Moderm Permanent Magnet AC (PMAC) motors and Brushless DC (BLDC) motors are very similar to each other. The big difference is is the shape of the current wavework flowing in the stator coils. PMAC motors have the stator windings and controller drive electronics giving an essentionally sine-wave current, making the motor mechanically quieter.
There still exist old-fashioned ac 3-phase motors, but brought (slightly) up to date by using a PWM 3-phase sine-wave inverter unit providing a variable output voltage and frequency to provide much greater control of the motor. These can provide a lower-cost solution for some applications, as you pay essentially the metal scrap value for the 3-phase motor (Although usually you have to pay the cost of rewinding them for operation at lower voltages). Industrial electrical scrap yards have plenty of 3-phase motors in them that are of little value. The problem is that the 3-phase motors were originally designed for optimum efficiency at 50 or 60Hz, and operating them over a wider frequency range gives good speed control, but the efficiency suffers. I have been involved with a group wishing to electrify a British canal narrowboat using this sort of motor, and I'm still not convinced that I have managed to show them the error of their ways!
Sent: 18 April 2013 13:36
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Orest have u considered AC motors
----- Original Message -----From: Andrew GilchristSent: Wednesday, April 17, 2013 8:18 PMSubject: [Electric Boats] Orest have u considered AC motors
Orest
there is another option – others here my have tried it
You may want to look at an AC motor . A DC motor's amp draw and torque level fall away at higher rpm, an AC motor has a lower start torque – but you don't really need much at low rpm, but the high end torque is better.
If that isn't an option a more efficient better sized prop than the current one could achieve very significant gains either in performance or efficiency
Yours,
Andrew Gilchrist
fastelectrics.com
Australia
0419 429 201
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