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Recent content by onatirec

  1. onatirec

    Electric motor type relative figures

    Lots of words up here. I guess I'm the only one surprised to see higher torque density in induction machines vs pmsm? I looked at your comparison sheet and don't understand it. E.g. I see columns for Nm and Volume [m3] and torque density [Nm/m3]. But the torque density column does not equal...
  2. onatirec

    Skin Effect

    I did run a quick, crude test on a motor we had mounted on the dyno. Frankly, I could not make sense of the results at the time and shelved it. Maybe I can revisit it with a better approach. What I did is spin the (smallish ~11kW) motor up to 3000rpm with a load of about 7Nm, held it there and...
  3. onatirec

    Skin Effect

    I don't think the inductance of the machine truncates the high frequency current ripples from the pwm switching. If you stick an accelerometer on a motor, you will see vibrations centered around the pwm frequency, fanning out at odd harmonics of the electrical commutation frequency. These are...
  4. onatirec

    Skin Effect

    I have to disagree about the skin effect being due to multiple turns or braids, but it is fundamentally due to magnetic induction in single wire strands and creation of Eddy currents therein. Op I think this is a very interesting question. I can say that we ignore pwm frequencies when thinking...
  5. onatirec

    Induction generator for short-circuit current contribution

    Are you asking about the 381.5A? The general approach with induction machines is a locked rotor test, wherein you ramp up the voltage at some frequency (e.g. 25% of rated frequency) until the current reaches the rated current.
  6. onatirec

    Scientific Calculator

    I use the TI-36X Pro. I'd recommend it over the 30X. They are both very reasonably priced.
  7. onatirec

    Engineering standards for a motor mounting plate

    Maybe there are standards for this, but I'm not familiar with anything. Seems like the type of application where you need to do some engineering based on material strengths and loads. There's going to be different required thicknesses depending on whether you're making it out of soft aluminum...
  8. onatirec

    1 RTD Temp Increase while 5 kept constant

    Lots of good information above. We design and manufacture electric machines at my place of work. In my experience, it's not uncommon to see up to 10-15C differences between thermal devices on our test motors that we dyno. We mostly use thermocouples, but have at least 1 RTD installed in every...
  9. onatirec

    material for making the motor of a field coil loudspeaker

    electrical steel is usually produced in thin laminations. What i can see on Carpenter, is that hiperco comes in .35mm and .15mm thickness. these are stacked into cores and welded or stitched together. we've turned down cores of silicon steel on a lathe here. you have to take light passes so it...
  10. onatirec

    material for making the motor of a field coil loudspeaker

    Search around for Hiperco 50 or Supermendur. This material was invented in the 50's. Permendur has been around since the 30's, so I'm not entirely sure what you mean by materials that did not exist until a few years ago. I would think that anyone who designs electric motors would be aware of...
  11. onatirec

    material for making the motor of a field coil loudspeaker

    Op is asking about soft magnetic materials, ie electrical steel. Permanent magnets are hard magnets. Though it's not clear op understands this distinction, as ferromagnetic material can be either soft or hard - and silicon steel is already soft. I will reiterate again, you need to look at BH...
  12. onatirec

    material for making the motor of a field coil loudspeaker

    Electromagnets are made of coils of wires. Magnetic field strength is proportional to both current and number of turns in series. 100 amps through one turn produces the same field strength as 1 amp through 100 turns - so it's not enough information to ask only about the current. The induced flux...
  13. onatirec

    Hipot versus Isulation Resistance Test

    I'm only familiar with these tests in regards to ac motors.. The primary difference (other than the magnitude) is the electric stress distribution across the groundwall between ac and dc tests. The ac hipot yields an electric stress distribution more similar to that found during normal...
  14. onatirec

    Motor question

    Electromagnetic torque is produced at the interface between field and armature fluxes or, considering that at least the armature is an electromagnet, as the product of electrical and magnetic loading. Torque estimates from geometry can be made, proportional to D2L, as an estimation of the airgap...
  15. onatirec

    PERMANENT MAGNET GENERATOR DESIGN-TO AVOID COGGING

    Flattered you remember me Pete. I used to spend a lot more time analyzing motors, but have been too bogged down in pm motor design to do that for a while now. Cogging arises from the non-uniform permeance the rotor poles see as they rotate relative to the stator. The permeance in the magnetic...
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