Hydro- have I got this backward?

[(unknown)]

Hey everyone,

    I'm still thinking about using that small 6' damn on my father's property.  

    I was thinking about first building the wheel and figurings it's RPM before building an alternator that would fit this RPM.  

Does that make sense, or do I have it backwards?

[bracken]

You are doing it the easy way. When trying a new design turbine, I always build the rotor first and get idea of how fast it spins before I match it to a generator. You could solve this before hand, but that typically takes more time and effort.

Best of luck!

Bracken

[hydrosun]

First is head and flow.  Six foot dam, but can you pipe the water to a lower point? Flow will help determine what type of wheel would work best for you. A reaction turbine like peltons would run at half the unloaded rpm. I'm not sure on a overshot wheel how it's loaded rpm changes.

Can you give a few more details on your site?

Chris

[bob g]

know your power source, then design an alternator that matches that source

as closely as you can.

determine which design of hydro is appropriate and fits your list of compromises

build the hydro unit

test its rpm and graph its output rpm vs torque with a prony brake

convert rpm/torque to hp or watts

plot on a graph, to find the max power point of rpm and torque

then design an alternator that matches that point as nearly as you can.

no since building a hydro, measureing rpm if you don't know torque or power available

you can have 100rpm at 10k watts or you could have 100rpm at 10 watts!

and there also is no reason to build a 10kwatt alternator to fit the 10watt power source, and also just as silly to do the converse.

thats my .02

fwiw

bob g

[tanner0441]

Hi

I don't know much about hydro but I think besides the head you also need the flow rate.

I am sure not too far back someone on here posted a graph or table showing power versus head and flow. It would deffinately be worth fixing some sort of pipe to it though. I would think mount a threaded flange low down then screw a pipe with a valve  into it. after you have made a hole

I am very enviouse I have a stream running across the back of my place, unfortunately the wrong side of my fence, and with only a couple of foot of fall not worth trying to buy the land to move the fence.

Good luck with it.

Brian.

[morglum]

Hey all,

Thanks everyone for the replies.  I'll try to reply to everyone at once.

I know that I also have to determine wattage (flow, head) before building the alternator, but again this wont change much to the wheel, will it?   Or maybe head, but not flow?  

(anyway, here are some details)

HEAD:

Can't really pipe it to a lower point, so 6' (or maybe  8') of head will have to do.  The reason is  that this is a stream that crosses many properties, each about 70 meters wide.  so I only have those 70 meters to work on.  The head from from a dam that was built decases ago  to hold irrigation water.

FLOW:

   I dont know exactly how much,

The following picture shows the waterfall where this creek falls before ending in the St-Lawrence river.  This is not on my property, so I can't use all the head there.

http://www.pbase.com/zobroc/image/85802593

At the top of the dam is a small rectangle where all the water goes through.  From memory I'd say it's about 1.5 feet * 1.5 inches.   According to the "weir table on page 35 of "microhydro: clean power from water", this would be at least 50 GPM.

(http://books.google.com/books?ct=title&q=microhydro+clean+power+from+water&btnG=Search+Books
)

[morglum]

thanks for the tips about the torque/rpm graph.  Wouldnt have tought about doing this.. would probably have looked at unloaded RPM and cut it in half of something...

[ghurd]

The dimensions of the wheel will partly be determined by the power it is expected to make.

A 2 meter diameter over shot wheel for 50 GPM will be different than a 2 meter diameter over shot wheel for 5000 GPM.

Firefox or Vista warning... It locks me up every time... except in IE8.

But the water wheel factory has some decent basic info.  Need to look around a lot to find it.  Some of the links do not look like links to me.  And it fully reloads when clicking 'back'.

Turbine types and history are good.

http://www.waterwheelfactory.com/index.htm

Maybe I did not do it right, but it looks like maybe 35W?

A cross flow looks easiest to me, and easy would be one of my priorities in a 35W setup.

G-

[morglum]

Agree with the water wheel sizing, but I was simply thinking about fitting the wheel simply so that is is "big enough to get handle the water"

Ill go give that site a look, thanks again Ghurd.

S.

[morglum]

Just to make sure.  

Is this the type of turbine you are talking about?

http://en.wikipedia.org/wiki/Cross-flow_turbine

Otherpower.com's  Banki turbine:

http://www.otherpower.com/scotthydro1.html

[ghurd]

Yes, mostly, but a bit simpler.

More like a combination of those and this,

http://www.otherpower.com/otherpower_experiments_waterwheel.html

G-

[Ungrounded Lightning Rod]

You want to design your alternator for the max power point RPM of the turbine.  This is computable from the turbine type and the velocity of the water as it enters the turbine.  For a pelton or turgo it's where the circumferential velocity at the radius where the jet hits the spoon is (trivially under) half the jet speed (because at optimum energy transfer occurs when the water does a 180-degree turn in the receding spoon, leaves "standing still", and drops away by gravity (or a small amount of residual velocity) before the next blade arrives.)  For a crossflow it's encoded in the angles of the blades where the water encounters and leaves them.  For reaction turbines it's also encoded in the geometry of the blades.  Don't forget the factor of 2 pi when converting from radius and circumferential velocity to RPM.  (You can estimate any residual velocity of the water from the efficiency of the turbine type because friction with the blades is very low.)

The initial velocity of the water is easily computed from the operating head (the actual head less the pressure drop from friction with the penstock).  You can compute it by computing the velocity of a free fall from the (effective) head.  (v = sqrt(2*g*distance),  g = 32 ft/sec^2, g = 9.8 m/sec^2)  Compute the effective head from the actual head by deducting the pressure drop from the flow in the penstock pipe using a table for the pipe size.

You'll adjust the water flow (by sizing and selecting/valving the number of jets in a pelton or turgo, the opening between the nozzle and distributor in a mitchell-banki crossflow, and so on for other types) to adjust the torque - within the constraint of keeping the penstock full to avoid wasting head.  This means the pressure / effective head is within a narrow range (varying only due to friction as you adjust the flow).

So your particular turbine will be at max power point in a narrow range of RPM which can be calculated in advance from head, flow, penstock size, and turbine design.

(You'll also be able to compute your torque, and thus your output current at a particular voltage and generator efficiency, from the available water flow, effective head, turbine efficiency, and RPM.)

[tanner0441]

Hi

I am using FireFox and it let me in and back out of the links, I did not download the plugins though.

Brian

[morglum]

Thanks ULR, another great and detailed post.

Guess that means I can't just make a "big enough" wheel

I'll get some actual measurements next time I visit them.

Thanks for the tips.

S.

[morglum]

I waas offered this for free... looks good?

http://pages.infinit.net/collins/images/Fan.jpg

[ghurd]

FREE is always good.

I have no idea if it is good for this project.

The project must start somewhere?

There are worse places to start.

G-

[scottsAI]

Morglum,

People may surprise you and be reasonable... ask about taping into the top flow on their property.

With the additional head, you can offer half the power to the owner of the Dam still come out way ahead! Show you know what your doing and will not create a problem with the Dam.

Not hard to draw the water over the dam not making any modifications to the Dam itself.

Have fun,

Scott.

[morglum]

Yeah, the project just keep on coming!    

I'll go fetch it this weekend.

Cant wait for the thaw!

[morglum]

Hi Scotts,

Good idea, will look into that once I know what I'm doing

Cheers!

Simon, who was just given two solar water panels....   (

http://www.fieldlines.com/story/2010/2/24/191647/185

!!!!!!)

[Ungrounded Lightning Rod]

Wheels are a bit different but you get the idea and ought to be able to figure them out.

For instance:  Max power on an overshot wheel happens at the RPM where the incoming water is at the circumferential velocity of the wheel (so it enters the bucket smoothly rather than wasting power sloshing around).  The wheel "elevators" it down to the outlet level and the bucket is shaped to let it out gently at the bottom of the travel.

[FoolAmI]

Actually maximum power is produced when the wheels rim is moving @ 92% the speed the water is moving when it enters the bucket.

http://www.waterwheelplace.com/electricity.html