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Old 30-05-2017, 17:20   #1
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Hydroelectric Generator

I'd given up on hydroelectric power some time ago because of the OBSCENE cost of commercially available units, but now I'm rethinking it from a DIY perspective. I know people have had success mounting alternators to their prop shafts. What I can't figure out is how to estimate the output to see how worthwhile this would be. Any idea how to do that calculation? Or real world numbers from your own experience?
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Old 30-05-2017, 18:30   #2
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Re: Hydroelectric Generator

The problem with alternator on propshaft is RPM.

You will need an alternator that is specifically built for low RPM operation i.e. one designed for hydro or wind generation.

The alternator spec should tell you what the output is at various RPM, you then need to estimate the likely RPM of your propshaft when freewheeling and reduce that estimate by a "fudge factor" based on the increased load of the alternator.
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Old 30-05-2017, 18:31   #3
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Re: Hydroelectric Generator

One of us is confused.

Generating power in a static location from naturally flowing water, tidal flows, wave motion, OK.

But trying to capture energy from movement powered by dino juice is forgive me a fools errand.

Like spinning a wind gennie by running a powerboat, the power lost to wind resistance is **much** greater than what you'd be trying to (re)capture.

Or am I misunderstanding?
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Old 30-05-2017, 18:49   #4
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Re: Hydroelectric Generator

Quote:
Originally Posted by StuM View Post
The problem with alternator on propshaft is RPM.

You will need an alternator that is specifically built for low RPM operation i.e. one designed for hydro or wind generation.
Yes, I've looked at the alternator from Wind Blue Power, reaches 12v at 130 RPM.

Quote:
The alternator spec should tell you what the output is at various RPM, you then need to estimate the likely RPM of your propshaft when freewheeling and reduce that estimate by a "fudge factor" based on the increased load of the alternator.
Any idea what that fudge factor ought to be?

Quote:
Originally Posted by john61ct View Post
One of us is confused.

Generating power in a static location from naturally flowing water, tidal flows, wave motion, OK.

But trying to capture energy from movement powered by dino juice is forgive me a fools errand.

Like spinning a wind gennie by running a powerboat, the power lost to wind resistance is **much** greater than what you'd be trying to (re)capture.

Or am I misunderstanding?
I'm talking about running an alternator from a prop that's moving because the boat is under sail - no dino juice being burnt. In fact, I don't intend to have an engine at all, so I'd have a prop dedicated specifically to running an alternator.
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Old 30-05-2017, 18:52   #5
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Re: Hydroelectric Generator

What proof do you have that these boats with alternators on their drive shafts make power? What about Entropy?
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Old 30-05-2017, 18:53   #6
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Re: Hydroelectric Generator

Aha, I see, sail-powered hydro 8-)

What is the advantage compared to spinning directly off the wind?
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Old 30-05-2017, 18:54   #7
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Re: Hydroelectric Generator

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What proof do you have that these boats with alternators on their drive shafts make power?
A. They have to make power, it's just a question of how much.

B. There are several old threads on this board of people saying they use them with success.

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What about Entropy?
What about it?
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Old 30-05-2017, 18:59   #8
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Re: Hydroelectric Generator

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Aha, I see, sail-powered hydro 8-)

What is the advantage compared to spinning directly off the wind?
More reliable (I suspect) and avoids the big weight up high
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Old 30-05-2017, 19:01   #9
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Re: Hydroelectric Generator

Quote:
Originally Posted by john61ct View Post
One of us is confused.

Generating power in a static location from naturally flowing water, tidal flows, wave motion, OK.

But trying to capture energy from movement powered by dino juice is forgive me a fools errand.

Like spinning a wind gennie by running a powerboat, the power lost to wind resistance is **much** greater than what you'd be trying to (re)capture.

Or am I misunderstanding?
I assumed he was talking about capturing energy from movement powered by the wind. As in attaching an alternator to a freewheeling prop shaft on a sailboat. The same thing that commercial hydrogenerators like the Watt & Sea, towed generators, and EP powered sailboats do.
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Old 30-05-2017, 19:05   #10
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Re: Hydroelectric Generator

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Originally Posted by john61ct View Post
Aha, I see, sail-powered hydro 8-)

What is the advantage compared to spinning directly off the wind?
No annoying heavy, noisy, unsightly, whirly thingamabob?
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Old 30-05-2017, 19:12   #11
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Re: Hydroelectric Generator

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Any idea what that fudge factor ought to be?
Not really, a lot would depend on the conditions, boat, and prop.
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Old 30-05-2017, 20:56   #12
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Re: Hydroelectric Generator

"What I can't figure out is how to estimate the output"
Easy ballpark estimate: Look up what a commercial towed hydro generator puts out. Now all you have to do is make an equally efficient generator to match that. Build a better (bigger) generator and use a bigger prop, and you should be able to beat it.
Put the prop in a tunnel (a Kort nozzle) and you'll boost the efficiency and output again.
But first see if you can even match what a commercial product would give you, as a baseline. And remember, using a low-mass replacement for the prop shaft (hollow carbon fiber tube perhaps) will allow more energy to be harvested. Got a budget?(G)
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Old 30-05-2017, 21:18   #13
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Re: Hydroelectric Generator

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Aha, I see, sail-powered hydro 8-)

What is the advantage compared to spinning directly off the wind?
The density of water allows you to convert more of it's energy at a lower speed. So, sailing along at 5 knts in 10 knts of breeze, the wind generator would be producing almost no power, while a water generator would.

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Old 30-05-2017, 21:27   #14
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Re: Hydroelectric Generator

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Originally Posted by KISS View Post
I'd given up on hydroelectric power some time ago because of the OBSCENE cost of commercially available units, but now I'm rethinking it from a DIY perspective. I know people have had success mounting alternators to their prop shafts. What I can't figure out is how to estimate the output to see how worthwhile this would be. Any idea how to do that calculation? Or real world numbers from your own experience?

Quick DIY hydro gen:


There are a ton of old wind gens for sale all over the internet with a low speed alternator and rectifier all ready installed.

Buy a working cheap wind gen.
Pull the blade off.
Mount it on your pushpit
Typically, there is a pin hole already in the shaft where you can attach a shackle.
Double braid rope from shackle to old prop shaft or solid metal shaft of some sort.
Attach 8-10hp outboard prop to shaft backwards.
Wire to batteries.

Watch what the thing does at different speeds and change to a prop pitch and size that works for you.

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Old 30-05-2017, 21:59   #15
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Re: Hydroelectric Generator

Quote:
Originally Posted by hellosailor View Post
"What I can't figure out is how to estimate the output"
Easy ballpark estimate: Look up what a commercial towed hydro generator puts out. Now all you have to do is make an equally efficient generator to match that. Build a better (bigger) generator and use a bigger prop, and you should be able to beat it.
Put the prop in a tunnel (a Kort nozzle) and you'll boost the efficiency and output again.
But first see if you can even match what a commercial product would give you, as a baseline. And remember, using a low-mass replacement for the prop shaft (hollow carbon fiber tube perhaps) will allow more energy to be harvested. Got a budget?(G)
The alternator I mentioned is about $200. The prop used on the largest Watt and Sea hydo gen is about $400 as a spare (way overpriced). Throw in the shaft, seal, wiring (maybe a larger MPPT). I bet you could do it for about $1000.
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