Water turbine - converting mechanical energy to electrical energy

[halab]

Hi,

I am working on a renewable energy project to teach kids about energy conversion. The idea is to design an apparatus to include a water turbine connected to a DC motor and from there to a circuit. The kids will be given a short rod (made from pixie glass and will be acting as a shaft) and other raw materials to design the water wheel. Each kid will design a different wheel depending on their creativity. Choosing pixie glass was based on testing wood, aluminum, and PVC rods by trying to glue parts on them using the glue gun. The rod made out of pixie glass allowed for maximum "stickiness". If there is another material that you recommend, I would love to know about it.

Upon completion, the pixie glass shaft will be mechanically connected to another shaft (drilled in the middle to create a female connector for which the pixie glass "male" connector will go in and fixed using a pin) that is connected to the rest of the apparatus. At the end of the female shaft, I will have a DC motor that will act as a generator.

I am wondering if you can help me with the following:
1. Type of DC motor I should go for: I am thinking that the motor might need to be geared DC motor but with very low frictional resistance. The idea that it will turn very smoothly and easily to produce maximum current to power up the circuit.

2. Kids need to see some sort of manifestation of the energy generated, so I am thinking of having a circuit with power meter made out of LEDs where more LEDs turning on means that the water wheel is more efficient at transferring the energy. However, I was also thinking of building some sort of a circuit that I can charge an iPhone or iPad on. It doesn't need to be charged fast, but just having the kids connect the concepts together will be very memorable. Any ideas on this part would be very helpful.

Thanks!

 

[jpanhalt]

1) What is pixie glass? Google seems to think it is Plexiglas (acrylic plastic) . But, there are other options, such as: https://pixie-glassworks.myshopify.com/

2) As for demonstrating the output, I thik an LED bar graph would be easiest to appreciate. It is instantaneous and the voltage produced could be tied to the number of LED's lit.
Here's and example and circuit:
https://www.digikey.com/product-detail/en/DC7G3HWA/754-1671-5-ND/3084383?WT.mc_id=PLA_3084383
https://www.google.com/imgres?imgur...a=X&ei=FnlGUqm3KYaQ2gXj3ICoBw&ved=0CFMQ9QEwAg

RadioShack used to carry everything you would need for that part.

John

 

[alec_t]

I am thinking that the motor might need to be geared DC motor but with very low frictional resistance. The idea that it will turn very smoothly and easily to produce maximum current to power up the circuit.

Unless you have a convenient Niagara Falls I think the gearing needed to generate sufficient voltage to light a LED will introduce so much friction that the turbine won't rotate. IMO an opamp to amplify the motor output would be preferable to gearing.
I've just experimented with a computer fan motor. It has very low friction and when spun by hand generates a few hundred mV.

Edit: Even a few hundred mV would be enough to provide the measurement input signal without amplification to a LM3914 bargraph display.

 

[jpanhalt]

After sleeping on it, I agree that doing something useful, like lighting LED's with the generated voltage, is unlikely. Just use a voltmeter. The students will get the same competitive spirit. As for the motors, consider the tiny motors used in servos, vibrators, and so forth.

One other thought: I drew the impression from your post that the turbines will all be some version of a paddle wheel. Those (radial designs) are harder to make than propellers (axial). If you allow propellers, then pitch, diameter, and blade cross-section become variables the students can explore.

How are you going to provide a controlled water flow to evaluate the different designs?

John

 

[halab]

1) What is pixie glass? Google seems to think it is Plexiglas (acrylic plastic) . But, there are other options, such as: https://pixie-glassworks.myshopify.com/

2) As for demonstrating the output, I thik an LED bar graph would be easiest to appreciate. It is instantaneous and the voltage produced could be tied to the number of LED's lit.
Here's and example and circuit:
https://www.digikey.com/product-detail/en/DC7G3HWA/754-1671-5-ND/3084383?WT.mc_id=PLA_3084383
https://www.google.com/imgres?imgur...a=X&ei=FnlGUqm3KYaQ2gXj3ICoBw&ved=0CFMQ9QEwAg

RadioShack used to carry everything you would need for that part.

John

Thanks for the input John.
I did mean plexiglass. Just didn't know how to spell it and got creative with it.

I will check out the circuit you linked to.

Cheers

 

[halab]

Unless you have a convenient Niagara Falls I think the gearing needed to generate sufficient voltage to light a LED will introduce so much friction that the turbine won't rotate. IMO an opamp to amplify the motor output would be preferable to gearing.
I've just experimented with a computer fan motor. It has very low friction and when spun by hand generates a few hundred mV.

Edit: Even a few hundred mV would be enough to provide the measurement input signal without amplification to a LM3914 bargraph display.

Using a signal amplifier is an interesting idea.
However, I am wondering if I want to make a circuit that only powers up with the generated voltage without need for external battery. Then I probably need a motor that will generate something bigger than mV. Something that can generate at least 5V. Then I would probably need a voltage regulator and potentially a circuit to hold the charge until the required level is reached. But maybe it is easier to just use a double or triple A battery to power up the circuit.

 

[halab]

After sleeping on it, I agree that doing something useful, like lighting LED's with the generated voltage, is unlikely. Just use a voltmeter. The students will get the same competitive spirit. As for the motors, consider the tiny motors used in servos, vibrators, and so forth.

One other thought: I drew the impression from your post that the turbines will all be some version of a paddle wheel. Those (radial designs) are harder to make than propellers (axial). If you allow propellers, then pitch, diameter, and blade cross-section become variables the students can explore.

How are you going to provide a controlled water flow to evaluate the different designs?

John

Currently, I am using an older design of the turbine and using a multimeter to show kids the numbers. However, it isn't as exciting. I interviewed a bunch of them and there seemed to be consensus that something more tangible needs to be implemented.

Having the bargraph is a good idea. What would be even cooler is to make something that they can relate to. Forexample, a circuit that the iPhone charger can plug into and the charging begins. Thoughts?

What I have right now is a bucket of water connected to a nozzle. The higher I hang the bucket, the more potential energy there is. The bucket will be at a fixed height with fixed water level.
Now interestingly enough, my interviews with the kids showed that they would love to have something that is continuous, i.e. that it wouldn't stop after a couple of minutes because we ran out of water in the bucket. Hence, I am thinking of using a fish aquarium pump to transfer the water back up. What do you think about this idea? Is there a better way than this?

 

[alec_t]

For example, a circuit that the iPhone charger can plug into and the charging begins. Thoughts?

I very much doubt you'll get enough output to power a charger.

Hence, I am thinking of using a fish aquarium pump to transfer the water back up. What do you think about this idea?

Just don't expect to power the pump with the turbine output

 

[halab]

Just don't expect to power the pump with the turbine output

haha I know. Thanks for the tip though

 

[jpanhalt]

My main concern about charging an iPhone is that it will take a very long time to see a noticeable change, and it would be difficult to compare the efficiency of the different turbine designs. The bar graph is tangible and could include an amplifier, if needed. An LCD would require less power, but still something on the order of 100 mV output will be needed for off-the-shelf units. Are you aware of MPJA.com ? It has some cheap components and meters.

I definitely like the idea of constantly refilling the bucket.

John

 

[Misterbenn]

I suggest a 6V bicycle hub dynamo. You won't get much power out of it but you should be able to get enough out to power some LEDs, you'd be very lucky to power a phone charger but its not impossible.
The big challange is to put enough energy into the system. These dynamos have a ~60% efficency then you need to take into account your turbine, lets say overall 33% efficency. That means that if you want a 5W output you need to put 15W in.

An turbine would work well but is better suited to high pressure, and thus water heads >10m. I assume this is impractical in a classroom but the waterwheel type can work well with water heads >2m, perfect. Even better with a hub type dynamo you could even use a bike wheel as the basic design!

Good, so we have a power requirement. From this we can calculate the kinetic energy of the water required. e.g with a 2 meter head, and 1kg/s of water. The water will be traveling at 6.26m/s at the moment it reaches the turbine. Kinetic energy is half mass velocity squared = 19.6W.

Maybe a toilet flush type system could give a 1kg/s flow? I dont know i've never measured it. It would make for a nice repeatable experement though.

Now if you wanted to be real fancy instead of LEDs just showing it instantanous power output you could intergrate it and get the total power output. You can then compair this to the known, and controled, power input and thus calculated the efficency of each turbine.

I should point out that while i am an Engineer i've never built anything like this and so my calcualtions / opinions lack real world experience and may not be compleatly reliable.

All the best,

 

[Misterbenn]

Also in terms of being able to power a circuit...

If you really cant get the power output then why not charge up a capacitor to a nice useful voltage. When the capacitor stops charging a circuit can switch on, read the voltage from that calculate the power delivered and display the result ... all before the capacitor discharges

capacitor energy is half CV^2. S0 for 45W (3 seconds of 15W .. about a toilet flush ~3l of water) and a max voltage of 6V (the max of the hub dynamo) is a quite big 2.5F capacitor. Get a 12V hub dynamo and that reduces to 0.63F which is a bit more realistic and gives you a good working voltage range.

 

[halab]

Very great ideas everyone.
Thanks for the feedback.

One thing I was looking at right now is using a fish aquarium water pump instead of the water bucket. This will save a lot of space and a lot of potential mess.

I have been experimenting with different materials to allow kids to build the rotor (wheel). What we need to do is give them a core and allow them to build around it. After a while of thinking and testing, I managed to put together a core using K'nex toys by glowing together a few similar parts (see attached photo Core.jpg).



The idea is to then allow children to build around that core. Their design will act as the wheel. They will also use different materials such as plastic cups, clear tape, etc... to fill spaces in between. This then will attach to a generic base which is attached to a motor to generate power.

For quick prototyping, I used K'nex to make a base (see attached photo Turbine.jpg).



The final design will be sturdier. I put together a mock up of the final turbine design in SolidWorks (see photos Top View and Back View.jpg).




But my question is this:

I would like to measure the electrical power output through a simple circuit. Can someone help me do that?
I need current and voltage with varying load (potentiometer). So I would like to vary the load and the power is quickly displayed somehow. I have an arduino UNO board as well.

Thoughts?