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  1. #1
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    Minimum c rating question

    What would you guys say the minimum c rating for a lipo using the seaking 180? Thanks
    Last edited by paulfromtulsa; 11-17-2013 at 09:30 PM.

  2. #2
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    Well its the motor that draws the amps. Whats the max amp rating on your motor? What motor are you using?

  3. #3
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    I would make the same recommendation for either the stock ESC or the SK180, target a minimum of 200 amp max discharge rate. As Socalirevo pointed out, it's the motor, prop, etc. that determines the amp draw, not the ESC.

    So if running 5000mah (5 amp) batteries, shoot for 40C or higher. (5amp x 40C = 200 amp)

    If you are propping up to larger diameter or higher pitch props, you might want to target 250 amps max discharge rate.

    Keep in mind there is no "standard" test protocol for determining the C rating on a battery, and some manufactures C ratings are, shall we say, somewhat less than reliable.

    200 - 250 amp max discharge rate should provide a safety margin that will keep your batteries safe.

    hog

  4. #4
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    Quote Originally Posted by Socalirevo View Post
    Well its the motor that draws the amps. Whats the max amp rating on your motor? What motor are you using?
    oh sorry i am using the leopard 1600kv/sk180. i am looking for batteries with longer runtime like a 8400 or 10000 mah but all of them seem to have low c ratings like 25c.

  5. #5
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    The higher the mah rating, the lower the C rating needs to be to still have a good discharge rating.

    To help you understand, and I apologize if I'm regurgitating stuff you already know:

    This is a simple explanation of battery capacity
    - Our batteries are rated in mah - or Milli Amp Hour
    - A milli-amp is 1/1000 of an Amp
    - So, if you divide the mah rating by 1000, you get Amp Hour rating
    5000 mah = 5 amp hour
    8400 mah = 8.4 amp hour
    10,000 mah = 10 amp hour etc etc etc.
    - The Amp Hour rating means that a 1 amp battery, can maintain a 1 amp load, for 1 hour, before reaching discharge.
    Therefore a 5 amp battery can maintain a 1 amp load, for 5 hours, OR maintain a 5 amp load, for 1 hour, before reaching discharge.

    So, let's say you just bought a 10000mah (10 amp hour) battery for your boat. If your boat draws 10 amps, you can run for 1 hour, If your boat draws 20 amps, you can run for 2 hours. etc etc.

    Now here's the issues,
    1. Our Spartans are capable of drawing upwards of 200+ amp spikes (depending on setup). I have confirmed this using an Eagle Tree data logger. The graph over ranged at 180 amps, and I occasionally observed spikes off the graph.
    2. Internal resistance of the cells in a battery. Early Lipo batteries had high internal cell resistance (difficult for electrons to move easily out of the cell). Technical advances are continually improving this, and lipo batteries are becoming very useful now for high power applications.

    This is where the C rating comes in. C stands for Capacity. And the C rating is a designation of of "how many times the capacity" can the battery deliver power without exceeding the internal resistance of the cell and damaging the battery.

    Therefore a C rating of 40 means the battery can deliver 40 times the rated capacity of the battery.
    eg. 5000mah (5 amp hour) 40C battery
    5 amps x 40 = 200 amps max discharge rate without damaging the cells.

    eg. 10,000mah (10 amp hour) 25C battery
    10 amps x 25C = 250 amps max discharge rate without damaging the cells.

    As you can see the capacity of the battery, and the C rating are inter related.
    Simply multiply the rated capacity of the battery, by the C rating, for an indication of Max safe amp draw.

    Some batteries are designated with two C ratings. For example 25-50C. This means the battery can maintain a load 25 times the rated capacity continuous, and 50 times the rated capacity for bursts or "spikes".

    Hope this helps
    hog

  6. #6
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    thanks hog!!! have any of you guys run a bigger battery (8000-10000 mah) in the spartan? does the extra weight of the larger battery effect the performance noticeably? thanks

  7. #7
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    The biggest ive run are 5400 50c 2s. Id be interested in larger batteries if the price was right... Where are you getting your batteries. Please dont tell me traxxas cuz I cant afford those pups

  8. #8
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    NOTE:
    There is a typo in my post above where I'm illustrating run times on a 10,000mah battery in boat drawing 10 or 20 amps.
    A boat drawing 20 amps would have a 1/2 hour run time. (not 2 hours as stated above)

    I have run 2 qty 6500mah 3s batteries in my Spartan, and have also run 4 qty 5000mah 3S batteries in my Spartan,

    Yes, the extra weight has some affect on the performance, hole shot, top end speed, and chine walk are notable.

    With 2 batteries you have the luxury of moving the battery position to help compensate for the extra weight and keep the hull from running wet.

    With 4 batteries the trays are pretty much full and you have what you have, a very heavy boat. (sits very low in the water when stationary and will swamp easily, even with small waves, if the hatch isn't sealed well)

    The extra weight helped, but did not completely eliminate chine walk.

    The boat tends to be a bit less nimble cornering.

    All in all though the boat still performs very satisfactorily with heavier batteries on board.

    hog
    Last edited by hog; 11-18-2013 at 09:41 PM.

  9. #9
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    These batteries work well for me.
    http://dinogylipos.com/2-cell-65c/65-5000mah-2s-65c

  10. #10
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    Hog you mean by this mah and c rating can be applied on both 2s or 3s Lipo?
    Sharing is the best thing to do on EARTH legally.

  11. #11
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    Yes, the C rating is really only an indicator of the internal resistance of the cells.

    The lower the resistance, the easier the electricity can flow out of the cell.

    This "rule of thumb" calculation works for any lipo battery, regardless of how many cells it has.

    An excerpt from an article.

    LiPo

    A true LiPo battery doesn’t use a liquid electrolyte but instead uses a dry electrolyte polymer separator sheet that resembles a thin plastic film. This separator is sandwiched (actually laminated) between the anode and cathode of the battery (lithium carbon coated aluminum & copper plates) allowing for the lithium ion exchange – thus the name lithium polymer. This method allows for a very thin and wide range of shapes and sizes of cells.

    The problem with true LiPo cell construction is the lithium ion exchange through the dry electrolyte polymer is slow and thus greatly reduces the discharge and charging rates. This problem can be somewhat overcome by heating up the battery to allow for a faster lithium ion exchange through the polymer between anode and cathode, but is not practical for most applications.

    If they could crack this problem, the safety risk of lithium batteries would be greatly reduced. With the big push towards electric cars and energy storage, there is no doubt some pretty huge developments will be made in ultra light weight dry and safe LiPo’s in the coming years. Seeing that theoretically this type of battery could be made flexible, almost like a fabric, just think of the possibilities.

    LiPo Hybrids

    All RC LiPo batteries out there at the time of this write up (January 2013) are actually a hybrid lithium polymer battery. The correct name for this type of battery is lithium-ion polymer, but the battery world of today simply calls them lithium polymer even though they are not a true dry type LiPo battery.

    By introducing a gelled organic/solvent based electrolyte to saturate the polymer separator, the lithium ion exchange rate between anode and cathode is improved immensely. LiPo hybrids like Li-Ion can still burst and catch on fire if over charged, shorted, punctured, or incinerated.


    DISCHARGE RATE

    Remember that third number I was talking about when you go RC LiPo battery shopping? Yes, discharge rate is that number. This one is probably the single most over rated & miss understood of all battery ratings.

    Discharge rate is simply how fast a battery can be discharged safely. Remember that ion exchange thing further up the page? Well the faster the ions can flow from anode to cathode in a battery will indicate the discharge rate. In the RC LiPo battery world it is called the “C” rating.

    What does it mean?

    Well Capacity begins with “C” so that should give you a pretty good idea. A battery with a discharge rating of 10C would mean you could theoretically & safely discharge it at a rate 10 times more than the capacity of the pack, a 15C pack = 15 times more, a 20C pack = 20 times more, and so on.

    Using our 1000 mAh battery as an example; if it has a 20C discharge rating, that would mean you could pull a maximum sustained load up to 20,000 milliamps or 20 amps off that battery (20 x 1000 milliamps = 20,000 milliamps or 20 amps). From a purely theoretical time stand point, this equals 333 mAh of draw per minute so the 1000 mAh pack would be completely exhausted in about 3 minutes if it's exposed to the maximum rated 20C discharge rate the entire time. Calculation as follows: 20,000 mA divided by 60 minutes = 333 mAh which is then divided into the 1000 mAh capacity of the pack giving us 3.00 minutes).

    Most RC LiPo Battery packs will show the continuous C rating and usually a maximum burst C rating as well. A burst rating indicates the battery discharge rate for short bursts of extended power that. An example might be something like “Discharge rate = 20C Continuous/40C Bursts”

    The higher the C rating, usually the more expensive the battery. This is where you can save some money. Getting an extremely high discharge rated pack when there is no way you could possibly pull the full amount of power is not required but it won't hurt either. The most important thing is you can't go with too low a discharge C rating or you will damage your battery and possibly your ESC (electronic speed control).

    So how do you know what C rating to get when purchasing your LiPo RC Battery Pack? The easy answer most will give is to get the largest C rating you can... If money is not an object I agree with that 100%; but for most folks, especially beginners & intermediate or scale fliers who won't be performing power hungry 3D maneuvers and drawing much current - stretching your RC battery budget by purchasing lower C rated packs when you're first learning so you can get a few extra packs makes much more sense in my opinion.

  12. #12
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    Thanks Hog!
    I'll be taking both 2s & 3s with good C rating and start the speed check between those LIPO's.
    Sharing is the best thing to do on EARTH legally.

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