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Old 17-06-2017, 09:10   #1
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Small generator + electric propulsion for dingy

I have been toying with the idea of getting a small inverter generator (found an 800W, 40 cc generator, 4-stroke, 20 lb weight for $269 on Amazon, see link below) and a Minn Kota style electric drive) for my inflatable dinghy. I understand that it produces the equivalent of 1 hp only and there will be safety issues with high voltage around seawater but may be the latter point could be mitigated through good insulation and protection. Then there is the issue of interfacing the AC output from the generator to the DC of the propulsion motor. May be I need to add a small lithium battery.

What do people think about this idea? The benefits I see are light weight (much easier to move 20 lb up and down), a nice place for the generator when producing electricity for the boat (when at anchor), low cost. The drawback is too many modules and complexity unless packaged well.


https://www.amazon.com/Dirty-Hand-To...XB9YPP260MPGJE

p.s. The ideal device would be a 2.5 hp outboard with a built in alternator, curious why no one makes them.
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Old 17-06-2017, 09:23   #2
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Re: Small generator + electric propulsion for dingy

It is significantly less efficient to use motive force to make electricity, to convert it back to motive force, best to use motive force directly.
I apologize if motive force is not the correct term.
However sometimes there are other factors that overcome the inefficiency, like a train not needing a transmission etc.

Be best if you use 120 VAC directly if possible, and try not to electrocute yourself as that is a very real concern, otherwise your going to have to have a transformer to convert 120VAC to 12VAC.
I am assuming a Minn Kota will operate on AC, or if not maybe rectified to pulsed D.C.?
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Old 17-06-2017, 09:26   #3
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Re: Small generator + electric propulsion for dingy

You would be much better off running the motor off a battery rather than a generator. Also much more quiet.

You can charge the battery from solar when you reach your big boat.
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Old 17-06-2017, 10:09   #4
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Re: Small generator + electric propulsion for dingy

Thank you for the replies. I understand the inefficiencies (we start with a 1.4 hp motor, the inverter only provides 750 watts = 1 hp, and the rectifier charger will lose another 15%). It would be great to use an AC motor but I am worried about feeding 110V below the waterline - not safe for me or people around me). A battery would be simpler but it is heavy (at least 50 lb for a group 24) and LifePo4 gets expensive ($700 for a 50 Ah battery).

For me dinghy propulsion will be part of the need, the other need will be just to run the generator at anchor, so it is a dual use setup but still debating if it is worth the hassle.
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Old 17-06-2017, 11:16   #5
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Re: Small generator + electric propulsion for dingy

How is a cheap air-cooled generator going to hold up I a wet salty environment of a dingy?

At the very least, get a secure location on the mother ship to mount the generator and then run 12v DC cables to a battery in the dingy.

Reality, is it's simpler to just get a small outboard for the dingy and a generator for the boat.

If there was a big demand, it could be done but to get a reliable system that would hold up in the harsh environment is a major design endeavor but there are better ways to do it, so no one has produced a commercial variant.
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Old 18-06-2017, 10:53   #6
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Re: Small generator + electric propulsion for dingy

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Originally Posted by Pizzazz View Post
Thank you for the replies. I understand the inefficiencies (we start with a 1.4 hp motor, the inverter only provides 750 watts = 1 hp, and the rectifier charger will lose another 15%). It would be great to use an AC motor but I am worried about feeding 110V below the waterline - not safe for me or people around me). A battery would be simpler but it is heavy (at least 50 lb for a group 24) and LifePo4 gets expensive ($700 for a 50 Ah battery).

For me dinghy propulsion will be part of the need, the other need will be just to run the generator at anchor, so it is a dual use setup but still debating if it is worth the hassle.
Heavy battery?? How about heavy generator, inverter, wiring, controller. You are trying to reinvent the wheel.
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Old 18-06-2017, 10:58   #7
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Re: Small generator + electric propulsion for dingy

How long of a time do you intend on motoring with the little electric trolling motor a simple small 12 volt 10 ah battery for kids power toys will easily get you to and from the dock. Recharge off solar when on the mothership. Another idea would be a 50 watt flex panel to charge while at the dock . Much better idea imho.
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Old 18-06-2017, 13:20   #8
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Re: Small generator + electric propulsion for dingy

A better solution is if you can find a generator that makes 12V DC directly...you know... like the alternator on your engine.
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Old 18-06-2017, 13:21   #9
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Re: Small generator + electric propulsion for dingy

I also have thought about this same solution, but haven't really addressed it yet. I have the dinghy and the dc trolling motor. The idea of having the generator for other uses and the increased reliability of the dc outboard is a good thing in my book. Most of the time I will row the dinghy, a couple miles is no problem, but if I needed to travel 25 miles in the dinghy I would want some other possible mode of propulsion.
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Old 18-06-2017, 14:06   #10
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Re: Small generator + electric propulsion for dingy

I can see a generator in a dinghy lasting about a week before it gets swamped or dies from salt water from the floor of the dinghy. That's not even considering the inefficiency of burning gasoline to make electricity to power the dink. If you want electric power for your dinghy and a generator, leave the generator on the boat and use it to charge a battery to power the dinghy moto and live with the limited range. But then if you worship at the holy grail of electric power, it all is justifiable even if it doesn't make sense.
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Old 18-06-2017, 14:28   #11
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Re: Small generator + electric propulsion for dingy

A 2 HP outboard would be lighter than the generator/battery/motor combo, would work better, be safer, more reliable...

Why does no manufacturer put an alternator on the tiny outboards? Why would they?
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Old 18-06-2017, 14:30   #12
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Re: Small generator + electric propulsion for dingy

Seems like folly.
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Old 18-06-2017, 14:37   #13
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Re: Small generator + electric propulsion for dingy

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A 2 HP outboard would be lighter than the generator/battery/motor combo, would work better, be safer, more reliable...

Why does no manufacturer put an alternator on the tiny outboards? Why would they?
Actually they do my tohatsu has a 6amp alternator built in .
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Old 18-06-2017, 15:33   #14
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Re: Small generator + electric propulsion for dingy

Aside from it being loud, dangerous & unreliable you'll also be breathing the exhaust from the generator while you're running it.
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Old 18-06-2017, 15:47   #15
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Re: Small generator + electric propulsion for dingy

My neighbor has been buying old 2 strokes that aren't running, fixing & selling them for years. Watch Craigslist & get yourself a cheap used outboard that's designed to do what you need. Regarding cheap Chinese generators, the reviews are not very favorable. I'd go with solar if you can't swing a Honda.
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