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Old 12-25-2010, 08:14 AM   #31
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Originally Posted by 1101 View Post
I think the real fact is Most companies dont manufacture lipo's, they rebrand them.
So they may be selling $20 lipos for $100, and in many cases are

exactly the same as chinese $6 2.4G RX's being just as good as the brand name $100 2.4G RX's
Same as the $80 Xerun escs being just as good as most of the $200 escs
same as $80 xerun's being rebranded & sold for considerably more
etc etc etc
Are you kidding me?? It's a well known fact that all the companies that sell lipos manufacture them in-house.....there are literally 100's of lipo manufacturers in this world. No company will put their sticker on a battery that is not made by them and tested by them, etc etc etc. A low dollar turnigy 2s 4000 mah 30c that costs 25 dollar will never even come close to the 100 plus dollar battery of the same rating. Sheesh man, haven't you learned that this is Rc'ing and the more something costs, the better it is??? Those stickers on people's rides don't come cheap.
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Old 12-25-2010, 08:35 AM   #32
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Ive read through this thread with some interest and I think that most of you are looking at the c rating thing from the wrong direction. Do you really think that the rc market is the primary driver for lipo battery technology? If you do you really need to remove the blinkers and look around. The rc market is a drop in the ocean and holds absolutely no sway with the cell manufacturers.
The truth is tha battery performance is driven by the demand for cordless power tools and mobile phones and laptops and the emerging electric vehicle market, not by a minority market like rc. Its always been that way as far back as I can remember even when Sanyo were producing 1200 Nicads. you dont honestly think they came up with the 1700 sce to make your buggy go faster do you?
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Old 12-25-2010, 08:44 AM   #33
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Are you kidding me?? It's a well known fact that all the companies that sell lipos manufacture them in-house.....there are literally 100's of lipo manufacturers in this world. No company will put their sticker on a battery that is not made by them and tested by them, etc etc etc. A low dollar turnigy 2s 4000 mah 30c that costs 25 dollar will never even come close to the 100 plus dollar battery of the same rating. Sheesh man, haven't you learned that this is Rc'ing and the more something costs, the better it is??? Those stickers on people's rides don't come cheap.
Do your homework bro, he is somewhat correct about the cells in batteries. Most are made in china, then bought buy manufacters and used in there products. There is a lot of truth begind this. And the more it cost the better it is, thats a joke. I had smc 4s 60c packs at 285 a pack for my buggy and they buffed in 2 race days, thats 8- 5 minute races. I have 2 turnigy 4s 5000 packs that have been charged over a hundred times that still work like the day I got them.not ragin on you, but there is only a handfull of factories in the world that make lipo cells..merry christmas
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Old 12-25-2010, 10:33 AM   #34
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Do your homework bro, he is somewhat correct about the cells in batteries. Most are made in china, then bought buy manufacters and used in there products. There is a lot of truth begind this. And the more it cost the better it is, thats a joke. I had smc 4s 60c packs at 285 a pack for my buggy and they buffed in 2 race days, thats 8- 5 minute races. I have 2 turnigy 4s 5000 packs that have been charged over a hundred times that still work like the day I got them.not ragin on you, but there is only a handfull of factories in the world that make lipo cells..merry christmas
i think the other guy was beeing sarcastic, or atleast i hope he was.
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Old 12-25-2010, 11:29 AM   #35
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Nope, ANY electrical component will have a higher internal resistance when heating up. I'm sorry, but that's just the way it is.
It is possible that the battery will have better performance when warm, but the internal resistance will be higher.
I'm sorry but i must persist that you are wrong on this one...
Just meashured my Gens Ace 5000mah 40c from 10deg celsius storage and they are 4mohm/cell but when roomtempered at 22deg they meashure 2mohm/cell.

It's a well known fact that Lipos IR reduces with increased temperature!
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Old 12-25-2010, 03:13 PM   #36
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i think the other guy was beeing sarcastic, or atleast i hope he was.
I thought that these ---> meant sarcasm.
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Old 12-25-2010, 03:55 PM   #37
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My 2 cents is that C rating isn't being measured to one Standard across the board of Brand names. Although I am only assuming C rating is amps over a given time, is that given time a nominal that all brands follow?
Is it outrageous for me to suggest that ROAR when supplied batteries for testing also test C rating? or just as good, is there a website/s that we can all goto to see independent testing?
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Old 12-26-2010, 02:08 AM   #38
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C rating means nothing without knowing the amps over a given time.IMHO it sould be more useful if they gave us the Av.voltage after discharge in a specific time and current (for example under 30A for 300sec).
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Old 12-26-2010, 02:49 AM   #39
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Originally Posted by snabbgas View Post
I'm sorry but i must persist that you are wrong on this one...
Just meashured my Gens Ace 5000mah 40c from 10deg celsius storage and they are 4mohm/cell but when roomtempered at 22deg they meashure 2mohm/cell.

It's a well known fact that Lipos IR reduces with increased temperature!
100% agreed....

For a long time back in the nicad days I have had better performance from warm batteries than cold batteries. I even convinced a few people to to convert to running packs warm after back to backing the same pack on a turbo 30 (charged with a fan on the pack and without)! The same thing applies to lipo and anyone who has done a little testing themselves knows that you get better numbers from the same pack when it is warm vs cold. Try running a pack heated to 40C vs a cold pack a feel the difference for yourselves.

Now with this in mind consider that lower C rating packs heat up more over a run. Due to this there is a point where a lower c-rating pack will be faster over a run than a higher c-rating. I personally prefer the a 40C pack over a run in 10.5 than a 50C. It just seems to hold more power over the run. Not sure about 17.5 or mad as I haven't had the chance to back to back the same cell with different C ratings but I imagine 50C or higher is actually slower with anything less powerful than a decent mod motor.
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Old 12-26-2010, 03:52 AM   #40
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Originally Posted by Born2Run View Post
C rating means nothing without knowing the amps over a given time.IMHO it sould be more useful if they gave us the Av.voltage after discharge in a specific time and current (for example under 30A for 300sec).
+1

C rating is useless if they dont tell us how they got it.

NI-MH matching printouts gave all info, not some random useless number.

Ideal would be a graphic of 10c/20c/30c/... discharge showing voltage over time.
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Old 12-26-2010, 04:12 AM   #41
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Default Cold V Warm

Below is a quote I found from a google search. Any racer who has tried warm v cold would no this to be true.

"Temperature is one of the factors that affects the rate of a chemical reaction. Batteries are electrochemical cells, so they behave predictably. The reaction that delivers charge proceeds more slowly at cold temperatures than at warm temperatures."

Electrical conductivity of metals is completely different though. The colder the better. This however is not a chemical reaction, were a battery is.

As far as C rating? It means very little. IR, voltage under load(both constant and varying) and Ave voltage for the amount of capacity you are likely to use is much more important. To verify todays "C" claims, ROAR would need to be able to discharge at up to 360 Amps. No RC connector or solder joint can sustain that for mare than a second or 2. The only way to be sure of a C rating is to have complete faith in the supplier of your Lipo.
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Old 12-26-2010, 04:38 AM   #42
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Originally Posted by rccartips View Post
Hi,

Would be helpful if those who believe or do not believe in C ratings share track test results.

Example, I've done lap times on a car where the only thing I've changed is the battery, back to back so track condition is the same.

Car = 1/10 on-road touring
Motor = Johnson 540
Test time = Time in seconds to complete 3 laps, done several times to get a consistent result

Orion Platinum 4800/25C (255grams) - 68 seconds
Peak Power 5000/50C (300grams) - 65 seconds

Conclusion: For me, the cheap China made Peak Power was 45grms heavier, yet 1 second a lap faster in a Silvercan TC class. 5% improvement in laptime is big.

hth.
Considering that the cars that won some of the stock classes in Vegas were running 25C lipo's I'm afraid I find your results to be a bit dubious, I'm not saying that you didn't get the results you claim, but there could be many other reasons. A 540 silvercan is going to use so few Amps compared with compared with even the lowest stock classes that I doubt the C rating will mean anything.
Even in 10.5 I took personal track records using a 40C lipo which has proved no better in 10.5 than my 50C (both Thunder Power)

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+1

C rating is useless if they dont tell us how they got it.

NI-MH matching printouts gave all info, not some random useless number.

Ideal would be a graphic of 10c/20c/30c/... discharge showing voltage over time.
I agree that C ratings tell us nothing without the data to back it up, or an explanation of the test procedure, but I disagree with the NiMH claims.

The stickers on NiMH's were always a little optimistic and as time went on the sticker voltages miraculously started to go up etc, yet there never seemed to be any difference on the track.

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Old 12-26-2010, 06:14 AM   #43
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Ok, claims where optimistic but C rating are too these days.

Ifmar should set up a test procedure and then maybe we'd have numbers that are realistic.

no ifmar tests= no homologations.

o the world would be so nice.
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Old 12-26-2010, 01:34 PM   #44
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Originally Posted by Dragonfire View Post
anyone who has done a little testing themselves knows that you get better numbers from the same pack when it is warm vs cold. Try running a pack heated to 40C vs a cold pack a feel the difference for yourselves.
Yep, but this has nothing to do with the IR, but with the chemical reaction. But I actually do tend to agree that the IR gets better with higher temps, because of the way a lipo is built.
On the other hand, people should stop looking for these milli ohms of better internal resitance, or a few C's more, because if you can't drive without a driving error for more then 5 minutes, you should get more track time and improve your skills.
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Old 12-26-2010, 01:58 PM   #45
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Here's what ROAR has to say on IR and heating:

Why were the new lipo battery rule addendums put in place?
8.3.2.5.3 Li-Poly battery maximum charge rate shall be 1C. C= charge amp
rate. Charge amp rate = mAh capacity/1000=XAmps.
Lipo charge rate has come under ROAR scrutiny at several large races and many club racing
venues around the country. We would like to present the plain and simple facts about charging
your lipo packs in excess of 1C:
1) Each charge of a Lipo pack beyond the 1C rate causes irreversible damage to the pack.
2) Continued charging in excess of 1C will severely shorten the useful cycle life of a Lipo
pack by as much as 90%.
3) Continued charging in excess of 1C increases the risk of a destructive pack failure each
time it occurs.
4) Charging in excess of 1C increases the internal resistance of the cells which reduces
their performance capability.
As you can see, not only are there are many negative destructive effects of charging in excess of
1C, there are absolutely no positive benefits to performance whatsoever.
This new addendum was added primarily for the safety of our membership and member tracks,
but also to protect our members from needlessly reducing the lifespan and performance
characteristics of this new long lasting and economical (if not abused) power source.
8.3.2.5.4 Maximum temperature for a charged li-poly battery pack shall be
ambient temperature +/- 5 deg.
8.3.2.5.5 The use of heating devices of any type to heat a li-poly battery is
strictly prohibited.
8.3.2.5.6 The use of cooling device and or freeze sprays of any type to cool
a li-poly battery is strictly prohibited.
It has been known for many years that Lipo packs have an optimum discharging temperature of
about 110degF. This means that a pack at 110degF will maintain higher voltage under load (due
to lower internal resistance) than the same pack started at 70degF. The pack started at 110degF
also tends to gain less heat during the discharge and finish the discharge cooler than the pack
started at 70degF when discharged near its full capability (again a function of lower internal
resistance). Warming lipo packs to or near their optimal discharge temperature has also shown
positive benefits to their cycle lifespan (how many times they may be charged and discharged
before showing degradation in performance, which signals the end of their useful life).
Why then is warming not allowed when there are so many positive benefits? For several
important reasons that were very carefully considered over the course of observing the first year
the technology was being approved and used by a large portion of our membership on a large
portion of our member tracks.
1) It was determined that the “tools” racers were using to warm their packs were in most
cases inadequate to accurately maintain a beneficial target temperature. We have seen
hot plates intended for cooking use, various body heating pads and electric blankets, and
even homemade apparatuses. While the majority of these “tools” in the properly
educated hands of a lipo expert could be used safely, the fact remains that the rest were
inherently dangerous and posed a serious safety risk to the user and all those near
him/her. In addition, “lipo experts” are still few and far between in the racing community.
So in general, the heating methods observed combined with the overall experience level
of those employing them pose a serious safety risk.
2) Another danger commonly observed was the fact that only a small minority of users truly
understood why they were heating their packs in the first place – beyond being told
somewhere that it “increases performance”. We at ROAR recognized at the outset of
publishing the initial lipo rules in the 2008 rulebook that the rules themselves were very
secondary to the more important task of educating our membership about the exact do’s,
don’ts, and the explicitly delineated safe minimums and maximums for not only
temperature, but voltage and charge rate as well. The maximum safe temperature that a
lipo pack should never exceed is 140degF. This guideline appeared in the 2008 rulebook.
Heating right to, and beyond that maximum safe temperature has been observed across
the country during this past year. So while heating to 110degF represents the limit of
being beneficial and heating to 140degF or beyond is immediately destructive to the
pack, this simple clinically proven truth is even now unfortunately being debated publicly.
So simply stated, ROAR believes the collective knowledge base of our users and tracks
is still lacking (despite our educational efforts) in the critical understanding of heating and
its positive effects in order for it to be used accurately and beneficially, rather than
destructively at the peril of the member and member track.
3) ROAR continually seeks to encourage the most fair and economically feasible racing
possible. Heating lipo packs clearly increases performance, but from the above it’s also
clear that the devices employed to do so come at an extra expense to the racer, as well
as being difficult to regulate with any precision. This cost factor combined with yet one
more factor potentially limiting performance unless extra costly and time/enjoyment
reducing measures are taken by the budget racer, weighed heavily in the decision to
essentially disallow any heating whatsoever.
So the summary of the situation is: ROAR believes that despite its benefits, lipo pack heating
cannot be allowed for the reasons of competition, cost, safety, and current member knowledge
base.
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