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Thread: Lipo Questions

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  1. #1
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    Lipo Questions

    Hey everyone. I have a few lipo questions and I hope you can help.


    Can anyone offer a laymans explanation of the following terms and how they apply to battery life ect... Also, how important is the 25C part of the equation?

    25C
    7.4v
    5000 Mah
    2s

    What kind of life expectancy should I get from the above battery? I expected better run times but only got about 15 minutes out of it. I was in a grass field and probably was full throttle most of the time. Stock gearing.

    I have the onyx charger and I can't really discharge my batteries. Is it better to store them fully charged and then put them on again before I use them?

    I was told if I buy a 3s I would need to make some kind of chasis modification. Can someone explian what is involved.

    Thanks for your help.

  2. #2
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    25c - how fast you can push fuel in our out, compared to the size of your fuel line. Importance depends on your ESC and motor. If the standard 25c rating exceeds the maximum draw of your system, buying more doesn't really buy you anything.

    7.4 volt - Horse Power, but can be helped or hurt by that fuel supply mentioned above.

    5000 mah. - Fuel tank size. Bigger = longer run time before you run out.

    2S = battery cell count. In this case, 2 cells. Cells provide 3.7 volts each, the S says they are in a series, so voltage is added per cell. A 3S is 3 cells, or 3x3.7 volts = 11.1 volts.

    Sent from a Galaxy S3, far....far away.
    Last edited by larry0071; 02-04-2013 at 03:03 PM.

  3. #3
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    So is 25c the highest rating for the standard VXL 4X4 brushless? I can't find anything about that in the manual for the speed control.

  4. #4
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    Quote Originally Posted by rml333 View Post
    So is 25c the highest rating for the standard VXL 4X4 brushless? I can't find anything about that in the manual for the speed control.
    You can definitely run batteries with much higher C rating. But they generally cost more. Opinions will vary on whether higher C ratings actually result in greater performance. Personally, my 25C batteries are more than fast enough in my E-MAXX brushless, which pulls more amps than your Stampede.

    Higher voltage is the most important factor when trying to go faster.
    Last edited by zippogeek; 02-04-2013 at 03:31 PM.
    Make it idiot-proof and along comes a better idiot

  5. #5
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    25C = the discharge rating of your battery. Higher C rating = more amperage (flow of electricity) to the motor = more speed. 25C is adequate for your 'Pede.

    7.4v = two 3.7v LiPo cells sandwiched together (AKA, "2S")

    5000mah = the storage capacity of your battery. 5000 is more than enough for the 'Pede.

    The reason why you had "only" a 15 minute run time may be two-fold:

    1. An inadequately charged LiPo,
    2. Running on grass at full throttle (which pulls a lot more amps than pavement, thus resulting in lower run times),

    or some combination of both!

    A 3S pack will not increase your run time; only a higher mah pack will do that. 3S = three 3.7v LiPo cells sandwiched together. This equals 11.1v total, which puts a LOT more strain on your motor and differentials. If you really want 3S speed, you'll probably need to change your gearing from stock to keep motor temperature at a reasonable level. You will also probably need to upgrade some things; I'll let the actual Stampede owners advise you on that.

    Good luck!
    Make it idiot-proof and along comes a better idiot

  6. #6
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    If you plan to store your batteries for more than a couple days, do not store them fully charged. Proper storage voltage is 3.8 volts per cell. AS for the 3s batteries, the only modification you need is a battery expansion kit.

    Sent from my Galaxy S2 Skyrocket, using Tapatalk 2.
    Last edited by 4-wheelin; 02-04-2013 at 04:26 PM.
    Who needs nitro, when you got LiPo?

  7. #7
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    Thanks Everyone. I really appreciate the advice / help I get here.

  8. #8
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    OK so based on what was said above about voltage I have another question. Why is the lipo faster than the stock nimh battery that came with the truck? It says it is 8.4 v as opposed to the lipo which is 7.4. Thanks

  9. #9
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    Quote Originally Posted by rml333 View Post
    OK so based on what was said above about voltage I have another question. Why is the lipo faster than the stock nimh battery that came with the truck? It says it is 8.4 v as opposed to the lipo which is 7.4. Thanks
    Very good question. I would like to know the answer as well.

  10. #10
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    That Lipo is at 8.4V full charged, and very slowly drops voltage over the run, nearly flat lining voltage for a portion of the time. Your 8.4V Ni-mh battery is likely around 9 to 9.5 volts fully peaked, but drops voltage at a near linear rate from the first touch of the throttle, until it's too weak to be useful. The ni-mh instantly starts dropping voltage, and never slows down dropping it.

    The Ni-mh will likely be more powerful for a very short time, but in just a couple minutes will be trailing the Lipo, and the longer you go, the more disparity you'll see in favor of that Lipo pack.

    Also, I noticed that the Lipo in my stock brushed E-Maxx seems more powerful than my 8.4 even from both at full charge, I assume this is from its ability to provide more amperage on demand? There is no downside to the Lipo experience. I was recently a skeptic, but I'm now a believer! I'm drinking the koolaid, and I've got to say....it's good!

    Sent from a Galaxy S3, far....far away.

  11. #11
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    +1 everything Larry said. Despite the fact that the NiMh pack has more voltage, it's lacking in another useful specification: amperage! The C rating (discharge amperage) of a LiPo is much higher than a NiMh pack, which makes for a faster car.

    Voltage = the size of the bullet
    Amperage = the speed of the bullet

    The two go hand in hand!
    Make it idiot-proof and along comes a better idiot

  12. #12
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    Thanks. Makes sense to me.

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