On Nov 21, 2010, at 2:42 AM, proaharry wrote:
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>> From the Australian agent for Torqeedo:
>
> Yes, the Torqeedo is more noisy then other electric motors. But it is the price to pay for better efficiency.... The Torqeedo is an AC motor not a DC and the gearing is quite different then other motors. Realie it as notthing to do with commutation but you will always have people that know it all....
Sorry I used the term commutation in place of switching. Every drive requires the switching of the supply to control the activation of the phase windings in the proper order (commutation) and to provide the desired thrust. Apparently the agent is counting on customers that know little.
AC vs DC topology isn't relevant regarding "gearing". As an aside, the most efficient electric motors are DC permanent magnet motors at this point in time.
"gearing" in itself is an enemy of efficiency - and gear noise is a side-effect of that inefficiency.
a lot of controllers switch in the audible range (sub-20 kHz, lower than that for a lot of us ;-) ) higher inductance in larger motors tends to discourage high switching frequencies to avoid switching losses, thus motors/systems tend to be noisier to us - and they often excite resonances in other parts of the system.
a slower motor turning a larger prop would exhibit far greater efficiency.
I will admit that a smaller motor geared down may be more cost-effective - from the motor but not system standpoint - but your agent is confusing marketing with science. Noise is a sign of inefficiency, whether in gears or control.
I'm a great believer in the future of electric propulsion, once the energy storage daemons are exorcised, but as it stands today, and as much as I hate it (I'm an EE) you can't beat the energy density of fossil fuels for vessels that need to be shore-independent for great periods of time. As far as regeneration goes, why slow the boat now so that you can use the stored energy to catch up later? Where regenerative systems shine are in intermittent use - accelerate/coast/decelerate/repeat, not in steady-state demand applications.
The two things I could like about electric drives are that 1) you could potentially use one engine to supply 2 drives, although the battery bank would probably cancel the weight of the second engine, and you would lose the redundancy and 2) for daysailing use, where you could rely on stored energy from dockside charging.
Mike
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> --- In harryproa@yahoogroups.com.au, Michael Gehl <mike@...> wrote:
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>> Motoring range *and* price... $3700US per motor plus ~$4K for 8KWh for a high-quality (a123 type, not the self-destructing Chinese) lithium battery pack plus probably at least $1K for decent electronics for charging, monitoring and control - then you need to find a marina that would let you "sneak-charge" the pack within the dock wiring limits. Which would give you about 1 hour of something near 2x9.9hp thrust.
>>
>> What's up with the noise level? I suspect a better commutation scheme might help there; it sounded well above that of conventional outboards.
>>
>> Mike
>>
>> On Nov 19, 2010, at 5:39 AM, Arto Hakkarainen wrote:
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>>>
>>>
>>> Electric motors would be handy on a proa if the motoring range issue can be solved. Weight of batteries and/or generator is probably an issue and the cost will be quite high.
>>>
>>> Arto
>>>
>>> --- On Fri, 11/19/10, Mike Crawford <mcrawf@...> wrote:
>>>
>>> From: Mike Crawford <mcrawf@...>
>>> Subject: [harryproa] 45' cat with electric motor pods
>>> To: harryproa@yahoogroups.com.au
>>> Date: Friday, November 19, 2010, 6:44 AM
>>>
>>>
>>> http://www.youtube.com/watch?v=mJv-lGPXxHc
>>>
>>> I'm not endorsing this setup because I don't know anything about it
>>> other than what the video shows. Nonetheless, electric motors on
>>> lifting pods have been discussed a few times on this forum, and I
>>> thought these were interesting. My guess is that catamaran weighs
>>> noticeably more than a Visionarry.
>>>
>>> - Mike
>>>
>>>
>>>
>>>
>>
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