Hi Kirk,
Actually as you posted, Lamb is a lead engineer at Sevcon, so I would expect a Sevcon-centric position (that's why providing proper citations and giving one's background is so important in these conversations), and I read his article as such. I know that James at Propulsion Marine helped Sevcon develop their current Gen4 program for electric boats. Members have contributed to articles in Practical Sailor, Wooden Boat, the ABYC journal "The Reference Point" and other respected mainsteam publications. Thre was a recent post that discussed the member's involvement in the ABYC standards, so there are members here that are already more involved than you may realise.
What kind of boat are you converting? Heck, maybe you've already converted... Are you trying to compete in a challenge? Are you messing about on a lake? Are you sailing offshore, like me? Ski boat? House boat? Dinghy? Trawler? Narrowboat? Different boats do take different solutions. They're all the same to a point, but since you keep bringing up specialized advancements, I can't quite figure out where you're coming from. This is just to satisfy my curiosity, so that I know a little more about who I'm talking to.
Back to your post. Let's agree that the World Solar Challenge motors that you're talking about are BLDC (not PMAC) motors, and most of the winners have had 97% efficient motors. So if BLDC motors are the most efficient option, why aren't BLDC motors being used more often?
First off, that specific BLDC efficiency comes from matching the motor to a fairly constant load profile, these cars are operating at a very specific power setting more than 90% on the time, at almost full power with little reserve. That doesn't work as well for regular cars or recreational boats.
Next, the cost of these 97% motors and controllers is very high compared to the more common motors that operate above 80% efficiency. Is four times the cost worth a 20% increase in peak efficiency? Only your pocketbook knows for sure....
When looking to power their high end cars, Tesla left no technical stone unturned. They went with AC induction, citing better average efficiency of induction over BLDC as one of the reasons, cost being one of the others (see previous answer).
Here's a quote from Tesla's website, "Likewise, when torque levels are low, the B field should be reduced such that eddy and hysteresis losses due to B are also reduced. Ideally, B should be adjusted such that the sum of the eddy, hysteresis, and I² losses is minimized. Unfortunately, there is no easy way of changing B with permanent magnets. In contrast, induction machines have no magnets and B fields are "adjustable," since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine – magnetic and conduction losses can be traded such that efficiency is optimized. This advantage becomes increasingly important as performance is increased. With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. With induction, as machine size grows, losses do not necessarily grow. Thus, induction drives may be the favored approach where high-performance is desired; peak efficiency will be a little less than with DC brushless, but average efficiency may actually be better."
What I've personally thought is that with common motors that deliver 80% efficiency, there just isn't enough room left for improvement to justify excessive spending for small increases. If there are other parts of the system that could show more improvement, for the Solar Challengers, better solar panels and reducing drag provided the biggest improvements. They used improved motors because after all the rest, small improvements can mean the difference between a win or a loss, but their success with those particular motors doesn't necessarily translate to our use case. I believe that our boats have easier places to improve practical range than motor efficiency.
Right now you can spend more money and get a more efficient driveline by purchasing an "off the shelf" Solomon Technologies drive for your mid-range auxilary sailboat. From a data sampling of one ST conversion, the only first person data that I've been given, shows about 10% better efficiency than my conversion for a similar boat. The drive system costs twice what I paid for mine. Is twice the money worth 10% more range from the same batteries in the same boat? For me, no. Some people here have questioned my choice of LiFePO4 batteries stating that they're too expensive. But it's a personal choice, for me, my batteries have been well worth the extra cost.
This is why I consistantly ask for measured performance results from anybody that is operating an electric conversion. It takes more real data to form objective evaluations of our various options. I've learned not to take promotional specs as gospel.
It's easy to while away the hours debating theoretical differences and accomplishing very little practical progress. I've always preferred this group specifically because we focus on electric boats in the real world, addressing practical problems with available solutions and helping others build the best conversions within their means. There's not as many people captaining armchairs like many internet groups, there's more people "walking the walk" instead of just "talking the talk". If you've got practical experience to contribute about electric boats, reach out past this group and you'll become one of the "experts" like some of the other members here have already done.
Fair winds,
Eric
1964 Bermuda 30 ketch, 5.5kW Propulsion Marine drive, 8kWh Lithium batteries
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
>
> Thats why I included the submission link
> If those that are doing it remain silent then Lamb is the defacto expert.
> Might attract some fresh blood/experiences??
> I would like to understand why efficiency is so low in the 10-30 hp motors/alternators.
> Especially when I read the motor in the Australian solar entry was 98% efficient.
> Would mean 30% more range on the same battery pack to most of us.
>
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