It sounds like a 5kw BLDC/PMAC motor such as the ME0201014201 or ME0907 would work okay for your boat, reduction gear ratio depending on prop size. However I would go for a 10kw to 12kw motor instead, such as the ME0913 or ME1306 instead. Only a couple hundred bucks more, and it would dissapate heat much better and last longer, I believe. The bigger motor, for the same power setting, does not use any more energy than the smaller, at least not enough to make any appreciable difference. You will want a controller rated for 100a continuous, even though you will seldom run that much power. Size matters. Smaller controllers are more subject to overheating. A bigger controller would be better but of course it would cost more. Your reduction gear can be a simple belt and pulley setup, and to experiment with different ratios you just change pulleys. You can buy a prefab belt and pulley reduction drive or you can easily fabricate one. You will need to fabricate a motor mount no matter what, so you may as well build the mount for the reduction gear and mount the motor to that.
If you get a Kelly controller make sure that it has the "stick shift" firmware. That enables you to control both direction and speed with one potentiometer, no FWD/REV switch needed.
You will want a 48v bank. To go cheap, get 6v golf cart batteries from a discounter or golf cart distributor. I have a 48v 220ah bank made up of 8 of these, bought for $85/each and I am quite happy with it after nearly 4 years of use. You will need to learn about battery charging algorithms and FLA maintenance in order to get maximum life out of them; otherwise they won't last two years. If you are too lazy to learn to maintain FLA batteries, you should stick with LiFeP04 batteries which cost a lot more but have many advantages over FLA so the cost difference in reality is not as great is it looks at first glance.
For battery and motor phase cables, go big or go home. I recommend, for cheap, 2/0 gauge welding cable. It is flexible and easy to work with and not lossy at all. Get good quality lugs for all terminals, and a swaging tool to put them on. Tinning the ends of the cables is a good idea if you can do it without melting insulation. Soldering makes the best connection but it can be difficult to not melt the insulation. Your electric soldering gun isn't up to the task. A propane torch at the very least, is needed.
You should be able to repower for under $3k, including batteries. Certainly under $4k.
A kit is much better for a beginner who is not much of an engineer. Components are properly matched and you can get technical assistance from the vendor. This may be worth it to you. If you are willing to do your homework and spend a year or so learning about motors, controllers, propulsion systems in general, batteries, chargers, etc then you may be better off sourcing components and designing your system yourself. It is not a trivial exercise, though.
Word of caution, in case you plan on just going for it. If you run direct drive, you MUST protect the motor from vibration, misalignment, and thrust from prop and shaft. The common way is with a Lovejoy coupling and a thrust bearing. Without at least a thrust bearing your typical axial flux motor will self destruct in minutes, spectacularly. With a belt drive system, you still need a thrust bearing of course, but it is not as critical and a failure will not destroy your motor. Plus no flex coupling is needed. Prefab belt reduction systems take care of all that, so if you are not an experienced fabricator, you would do well to get one.
Direct drive has the disadvantage of often/usually running the motor too slow for the built in cooling fan to adequately cool the motor. Another reason to most strongly prefer use of a reduction gear of some kind. Props love low RPMs. Motors like high RPM. To keep them both happy, use a reduction gear somewhere between 2:1 and 4:1.
What your boat weighs is how much it displaces.
I know you probably would prefer to go cheaper, but it would be very difficult to do so without some knowledgeable and creative salvaging. Electric forklifts are a possible source for usable motors, as well as golf carts. Electric cars generally operate at high voltages and the wiring and electrical standards are tougher to meet once you go over 50v, which is why so many electric boats are 48v. Lower voltages suffer greatly in efficiency. For a dinghy, 36v or even 24v might be satisfactory but for a 3000lb boat you should go with 48v. You will be glad you did. If you are up to the challenge though, salvaged motor, controller, and battery pack from an electric car, with the proper gearing, would certainly work but actually be more suitable for a bigger boat.
Don't use a brushed motor if you will ever have propane or gasoline fuel or accessories aboard, for obvious reasons. Even with proper ventilation this is inviting catastrophe and tragedy.
Considering the hull speed of your boat, a low pitched prop would be preferable to a higher pitch. Pitch should probably be not more than 75% of diameter in your case, I am thinking. This rules out most motorboat props so it may be difficult to find such a prop and you may have to have it custom cast, or learn to cast bronze yourself, if you want a truly optimum prop. Higher pitch will work but definitely don't allow pitch to exceed diameter. Diameter should be the biggest prop you can swing and still have a couple of inches hull clearance. Cupping is sort of optional but I would prefer very moderate cupping. Keeping your RPM under 1000 at top end and down around 300 or so on cruise will minimize cavitation and make the system more efficient. 2 blades is more efficient than 3. 3 blades is more efficient than 4. More blades might be necessary if clearance is limited and a 3 or 2 blade prop underprops the boat. It is a balancing act. Key to making it all work is flexibility in reduction ratio. This is a very good reason to first try a belt drive system, because you can easily change the ratio with different size pulleys. Stay away from chain and sprocket drive. It slings oil everywhere. An enclosed gearbox is very nice but then you can't easily and cheaply change the gear ratio.
Keep in mind that these are just guidelines and not absolutely written in stone, but your final satisfaction with your system may well lie in following them. Otherrwise, have an experienced installer put a full turnkey system in your boat. If the boat isn't worth it, then perhaps it is not a good platform for an electric drive system.
---In electricboats@yahoogroups.com, <kimgye@...> wrote :
I have looked at plug and play systems from the bigger companies but they are $5500 us and up which is above my budget for a drive system before batteries. I have found two companies that have sail boat systems for about $1600 us (Thunderstruck and Electricmotorsport) they are both in California. Does anyone have any advice or can point me in the right direction? Thanks in advance.
Kim
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