Hi Neil,
I commend your project and you have already acknowledged that for a given drive system, one can optimize the components to hit their peak efficiencies at the same time. However, you go on to explain that you are looking for either a system that has 2 efficiency peaks, or a system that delivers peak efficiency over more than 70% of it's operating range.
As you look at each component, you'll see that none of them can deliver their peak efficiency at 2 widely seperate operating conditions. It seems like your best bet would be some way of running the motor at it's most effficient speed and adjusting the gear ratios to get the desired speed.
I don't know of any system that can do that without introducing aditional losses, which is why most people here go with a fixed reduction ratio and tune the system for their most common use.
I look forward to your progress.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "F Neil Simms" <f.neil.simms@...> wrote:
>
> Sorry if this has been discussed before, but most of what I've seen here over the years relates to high efficiency running with props in the 1k rpm or less range, and motors in the 2kw or higher range. With proper reduction, it doesn't seem to be too hard to hit the high efficiency 'sweet spot' for such systems.
>
> What I'm looking for is a motor configuration that will drive a light, long boat (24' x 2' at WL, under 500lbs all up) at high efficiency (90%+ for the motor), with prop speeds in the 300-700 rpm range. I would like this boat to be capable of both high speed (relatively, say 8 to 10 mph) at around 1 to 1.5 kilowatts, and long distance cruising at very low power levels - 50 to 100 watts. I wouldn't necessarily need both at the same time, so changing reduction or even motors and reduction to achieve one or the other for a particular outing would be acceptable.
>
> I am able to find DC motors that will operate at 90% efficiency at the upper end of this speed range, with appropriate reduction, but have been unable to find a motor that will maintain that level of efficiency at power levels less than 200 watts, if I'm reading the specs and performance charts correctly. Many that do 90% at 1 kw or higher appear to do 50% or less under 200 watts...
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> This boat should be capable of very long runs in the 3 to 4 mph range with only modest battery sizing, if I can figure out how to get the motor to work efficiently at such low power levels.
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> Any suggestions?
>
> Neil S.
>
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