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  1. #1
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    Unclear on LiPos

    There are many threads on this subject, but none entirely clear on this one topic.

    To my understanding the Slash 4x4 takes between 60 and 80 amps. I purchased a 3s lipo 5000mah 20c continuous with a burst rate of 30c... making it 100 amps. But are there any performance differences between a 20Ah 5c and a 2.5Ah 40c lipo? Both are 100 amps. I bought the battery for speed runs only and I want power over all else, so I guess what I want to know is is if I could have gotten more power with a higher c rating.

    On a side note, can my vehicle run 4s/5s/6s etc. lipos? How high can I go before the damage to the Slash is immediate and unavoidable? What is the absolute fastest gearing ratio if I will only be driving it for seconds at a time?

    Note: I am not interested in upgrading the ESC or motor at this time.
    Last edited by dzylon; 10-17-2011 at 04:10 PM.

  2. #2
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    sorry i can`t help you. i don`t no that much about lipo`s, but i do know that for specific (slash 4x4) questions,... there is
    this part of the forum
    http://traxxas.com/forums/forumdisplay.php?73-Slash-4X4
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  3. #3
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    It really is more of a general question, but OK.

  4. #4
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    if its the standard esc then it can only take 3s or so traxxas say as ive heard of some people killing the esc using 3s after short runs and the higher the c rating the more power just what ive read elsewere so i could be wrong but i would stick to 2s for now or use 3s sparingly

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    It's only said to handle 3s. But like I did to my erevo, my esc on that is rated for 4s lipo but the esc handles 21 volts and that is 5s lipo. I wouldn't recommend that.

    As for c rating and mAh. More mAh the longer runtime and more c or amp output the more get up and go and torque I've found. Voltage is voltage. Voltage is top speed. I doubt you'll find much if any speed difference between a 20Ah 5c and a 5Ah 20c.


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  6. #6
    RC Champion Mr Wolf's Avatar
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    Quote Originally Posted by dzylon View Post
    To my understanding the Slash 4x4 takes between 60 and 80 amps. I purchased a 3s lipo 5000mah 20c continuous with a burst rate of 30c... making it 100 amps. But are there any performance differences between a 20Ah 5c and a 2.5Ah 40c lipo? Both are 100 amps. I bought the battery for speed runs only and I want power over all else, so I guess what I want to know is is if I could have gotten more power with a higher c rating.
    Your understanding in mostly accurate but I may be able to add a few things.

    Lipos have an ability to provide a higher amount of current (amps) for short periods than they can continuously. This is often called the battery's "burst" rating. e.g. My 5000mah 2S packs are rated at "20C continuous" and "30C burst". These packs can (in theory) therefore offer up 100A continously and up to 150A in short bursts.

    A motor can draw current from a battery is a similar way. If you gun the throttle the motor will draw high amps in an attempt to do what the ESC is telling it to do - spin fast. This draw will settle down as speed picks up.

    The Velineon is rated by Traxxas at 100A peak current draw, 65A continous current draw. The peak rating has proved to be fairly accurate by some independent data logging.

    IMO to be certain that a battery is not holding back performance it's best to use a battery that can meet a motor's peak demand fron its continuous amp capability, not its burst capability. This may seem overkill but I wouldn't want to put my faith in a battery's burst period being at least as long as the motor's/peak period as neither are defined or known.

    So for a Velineon I would want a battery that could deliver at least 100A continuously, that way I wouldn't need to even consider the whole peak/burst thing and would know that my lipo should never be unduly stressed and should therefore live a longer, happier life.

    As regards what's the best 100A battery spec (e.g. 5000mah 20C, 4000mah 25C, 2500mah 40C) I would go with the higher capacity lower C rated battery every time for two reasons. First the obvious - it's going to give more run time. Second, it will probably be able to deliver the most punch/current as its capacity rating is much less likely to be be oversstated than its "C" rating.

    A battery's capacity can be quickly proved fairly accurately on almost any cheap digital charger and an exaggarated capacity claim would be quickly exposed in the market leading to legal and reputational issues for its supplier.

    A "C" rating cannot to be proved easily as it requires very expensive equipment and, more to the point, there is is no common definition of it. For "C" ratings to be comparable they would have to all reflect the same safe level of maxiumum discharge rate. E.g. at a common discharge temperature but even then, due to differing constructions, some may be able to support higher safe discharge temperatures than others.

    For a Slash 4x4 I would go with a minimum 150A continuous discharge battery (that was at least 5000mah) as I might want to upgrade the motor at some point to something like a SCT 3800 and not have to buy a new battery. That motor has known to spike up to around 150A.
    Last edited by Mr Wolf; 10-17-2011 at 09:54 PM.
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  7. #7
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    Agree with most of the previous post except for going low on C rating. You want a C rating higher than what your motor/esc will demand. i.e. If the minimum constant required is 25c, you should consider a 30c or higher battery. This will improve your battery life as the current draw is less likely to constantly be at or near its limits.
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  8. #8
    RC Champion Mr Wolf's Avatar
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    Quote Originally Posted by LaTuFu View Post
    Agree with most of the previous post except for going low on C rating. You want a C rating higher than what your motor/esc will demand. i.e. If the minimum constant required is 25c, you should consider a 30c or higher battery. This will improve your battery life as the current draw is less likely to constantly be at or near its limits.
    I'm sorry but you appear to misunderstand what a "C" rating actually is - for a start a motor doesn't "demand a 'C' rating", it demands amps. A Lipo's ability to deliver those amps is a function of both its capacity (mah) and its ability to discharge that capacity ("C"). "C" ratings mean nothing without the capacity. Mah/1000 x C rating = Amp output capability.

    Battery manufacturers know that many people erroneously equate the "C" rating to being battery's current output and therefore have a vested interest in overstating it.

    I repeat, "C" rating does not equal current output. If it did it would be quoted in amps. It refers to the rate at which a battery's capacity can be discharged, you need to calcuate the amps yourself.

    My comment about a low "C" rating being preferable was only in relation to batteries that had the same amp output capability. i.e. 5000mah 20c is preferable to 2500mah 40c because the 40c on the second battery is more likely to be overstated than the 5000mah of the first one. Of course for two batteries of the same mah capacity a higher "C" is better than a lower one.
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  9. #9
    RC Turnbuckle Jr.
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    Yea wolf is pretty much spot on....

    But these conversations should be getting more rare. Its rare to see a lipo that can't provide the amps these days. Go buy any 5000 mah lipo, and it'll do just fine in a Slash. If you wanna buy the highest C rate you can, go nuts. Its not that much of a difference.

    I typically look for the highest watt-hours I can fit.... meaning what battery has the most total potential?

    But are there any performance differences between a 20Ah 5c and a 2.5Ah 40c lipo?
    We gotta assume the same cell count on each pack to be fair.

  10. #10
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    Quote Originally Posted by Mr Wolf View Post
    ... Battery manufacturers know that many people erroneously equate the "C" rating to being battery's current output and therefore have a vested interest in overstating it.
    Not all overstate C ratings.

  11. #11
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    wolf you know you said that it would be better for a higher mah than c rating this is true and will provide a more accurate result of how many amps the battery can provide but I think (correct me if I'm wrong) that say that when only 2500mah is left in your 5000mah 25 c pack it will only provide 62.5 amps rather than 125 but if you go with say a 2500mah pack with 50c and you run that to half way empty so 1750mah you'll find it can supply 87.5 amps which is some amount more and surely if this were correct you wouldn't get so much voltage sag and premature lvc's
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  12. #12
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    If the cells in a pack are accurately rated, the cells should give up the complete "C x Amps" rating from full down to 3.0 Volts, while providing a minimum of 90% of the stated capacity.

  13. #13
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    Quote Originally Posted by Jakey View Post
    Not all overstate C ratings.
    Considering there is no known standard for testing C ratings in the first place, you can't possibly know this.

    Quote Originally Posted by The VXL View Post
    (correct me if I'm wrong) that say that when only 2500mah is left in your 5000mah 25 c pack it will only provide 62.5 amps rather than 125
    you wrong!

    Just look at the total capacity on the pack when estimating amps.
    Last edited by cooleocool; 10-20-2011 at 07:23 PM. Reason: merge

  14. #14
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    Quote Originally Posted by ducati777 View Post
    Considering there is no known standard for testing C ratings in the first place, you can't possibly know this.
    Oh, but I do know!!!!
    In my response that you quoted, I listed the C rating standard.

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    Quote Originally Posted by Jakey View Post
    Oh, but I do know!!!!
    In my response that you quoted, I listed the C rating standard.
    I don't see any standard, I see a theory on how the math should work on a C rate.

    I don't see any companies stating how they test their C rates.

    There simply isn't a standard, when a company like maxxamps claims 150C, do you think for 1 second their pack can actually deliver 150C in amperage?

    When my ****'s say 25-50C, whats that mean? How long can I get 50, if I can get it at all? Are you saying that I could discharge the entire pack in just over a minute and not expect any risk?

  16. #16
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    'Tis true, there are no set or agreed upon standards when it comes to how a C rating is determined. I wouldn't expect a lipo to still provide maximum punch and discharge capabilities when depleted to 3.0v per cell, generally 3.2-3.4v is where the LVC is set and that's when I'd expect to see the performance drop off too, with the voltage rebounding slightly once the load is removed.

    I'd like to see some documentation or press releases/ spec sheet showing how the c rating was determined & what voltage was deemed to be the minimum allowable for the given amount of current draw; can't say I've ever seen such info released by any manufacturer, at best I've seen a few dozen comparison graphs that show current draw far below what the packs are supposedly rated for...

    ------------

    Back to the OP though, a pack that has a very large capacity but very low C rating will struggle to supply the current as efficiently as a smaller but higher quality pack with a higher C rating. While it is true that the total current output is the same in the examples suggested, low discharge packs have a much higher internal resistance that naturally restricts current flow, such is the case with normal nimh batteries found in tv remotes or cameras- those can get quite warm when pushed 'hard' as they aren't designed for high discharge and charge rates like r/c grade or truly high discharge batteries.

    All things considered, a 5000mah 20c pack would be much better than a 20,000mah 5c pack...
    Last edited by ArmyofDarkness; 10-18-2011 at 04:28 PM.
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  17. #17
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    Just because some companies blatantly ignore a standard, does not mean it doesn't exist.

  18. #18
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    Some companies have higher standards than others, thats for sure...
    Jakey, what is the standard way to c-rate a pack?
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  19. #19
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    In theory, you hook the cell directly to the test equipment, and apply fixed loads ( of different sizes, in amps ) whilst plotting the discharge; once the cells fall below LVC level you stop the test. You can then look at the graph and see how much the voltage dropped with each given load, and ( in my mind atleast ) use the load which resulted in the best runtime vs voltage held ( without dropping too low too early )result to determine the C rating. It's then a simple matter of dividing the load by the capacity to arrive at the C rating, for example:

    100amps / 5Ah ( where 5Ah = 5000mah ) = 20C.

    As said before though, there is no agreed voltage at which the C rating is determined, everyone has their own ideas which can and does cause a lot of disparity in the ratings you see out there with some brands ( I think maxamps use 0.1v, lol ).

    You can test a C rating very easily though, it just means trying to draw as much current as it is rated for ( with some $$$ equipment ) and seeing how low the voltage drops per cell- if it drops below ~3.2v then you know it's over rated, and you can use the same methodology to determine the true C rating ( look where the voltage only drops to just above LVC level and see how much current was drawn there, then divide that amount of current by the capacity ).

    If only companies added a little '@3.2v per cell' or whatever voltage they use after the nice big continuous & burst rating info, then it would solve all of this discussion and arguments in an instant; they wouldn't even need to use the same voltage so long as they were honest about what voltage they used, so that it could be tested and found to be true or not....
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  20. #20
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    Quote Originally Posted by ArmyofDarkness View Post
    In theory, you hook the cell directly to the test equipment, and apply fixed loads ( of different sizes, in amps ) whilst plotting the discharge; once the cells fall below LVC level you stop the test. You can then look at the graph and see how much the voltage dropped with each given load, and ( in my mind atleast ) use the load which resulted in the best runtime vs voltage held ( without dropping too low too early )result to determine the C rating. It's then a simple matter of dividing the load by the capacity to arrive at the C rating, for example:

    100amps / 5Ah ( where 5Ah = 5000mah ) = 20C.

    As said before though, there is no agreed voltage at which the C rating is determined, everyone has their own ideas which can and does cause a lot of disparity in the ratings you see out there with some brands ( I think maxamps use 0.1v, lol ).

    You can test a C rating very easily though, it just means trying to draw as much current as it is rated for ( with some $$$ equipment ) and seeing how low the voltage drops per cell- if it drops below ~3.2v then you know it's over rated, and you can use the same methodology to determine the true C rating ( look where the voltage only drops to just above LVC level and see how much current was drawn there, then divide that amount of current by the capacity ).

    If only companies added a little '@3.2v per cell' or whatever voltage they use after the nice big continuous & burst rating info, then it would solve all of this discussion and arguments in an instant; they wouldn't even need to use the same voltage so long as they were honest about what voltage they used, so that it could be tested and found to be true or not....
    Didn't I basically say this in post #12?

  21. #21
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    Quote Originally Posted by Jakey View Post
    Didn't I basically say this in post #12?
    In a brief way you did, but I likes me drawn out explanations, does I....
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  22. #22
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    Quote Originally Posted by Jakey View Post
    Didn't I basically say this in post #12?
    I don't think so, I think you just made a vague reference to accurately. AOD threw around numbers that make up his version of a standard. We know what the "standard" means to him, although its no more accurate in how that little C rating ends up on the sticker.

    Quote Originally Posted by Jakey View Post
    If the cells in a pack are accurately rated, the cells should give up the complete "C x Amps" rating from full down to 3.0 Volts, while providing a minimum of 90% of the stated capacity.

    My point, like AOD's, is there's no voltage sag standard, no time standard, no capacity standard... Some are testing at the cell, I'd prefer at the pack level... so when you act like there is a "standard" system to rate lipos, its false. I'm yet to find a manufacturer that gives that sort of actual data.

    And the term standard itself... implies that 2 companies would have to use the same method to make a comparison. That doesn't exist. We like to believe the companies are at least testing their own packs in some sort of controlled method. That way there's a difference between a ******* 20C and a ******* 40C. I'm not even convinced of that, I think the marketing department says 65C is the new 30C!!!

    But no comparison can be accurately made between brand A's 20C, and brand B's 20C.
    Last edited by ducati777; 10-19-2011 at 03:34 PM.

  23. #23
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    Quote Originally Posted by ducati777 View Post
    I don't think so, I think you just made a vague reference to accurately. AOD threw around numbers that make up his version of a standard. We know what the "standard" means to him, although its no more accurate in how that little C rating ends up on the sticker.




    My point, like AOD's, is there's no voltage sag standard, no time standard, no capacity standard... Some are testing at the cell, I'd prefer at the pack level... so when you act like there is a "standard" system to rate lipos, its false. I'm yet to find a manufacturer that gives that sort of actual data.

    And the term standard itself... implies that 2 companies would have to use the same method to make a comparison. That doesn't exist. We like to believe the companies are at least testing their own packs in some sort of controlled method. That way there's a difference between a ******* 20C and a ******* 40C. I'm not even convinced of that, I think the marketing department says 65C is the new 30C!!!

    But no comparison can be accurately made between brand A's 20C, and brand B's 20C.
    I must ask .... When you purchase a new full-sized car, do you ask to see the standards that were used in the design and manufacture of the of car's components? If the standards are not provided along with data and empirical numbers, to you cynically label them as false standards? How about appliances in your home? Do you ask for standards and number/data examples to support said standards while talking with the salesman at Best Buy or Sears? If not, why?????

    As for some RC battery companies using one C-rated cell and then building/marketing/selling several different C-rated packs around that one cell, well yes, that does happen. You hit the nail right on the head with that one, however that does not mean the guilty company was not aware of the true C rating of the cells in the first place. The cells were manufactured and tested to a standard in order to determine their rating. The cell factories are very aware of the true C rating and capabilities of their cells. The standards do exist, but sadly some RC battery companies simply chose to ignore them.
    Last edited by Jakey; 10-20-2011 at 08:47 AM.

  24. #24
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    Guys, this debate really needs to stop. Thanks.
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