Portable submersible water generator design? - Mountain Buzz

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Old 07-11-2016   #1
Electric-Mayhem's Avatar
Lakewood, Colorado
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Portable submersible water generator design?

First off....I know some, if not most, of you are anti-gadget on river trips. This thread isn't for you and I frankly just don't even want to hear anything from you. There are some trips that I like to go that way too, but I'm also a techy nerd and if not for any other reason than to see how it works I wan to try this but I'm just not interested in hearing from the anti-tech crowd on here....at all. I'm serious.

Ok, now that I have that out of the way....

So it has occurred to me that when on the river, we have a an abundant resource for power generation flowing by the whole time. I have a solar charger, but its slow and if its not bright enough it just doesn't work at all. Most camps have decent current and plenty of places to hook a tether.

I've seen a few designs on the net that are essentially a waterproof pod with an electrical generator inside and a propeller attached to the generator through waterproof coupler. It seems really simple, but they want like $1200-2500 for it or something crazy. Here is a picture and video of it in use...

I have the tools to make it (Mill and Lathe and welding equipment), but lack the electrical engineering expertise to know how to calculate things and to know how fast a generator needs to spin and such. I'm assuming the unit has some gearing to spin the generator faster, but I'm not sure.

The people who make the expensive one claim 100 watts of power at 12v, 24v, or 48v...which is honestly enough to run a laptop or other more power hungry devices if you wanted to (the one in the video is evidently powering a street light on a bridge nearby). I'm not saying that is what I want necessarily (though movie night halfway through the grand canyon might be pretty cool). Mostly what I would want it for would be enough to charge a GPS, Camera, or GoPro on occasion with a more reliable way then Solar. I'd change the design a bit to be something tethered to shore that you just drop in the water and let it run.

I know there are some engineer types on here, so let me know if you have any ideas about this. I'm sure there are patents on this kind of thing, so at this point I'm not really interested in making this as a product, but who knows what the future brings.

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Old 07-11-2016   #2
Aurora, Colorado
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I've had the same thoughts in the past, and while I'm not an engineer, I've done quite a bit of research. So, a few comments:

1. It looks like some pretty swift current there- it's just about to go super-critical over that low-head looking obstruction. So, it's probably cookin' at 10(?)mph. That's pretty quick water. On most of the desert trips I run, we're pretty lucky to have 4 or 5 mph flowing past the back end of the boats.

If I'm not mistaken, the energy in the water isn't directly related to the speed of the water, but rather is exponentially related to it. So, faster current is key.

2. It seemed, from my lay research, that the swept area of the turbine is also key. If you have a tiny little fan blade, it's only catching a tiny little bit of the energy in the river.

3. Sealing the whole unit seemed to be the tricky part to this type of design, to me. Maybe you've got that dialed in, but from my perspective (pretty handy, but don't have a machine shop) keeping water out of places that you don't want it is nigh impossible.

4. Most electric motors (generators) and alternators like to run at pretty high RPM. This leaves you with the problem of gearing up so that you get the desired RPM at the alternator shaft, especially if you're dealing with relatively slow current.

I can look back in to my research notes on this, and see if there's stuff I'm forgetting. I'd love to see what you come up with!
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Old 07-11-2016   #3
utah county, Utah
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for desert rivers, think about silt proofing. maybe a small water wheel design floating on pontoons with an automotive(marine) alternator suspended out of the water?

sounds like a fun project.
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Old 07-11-2016   #4
Aurora, Colorado
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That's the direction I was leaning. An undershot water wheel isn't especially efficient, but there are some design benefits- your electronics can all be out of the water, for one. Also, if you have a pretty decent size radius, there's a lot more leverage on the center axle to gear things up so that the alternator will spin faster. We'd also looked more at alternators, and having a rectifier in the battery box since AC travels over distance better, but if you're only talking a few feet, the difference might not be worthwhile. If I remember right, we were leaning toward building our own alternators because they can be built to require lower RMP. That minimum RPM is a killer on commercially available generators/alternators.
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Old 07-11-2016   #5
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All good points and sort of what I was thinking too. I do like the simple nature of something you can just pull out of a bag and drop in the water. If you use the right power cable, I think it would even work without having a separate mooring line. A little floating platform sounds kinda cool too..but it also sounds kinda clunky and hard to store while not in use. Also, my understanding of river mechanics says that the current will likely be stronger under the water then at the surface. I would definitely have a way to control trim and balast and to have it be able to steer itself into the current better using adjustable fins.

As far as actual placement of the thing...you'd have to pick campsites that were next to faster flowing sections. I've certainly stayed next to rapids that had 10+ MPH flow and would work great for this. That is especially true during peak flow.

Waterproofing is certainly a challenge, but I think with a nice machined aluminum chassis and several layers of o-rings, it should be pretty water and silt tight. The one pictured in my first post is actually filled with mineral oil to provide non-conductive support for the generator/alternator and whatever electronics that they have inside. I haven't seen a picture of the inside of the thing so its hard to say exactly whats going on. I think the hardest part would be waterproofing the propeller shaft, but I do think its doable with axle shaft style seals a couple deep.

Since I'm not hoping to have it power a house or high draw electronics, it seems like you could design it with a lower turning speed in mind. If you can get 5v and a 5-10amps out of it, that would be enough for most stuff people use on the river. Ideally it would be 12v and at least 10-20 amps though, so you could use automotive accessories. I still haven't seen a good charging solution for high end camera batteries(for DSLR's) in the wilderness, but I know they make car chargers that can charge them.

I also do rock crawling and I know they make alternators for lower rpm duty, so if we could figure out a good one of those for this application, it would be a relatively easy task to design a housing for it (he says never having done so). Then you'd just need to figure out how fast it needs to turn and what torque to turn it and that would determine the propeller and whether you need to use a gear system. There are enough small form factor planetary gear systems out there that I'm sure you could find something off the shelf to work.

I think this is the right time for this, as there are all manner of off the shelf electronics solutions with the combo of the "maker" movement and electric bicycle technology. Battery tech is really good too, with small form factor high capacity batteries being reletively plentiful. I'll admit to being a novice with propeller calculations and building water tight containers, but its a fun project and it'll be cool to at least turn my brain to it.
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Old 07-12-2016   #6
Aurora, Colorado
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This site seems to have a lot of products and info that will be helpful:

Windstream Permanent Magnet DC Generators |
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Old 07-12-2016   #7
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I have a couple thoughts,
I recall from fishing discussions the faster flowing water is at the top of the water column, so a small turbine near the surface may be better.

I haven't taken much time to research this myself, but I have heard of a couple ideas surrounding irrigation canal generators- I imagine a small paddle wheel looking device. You might be able to fabricate a small floating trough to funnel water through something similar. A quick Google search for "irrigation canal electric generator" lead me to a website called treehugger.... in which I clicked on micro generators. This discussed having a mini turbine within PVC pipe. Again, not much research on my part but a couple ideas FWIW.
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Old 07-12-2016   #8
Carbondale, Colorado
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I'm a hydroelectric engineer. Designed, installed, REAL hydrokinetic turbines in the Mississippi and tried get these smaller ones to work in off-grid applications. The power output is minimal unless you have at least 6-8 fps and even then not a lot of power - maybe 50W. Your a whole lot better off (cost and hassle factor)keeping it simple and use a solar panel
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Old 07-12-2016   #9
laramie, wy
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I saw this a few years ago on Kickstarter

The World's Smallest Hydropower Plant | Blue Freedom
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Old 07-13-2016   #10
Meridian, Idaho
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A small prop or turbine setup in the back of a cone like a drift sock might help witht the slow current issue. I had been considering this at one point too, an old guy in a bar suggested starting with some testing using an old electric trolling motor. He was inclined to think that if you reversed the prop spinning the motor backwards it would generate power and is already sealed. He wasnt talking about an end user product at that point but was thinking it might provide some data and a low cost starting point.
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