FEMM: Modeling the 9C 2806

[Alan B]

CA measures battery current, phase current is generally greater. According to Jusin's measurements, max phase current on a 7 turn 9C is about 60 amps and torque about 70 newton meters, if I remember correctly. Much beyond that something starts to saturate and efficiency drops. It is in a thread here on ES.

[Kingfish]

Hi Alan

Understood, and appreciated!

Then my presumption of the CA MaxA = 35 Amps is really measuring battery current, yes? And if so, then we need to change this to 35 * √3 to get ≈ 60.62 Amps for Circuit A @ 0 SIN, yes?

Hopeful, KF

[John in CR]

Luke or Justin are the ones to ask about stator saturation. I recall Luke saying that 90A was the saturation number, but I don't remember any clarity about whether that was battery current or phase current, though at full duty wouldn't they be the same?

[Alan B]

Justin's testing was without controller, so it was phase current.

Our controllers run the phase current through two coils in series at one time. The third coil has no current.

Even at wide open throttle the PWM will be active if any current limiting is going on. Not common to have no PWM occurring, generally only happens near max speed.

Phase current is 1/pwm duty cycle times battery current.

[Biff]

Hi Biff

Any idea why the nodes would not rotate?

Especially thankful, KF

The nodes have to be in the group as well as the block label. It doesn't matter what group the lines / arcs are in, but I like to put them in the group aswell, so when you select the group in the simulation editor (click on group selector tool, and right click near one of the blocks in your group) everything you want to rotate turns red.

Post your new model and I'll have a look

-ryan

[Kingfish]

Thanks Biff

Here ye be... sans scripts (only the file name was changed in the scripts)

Much appreciated, KF

[Kingfish]

Epiphany!
OK now I get it! I changed the arcs and lines to Group 2 and re-ran the scripts; it chugs along very quickly without errors.

Amazing; thank you
~KF

[Biff]

New Model looks good.

here are some comments:
1) You could keep the slots with square bottoms and tops, it makes simulation faster
2) The slots are still fixed width which causes a taper in the tooth body pinching the flux at the base althought less so because of the round slot bottoms. I doubt that is how the NC motor is really built, typically a motors tooth is fixed width and have tapered slots.
3) with the magnets in their current position your phases are about 28degrees behind of phase A lying on the x axis, i.e the phases are A= 152 degrees, B = -88 degrees C = 32. Either change my torque scripts to use those angles to get the right toruqe, or move the rotor about 1.22 degrees (clockwise). If you use my running torque script without changing the angles, you will see that the torque will vary quite a bit during a cycle. Once you correct for the phase change, the torque will be more constant, but will still vary as the poles move past lowest reluctance points.

-ryan