Tom,
Ok, got it. Many people believe that BLDC and PMAC motors are identical, while they are physically similar, there is a subtle difference. I posted some relevant info on this group last September, post #15389. Here's most of that post...
"Although BLDC motors are practically identical to permanent magnet AC motors, the controller implementation is what makes them DC. While AC motors feed sinusoidal current simultaneously to each of the legs (with an equal phase distribution), DC controllers only approximate this by feeding full positive and negative current to two of the legs at a time. The major advantage of this is that both the logic controllers and battery power sources also operate on DC, such as in computers and electric cars. In addition, the approximated sine wave leaves one leg undriven at all times, allowing for back-EMF-based sensorless feedback.
Vector drives are DC controllers that take the extra step of converting back to AC for the motor; they are sophisticated inverters. The DC-to-AC conversion circuitry is usually expensive and less efficient, but these have the advantage of being able to run smoothly at very low speeds or completely stop (and provide torque) in a position not directly aligned with a pole. Motors used with a vector drive are typically called AC motors. When running at low speeds and under load, they don't cool themselves significantly; temperature rise has to be allowed for.
A motor can be optimized for AC (i.e. vector control) or it can be optimized for DC (i.e. block commutation). A motor which is optimized for block commutation will typically generate trapezoidal EMF. One can easily observe the shape of the EMF by connecting the motor wires (at least two of them) to an oscilloscope and then hand-cranking/spinning the shaft." A BLDC motor will show up as an angular pattern on the oscilloscope, a PMAC motor like the Mars ME0907 or ME0913 show up as a sinusoidal curve.
While either type of controller will work with each type of motor, matching them correctly should result in a more efficient and quieter drive line. Most of the controllers that I have researched in our power range (Millipak, Kelly, etc.) are BLDC controllers. The Gen4 is the only readily available PMAC controller that I've seen (there could be others) in the sizes that we're looking for.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Tom" <boat_works@...> wrote:
>
> Eric,
> I should have been more clear.
> The ringing or singing noise is definitely coming from the motor, not the controller. But James suggested that the noise is a result of the controller not being the optimum match for the motor, and the motor is "acting like a speaker" to radiate the sound. This noise is present even when the motor is operated out of the boat.
>
> I wasn't surprised to hear a high pitched whine coming from the controller whenever the contactor is energized, but the noise (only at certain speeds)is something I'd like to reduce as much as possible.
>
> I have de-coupled the motor mount from engine stringers with rubber mounts, about the loudest mechanical noise (other than the growl at low speeds) is the normal motor operation and the synchronous belt going around. And that doesn't irritate me.
>
> So maybe a correctly configured Gen4 is an improvemnet...
>
> -Tom
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > Tom,
> >
> > I haven't heard anything from the Gen4 controller. As far as I can tell, it is truly silent. My experience with DC controllers in EVs is that some will "whine" at certain settings, I think that it's some sort of harmonic related to PWM or something like that....
> >
> > Fair winds,
> > Eric
>
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