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Brady
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Posted: 18 August 2017 at 9:53pm | IP Logged Quote Brady

Hello,
I've come across other forums covering similar themes before, however none of them have been active recently, unlike this forum. Judging from the posts and articles you guys know what you are talking about, so I wanted to ask you guys a few questions to help me out.
Let me start from the beginning. I'm not going to go into detail about criteria and such, but simply put, we were able to explore and make stuff which had to do with something in science, technology, engineering, art and mathematics. We had to find a problem in the world, and attempt to fix it.
ANYWAY, our group decided to look into the lesser known forms of renewable energy. We looked into geothermal, kite, wave energy and biofuels.
We chose wave energy, and we continued to explore it more so. Our end goal was to power a battery to charge a phone, using the river we had access to. This is still our goal, but we recently learnt that the river, well, doesn't produce any waves. *sarcasstic clapping
While the river didn't produce enough waves, it had some powerful tides. So we looked more into tidal power systems, and discovered underwater tidal turbines. Which used the flow of water to spin a turbine and power a generator.
I fully understand that this post is in the "windmill" topic. But from my basic knowledge, wind turbines are very similar to underwater turbines. If this post needs to be moved to another thread please do so, I just couldn't find another thread to put this post in.
Let me describe the river before I get into the design of our system. To get across to the other side of the river there is a small footbridge. In the middle of the footbridge is a gate, which only the teachers can unlock. The river itself is relatively wide, but the banks are very difficult to access due to a lot of bush and mud. The most powerful part of the river is in the middle of it, which is hard to access from the banks. Conveniently, the gate of the footbridge is just over the middle of the river. Remember that, because it becomes important to our design later on.
Here's a picture of the design we are aiming for

The pole will be attached to the gate, and it will go down under the water. Under the water, on the pole, will be two turbines. Both will be powered by the tides, and we hope to be able to charge a battery. Keep in mind, the is only a school project, it's not going to be titanic in size. The proportions in the image are VERY wrong, and it was only made to give you an idea of what we wanted to do.
Our knowledge of motors and turbines are very basic. From my knowledge, the turbine is connected to a large gear, the large gear is connected to a smaller one, to get to a higher rpm, which powers the motor. We are going to make these parts using a 3D printed That's all we've come to understand. Which is where I want your help. We want someone to explain to us, as simply as possible, how this all works. From the turbine design, to the gearbox, to motor and how they are all connected. Also, how would we water proof it? Could last overnight without breaking?
We would greatly appreciate a response, Thanks a lot for reading it all.


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Warpspeed
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Posted: 18 August 2017 at 11:08pm | IP Logged Quote Warpspeed

Before you even start, you need to find out two things.
1/ how much electrical power you need.
2/ how fast the water flows.

You need to find out how much capacity your phone battery has, and how fast you need to recharge it. Big difference between the amount of power needed to recharge it in one hour, and the amount of power to recharge it over several days or weeks.

The other thing is how fast the water flows. Is it barely moving, or is it like foaming white water rapids ?

When you know how much power you need, and how powerful the water flow is, only then you can begin to size the turbine.

Suppose it turns out that it needs to be very large, much larger than the depth of the water ? Or larger than you feel comfortable in building ?

So first we need to see if this is even practical.

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Boppa
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Posted: 19 August 2017 at 6:18am | IP Logged Quote Boppa

You really need to find the flow as that will determine the power you will extract from the turbines
easiest way is to throw a stick (or anything else that floats) into the center, after having measured out a set distance downstream (say 100m) and time it from launch until it floats past the set marker position

Then you will need to find out the efficiency of your turbine prop and that will determine the size turbine you will need (flow rate will give your energy m^2)

The other issue is on a river speed of the flow will likely be fairly low most of the time, but alternators/gennies (unless custom built) will likely need fairly high speeds, requiring gearing- which makes it harder for the water to spin the turbine (it's more likely to stall the water directly in front and send most of the flow around the turbine- thats why they use dams as it forces the water to go through the blades)
You will almost certainly need to build a small scale prototype and use it to get base figures for your individual setup

I have seen plenty of people want to make something like this (I did when I lived on a local riverbank) but not many end up going ahead

Remember too that unless it is very small, considerable forces will be acting on your pole mount, so you will have to ensure the bridge itself can handle the load
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Posted: 19 August 2017 at 6:32am | IP Logged Quote Warpspeed

Boppa is 100% correct.

No point in building a yacht from scratch if there is no wind.

Or building a down hill racer if you live in totally flat terrain.

The very first step in any engineering project is to see if its even possible.



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Boppa
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Posted: 19 August 2017 at 2:15pm | IP Logged Quote Boppa

Now I dont have to rush off to work, some more ideas about your gearing waterproofing etc

longterm waterproofing is a major hassle, if you just want it to run for a few days, then its easier
As you are looking at constructing the gears etc yourself, one suggestion I have (from a long time friend who is into microhydro) is keep the sparky bits away from the wet bits as he put it lol
He lost several installations due to creek flooding and now uses vertical drive instead- either a variation on Gorlov turbine with the axle extended above the waterline and possible flood zone. His original ideas were in fact very close to your own design, but long term waterproofing and maintenance stopped his following that route

As you want to use the pole mount and a horizontal axle turbine design and making your own gear to up the speed, why not think of a right angle bevel drive if you want to experiment with it- that way you keep the sparks away from the wet easily, plus it allows much easier or even no waterproofing required for the generator end which can be mounted up at the bridge end for easier access for modifications/maintenance
The bevel gear lets you turn the rotational axis from horizontal to vertical and also allows a change in gearing ratios (to help with speeding up to the speed of the genny)
The best bit is it will allow you to run an axle up inside your supporting pole and at the top, it pops back out- ready to either add/change the gearing more or mount the genny- safely out and away from the water- minimizing waterproofing needed

By making the bevel gear out of either non oxidizing metals (brass/bronze) or plastics, you minimise the lubrication required, and also the waterproofing needed at the prop end- in fact with the right design and keeping speeds down at the water end- you might find it possible to actually not bother with waterproofing at all and simply let the water flow through the gears and support bushes- acting as the lubricant (at slower speeds obviously)

This also has the advantage that if you dont get enough speed out of the turbine blades, you can add extra gearing at the top (belt drive or more cog gearing) to change speeds, plus you can easily get at the genny to maintain or modify it (or even swap over to a new design easily- build several different generators with different number of poles/permanent magnets/ electromagnets etc and by using a belt drive from the top of the axle, swap out each to find the different advantages of each- something not so easy to do with a underwater pod design
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Boppa
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Posted: 19 August 2017 at 2:55pm | IP Logged Quote Boppa

One idea for very small scale charging (and would be easy for 3d printing etc) would be getting a 'small' dc motor eg Jaycar 12vdc motor and use that as a basis for experimenting with different props/gearing ratios etc.
As you are unlikely to get much above 60-100rpm prop speeds I suspect, you would need to make up a gearbox that could give you a 10:1 step up in speed, and a prop that is big enough to overcome the stalling effect that level of gearing would require (Note that such a small motor would be unlikely to get more than 1/2Amp into a 12v battery- and only then that would be its Max, likely much less
look up 'marine packing glands' for ideas on how to waterproof axles passing through into your watertight box if you decide to go that route- There are many ways to do it, most use cheap and simple packing materials like cotton waddiing and grease (altho some actually use water as a lubricant for the shaft)

For your power wires either hot glue/sellys silicone sealant or you can use waterproof glands like these waterproof glands (Note you would need 2 of these glands- positive wire goes through one, negative goes through the other- dont use with 'fig8' dual wires, they wont seal)

So theres some ideas for you at least to think about

edit to add

If using a DC motor in this fashion ie a generator; to wire it up you will need a 'anti motoring diode' otherwise when the flow rate is too low; the battery will make the motor turned into a genny back into a motor again and it will discharge the battery trying to push the river along faster!

To wire it up the motor/genny will have a + and a - connection; you will have to wire the motor - to the battery -, and in the + wire you will have to put a diode IN4004 will be fine for a small motor like the one mentioned before.
The diode is black and has a white stripe at one end- that end with the stripe is connected to the battery +, the other end without the stripe goes to the motor/genny + terminal

This stops the battery backfeeding or 'motoring' the generator when the flow is too low

(btw I dont work for Jaycar or anything, its just they are the ones I usually buy from and I know their cattledog well, other suppliers can usually be found by a quick google, the links I provide are to show what I am talking about)

Edited by Boppa on 19 August 2017 at 3:44pm
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flc1
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Posted: 19 August 2017 at 10:52pm | IP Logged Quote flc1

Gday Brady,

Just a suggestion for a slightly diffrent idea which may be easier to build?
useing your pole from your bridge ..mount a floating platform which can rise up and down on the pole,or have a swingarm, and on that platform you mount a paddle wheel, the same as you see on the old paddle steamer boats with gearing from pulleys ,belts or cog gearing.
Your generator is on the platform so its not going to be much of an issue to keep the water out of it,
you have a wide paddle wheel.. which will give you plenty of power to use with your gearing, just have to test what size paddle wheel you need in regards to how much flow there is in the river..... this is how I would do it .

Edited by flc1 on 19 August 2017 at 11:00pm
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Posted: 19 August 2017 at 10:57pm | IP Logged Quote Warpspeed

This is a school project, really a practical exercise in putting something together that can be demonstrated to work, without spending a great deal.
Ingenuity is probably the main feature, and it should be fairly simple to put together, not requiring much in the way of tools or a fancy machine shop to make parts for it

We don't know how deep the water is, or how fast it flows, probably not that fast. So we are going to need something fairly large that is inevitably going to turn very slowly, but generates a fairly high torque, at least sufficient to overcome the inefficiencies in the gearing up process.

I agree that all the electrical bits should be kept high and dry and well clear of the water.

I see the submerged turbine part as a bicycle wheel with turbine blades attached. How about the fan blades from a pedestal fan, or large multi bladed car radiator fan attached to the spokes with plastic cable ties ? A string around the outside of the rim would make for a fairly efficient way to transmit the very slow motion of the turbine up well clear of the water. I am sure that could all be put together at zero cost and not require much in the way of tools.

Now we need a dc generator, which is really just a permanent magnet dc motor. Ideally it should only need to run at very low speed to do the job, making the gearing up process more efficient and easier to do.

The most suitable thing I can think of right now might be a treadmill motor. These are quite large, but the advantage is that they are a high voltage permanent magnet motor, that typically run at 180 volts dc at perhaps at 1,800 rpm.

If we spin this as a generator up to 1,800 rpm we would get 180 volts from it.
But as the speed is reduced, the output voltage also reduces in proportion.
For this example 10 rpm for every volt.

Assuming we might need about four or five volts we might get away with needing only 40 to 50 rpm to turn the generator. I have no idea how fast the water flows, or what speed the generator must run. But a speed increase of about something like 10:1 might do it. It may even be possible to drive it directly from the string around the bicycle wheel, I really do not know.

As Boppa says, a diode will be required between the generator and the battery, but other than that, its about all you might really need.




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Posted: 19 August 2017 at 11:48pm | IP Logged Quote Warpspeed

flc1 wrote:
Gday Brady,

Just a suggestion for a slightly different idea which may be easier to build?
using your pole from your bridge ..mount a floating platform which can rise up and down on the pole,or have a swing arm, and on that platform you mount a paddle wheel, the same as you see on the old paddle steamer boats with gearing from pulleys ,belts or cog gearing.
Your generator is on the platform so its not going to be much of an issue to keep the water out of it,
you have a wide paddle wheel.. which will give you plenty of power to use with your gearing, just have to test what size paddle wheel you need in regards to how much flow there is in the river..... this is how I would do it .

That would be perfect if the water is fairly shallow and fast flowing.

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Boppa
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Posted: 20 August 2017 at 12:19am | IP Logged Quote Boppa

Many microhydro guys use paddlewheels, either undershoot or overshoot depending on location and conditions, and the most common microhydro turbine is in fact a modified paddlewheel inside a housing (being the pelton wheel)

A small pelton wheel for home microhydro systems using a small modified car alternator to generate electricity ie a few hundreds of watts up to large ones up to 300MW (amazing what you buy off the internet
from Alibaba.com $10 grand pelton wheel


Rainbow Power Company has a lot of details about setting up microhydro and things to look out for, how to measure flow etc
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flc1
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Posted: 20 August 2017 at 12:29am | IP Logged Quote flc1

I think if you make the paddles large enough ,you could easily gear it up,, there is alot of power in moving water.
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Posted: 20 August 2017 at 12:41am | IP Logged Quote Warpspeed

First we probably need to hear more about how deep the water is, and how fast it moves.

A floating drum on the end of a boom, with paddles attached certainly sounds like an excellent idea.

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