Results 1 to 15 of 15
  1. #1
    RC Enthusiast
    Join Date
    Dec 2013
    Location
    Bloomington, IN
    Posts
    34

    Lightbulb Lipo 2s 100c vs. 50c questions, need your input

    1st). What advantage would a lipo 5000mah 2s 100c have over a 5000mah 2s 50c in a Stock Slash 2wd running the XL5 and Titan 550 motor?

    2nd). What advantage would a lipo 5000mah 2s 100c have over a 5000mah 2s 50c in a Slash 2wd with a Velineon or Castle 3800?

    I know there is the capability of the higher output with the 100c but is the a point when it doesn't matter?

  2. #2
    RC Turnbuckle Jr. JimmyNeutron's Avatar
    Join Date
    Oct 2009
    Location
    Alma, Michigan
    Posts
    12,316
    The extra capability doesn't matter when you are a good margin above what the power system is rated for.

    I also hope the 100C was just an example... I have yet to see a pack that is actually 100C.
    Whatever it is I just typed... could be wrong.

  3. #3
    RC Enthusiast
    Join Date
    Dec 2013
    Location
    Bloomington, IN
    Posts
    34

  4. #4
    RC Turnbuckle Jr. JimmyNeutron's Avatar
    Join Date
    Oct 2009
    Location
    Alma, Michigan
    Posts
    12,316
    Just my opinion... but from what I understand on their testing alone that pack is not 100C.
    Whatever it is I just typed... could be wrong.

  5. #5
    Marshal ksb51rl's Avatar
    Join Date
    Nov 2006
    Location
    Northern NJ
    Posts
    17,377
    Agreed. I am reasonably sure 100C is not possible with the state of LiPo technology.
    Alt-248 on the number pad =

  6. #6
    Traxxas Employee TireSlinger's Avatar
    Join Date
    Sep 2010
    Posts
    585
    The standard accepted value for C rating as I understand it is the capacity of the pack x the C rating. The pack pictured above is 5.6A x 100c = 560 amps. I cannot believe those bullet plugs or wires will handle that, much less the cells.

    Realistic C ratings are usually in the 15 - 35C range from my experience. A 5000mah 25C battery for example can deliver 100 amps continuously without damage. Most batteries can also handle a 'burst' current of up to double the continuous rating, so 200 amps for a short duration. This depends on the pack's design and manufacturer however.

    If your packs are adequate for your system C rating really isn't a huge factor. If your system pulls a max of 100 amps at burst load and you have packs that are rated for 100 amps continuous load then going to a pack rated for 200 amps continuous isn't going to do much, the system only pulls the power it needs.

  7. #7
    RC Turnbuckle Jr.
    Join Date
    Dec 2004
    Posts
    3,764
    Quote Originally Posted by TireSlinger View Post
    The standard accepted value for C rating as I understand it is the capacity of the pack x the C rating. The pack pictured above is 5.6A x 100c = 560 amps. I cannot believe those bullet plugs or wires will handle that, much less the cells.

    Realistic C ratings are usually in the 15 - 35C range from my experience. A 5000mah 25C battery for example can deliver 100 amps continuously without damage. Most batteries can also handle a 'burst' current of up to double the continuous rating, so 200 amps for a short duration. This depends on the pack's design and manufacturer however.

    If your packs are adequate for your system C rating really isn't a huge factor. If your system pulls a max of 100 amps at burst load and you have packs that are rated for 100 amps continuous load then going to a pack rated for 200 amps continuous isn't going to do much, the system only pulls the power it needs.
    Unknown to most, it is not the pack that is "C" rated but rather the cells within the pack, but somewhere during the several years of LiPo adaptation to RC, C rating was redirected or misunderstood to mean pack continuous discharge. However your point about the assembled pack (wires, connector, etc.) not handling such large loads is incredibly correct!

    One step further - The true definition of C rating as it applies to the cells should be viewed more as the maximum Amp discharge rate the cells can sustain before damage occurs. Think of the C rating as similar to the RPM redline limit in your full sized car. As the engine approaches the redline the likely hood of potential damage increases, which is also directly related to a potential decrease in total engine operating life hours. Taken to the next level and exceed the redline and damage will occur. The C rating of LiPo cells is very analogous, well at least to make it understandable.

    As for higher C ratings not making much difference in performance, especially if the vehicle and motor system is not that demanding; well that is not completely true. First of all we have to assume (I know, I hate doing that) that when looking at packs available from a vendor and with each step up in C rating, there is truly a relative improvement. This improvement if present can be readily measured as a decrease in cell IR's. By the way, this is the real world and best way LiPo packs and cells should be performance-rated, by cell IR's. This would completely eliminate all the bogus C ratings. Anyhow, if the IR numbers improve as the relative C ratings go up, this means that for any given Amp load, the pack with the best (read lowest) IR's will hold voltage better under that same load. This higher voltage will immediately translate to more power generated by the motor.

    Lastly, the vehicle does not "pull" Amp loads. All energy for a RC vehicle starts with the battery pack potential which is then released as the connected downstream impedance allows.
    Last edited by Jakey; 02-27-2014 at 12:29 PM.

  8. #8
    Marshal ksb51rl's Avatar
    Join Date
    Nov 2006
    Location
    Northern NJ
    Posts
    17,377
    Quote Originally Posted by Jakey View Post
    ...Lastly, the vehicle does not "pull" Amp loads. All energy for a RC vehicle starts with the battery pack potential which is then released as the connected downstream impedance allows.
    So the battery "pushes"?

    I know, I know: it's neither, but it helps some of us to analogize, even if not technically correct.
    Alt-248 on the number pad =

  9. #9
    RC Champion
    Join Date
    Nov 2012
    Location
    Nashville, TN
    Posts
    2,009
    In a nutshell:

    1- no noticeable difference
    2- no noticeable difference

    None of those systems can pull enough juice to hit the theoretical limits of those lipo specs. The quality of the lipo cells, and how high they hold their voltage under load, will make more difference. That's not represented by just the C rating.

  10. #10
    Traxxas Employee TireSlinger's Avatar
    Join Date
    Sep 2010
    Posts
    585
    Quote Originally Posted by Jakey View Post
    As for higher C ratings not making much difference in performance, especially if the vehicle and motor system is not that demanding; well that is not completely true. First of all we have to assume (I know, I hate doing that) that when looking at packs available from a vendor and with each step up in C rating, there is truly a relative improvement. This improvement if present can be readily measured as a decrease in cell IR's. By the way, this is the real world and best way LiPo packs and cells should be performance-rated, by cell IR's. This would completely eliminate all the bogus C ratings. Anyhow, if the IR numbers improve as the relative C ratings go up, this means that for any given Amp load, the pack with the best (read lowest) IR's will hold voltage better under that same load. This higher voltage will immediately translate to more power generated by the motor.
    I would have to argue the point here that to most RC users are not going to see this change in the real world. In the end everyone wants the most bang for their buck and a small increase by buying more expensive (Lower IR hopefully) packs is probably not going to get noticed over a less expensive battery that is still adequate for handling the power requirements of the vehicle. Especially given the over-powered nature of today's vehicles with modern brushless systems. (IE: E-Maxx Brushless flipping over backwards on a 60mph run will flip even faster/harder with "better" batteries because the packs maintain a little higher voltage under load.)

    I see your point about the voltage drop however, and if I'm racing and worried about my lap times down to 1/10 of a second then the high dollar packs are probably worth the coin. For myself and other bashers I would go for having more of the less expensive batteries and run longer overall.

  11. #11
    RC Turnbuckle Jr.
    Join Date
    Dec 2004
    Posts
    3,764
    In my last post I never meant to imply "high dollar packs were required", only that lower cell IR's do result in less voltage drop for any given Amp load, even if that Amp load is well below that in which the cells are capable of. Now if in fact the end user does not care or cannot tell the difference between a pack with cell IR's of 4.0mΩ per cell versus a pack with cell IR's of 1.8mΩ per cell, OK, that is fine, but I was just pointing out the EE side of the issue.
    Last edited by Jakey; 02-27-2014 at 03:06 PM.

  12. #12
    Traxxas Employee TireSlinger's Avatar
    Join Date
    Sep 2010
    Posts
    585
    I don't have an engineering background so I'm spitting into the wind trying to talk intelligently about that kind of thing. My experience is all from running things and watching others run. It's neat to get input from people who have specific experience, information and hard data about how these things function internally.

  13. #13
    RC Turnbuckle Jr.
    Join Date
    Dec 2004
    Posts
    3,764
    No problem at all.

  14. #14
    RC Enthusiast
    Join Date
    Dec 2013
    Location
    Bloomington, IN
    Posts
    34
    Thanks for the input.

  15. #15
    RC Champion
    Join Date
    Dec 2001
    Location
    Brighton, Illinois
    Posts
    1,409
    I have to give some props, here! I used to race and bash several years ago. Bought my Stampede and Bandit back in 2002 and am in the process of rebuilding them. I just rekindled the flame for r/c...so I have a LOT to learn. For example, my NiCad batteries are not only toast, they've been left in the dust with the newer technology, today. Not only have I missed out on NiMh batteries, there's this new thing called "Lipo" (I know, short for Lithium Polymer). Anyway, I'm doing my homework...quickly trying to come up to speed with the new technology. Heck, brushless was just entering the market when I got out.

    Oh...yeah. Back to my props. Thanks, guys, for this thread! I just learned a ton in a short amount of time! As I DO have a technical background (mechanical designer for an electric motor manufacturer), I appreciate the depth of this discussion. Thanks for helping a brother out!
    Anti-Signature Users Unite!!!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •