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How Much of a Battery is Too Much

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  • How Much of a Battery is Too Much

    I was wondering if a 4s 2800 mah battery would be to much for a 30a ESC from an old Apprentice?

  • #2
    It might be a bad idea. My "rule of thumb" is that for a 4s battery to be safe, the ESC should be at least 40amps BUT the motor must also be able to take it. Of course, you could limit the max throttle to about 70% for some insurance if you are going to use the 30A ESC.

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    • #3
      Depends what you are doing.

      I recommend against using throttle limit attempting to preserve an overloaded ESC. The ripple current feedback issue of ESCs is WORSE in mid-range than at full power. Often this blows out the ESCs input capacitors before you overheat the ESC.

      If you are pushing an ESC's limits, it may just be time to get a new ESC.

      I do not know the voltage ratings of the ESC from the Apprentice. You don't want to be significantly above its max rated voltage. You never want to push an E-Flite ESC past its label rated max current based on full throttle.
      Note that in flight the max current can be higher than when doing a ground check, because the prop can be stalled in ground testing. Add airspeed and the prop will load up if that occurred.

      An example of OK is a Castle Thunderbird 54 on 4S. The label rating is 3S, but calculate the max voltage of the NiCd rating (based on full charge) and its less than 1 volt below full charge for LiPo. I've run Castle 54 Thunderbirds on 4S LiPo for years.
      (Castle ESCs are well known for handling MORE than rated current and voltage at the same time, if you provide good cooling, E-Flite are not.)

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      • #4
        Originally posted by fhhuber View Post
        Depends what you are doing.

        I recommend against using throttle limit attempting to preserve an overloaded ESC. The ripple current feedback issue of ESCs is WORSE in mid-range than at full power. Often this blows out the ESCs input capacitors before you overheat the ESC.

        If you are pushing an ESC's limits, it may just be time to get a new ESC.

        I do not know the voltage ratings of the ESC from the Apprentice. You don't want to be significantly above its max rated voltage. You never want to push an E-Flite ESC past its label rated max current based on full throttle.
        Note that in flight the max current can be higher than when doing a ground check, because the prop can be stalled in ground testing. Add airspeed and the prop will load up if that occurred.

        An example of OK is a Castle Thunderbird 54 on 4S. The label rating is 3S, but calculate the max voltage of the NiCd rating (based on full charge) and its less than 1 volt below full charge for LiPo. I've run Castle 54 Thunderbirds on 4S LiPo for years.
        (Castle ESCs are well known for handling MORE than rated current and voltage at the same time, if you provide good cooling, E-Flite are not.)
        I know it states on the label that it can handle a 3s and 4s battery. But I thought about the same thing Viper had said. I know this would just save me from buying another ESC. This came out of a wrecked Apprentice that a friend of mine had given me when he got out of the hobby. What I may do when I get back home is take a pic of the label and post it on here so you can see. I'm still pretty new at this stuff and don't have everything I need to read and the knowledge of the voltage testing that you are speaking of.

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        • #5
          ESC does not limit current... it attempts to deliver what is demanded by the motor/prop combo.

          The ESC provides a variable voltage, variable frequency simulate 3-phase AC to the motor.
          Our "brushless DC" motors are actually variable frequency, variable voltage, 3 phase AC motors. using permanent magnet rotors.

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          • #6

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            • #7
              I just did a screen shot of it.

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              • #8
                This goes in a ST Model Acrobat 3d plane. The plane is discontinued!

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                • #9
                  That's a fairly common Eflite ESC. They use those in Radian sailplanes. I've got about 3 of them that people have given me and from my own downed Radian. Radians fly on 3s. We've all replaced them with 40A to 50A when we change to a bigger prop or a triple blade. The 30A can't quite handle it, so I'm leery about it handling 4s, especially if you put it in a plane that is flown more aggressively or pulls more amps/watts. Even in the Radian manual, it says to NOT power up for more than about 30 seconds at a time. In a EDF with high kv or high blade count on 4s, I think it'll blow, maybe even on 3s.

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                  • #10
                    Thank You for the info Viper! I haven't really thought about the aggressive flying like a 3d plane will be doing. I may just put it in for a very short run just to see if the ESC is my problem with it since I found one in my stash that I forgot I had. I've had an issue with it not knowing if its the ESC or the motor. Thanks a million.

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                    • #11
                      Pauly, do you have a watt/amp meter? It is one of the most useful devices in RC. The amperage consumed is a function of the voltage applied to the motor and the prop (make sure your motor can handle 4S). The only true way to know the amp draw is to hook a meter between the battery and ESC. This is one of my favorites: https://www.motionrc.com/collections...escription-tab

                      This one is bare wire so you will need to solder on the connector of your choice (I assume EC3 in this case). Click the spare parts tab on that page for a selection of connectors. When you run the throttle up with the plane on the ground, you'll know exactly how many amps are drawn.

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