Well Jack,
First, the "Sevcon Brushless Sailboat Kit - 8.5KW" is an AC motor, at least the Sevcon Gen 4 controller is an AC controller.
The AC-09 system as spec'ed looks like it would work, though I've never heard of anyone running one of those systems in a boat. That drive seems better suited for a motorcycle or a light car. A 350A x 48V system works out to almost 17kW, and even the output of 18hp is 13.5kW (which works out to 80% efficiency). Going back to your boat's requirement of 7kW, this motor looks like it may be twice the power that you need. The good side of this is that your system will never be close to overloaded during normal operation. The bad side is having to build your system to handle 350A, the cables, fuses and batteries will need to be pretty stout (heavy and expensive). It is my personal guideline that the battery should have a usable capacity that can sustain at least 1 hour at max throttle. By that standard, this system would need 1000Ah x 48V of flooded batteries (2100 lbs), 640Ah of AGM batteries (1600 lbs), or 480Ah of Lithium batteries (600 lbs).
You may not need that much electricity storage for normal usage, but you don't want to be blowing fuses, melting cables or damaging your batteries if you apply full throttle.
Perhaps you can make it work. If you do go this route, report back here because you will be exploring options that haven't been covered here before.
Good luck and fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, merit131 <no_reply@...> wrote:
>
> Thank you Eric for your help. I spoke to Mark of Thunderstruck Motors a few days ago. I thought the a DC motor was the answer, I believe it was the same you spoke of. Mark thought an A/C motor would be best in my case, he suggested the AC-09 Kit, he also suggested a reduction of 4-1. And a prop w/ a high pitch. The following is the data from the website.
>
> This Kit features a Curtis 1236-5301 controller that operates at 36-48V and can draw up to 350A producing up to 18HP and 75ft-lbs of torque. This kit works very well in a medium size sail boat, motorcycle or kart.
> Peak HP 18
> Peak TQ 75 ft lbs
> Controller Weight 9.1lbs
> Motor Weight 46lbs
>
>
> This Kit includes
> - Curtis 1236-5301 AC Controller
> - Hiperformance EVs AC15 6.7" x 11" NEMA C Face, 7/8" shaft.
> - Curtis Spyglass 840 Display (dispays: Amps, Voltage, RPM, MPH/KPH, Motor Temp)
> - Wiring Harness and wiring instructions
>
> Do you think this would be the way to go?
>
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > This has been discussed here before. I posted an analysis of the "Sevcon Brushless Sailboat Kit - 8.5KW" from Thunderstuck in post #17601 on March 3, 2011. Here's some of the salient points:
> >
> > "The picture on the website shows what appears to be a Mars ME0907 single stator motor. The manufacturer rates this motor for 100A continuous for 48V DC. That works out to a continuous motor rating of 4.8kW
> >
> > The picture shows a Sevcon Millipak controller which is also rated for a 48VDC max power output of 4kW (from the Sevcon webpage). However the Thunderstruck webpage lists a Sevcon Gen-4 275Amp, programmable, regen controller. The only Sevcon Gen-4 controller that mentions 275A in its ratings is the G4827 controller. This controller is rated for 110A continuous (60 minutes)with a maximum nominal voltage of 48VDC. That works out to be almost 5.3kW.
> >
> > But a drive system can only be driven as hard as its weakest component. In this case, the ME0907 motor will only take 4.8kW continuous current at 48V. And these ratings are in ideal conditions. In a boat, you will probably find that one of the components will overheat at somewhat less than maximum ratings unless measures are taken to maximize the cooling for each of the key components."
> >
> > So at best, the "Sevcon Brushless Sailboat Kit - 8.5KW" looks like it should be rated as 4.8kW, not 8.5kW.
> >
> > I would expect that a vendor should be able to provide supporting data for their claimed power ratings in a marine environment. I know that Propulsion Marine states that their 5.5kW drive will operate its rating for an hour with controller and winding temps of less than 100C. In my boat, I've operated above 5kW for 15 minutes with controller and winding temps lower than 75C and backing off to 4kW for less than 10 minutes cooled the motor to 72C. Given my experience, I find James' claims believable. All of the components have manufacturer ratings that are considerably higher, but running slow in a bilge is not an optimum environment.
> >
> > Fair winds,
> > Eric
> > 1964 Cheoy Lee Bermuda 30 ketch
> > Marina del Rey, CA
> >
