I read that the surge current for an Indction motor is higher than that of other motors. Therefore when one wants to power a 3phase IM the inverter rating should be much higher than that of a BLDC (when the supply is DC ). Is it true?

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Link to this: http://www.diygokarts.com/vb/showthread.php?t=9700

I am gonna start designing an electric go kart(for an event). I wanted to use an induction motor because of the following reasons:

  • Better overall or avg efficiency.

  • lower weight

This is from where I was like convinced to use an IM against BLDC: https://www.tesla.com/blog/induction-versus-dc-brushless-motors?_ga=2.70427863.694368311.1506343498-425824400.1494234243

Specs of the motor and batteries that I'm allowed to use [some extra info if it's needed ]: - Motor rating <= 3kW - Battery voltage = 48 V - 20 Ah <= Battery capacity <= 50 Ah - Max rpm = 3600 - Max torque = 10 Nm

Any advice is welcome.

  • 1
    \$\begingroup\$ My kitchen lights don't dim when my fridge turns on. I'd find a better source of information if I were you. 1 kW is about 1.3 horse power - top speed and acceleration is going to be very sedate (kind of suitable for pensioners really). \$\endgroup\$ – Andy aka Sep 30 '17 at 8:38
  • \$\begingroup\$ @Andyaka so no problem if it's a IM then. And I'm planning for a 3kw motor \$\endgroup\$ – asr Sep 30 '17 at 8:50
  • \$\begingroup\$ He's talking out of the thing he sits on. The surge current is entirely down to how the controller is programmed. \$\endgroup\$ – Neil_UK Sep 30 '17 at 8:51
  • \$\begingroup\$ What Neil said. Also, you know, a BLDC is actually only a synchronous motor with integrated inverter. So the whole "you avoid the expensive inverter" thing doesn't fully fly – there's an inverter in there, anyway, and it controls the inrush current (among other things). Your external IM inverter would need to do the same anyway, and then you wouldn't buy it spec'ed for the theoretical step response inrush current (that'd be stupid). \$\endgroup\$ – Marcus Müller Sep 30 '17 at 8:54
  • \$\begingroup\$ @asr: Wikipeda IM: Starting. \$\endgroup\$ – Marcus Müller Sep 30 '17 at 10:36

Is it true?

Absolutely not. The quoted statement is totally nonsense.

However there is definitely a right way and a wrong way to use an induction motor. You must have an inverter that is specifically designed to control an induction motor. More specifically, you need a variable frequency drive (VFD). A VFD will start the motor at a low frequency and proportionally low voltage. To accelerate the motor, the frequency are increased together. If that is done properly, the motor can produce 150% of its rated torque at any speed up to the rated speed.

A sensorless vector VFD can get more out of the motor, more consistently and have an easier set-up procedure. Don't use a VFD designed to drive fans and centrifugal pumps, that is, use a constant-torque rated VFD not a variable-torque model. If a product line lists "standard-duty" and "heavy-duty" models, use the heavy-duty one.

Be aware that you can not get the performance of a Tesla, not even a "scaled down" version of that performance. Both the Tesla motor and the Tesla VFD are very special designs that "are not sold in stores."

Note that a Tesla uses a high battery voltage. You will probably not find an adequate motor and VFD that require a battery voltage less than about 300 volts.

Neither an induction motor nor a BLDC motor are really good choices for the first effort of this sort by someone without experience with those technologies. A DC motor with a commutator will be best in that case.


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