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Thread: Spartan Problem

  1. #1
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    Spartan Problem

    Hi guys I took my Spartan for a run today everything was running fine. Was going easy on it (no more then half throttle) because it was windy. After about 8 to 10 minutes it just stopped. I took the top off to find one of the battery terminals had started to melt and that the solder on the negative side had let go. everything was hotter then normal. I'm running 2x 3s 4200mah 30c batteries and a Octura X442 prop and I have upgrade to a dual pick up rudder and a metal water jacket. Is this the right set up or what would have caused everything to get hot. I know the water was flowing and wasn't blocked.

  2. #2
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    i have read that going slower with the spartan is harder on it then flying around.i don't have that much experience with the boat i only had mine for 1 season so far so maybe with more will chime in

  3. #3
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    Did you lubricated the liner? Another issue is the alignment of the shaft due to friction or not centered unto the drive shaft better check those, the esc stopped because of overheating cause by friction and that happened to the esc's negative wire.


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  4. #4
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    The "better to run a full throttle" is because the ESC is less efficient at lower throttle positions, and more of the electrical energy is converted to heat energy.

    It has to do with how the FET's (transistors) control power flow through the ESC.

    Not my area of expertise and I only have a general understanding of the concept.

    Below is an excerpt from "the net" that may help provide some understanding.
    (the photos referred to in the excerpt did not copy over)


    At full throttle, some of the better ESC's are as much as 98 to 99% efficient. At lower throttle settings this can drop to 95% or so. This may sound like extreme efficiencies, but whe you look at how much power is actually going through the ESC, that 1 to 2% of inefficiency adds up!

    For example, if you have a 6-cell ESC that is running at 100 amps at full throttle, you have 22.2 volts x 100 amps of 2220 watts of power going through the ESC. At 98% efficiency, you have 2% of energy lost to heat. 2% of 2220 watts is 44.4 watts of heat energy, which is significant. If you figure that the average soldering iron puts out 40 watts of heat, you get teh picture on how much heat that actually is!

    FET transistors are marvelous little devices that essentially act like a switch. When they are turned off, the resistance is virtually infinate, when turned on, the resistance is extremely low, often just a few thousandths of an Ohm. So when the FET is completely on or completely off, there is very little power dissipated in the FET's. The only thime they really generate significant heat is in the process of turning on and turning off. During this transition, the FET's are operating in the linear range of operation, and it takes a small but finite amount of time to turn on or off. During this brief time period, the transistors generate most of their heat.

    When a Speed Controller is running at 100% throttle, each set of FET's only turns on and off once per phase cycle. You can see this in the photo below that shows the voltage output of one phase of a brushless ESC with the throtle at 100%.





    Whenever you run at less than 100% throttle, the PWM effecet of the ESC kicks in, and the FET transistors start to switch on and off multiple times during each phase cycle of the ESC. This usually takes place at 8000 times per second, or 8KHz, which is the PWM switching frequency of most ESC's. The photo below shows a speed controller running at 60% throttle, in this example, you can see how the FET's are turning on and off 4-5 times per phase cycle.





    This extra switching places the FET's in the linear region for a longer period of time, which causes more heat energy to be generated. If you have 5 switching cycles per phase pulse, as seen above, you have 5 times as much time that the FET's are in the linear mode. If you are running at 60% power, then your average current would drop from 100 amps to 60 amps, so most people would think tha the ESC would run cooler. Unfortunately, this is not the case! Even though you are only pulling 60% of the original current, the FET's are subjected to the current 5 times more often, so in the end, the ESC has to dissipate almost 3 times as much heat energy running at the lower throttle setting than it did at full throtle. This is why it is foolish to think that it is OK to run an ESC at lower throttle settings to account for an ESC that is actually too small for the job.

    The best thing you can do is ALWAYS, ALWAYS, ALWAYS use the 80% rule when sizing components. Never use an ESC, Motor or Battery at more than 80% of it's rated value. If you need to pull 80 amps, use a 100 amp ESC, if your motor is capable of handling 50 amps of current, never pull more than 40 through it and so on. If you abide by these simple rules, you will virtually never have problems with your electrical components.

    Lucien


    hog

  5. #5
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    Its also cooling, my boat runs cooler the faster you go.
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  6. #6
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    Thanks for the help. Do you think that my batteries and prop suit each other or should I be running a different size.

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    Your prop is fine. The X442 is essentially a metal equivalent to the stock fiber prop.

    Your 30C batteries are a bit under rated for the amp draws this boat is capable of pulling.

    4000 or higher mah at 40 to 50C discharge are more suitable.

    hog

  8. #8
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    Quote Originally Posted by hog View Post
    Your prop is fine. The X442 is essentially a metal equivalent to the stock fiber prop.

    Your 30C batteries are a bit under rated for the amp draws this boat is capable of pulling.

    4000 or higher mah at 40 to 50C discharge are more suitable.

    hog
    The only exception I have found to this rule hog, is the Traxxas 3S lipo batteries they are underrated for 25c.
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  9. #9
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    Boats also run hotter when going slow because they aren't on a good plane. Once the boat gets on a plane there is much less resistance. Also any c battery will work, just because the boat is rated for more power doesn't mean it actually needs that much power to operate, it just means it has the potential to. I originally ran 20-30c batteries without problems. I have experience with traxxas batteries and they are no doubt a nice battery(overpriced IMO, I picked some up for 40 bucks each shipped) but my 5000mah 35c batteries definitely put out more power than the traxxas 2s 5000mah lipos. Now the 10000mah 25c traxxas batteries put out some power!

  10. #10
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    In good conscience I cannot recommend running low C batteries in the Spartan, and respectfully disagree that running low C rated batteries is OK in high amp draw applications.

    The C rating is an indication of the "safe" maximum amp draw the battery can deliver. It is the manufactures determination of how much power can safely flow from the battery based on the internal resistance of the individual cells, wiring, etc.

    The battery cannot regulate this flow, so if the demand load amperage is higher than the "safe maximum" flow (C rating), the battery will still try to flow as many amps as possible meet the amperage demand. If the "safe" internal resistance of the cells is exceeded, the battery will over heat and puff, and the cells will be damaged.

    This is why we see posts asking, "why are my batteries really hot and swollen after only a few runs"??

    Exceeding the batteries ability to provided the power demand of the system can also result in low voltage or "brown out" conditions which can damage other electronic components, such as the ESC.

    In my opinion, it is best to have the motor, ESC and batteries relatively well matched to each other to avoid potential problems.

    hog

    EDIT: There is no standardized test to determine C ratings. Each manufacture is free to test and claim the C rating as they see fit.
    Because of this, there are always "exceptions to the rule".
    Companies that stand behind their products and reputations are more likely use conservative C ratings and their batteries may well perform "beyond the rated limit".
    Companies that sell strictly on price and volume may be inclined to embellish their C rating numbers, and these batteries could well fall short of performing to the "rated limit".
    Last edited by hog; 02-01-2014 at 12:02 PM.

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