Discussions

What battery? [SOLVED]

Posted by Bravo Sierra 80 on July 18, 2014 at 7:21pm

I have 4 hobbypower motors at 1000kV that draw 4-10 amps. I have a KKmulticopter flight board V5.5, and hobbypower 30A ESCs. I am just curious. If i am thinking correctly, I believe I need at least a battery for a 4000 maH for the motors alone.Correct? I figure a 2200maH would be insufficient, if even able to turn the motors at all. If not, please help!

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Replies

            • Moderator
              Dwgsparky > Stuart Brookes July 20, 2014 at 12:21pm
              There is nothing in an esc to reduce the voltage. It generates a square wave on 3 wires 120 degrees out of phase with the previous wire ,your esc controls the %age and frequency. Battery current still equals motor current + esc losses. It's still a series circuit.
              • Stuart Brookes > Dwgsparky July 20, 2014 at 12:23pm

                you say %age, percentage of what?

                • Moderator
                  Dwgsparky > Stuart Brookes July 20, 2014 at 1:02pm
                  %age of pwm or mark / space ratio
                  • Stuart Brookes > Dwgsparky July 20, 2014 at 1:07pm

                    ok. so there is voltage control them :)

                    are you saying the pwm is only used to create a full voltage waveform and isn't used to create a lower voltage one like I though should happen at lower speeds?

    • Bravo Sierra 80 > Phillip Schmidt July 18, 2014 at 8:30pm
      Thank you for replying. I was going to order 10 x 4.5 props, what other specs did you need for the motors?
      • Phillip Schmidt > Bravo Sierra 80 July 18, 2014 at 8:51pm

        make and model and kVm, would help.  If you know what your complete flying weight without battery that would help as well.

        • Phillip Schmidt > Phillip Schmidt July 18, 2014 at 9:27pm

          2100mAh should give you roughly 10min hoovering, while 4000mAh will be roughly 18min.  More aggressive flying will reduce these numbers.

          • Bravo Sierra 80 > Phillip Schmidt July 19, 2014 at 9:48pm

            But these motors take 4 to 10 amps, so I assume I at least need the 4000 mAH? Assumming? I know I can use the 2100, and I understand the amp draw gives me a smaller flight time. So if I use a 4000, I am getting a bigger battery, and that is really my only concern correct? It is simply an issue of weight?

            • Phillip Schmidt > Bravo Sierra 80 July 19, 2014 at 11:09pm

              mAh is a unit of electrical energy storage capacity (similar to the size of an car's fuel tank).

              The Amps your motors may draw indicates how quickly it will use up the battery.

              If you had 4 motors each pulling 4 amps (16A total) from a 4000mAh (same as 4Ah) battery, then you could fly for 0.25h (4Ah / 16A = 0.25h = 15min).  Unless your ship is heavy, you will probably hover at ~3A per motor (but use more when maneuvering.)

              So the only real difference is that one weighs double and has twice the capacity.  Either one is capable of powering your quad.

              • Stuart Brookes > Phillip Schmidt July 19, 2014 at 11:38pm

                Motor amps and battery amps aren't necessarily the same either confusing matters.

                you need to work it out as watts and work back. very (i stress very) simplistically, the motor may be applying 10A say, but only at half of battery volts (say half of 11 volts) of 5.5V, thats 55 Watts in the motor. Ignoring efficiency losses, assume that is 55W from the battery for that motor, so 55 Watts from 11V battery equates to 5 Amps per motor from battery.

                also ecalc.ch is quite useful at estimating, but I find the throttle percentage for hover to be higher in real life.

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