Low rpm generator for small water wheel

[caldoverde]

I know this question gets asked a lot, but having been through umpteen threads on the subject (not to mention hundreds of sites), I haven't found anything that quite addresses our situation, so I'm afraid I'm going to ask it again!

We have a small (1m diameter) overshot metal water wheel installed in our stream, which takes the entire flow of the stream via a chute, but are having problems trying to find the right generator for it. We've tried two off-the-shelf wind turbine permanent magnet generators/alternators so far. Both looked fine on paper, but turned out to be useless in practice; the first because it had too much cogging resistance to reach generating speeds, the second because the output claimed for the units at low rpms proved to be somewhat ... ummm ... wildly optimistic.

The stream flow averages 1 to 4 litres per second, depending on season. 2 litres per second is the bottom end of flow rates for the wet season (Oct-Apr). We don't expect to generate usable power in summer. We are off grid with a 24V system that includes PV. The water wheel is intended to give us most of our power in winter. We're not heavy users of electricity so are not looking for much. Just a steady average of 24-28V and 3-7A, which should be achievable IF we can find the right motor.

The calculations for the wheel aren't straightforward because the major part of its drive comes from the incident velocity of the water, not the weight of water in the buckets. The combination of both gives it an unloaded rotational speed in the range 120% to 130% of the water velocity in the chute. I've been studying calculations for water turbines, water wheels and wind turbines to try and derive an appropriate equation for calculating the power of the wheel, and estimate that the power available at the shaft ranges from 150 to 350W depending on flow, basing calculations on a flow range of 2-4 litres per second. Losing between 30-50% of that in the process of generation gives us around 80-200W expected output.

We have a range of sprockets available to gear up the wheel's rpm by 1:4, 1:5 or 1:7. We could also increase the incident velocity of the water by raising and lengthening the chute, and fitting an adjustable end to it so we have more control over the angle the water hits the wheel under different flow conditions.)

So can any of you great people on this forum point me in the direction of a robust low rpm generator in the region of 500W capacity which will operate in the range of 200-400rpm with minimal resistance to convert the wheel's power to electricity? Although we've tried AC generators so far, the wheel is only 12m or so from the battery shed, so DC isn't out of the question if it offers significant advantages.

Just one thing - please don't tell me to go get a turbine! The wheel was chosen for a number of good reasons. Its prototype uses a 1100W PMG (unfortunately not manufactured any more) which produces more power than its family of 3 uses for a lot of the time, even when it's only generating 100W, so we know it CAN be done. If we have to, we'll build our own generator modelled on the discontinued one, but if there's a ready off-the-shelf or off-the-dump solution, I'd love to hear about it.

[ghurd]

As I am sure you know, speed makes cheap power.
Is there a reason the alternator must be in the 200~400RPM range?

If it because of the sprockets you already have, I think the viable options will increase exponentially if you would get more sprockets,
and it will probably be cheaper too!

There are many options for the 84W low end, if new sprocket ratios are not out of the question.
G-

[caldoverde]

As I am sure you know, speed makes cheap power.
Is there a reason the alternator must be in the 200~400RPM range?

If it because of the sprockets you already have, I think the viable options will increase exponentially if you would get more sprockets,
and it will probably be cheaper too!

There are many options for the 84W low end, if new sprocket ratios are not out of the question.
G-

We can always have more sprockets made, though the potential is limited with the present set-up which is based on 3/4" pitch chain (UK not US)
Primary sprocket mounted on wheel shaft = 355.4mm diameter with 57 teeth
Secondary sprocket mounted on alternator (1:5) = 75mm diameter with 11 teeth
The 1:7 has 8 teeth. Can't go a lot smaller than that!

The wheel's unloaded speed at 2 litres per second is 66rpm, 3 litres per second 73rpm. It maxs out at about 85 rpm because a lot of the water at high flow volumes overshoots (hence the idea of having a nozzle-like adjustable end to the chute).

[ghurd]

You are in the UK?
"Off the Dump" selections and solutions vary by location.

How much power do you actually require?

Is a jack shaft out of the question?
57 tooth to 11 tooth on a jack shaft.  35 tooth on the jack shaft to 11 on the PMA.  (just pulled those numbers out of thin air)
Might make a lower resistance PMA more efficient even with gearing losses?
I do not know if it is a good idea.  Just throwing it out there.

What, specifically, "two off-the-shelf wind turbine permanent magnet generators/alternators" did you try?

Not that I have any good answers, but the people who do will want that info.

Brain fart earlier.  My brain interpreted 1:7 as 1:1.7.
G-

[caldoverde]

You are in the UK?
"Off the Dump" selections and solutions vary by location.

I'm in Portugal, but have reasonable access to "off the dump" in the UK.

How much power do you actually require?

We adapt our requirements to what we can generate. Bottom line is lighting, 2 computers and the washing machine. Not a lot really.

Is a jack shaft out of the question?
57 tooth to 11 tooth on a jack shaft.  35 tooth on the jack shaft to 11 on the PMA.  (just pulled those numbers out of thin air)
Might make a lower resistance PMA more efficient even with gearing losses?
I do not know if it is a good idea.  Just throwing it out there.

Worth considering. I'll run it past the engineering brains ...

What, specifically, "two off-the-shelf wind turbine permanent magnet generators/alternators" did you try?

The first was a Scottish-made Miniwind 2200W PMG which was the replacement the company made for the 1100W model that runs so well on the prototype wheel. That's the one which had too much cogging resistance for our site, but neither are made any more. It was a sideline rather than the company's main business and I think the guy's now retired and isn't building generators any more. That one wasn't so bad as I could sell it on for another wheel where the resistance isn't a problem under much higher water volumes.

The second ... hmmmm ... thereby hangs a tale ... a US-made Presto Wind M-24. We had the 'benefit' of being able to trial 2 of them as my neighbour further down the stream decided to go for a wheel too. Suffice it to say that their power curves are not accurate at lower rpms measured under the same test conditions (ie. open circuit, no load), and their 'customer service' was very much of the 'nothing to do with our unit, nothing we can do' variety, even when we proved beyond all doubt that it was. Have since heard of a couple of other people using them in wind turbines with the same complaint.

Brain fart earlier.  My brain interpreted 1:7 as 1:1.7.

Glad to know yours does that too!

[Simen]

Sounds to me that if you are able to build one pma yourself based on the ones at otherpower/here, you'll get exactly what you need?

[caldoverde]

Sounds to me that if you are able to build one pma yourself based on the ones at otherpower/here, you'll get exactly what you need?

Well that is one option, and probably the best ultimately since the generator can be tailored to its precise operating environment, but it does mean a lot of time spent in learning, experimenting, testing ... and meanwhile the LPG-powered generator we've been using to keep us going through winter is costing €25 a week in fuel.

So if anyone knows of a motor out there that WILL do the job, I'd like to hear about it.

[97fishmt]

Look into ac servo motors.
I have bought over a dozen over the past few years off eBay for next to nothing.
8 pole permanent magnet 3 phase rectified to dc around 100 to 200 rpm for 12 volt or 24 volt battery charging.  No cogging and capable of around 4 to 5 times the rated amps out from the name plate.  
You have to be patient but you can get them for about $30 + shipping @ around 15 to 20#.

Look for something like this

Or this


Good Luck

Mike

[caldoverde]

Look into ac servo motors.

Interesting! Thanks! So the sort of motors that power conveyor belts, exercise treadmills, etc?

The two you illustrate have quite high rpms. What sort of applications are lower rpm models used in?

Was just taking a look at UK eBay and there are a few. Some very expensive (Siemens, mostly). Remarkable shortage of specifications and a lot of manufacturers' product codes. Do you happen to know if there's any good ready reference sources that list product codes against specs?

[97fishmt]

Maybe take a look at the FAQ's section (frequently asked questions) under
will this motor work as a generator.  It might help answer some of your questions.

I am using these motors as low speed alternators for wind turbines.  They are perfect
for low rpm generation.  I hope you aren't afraid of reading, it will take
a lot of it to research what you are after.  Have fun.

[caldoverde]

OK. Thanks. Will do. No, not afraid of reading, but I'm no electrical engineer, so guess I'll be needing to learn a lot along the way too. This sounds really promising.

[Jon Miller]

Cheap electirc bike motor off ebay.

If you get a  rear wheel one they have a thread for a gear cluster then you can play with gear ratios to you get what you want.

http://cgi.ebay.co.uk/48V1000W-electric-bike-bicycle-motor-conversion-kit26-/160541526253?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item25610548ed

Email the seller and ask them to sell you just the motor?

They are a good option for example the future energy turbine uses a 500 watt electirc bike motor:

http://www.futurenergy.co.uk/turbine.html

If you can get the motor/generator away from carrying any thrust then i think this may be a good option.

Jonathan

[XXLRay]

Have you ever thought of building your own axial flux alternator? Several here have done so for wind turbines. Thus it should not be too diffcult for you to build one that fits your needs.

[ghurd]

I would be hesitant to spend much money without greater details.
Servo motors will operate in a fairly narrow RPM range with a fixed power input, and it would have to match what the wheel can supply or efficiency would be terrible.
Same thing with the bike motor.
Neither is easily modified, as far as I can tell.

If I was going with that line of thought (and I would), I would probably start with an F&P or GE ECM because they can be modified to get some kind of power output, at a specific voltage and RPM.
I bet either could be had for under £100 with shipping.  (FYI- I have sent ECMs to the UK, with bridges, etc, and the grand total was under £90)
G-

[birdhouse]

i'm not saying ghurd doesn't know what he's talking about by any means, but the servo that fish posted seems like it might be right up your alley. 

1500rpm and 400 volts.  that's .2666 volts per 1 rpm.  with your 85 rpm peak, that should yield 22.6 volts.  that's pretty close to battery charging voltage for a 24v bank.  looks like minimal gearing would be needed to make that servo work. 

i play with these larger servos as well.  they are a delight, as they already have magnets in them, are ready to produce power out of the box, have almost no cogging and are cheap to buy.  if you can find the star point, then lower resistance/higher rpm options are available from the same motor.  you might need to adjust your gearing accordingly. 

the only thing that sounds funny, is when you mentioned cogging in a previous PMG that you tried.  does you water wheel have decent torque?  i'm wondering if anything but the smallest PMG puts you wheel into serious stall due to the torque needed to create the electricity.  if this is the case, maybe an ametek or similar low torque/low output type would be better matched to your wheel. 

adam 

[hydrosun]

I would second the idea of the Fisher-Paykel. From  what I understand it has multiple windings that allow you to vary the speed and strength. As someone said you need to match speed and strength of resistance to match what your wheel is providing. In commercial microhydro like the Harris and ESD units you either change stators or reconnect separate windings to get the voltage needed at the speed of the turbine. Then the magnet strength is varied by changing the air gap. So that is what you are trying to replicate. A stock fixed motor will have one rpm and input that will work well. So to increase your odds of hitting a winner you want multiple windings in your motor.  So by changing sprockets on the wheel and windings in the motor you should be able to get close. A lower output dc motor might also be closer to the range your wheel can provide.
Chris

[caldoverde]

This is brilliant!! Many thanks to everyone contributing

Adam: I'm a bit confused by your calculations. I didn't think that straight line voltage/rpm extrapolations were valid? Hence power curve? Isn't it the case that these motors have an optimum operating range, and that when rpm falls below the lower end of the range then power tends to drop right off?

In answer to your question, the wheel doesn't develop a massive amount of torque under our water flow rates - it's only 1m diameter, after all. With the first PMG though, the resistance was such that if you'd have tried a bench test with a drill attached to the shaft, you couldn't have held the unit down with your hands. You would have had to bolt it down to a solid surface. We later found out it was built with Scottish winds in mind. At 2 litres per second, the wheel would do about 20rpm with this one. It was wired internally in delta (so we couldn't change that without voiding the warranty), and its minimum generating speed (ie. to produce 24V) was 200rpm, so the wheel had to get up to 50rpm to hit that (we had a 1:4 ratio at the time) and it would only do that under 5 litres per second, ie. storm conditions. Higher gearing simply slowed the wheel down proportionately, so it was obvious that our average flow rates were too low for this unit.

Chris and G: many thanks - away to do some research on the Fisher-Paykel and GE units. This makes a lot of sense to me.

[birdhouse]

caldo-
the voltage per watt is not purely valid.  but it will get you in the ballpark.  for example a 6,000rpm servo motor rated at 110volts would be a very bad candidate.  optimum range for these servos is anything above charging voltage.  their down side is there is no adjustable air gap, and unless you can figure out where the star point is, there is little you can do to change their performance. 

i'm building a wind turbine with a 140v 2000rpm 20amp servo motor.  that hits 24v cut in at 220 rpm on the bench, and yes it has to be bolted down to get decent wattage from it.  i'm hoping a 8.5' blade diameter is going to suit the power curve well, but think it might be too small. 

i think you would be well off with a F&P setup, as you can alter it easily, or a 5-10amp servo with high volts and low rpm might be a good fit too.   

adam

[WoodWaterWheel]

High voltage servo motors set up as alternators but when used at much lower voltages they are very limited in the amps they can put out before burning up.      Using a servo motor with a voltage rating closer to your required voltage allows it to handle the amps better but makes it require more gearing so pick your poisen.        Blue Wind and Hurricane alternators would be the closest premade units I know of but the  Hurricane CAT 5   http://www.hurricanewindpower.com/servlet/the-175/low-wind-PMA-,/Detail    is probably the closest match for what you're looking for with the lower RPMs and higher potential amprage.
Spencer

[caldoverde]

... the  Hurricane CAT 5   http://www.hurricanewindpower.com/servlet/the-175/low-wind-PMA-,/Detail    is probably the closest match for what you're looking for with the lower RPMs and higher potential amprage.

Spencer, the Hurricane low wind PMA is a re-badged Presto Wind alternator (we wrote to Hurricane and asked because they looked suspiciously similar). I think Hurricane may specify different windings on one or two of 'their' alternators, but after our experience with the Presto Wind M-24s (see above), I wouldn't go down that road again.

As far as I can gather, what you say is true of a lot of servo motors, but the F&P and ECMs are adjustable (as per Chris's post above) so it's these I'm looking at just now.

In the process of doing so, I came across Jonathan Kraidin's F&P modifications (http://www.mindchallenger.com/wind/) and as a result got very curious about axial flux alternators. Having looked at the record of his build, Hugh Piggott's manual, and Dan & Dan's improvements, this is certainly something we'd be capable of doing, so can someone possibly encapsulate in a single paragraph what pros and cons an axial flux alternator has vs a modified F&P or ECM? Am I right in thinking they're a lot more efficient?

This is all starting to feel pretty good, so I have some more questions for those who have a lot more experience in these things than I do.

I mentioned in my initial post that I'd been studying calculations for water turbines, water wheels and wind turbines to try and derive an appropriate equation for calculating the power of the wheel. I'd like to run this by you and ask whether it sounds reasonable since clearly I'll need to be confident about this in order to get the generator side of things right. Because the wheel doesn't behave like 'normal' water wheels and is driven more by incident velocity than weight of water, the equation I've used to work out the available power at the shaft is:

Weight of water in buckets in kg x vertical drop in m x water speed in m3/s3 x efficiency

Each bucket holds 3 litres of water and there's roughly 3 full buckets' worth in the wheel at any time. Vertical drop is 1m. Efficiency I've taken to be a constant 0.85, though it's higher at lower volumes and lower at higher volumes due to the changing arc of the water and the angle it hits the wheel.

Velocity of water in chute at 2 litres per second = 2.7m/s
Velocity of water in chute at 3 litres per second = 3.2m/s
Velocity of water in chute at 4 litres per second = 3.6m/s (extrapolated from previous 2 readings - we've had hardly any rain this winter ...)

This gives 151W at 2l/s, 244W at 3l/s and 369W at 4l/s at the shaft. Subtracting a conservative 50% generating losses, this gives expected output of 75W, 122W and 184W respectively. It feels like a decent baseline to me, based on observations of the prototype and what it's producing. The engineer reckons higher, and he may be right, but I'm being deliberately conservative.

And since a picture is worth 1000 words, here are some photos of the wheel and chute during construction:

Wheel installed on framework



Chute + wheel. Water volumes here are pretty low. The upturned plastic box is, I hasten to add, a temporary cover for the PMA



Volume here probably between 2 and 2.5 litres per second

[ghurd]

I am quite curious what Chris thinks about that water chute.


"can someone possibly encapsulate in a single paragraph what pros and cons an axial flux alternator has vs a modified F&P or ECM"
Everyone will have a different perspective.

Axial is predictable and somewhat adjustable.  
No iron loss.  No cogging.
Magnets, wire, and resin are sort of expensive, and possibly hard to acquire some places.
Building one is sort of Big Hammer type work.

ECM is not very expensive (some places), very expensive some times.
Has iron loss.  No cogging.
Not metric, 1/2" shaft  (if someone sends one, might be a good idea to get a 1/2" drill bit at the same time?).
Somewhat adjustable via hard wiring, or with a Star/Wye switch.
Modifying one is sort of delicate soldering type work.

F&Ps get complicated, in my opinion.  Stator from this version and rotor from that version to get the cogging reduced, 7 phase(?) wiring in 52 coils to contend with, etc.
Plus, I think it is mostly plastic?
I understand why the use them in AU (Off-the-Dump, common, and they work).

I believe a lot of it comes down to what tools are available,  Materials available in a location,  Type of hands-on experience the builder has.
I can make a pretty decent little induction motor conversion in 6 hours for $20, or properly reconfigure and fasten the wiring in an ECM in a day.  
A small axial from bicycle parts that works worth a hoot seems past what I can accomplish with the tools I have available.
G-

[hydrosun]

Wow, a picture is indeed worth a thousand words. You must not want much power because you are throwing most of it away.  Most of your power is lost in the open chute in friction losses, because the water is moving so rapidly. If you would use a closed pipe that is full of water and a nozzle to let out the right amount of water, the water would move much slower and the pressure could be used on a pelton or turbo that is much smaller and at a higher rpm. That would allow the use of a higher speed motor as generator.  What is the elevation difference from the top of the chute to the bottom? 
Sorry that was my first blurt out impression, I don't normally react so negatively. Your setup seems to be well built and it will produce some power.   What are your reasons to use the chute? Even with your wheel you could use a closed pipe and nozzle to  get more power and higher rpm. The nozzle would have to be changed for different water flows to keep the pipe full and efficiency high.
Normally chutes or flumes are used that are almost level and then changed to a closed pipe at the end to use the pressure and or on a over shot wheel use the long arc of a large wheel to use the weight of water. Some overshot use some of the velocity of quickly moving water as well as the weight, but not a chute as steep as yours.

I think the main advantage of building your own alternator is the ability to adjust the air gap of the magnets to match the power available with your turbine.

[jlt]

You look to have a great site for water power.But using  the water whee as it is now you are only getting a small % of it .You are  dead set on using  a water wheel. my Thoughts are to reshape the wheel into a cross-flow turbine so the water goes threw the wheel. will still look like water wheel. You will still have to gear it up. I would use a trans axle from a small front wheel drive car .It would  plenty Of rpm.And you could change the gear ratio to suet your alternator.   

[97fishmt]

High voltage servo motors set up as alternators but when used at much lower voltages they are very limited in the amps they can put out before burning up.      Using a servo motor with a voltage rating closer to your required voltage allows it to handle the amps better but makes it require more gearing so pick your poisen.        Blue Wind and Hurricane alternators would be the closest premade units I know of but the  Hurricane CAT 5   http://www.hurricanewindpower.com/servlet/the-175/low-wind-PMA-,/Detail    is probably the closest match for what you're looking for with the lower RPMs and higher potential amprage.
Spencer

Uh..?  I don't get it.  Why would you buy a box full of hype (and crap) if you were able to get a high quality and high tech servo motor.  I was only suggesting a different approach for generating electricity.  I have never burnt out a servo motor or even got one hot.  The issue here was to find something cheep.  Just my take on doing it.  It has worked for me for many, many, years without any maintenance.  Very robust motors. 

[Jon Miller]

I would be hesitant to spend much money without greater details.
Servo motors will operate in a fairly narrow RPM range with a fixed power input, and it would have to match what the wheel can supply or efficiency would be terrible.
Same thing with the bike motor.

direct drive bike motors are axial flux design and as I explained seeing as the loaded speed is yet un known for sure, having a gear cluster on the motor will allow for 21 + gear ratios to easily and cheaply be changed.

Jonathan

[ghurd]

direct drive bike motors  having a gear cluster on the motor will allow for 21 + gear ratios to easily and cheaply be changed.

I would not put that much faith in bike chains and gears.
A high end Campy set, properly lubed daily, and throughly deep cleaned every 100~150 miles, is not good for very many hours.
Pushing the limits on an overly maintained chain gets maybe 1250 miles with my skinney wife on it.  Most recommendations are 750 to 900 miles.
Gears need changed every other chain.  Maybe every third with luck and not pushing the chain past its limits.

1000 miles at 16MPH is 62 hours for a ($70) chain.  124 hours for the gears (>$1000).
Cadence at 90 (a bit higher than the water wheel), full size groupset.
Chinese parts would be cheaper, and I expect not last as long.

Figure most people can not make 150W for more than an hour, and the hydro can, and bike chains and groupsets don't sound like a great idea to me.
Even if the parts could manage 10X longer than on a bike, it still doesn't seem very cost effective.
G-

[caldoverde]

Chris, the open chute was chosen because we get sudden flash floods down the stream with rain storms and it deals with the volume of water and debris much more effectively than a pipe which would easily get blocked and jammed. With the chute and wheel, floods and debris just overshoot.

According to my initial calculations, if we'd installed a turbine here we'd need to use the entire head available on the site (around 30m) to get around 200W. It would require pretty extensive civil works to install. We would have to divert part of the stream into a holding tank to feed a penstock and then take the penstock back into the stream because it's the only place it would get a straight run. There's no obvious place to carve out a holding tank in the upper part of the stream: it runs over solid rock down a slate built barroco - a man-made channel that's designed as a kind of a storm drain to carry excess water that isn't diverted for irrigation and which is probably around 500 years old. The digging would have to be done by hand in solid rock as the site is inaccessible to heavy machinery. Running the penstock down the barroco risks damage under flash flood conditions. The cable run to the battery shed would be much longer with a turbine at the bottom of the property. Then there's all the problems with debris ... All in all, I reckoned the wheel was a better bet as we figured we could get the same 200W out of it by using the entire stream flow without having to use all the available head on the site. Short cable runs, no problems with debris, and minimal disturbance to the stream and all its other uses (household water supply, irrigation). Plus none of the other problems with turbines like cavitation when water flow drops down to minimal operating levels.

There's a number of folks round here have tried turbines. most of them have been abandoned because of endless problems caused by storm floods and debris. Now that's not to say that a real hydro expert couldn't have sorted better installations for them, but those experiences did feed into my decision as well.

Forgive my stupidity, but I'm trying to get my head round ...

Most of your power is lost in the open chute in friction losses, because the water is moving so rapidly.

Friction slows the water down, no? So if the water is moving fast, how is it losing power because it's moving fast? I would have thought we'd want to maintain or even increase that speed because it's what's mostly driving the wheel? In a pipe it will move even faster surely? I get the good sense in having a directional nozzle as I'd already thought of that after observing how much power we waste in higher flow conditions because it doesn't hit the bucket walls at 90° any more.

[hydrosun]

OK I get your reasoning for using the chute. A hydroscreen would be low enough that any debris and floods would go right over it. Check them out at hydroscreen.com. Bob has several designs that work for different situations. I usually use the one foot screen with a 1 foot stainless acceleration plate and make a small concrete box to collect the water that goes into the pipe. The whole thing is cemented into the stream. Essentially a short chute directs water across a screen and into a pipe.   It eliminates the need for any holding tank. Then a pipe could be attached to the rocks on the side like you did the chute down to a lower level.
You want the pressure to change to speed as it hits the wheel. In your chute the water is in contact with a surface that is slowing it down. That is why the velocity is lower with lower flow. A bigger percentage of the water is in contact with the bottom of the chute.  In a pipe the water is flowing slowly and the pressure pushes it out a smaller nozzle. The faster the water moves in the pipe the more pressure is lost. That is why it is important to size the pipe large enough so it can move the volume needed without losing much of your head.
If you used 30m and 2l sec you would get 270 watts with a 50% efficient setup.  5l would give 670 watts. So you could use a shorter section of the stream if less power is needed. I'm not sure how you got the figure of 200 watts.
Your setup obviously works, I just wanted to point out that more power is available.
Chris

[ghurd]

Not sure if anyone considered fancy gutter devices for small filters.
I can tell you the reverse curve Coanda type work quite well.
Could add a screen type after the Coanda type.

A link showing both types, though twisted to favor the type they sell-
http://www.leaflessinseattle.com/gutter-guard-comparison/reverse-curve-systems/

I don't believe it would take many feet of width to deal with 5L.
Even if it could only deal with 2.5L, the extra would flow over, and 2.5L at more than 2X as efficient is about the same as 5L now, so the output would still be better?

"a picture is indeed worth a thousand words"
G-

[caldoverde]

Chris - I like the sound of the hydroscreen. That would be possible if I can find part of the stream bed that isn't solid rock. Or alternatively I guess we could build a collecting basin off the edge of a drop-off with a screen over the top of that? I totally get that a wooden chute is much less efficient than a plastic pipe, but I'm still not quite understanding how the pipe works. Does it completely fill with water which then effectively gets 'injected' onto the wheel? Presumably then you would have to size it for the lower end of flow rates, which would mean losing any gains from additional flow?

Another thing with the turbine is that to use all the power available in the stream would mean using all of the stream's flow for the entire length of the its passage through my property. This isn't on as it has to supply irrigation and water to several buildings as well as generate electricity, so it's about optimising all uses of the water.

The present 9m chute has 3m of vertical drop. I can increase that to about 7m drop for about another 6m of so of pipe without compromising the other uses the water is put to. What sort of size pipe would we need?

Do my calculations seem OK to you?

G - thanks for that. I'll take a look.

[zap]

Here's a pdf from Google/Homepower?  with many different setup examples of intakes/screening.
I'm not sure how long the link will work, you might want to save the pdf locally.

[caldoverde]

G: Had a look at the gutter screens. Wondering how they'd stand up to sizable rocks? This stream drops 200m in about 500m so some fairly hefty chunks of mountain come down with it on occasion.

zap: Many thanks. Looks good. Downloaded and saved for studying later this evening.

OK. So now this subject has grown a bit to encompass an improved delivery system as well as a generator, can anyone help me sort out the equations - calculating pipe/nozzle size as well as generator size? Then I can start planning adjustments so when the engineer gets back next week we can get onto this. I'm thinking we could use the existing chute to support and guide a pipe-based deliver system, and just take the intake further up the stream for more head?

[ghurd]

I will leave the math on that one for Chris.

The gutter things I have experience with are thin aluminum.
They will suppost a ladder, not sure about "sizable rocks"!

There are some made of plastic too.

2 meters of level chute should stop most rocks?
Maybe a screen made of 10mm steel bars half way down the chute, or over the aluminum/plastic?

The stuff is not very expensive for the plastic type.  Pretty sure it could be installed so it was easy to replace.

"and just take the intake further up the stream for more head" would be a good idea.
Might find it can operate one of those reworked car alternators you have.
G-