as it would be able to deliver and withstand a higher amp draw.
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Old 07-06-2007, 05:24 PM   #246
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Originally Posted by MrBlack View Post
NiMh are only faster at the beginning of a run and only with certain Motor sizes due to the resistance both internal as well as external that NiMh cells have.

The curve of a NiMH is like an arch going down steeper and steeper from the first second. A LiPo has more of a straight slanted slope so within the first minute or two the NiMH begins to show less voltage then the LiPo.

For some people speed is measured before the first lap so for them it is safe to say a NiMH with 6 cells that tops out at close to 9.6V volts delivers more power and a LiPo that tops out at 8.4 delivers less. However it is not that black and white as LiPo have less internal/external resistance (this is why NiMH get so hot, that is power being wasted) and can deliver that power more freely.

Think of it like a garden hose hooked to a bucket. if both batteries are the same capacity then the LiPo has a bigger hose where the NiMh has a smaller hose giving it more pressure but this creates leaks as it flows which wastes water.


MrBlack,
I plotted the discharge curve (voltage against time) for my lipo pack and compared it against the same for my IB4200. I used a CE Turbo 35 set at a 30 amp discharge. What I found was that the IB4200 pack was far superior to the Lipo throughout the entire cycle.
I'm not slamming lipos or singing the praises of Nimh. I was just surprised that the lipo didn't produce as much power as I had anticipated.
I ran the the lipo at my local track and it was .2 to .3 off of my Nimh lap times.That's why I decided to plot the curves.
I run 19t TC, rubber.
Thanks.
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Old 07-06-2007, 05:56 PM   #247
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Originally Posted by jag88 View Post
MrBlack,
I plotted the discharge curve (voltage against time) for my lipo pack and compared it against the same for my IB4200. I used a CE Turbo 35 set at a 30 amp discharge. What I found was that the IB4200 pack was far superior to the Lipo throughout the entire cycle.
I'm not slamming lipos or singing the praises of Nimh. I was just surprised that the lipo didn't produce as much power as I had anticipated.
I ran the the lipo at my local track and it was .2 to .3 off of my Nimh lap times.That's why I decided to plot the curves.
I run 19t TC, rubber.
Thanks.
The biggest misconception about Lipos is that they will give drivers that use them an unfair advantage, especially in the stock and 19T classes. This is false. Lipos give the greatest advantage when the load placed upon them increases. So modified racers will see the greatest inprovement in performance. Or those who donot want to buy new batteries all the time.

Linear discharge testing will not show the advantage of LiPo. Thirty amps is below what a battery will see in competition - even in stock. So this testing is not a true indicator of performance.

This might not be true in your case, but if you simply install a Lipo and run laps without any changes to your vehicle, chances are you will run slower. Balance and weight distribution change significantly. And the car's setup must be adjusted accordingly.
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Old 07-06-2007, 06:04 PM   #248
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Quote:
Originally Posted by Rick Hohwart View Post
The biggest misconception about Lipos is that they will give drivers that use them an unfair advantage, especially in the stock and 19T classes. This is false. Lipos give the greatest advantage when the load placed upon them increases. So modified racers will see the greatest inprovement in performance. Or those who donot want to buy new batteries all the time.

Linear discharge testing will not show the advantage of LiPo. Thirty amps is below what a battery will see in competition - even in stock. So this testing is not a true indicator of performance.

This might not be true in your case, but if you simply install a Lipo and run laps without any changes to your vehicle, chances are you will run slower. Balance and weight distribution change significantly. And the car's setup must be adjusted accordingly.
Rick summed this up spot on! If you were use a higher discharge load, such as 50 amps as a representative for modified racing, you would see the lipo pack will excel for greater than any of our current IB or EP packs, period.
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Old 07-06-2007, 06:49 PM   #249
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Thanks Rick/Stephen.
I run in a 19t rubber series where the Money motor is the spec motor. The Money motor likes to be geared up and I run mine around a 1.20" r/o. The guy I'm chaseing runs his around 1.40 !! He's running a lipo and I'm running Nimh. He's about a tenth or two quicker. If the lipos like amp draw then that's maybe why he's quicker. It's got to be tough on the motor but I'll give it a try .
Thanks.
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Old 08-22-2007, 12:53 PM   #250
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Bumping for those new to RcTech and/or Lipos
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Old 08-22-2007, 01:22 PM   #251
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I love you, "LiPo Awareness" thread. *sniffle*
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Old 08-22-2007, 06:40 PM   #252
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In my understading I always thought the major benefit of lipos is found in the 1/8th scale conversion side of things. Lipos can deliver the required amps while also reducing massive weight from batteries. I had an lst2 converted to lipo/brushless and I couldn't imagine the weight and the resultant strain that using nimh batteries would cause.
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Old 08-22-2007, 07:26 PM   #253
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Gentlemen, I believe we have our standard size.

http://www.redrc.net/2007/08/velocit...mah-lipo-pack/
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Old 08-22-2007, 07:31 PM   #254
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Quote:
Originally Posted by syndr0me View Post
Gentlemen, I believe we have our standard size.

http://www.redrc.net/2007/08/velocit...mah-lipo-pack/
That would probably make it identical to the Schumacher Core 5000 mAh packs then right? Wonder if they'll disclose the cell maker.
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Old 08-22-2007, 07:51 PM   #255
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Originally Posted by syndr0me View Post
Gentlemen, I believe we have our standard size.

http://www.redrc.net/2007/08/velocit...mah-lipo-pack/
I like the design better than all the other packs I've seen. All the ports on top are a nice feature.
Its going to be tough to limit batteries with out limiting the classes to minutes.
Most of the people running lipos are going to the most Mah's as possible.
I hope they don't impose a size before considering just how many 6000 and higher are out there.?
I think they can squeeze 8000 mah's into that size with out a case.
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