Tuesday, November 9, 2010

Re: [Electric Boats] Drive train noise

 

Floor boards radiate sound pressure.
What is created is a low frequency hum that must be redirected towards itself.
Adjusting the pmac controller correctly ( as James Lamden stated previously) will reduce the noise to a mere bee buzz.
Then to silence noise, you must send the same sound back at the unit. All frequencies cancel out. Using sound absorbing materials are not the smartest solution on a boat but design the surounding area like a sound room and send it back.
BTW... using this concept and taking into consideration surrounding areas that should also dissipate heat quickly....and you have a winner
As i said a few times on electric boats......the sail boat will never achieve a 'true' design unless someone takes it back to the drawing board, the hull must be redesigned to capture the energy it absorbs....unless your a racer.
Good Luck
Rick

--- On Tue, 11/9/10, Kevin Pemberton <pembertonkevin@gmail.com> wrote:

From: Kevin Pemberton <pembertonkevin@gmail.com>
Subject: Re: [Electric Boats] Drive train noise
To: electricboats@yahoogroups.com
Date: Tuesday, November 9, 2010, 9:38 AM

 
Hey Tom,

The hum you get is common with most motor controllers. Call it the carrier frequency like is used to broadcast FM radio.  This this is what makes low loss three phase output a reality.  On an industrial controller this frequency can be changed but typically around 1000Hz 

The perm magnets are what make the motor a torque motor vs. a standard induction motor. The slip is what you loose but this should not make any vibration, and not likely the noise you are getting.  What you are getting is the motor acting like a speaker. This is a typical problem with VFDs and may be caused by a loose winding, a loose name plate or other item close to the motor like connection wiring not located where it can't vibrate, or just action with the armature.

Kevin Pemberton

On 11/08/2010 07:07 PM, Tom wrote:
 
A few notes on noise aboard Grace, our 21' launch:

I ran my MARS PMAC ME0201013001 motor with the Sevcon MilliPak controller outside the boat before installation just to get a baseline on the noise I could expect.

I wasn't expecting silence, but was hoping for something equivalent to an AC induction motor, since there would be no brush noise.
Well, I was being too optimistic.

The controller makes a distinct, unvarying, and piercing whine at all speeds, even at rest. It is easily heard, but not obnoxious, with the floorboards down. The manual says it is inaudible in operation. I'll have to disagree.

The motor has a distinct cogging effect when rotated slowly by hand, so I had my suspicions that it wouldn't run as smoothly at low speeds as an AC induction motor. In fact, there is a loud rumble at very low speeds. This isn't really a consideration, since the motor is rarely run at such low speeds.

At any other speed the motor is reasonably quiet, and very smooth running.

The controller creates a loud singing noise at various speeds. At other speeds it is silent (except for the continuous whine)At first I was convinced that the prop was at fault (15x12 3 blade), but Dennis Wolfe asked me to look into whether the noise could be coming from the motor, as a function of the output of the controller, and it certainly is.

The synchronous belt reduction gear (2.8:1) is very quiet, allows for very easy and exact alignment with a self-aligning thrust bearing, and might serve as a weak link in the system in case of hitting a log with the prop (let's hope we never find out).

Grace has isolating bushings in the motor mounting plate, but no other sound reduction, yet.

I don't mean to sound negative, I really like being electric, but I did have very high expectations of near silence, which doesn't seem to be realistic.

-Tom

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