Thank you for the clarification, Matthew.
I was not aware that AC had been so recently adopted to the traction drive systems in trains.
Boaters are a tough sell for new technology, as you state. Not long ago, the idea that a "water screw" would replace the tried and true paddle wheel seemed ridiculous as well...
There are still many valid brushed motor applications, and there will be for years to come. Children's toys, automotive fuel pumps, and battery-powered tools are good examples. An in-tank fuel pump with gasoline running through the motor provides both brush lubrication and armature cooling. In battery powered tools, the batteries will tire long before the brushes wear out, and toys don't have the market headroom to support a switching controller. (After developing a brushless motor for Bosch, I'd put them in the same category as well).
Boats have their own set of issues. Dependability certainly can be considered as paramount, and the reliance on a switching controller is a major factor in the equation. Offsetting that, however, is the explosion risk posed by un-covered brushes, the cooling issues posed by enclosing the motor (as the vast majority of waste heat is developed in the armature, i.e. trolling motors), and corrosion of the copper commutator bars in a salt air environment. Both systems are vulnerable to lightning strikes (one boat per thousand is struck each year, according to Boat Magazine).
As systems advance over the years, brushless motors, like the propeller, will be the new standard of reliability and safety. One test motor/controller operated a circulating water pump on a 55gal drum for over 30 months, 24/7, until the power supply regulator failed and over-voltaged the 24v controller. I use the same controller in my motors. The motor showed no sign of wear, save a little more play in the sealed bearings. I use the same motor design as well. The integral thrust bearing in my design can be replaced without removing the motor.
Although I've been involved motors and controllers for many years (primarily in manufacture and testing protocol) , I'm still a newbie in the field of boating. I love finding new applications for motors, and have yet to to make a dime messing around with boats. Currently, I'm building a 10kW brushless DC motor to replace one of two Volvo Penta AQ170 in my 1976 Skipjack. The fumes and noise while cruising SF Bay were nasty. I hope to be a professional boat motor designer/manufactur
Thank you, Myles.
Be Well,
Arby
www.advancedmarinee
____________
From: Matthew Geier <matthew@acfr.
To: electricboats@
Sent: Monday, August 3, 2009 1:40:31 PM
Subject: Re: [Electric Boats] Abusive and dangerous Re-Epower technical specification
Arby Bernt wrote:
> Locomotives use AC drive systems due to the complexity of coupling the engine to the drive wheels. Before AC coupling was available, the slip between the drive wheels and the track was nearly impossible to control, as the friction of a non-slipping drive wheel can transmit more force than than a slipping wheel. By comparing the rotation of a drive wheel to a static wheel, the speed difference can be maintained at under 0.5%.
Most of the world's railway 'diesel electrics' are DC motored. AC
motors have only come in over the last 10 years and then only at the big
end. Railways have been reluctant to switch from series DC motors.
'Switchers' would still mostly be series connected DC motors, AC
traction motors are still working their way down the feeding chain.
Even then they are not all induction motors - the French were big on
Synchronous motors with slip rings for a while - I presume so they could
control the current in the rotor coils.
EMD apparently built their first AC motored locomotive in 1987, but the
first big order wasn't till '93. The same source says at 2005 , 50% of
the market was still DC motored, EMD's split was 60% AC, 40%DC.
Sounds sort of like us electric boaters - those 'new fangled AC motors'
are still not quite trusted yet :-)
[Non-text portions of this message have been removed]
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