Small scale domestic hydro power generation project

[SteamyTea]

If yo want to increase the head, why not make and fit a ram pump, then pump and store some water up high (a tree maybe).

Then, when you need a decent amount of power, let the water flow back down into the turbine.

Overall you may get less energy, but you may get a usable amount of power.

Edited June 15, 2022 by SteamyTea

[Radian]

1 hour ago, dpmiller said:

@ProDave I dunno if that servo motor is the best choice tbh, they can be very delicate. What's the I reckon you've got enough power for something a bit meatier- a 380 RC motor or a pillaged small cordless tool motor maybe?

Brushless is best. A Stepper Motor salvaged from a laser printer perhaps? They generate useable AC power at far lower rpm than brushed motors (I've got a pile of those as often you can buy a new printer with a full set of toner carts for little more than the cost of a refill. Hopelessly wasteful unless you turn them into parts!).

 

Still think a traffic cone would be good to funnel the water in...

[dpmiller]

stepper is a good call, I'd never have though to go that direction, lol

[ProDave]

On 15/06/2022 at 21:12, Onoff said:

 

My lad will have a go of course. 

 

Elsewhere "we", that's me and nerds from another herd, are on the brink of investment casting in brass from an original 3D print so that's (brass impeller) a possibility for the future.

So I would be looking for something a bit like this

 

Outside diameter 75mm, height 38mm and the bore of the central hole 6mm

 

Is that possible to 3d print?  if so I would suggest the inner hole a bit smaller and I will bore it out to fit the motor

[Onoff]

3 hours ago, ProDave said:

Is that possible to 3d print?  if so I would suggest the inner hole a bit smaller and I will bore it out to fit the motor

 

Almost certainly printable. The thing with drilling 3d printed parts is that, in essence, holes have a limited area of "solid" reinforcement around them. The "skin" of the print is similarly solid but the rest is an infill, like a honeycomb. 

 

Thus it's no use printing at 6mm ID then hoping to drill out to 8mm later...you'll be into the infill. Best to print as near as to the shaft size.

[Onoff]

Hope that makes sense, I have been to the:

 

[Marvin]

Just now, Onoff said:

Hope that makes sense, I have been to the:

 

It's supposed to be for the slugs!

[ProDave]

40 minutes ago, Onoff said:

Almost certainly printable. The thing with drilling 3d printed parts is that, in essence, holes have a limited area of "solid" reinforcement around them. The "skin" of the print is similarly solid but the rest is an infill, like a honeycomb. 

That could be problematic.  The shaft is 6mm diameter, but it is a D shape with a flat, and I would be expecting to drill and tap a thread for a grub screw to tighten down on the flat on the shaft.  That seems unlikely then?  Could you print a D shaped hole and I would just glue it onto the shaft?

[Onoff]

4 minutes ago, ProDave said:

That could be problematic.  The shaft is 6mm diameter, but it is a D shape with a flat, and I would be expecting to drill and tap a thread for a grub screw to tighten down on the flat on the shaft.  That seems unlikely then?  Could you print a D shaped hole and I would just glue it onto the shaft?

 

Can print the D shape hole with the ready tapped hole in the side...

[Onoff]

1 hour ago, Marvin said:

It's supposed to be for the slugs!

 

The first pint of British Bulldog was no good, switched to Spirit Of Kent .

 

@ProDave, any of these take your fancy:

 

https://www.printables.com/search/all?q=Impeller

[JohnMo]

Lorry turbo impellor?

[SteamyTea]

To get maximum power out of an impulse water turbine, the turbine speed at the impellor tips needs to be half the incoming water speed (seemed to remember that from a lecture a while back).

So if the water speed is 2 m/s, then for a 1 m diameter turbine (or water wheel), the RPM needs to be about 90.

[ProDave]

13 minutes ago, SteamyTea said:

To get maximum power out of an impulse water turbine, the turbine speed at the impellor tips needs to be half the incoming water speed (seemed to remember that from a lecture a while back).

So if the water speed is 2 m/s, then for a 1 m diameter turbine (or water wheel), the RPM needs to be about 90.

This will be a LOT smaller than that.

 

I am not talking of a pelton wheel which technically runs "dry" and gets propelled by a very fine very high speed jet of water.  Rather I am talking of a "wet" running turbine.  With no load, the peripheral of the turbine would pretty much rotate at the speed of the incoming water, i have not measured that, but by going small the idea is to get a much higher rpm.  I think the half speed you talk of, is the optimum power out will be when you load the turbine so it is running at half no load speed.

 

I keep finding lots of people who have built DIY small scale turbines but very little detail.  so I am to a large extent guessing what I want and hoping to find a project that worked with proper details to replicate it.  Lots of people with their DIY turbines showing the voltage they generate, but very few putting a load on and quoting what power they get.

[SteamyTea]

3 minutes ago, ProDave said:

think the half speed you talk of, is the optimum power out will be when you load the turbine so it is running at half no load speed

Yes, and you don't by governing the load, simple feedback governor. 

A smaller diameter 'wheel', as you say, needs to run faster (more RPMs) for the same power.

With turbines, there is a different formula for gas and liquid ones, would have to get my old books out to find out.

 

[ProDave]

And there is also a big difference between a pump impeller and an impeller for a generating turbine.  I have an old dead submirsible pump somewhere, but it's impellor is just completely flat blades, no "scoop" to them, and they are a lot smaller than the cavity they run in.  I struggle to get my head around how that can be "efficient"  but suspect that allows the pump to work at differing heads and flow rates rather than usinin minimum electricity, and feel if I tried to use the impeller from that, it would be very inefficient as a lot of the water would simply go around the blades rather than push them.

 

Water wheels are a lot easier to understand.