Electrical Engineering Question

Sure if you dont mind them being about 15 - 20 feet across.

Sure if you dont mind them being about 15 - 20 feet across.

Rational thinking and on topic, tcmtech. Thankyou, but the devil is in the detail! Gerry D.

Thanks for your comment tcmtech. I interpreted it as yes, it is possible so inform yourself. Thanks again Gerry D.

'....25kw of torque....'

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um, what???

's right Guru, 3 tons of water in the buckets, and that goes up to four if the load slows the wheel down a little, but it sure is not high speed. The faster it goes the less water in the buckets and that acts as a speed governer! Does that make sense to you? Gerry D

It's just that quoting 'torque' in 'kw' means some helpless little 'inverse seconds' has been abandoned somewhere...

...the units don't agree.

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Not really important at the moment. I was kind of knit-picking I guess.

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To your question: Increasing the number of poles in your generator design is another way to work with reduced RPM.

Thanks for the upload Guru, your latest info is a lot more helpful. I'm no genius, just a retired Irish fisherman with fairly good hands and an idea, looking for some helpful information and I know there are a lot of knowledgeable guys out there who are prepared to help. I also know that there are a lot of smart-asses out there too but I can take a bit of flak. Anyone wanting help about big diesels, or trawling, or seine-netting I might well be able to help. I suppose it should have been Newtons but I know more about BHP & KW. Thanks again, Gerry D

Perhaps this might be helpful?

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Can you elaborate on the motivation to avoid gearing? Maintenance? Efficiency?

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What kind of size restrictions do you have?

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Other specifics you provide increase the chance that someone will be able to suggest something beneficial.

Hi Guru, thanks for responding. Maintenance & novelty. Aiming for 15year major maintenance period. Not much restriction, plenty of space. Aiming to hook up to national (UK) grid and will outsource, if we can, the control gear neccesary to do so. Gerry D

Perhaps you can scale-up something like what I've seen built for home-made wind turbines. I recall one was built with two wood disks -- one with magnets, the other with hand-wound coils.

There are quite a few "how to" pages on instructables.com, and other sites I found via Google.

If you youare aiming at hooking up to the grid, this paper has a lot of information you may find useful. It is about generators used in wind turbines, but much of it crosses over for applications like yours.

The link wouldn't open Guru. Regards and thanks from Gerry D.

Thank-you 'Truth is not a compromise'. I got both your attachments opened and they are very helpful. "May much good be at / with you". (translated from Gaelic) Gerry D.

Engineering Disasters of the 21st Century, Direct Drive Water Wheel Generators; D. Gerry, et al, 2012.

On Topic, but not very useful. Have you no 'more positive' ideas, even if they are to explain your remark. Nevertheless, thank you for taking the trouble to reply. txmedic3338, I'm not highly educated and wonder what 'et al' means in this context. Gerry D

Hello Gerry D. "et al" means "and all the others" in this context. I was smarting off. This has been tried and it has failed. Tried by many others, who have endeavored to build their own generator direct-coupled to a slow-revolving water wheel. It's been on television on the survivalist shows, and in many "do it yourself" magazines. It never works. That's why there's not much information on the web about how to do it... because there's not a lot of people putting effort into documenting how to do something wrong. You will be much better off to find a commercially available generator/alternator to couple to your water power, and to use the gearing to achieve the optimal RPM. If you can give us gallons or liters or cubic feet per minute, some kind of flow rate, and also the head height you have now, or could obtain if you made changes, we can calculate the KW you can expect to generate and help size the devices. Sorry for smarting off. I'll retract that and just say "this won't work"... at least with the information at hand.

I'd suggest sourcing the generator or building one to a convenient scale based on available materials/resources and then adjust the gearing to suit.
Gearing is much easier to change and experiment with than the generator.
Del

Thank you Del the cat. Your advice to stay within the box is sound I know, but getting it right first time is not crucial. Gerry D

The answer's "Yes" but it's probably not the best way to do it.

Any generator/alternator you buy will be far superior and cheaper to anything you can build yourself. So buy something off the shelf and adjust the gearing to suit.

In general it often pays to look up the basic formulas for Power etc. before you do anything and so get a handle on what size equipment you'll need.

As an example, Power = eff*m/s*g*h = efficiency * kg/sec * 9.8m/s^2 * Head. So (guessing) 100l/s water supply, 5m drop on to turbine blade, efficiency .5, gives Power = ~2450W (obviously you'll use your own numbers).

Gerry,

If you want to try building a direct drive generator you will need something pretty large diameter to get the necessary speed of the magnets past the coils. Additionally, to get 25kW out, you will need a substantial generator design, which will likely be beyond what you could get from a homebrew design. You can get info on homebuilt slow speed generators from the wind energy crowd, who have the same problems. Google is your friend here.

I would suggest that if you are the type of guy who is willing to experiment, playing with speed increasing gearing would be the way to start. Going this way allows you to use commercially available alternators or generators...whatever you can lay your hands on inexpensively. If you are 50Hz in your part of the world, then you can look around for an old alternator that maybe was wound for an old slow speed diesel engine. A 4 pole alternator would have to run 1500 rpm, but if you could find an 8 pole alternator you could run it at 750 rpm. Which is about a 35:1 speedup from your 20 rpm water wheel. This is quite achievable in about 4 steps of around 2.5:1 speedup per step. You might consider roller chain for the first couple of steps and then go to V belts or toothed belts for the final steps where the speed is higher. I'm suggesting this route because it can be done with used stuff.

Hope this helps,

Jon.

I agree with you sawmill.The first thing that comes to mind is motorcycle sprockets and chain.

My dirt bike used 12/40, or 10/40, depending on terrain. This is an easy 4:1 ratio.

Do this 3 times, and Bingo!Actually, more than needed,so adapt final ratio to suit application.An even multiple of the desired frequency would make finding an alternator easier.

I am presuming an inverter after an A/C generator to regulate frequency or charge a battery set.

Industrial chain of larger sizes are available to accommodate higher torque.

25Kw as stated by OP would be "Roughly" 50 hp,which is very reasonable for #50 roller chain.

And the sprockets do not have to be huge.

My dirt bike exceeded this hp with no chain load failures.

Chain is very durable and easy to maintain especially in a clean environment.

Yes, you can attach powerful permanent magnets to the rim of your water wheel, but bearings of the wheel are going to have to be very accurate to get the close clearances necessary to develop any significant output. You can buy very strong square ferrite-in-epoxy magnets with a hole in the center for little money from Radio Shack. Hold them in with flathead screws of exact size, and shim them so they are extremely close to your coils, which you can wind with motorwinding varnished copper on soft iron cores made of cheap stovebolts, which will allow adjustment to the magnets. It will be tedious, and each coil will need a diode. I presume you're going for DC current, unless you're good with circuits. I'd suggest feeding a few heavy diesel starting batteries, and inverting from there. Depends on what you want to do with the electricity. This Xmas they've come out with strings of LED white lights that are molded right into the wires. Very very low draw at 3 volts for a twenty foot string. Would that make a pretty water wheel!

As suggested by #15, you could produce DC current with the conditions stated.

But 1st: With such a turbine, buckets carrying 3 tons of water, I am sure that the structure will have to be sound. The issue is how accurate the shaft and bearings are in view of having a minimum excentric deviation per rev.

In any case, you can have a flexible coupling to drive your generator rotor / stator assembly, which wiil be built with the exact tolerances.

the 2nd issue is the diameter of the Rotor (and stator) required to obtain decent DC current, without too many ripples.

The 3rd: You need to get enough voltage to be able to charge the batteries that will be used. You can select 12V, 24V... But this requires designing the Generator to suit the requirement.

The 4th: What amount of energy you would like to extract/produce from that generator: How many Watts or KW?

All these points need to be worked out.

You will need some local help from an electrical engineer to come along and work with you to see what are the alternatives depending on what the turbine looks like and your final objective.

On the other hand, the easier way is to gearup the revs to suit what is available in the market and get the power type and capacity.

Can't help you at all , but would be fascinated to see what you have got there , and know how you built it , as I'm just starting to do something similar but smaller . Have you got it on a web at all ? Or if you have any photos , I could send my email address . Would really appreciate seeing it . I'm a bit like you , I can offer advice on shearing a sheep or building a fence , but that there electrification stuff is pretty obscure . Not many people seem to need advice on shearing sheep these days.

Hi sheep farmer, and other corespondents, thank you all for responding. The turbine is just a big millwheel with a dam which diverts some of the river water. No speed involved, just weight of water. It used to drive a corn mill and was a typical 'creaking old mill' wheel untill we modernised the shaft and bearings. made a new wheel with and bigger and wider buckets, and fibre-glassed the lot. If the buckets on the decending side were all full the weight would be well in excess of four tons but when it is turning freely the buckets don't have time to fill. We rigged a temporary brake on the shaft and when it is doing about 20rpm the buckets are almost full and there is heluva torque on the brake. Gearing up the speed is the obvious answer but gears need lub. and this is a green area. (the old folk used tallow!) I think that it should be possible to make a large diameter, slow turning pmg genny to convert this torque into electricity. We are not sure if our thinking is right and it would be too expensive to go ahead uninformed. Information is bound to be available somewhere but I can't find it. My thinking is that with a large dia. the magnet array (rotor) would be passing the coil array (stator) fast enough to do the job. I'd like to read up about it if I knew what to read! Any informed opinions or suggestions out there? Gerry D

Hi Gerry. Sound like you've got an interesting project there.

If you include a sketch showing how many buckets with some dimensions and flow rates we can calculate what sort of power you could expect.

Alternately you could use your shaft brake and some scales to estimate the Torque and work out the available Power that way. Let us know if you need details.

It's certainly possible to build a generator using magnets mounted to the wheel but, as has already been mentioned, it's going to be extremely inefficient.

Is the water wheel regular enough that you could run a simple idler wheel on the outside?

Is this the kind of paper you have in mind?

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Yes indeed Guru, this is the kind of thing I can deal with. Time is not the essence, I want to do the homework before I spend the money. Copper wire and PMGs don't come cheap and my idea would need a lot of both. Thank you for the attachments. Gerry D.

Take a normal generator, whatever is available used but good, and what you can maintain. A factory knowing and till acknowledging it is a definite advantage. You might need a brush for the exciter, for example.

Then a large, sealed, oiled gear to convert the high torque from the wheel to some higher rpm with corresponding lower torque. Let's assume 400 rpm for the conversation. Then you can go the rest of the way with 2 or 3 stages of cogwheel / cogbelt combo. These are used in sawmills under the dirtiest conditions, with 5 years and above life expextancy. I think they take standard shafts and bearings etc. At that point you will work with the supplier on the details, like any other customer. Nobody knows enough to do the selections alone.

I propose You kick off the proiect by correctly measuring the big wheels torque the way you tried to slow it down. If the pivot point of the braking bar is 1 meter from the big's axle (vertical line to vertical line), and it reaches over another 10 meters, then you keep hanging weights there. If, 50kg slows it down to your liking, then the torque is: 50x10=500kgmeter. Counting the rpm and measuring the braking from light load to (almost) standstill, say at 6 or 10 points, you have a very good description of the big wheel under load. This site has a few good pump expert to go from there with confidence.

If you do know seasonal variation in the flow, fine, otherwise estimate for a starter.

Some excellent pointers on measuring torque.However, IMHO, chain drive is simpler than a gear box,and easier to service.Presume an initial RPM of 20 RPM.A 10 to 1 ratio with #50 or #80 or even up to #160 chain is a reasonable size.This will give 200 RPM.Now mount another similar set on first output stage shaft to get 2000 rpm on the third stage output (final) output stage..(A smaller size chain can be used as RPM goes up and Torque goes down) A 4 pole motor or generator at 60 cycles requires 1800 rpm, so this is more than adequate and allows for slip.

If noise is a concern,especially on final output, belting is better,and requires virtually no maintenance,but chain will last longer if properly lubricated.A drip or bush feed oiler is simple and easy to implement.This is especially true in High Torque applications, such as the first stage.I know there are many arguments pro and con of belts vs chain, but when you see a D9 dozer with a belt drive, let me know.

In my mind's eye, I see a very compact 3 shaft drive with chain coupling.Perhaps the final stage could be cog belt for noise reduction.

Used chain sprockets are normally easier to find than cog-belt sprockets and are usually cheaper also.

Of course, this is merely the way I would do the mechanical aspect of the project.The speed and voltage regulation is another can of worms that I don't wont to dig into right now, but if the OP insists,I will do my best to advise.

It is easier to eat an Elephant if you do it one bite at the time.

Not that I condone killing or eating of elephants, or any other endangered animals, not to be construed that they are more valuable or important than non-endangered species, or should have more rights or privileges than any other animals.Nor should it be interpreted that am more or less empathetic to one species or the other.

Or Plant species either.Or bacteria or viruses for that manner.

Any life form,foreign, domestic, or alien for that matter, that has been omitted was not deliberately slighted,but merely an honest oversight of an aged brain.Not to say that old people are dumb.Or not...bla bla bla....

If you are offended by my statements, then I am offended that you took offense at my statement.Our lawyers will have to work it out.

See how far this can go?

hoe many Shetland ponies is that?

If this is any other type of horse, it probably is't a Shetland Pony....

...

It would have to be Potamus (river) horse. Know what I mean?

Are boat motors rated in seahorse power?

On the more practical and realistic end of things for gearing there is nothing wrong with using a good sized and properly rated gearbox. A used unit from a large conveyor system like what is used in a gravel pit for stacking material will easily fit into your power and speed plus gear ratio requirements. Same with a used semi truck axle. Even at 50+ Hp input at 20 RPM you will never wear out a heavy truck rear end in your life time plus if you get one with a two speed set up low range should be good for at least a 10:1 or better speed increas right from the get go.

What are you going to do with the power once you have generated it it is also a very important decision regarding what type of generator or alternator system to use. If its just basic co gen you don't actually need a generator system at all. Just take a common Ac induction type electric motor and spin it faster than its rated speed. That it no big expensive grid tie inverters required.

As far as the 'Going green" excuse give me a break. That's the battle cry of the cheap lazy and clueless.

You already used modern bearings and fiberglass on it so don't bother trying to feed us that "going green" nonsense. Use the properly designed and rated parts and materials and be done with it.

You sound intolerant mister! What's wrong with a little thinking outside the box now and again. You obviously are a person with good ideas. Fair enough! but be tolerant of the, silly seeming, ideas of others. "That's the battle cry of the cheap lazy and clueless"???. Insulting or what! Gerry D.

I wasn't trying to be intolerant.

Rather look at it from my perspective. I have been playing around with all sorts of AE stuff since I was in my early teens which was 25+ years ago now and I can assure you from my personal experience that when it comes to AE the vast vast majority of those who are interested in picking my brain are the very same people that are and would be considered cheap lazy or clueless in all practical definitions.

The main categories are those who are too cheap to spend a dime on anything even if they have far more than enough and AE is most associated with "free".

Those that are dirt poor and cant afford squat and want AE to solve their problems because they are too lazy to go out and do any level of work that has any value to it whats so ever.

Then lastly those too clueless to ever begin to understand that what they want from AE power is so far out of their reach in price practicality and workability it's sad.

Sorry to offend but as any long term members of this forum can attest to by far and wide margins the most AE related questions and or topics that come up are fueled exactly by these three main categories and every single one is flying the "Going Green" flag with all their furry.

Do a forum search here for these guys and you will soon see what I am talking about.

DAS, Joe Fordham, Kastrupsky, Kennynabb6. The top four representatives that come to my mind relating to the "going Green" movement here without a clue about cost, practicality, functionality, workability or general physics and sciences behind AE in general.

To be honest the only issue I have with your concept is the giant slow turning generator concept. Its just not practical cost effective or likely to have any long term effects or gains that will justify its overall complexity time investment and general work involved that will justify its existence where as if sourced out right a simple off the shelf parts based gear drive and generator/alternator system is.

BTW most of the giant industrial generators that run in hydro electric plants spin at 90 RPM and even then they are some 30 - 50 feet in diameter and are very high precision devices built to a few thousands of an ich tollerances despite their shear size and weight. A bunch of magnets glued to wood will never hack it.

I guess you want to generate Alternate current (AC) and not Direct Current (DC). In case of generation of AC, I presume that you are staying in the country where the frequency is 60 Hz. The formula for the number of poles is P = (120*f)/Ns where P is number of poles, f is frequency and Ns synchronous speed.

Hence if you are firm on using the direct coupled generator to your turbine the poles shall be 360 in numbers, as f is 60 cycles per second, Ns is speed of generator = speed of Turbine = 20 RPM given. That means every degree of angle you should have a N or S pole on the rotor which will increase the diameter of your rotor and ultimately stator also of your generator, to accomodate the pole at every degree (360 poles at 360 degree). However if 90:1 Gear Box is used, then only 4 poles are required and will reduce the diameter drastically, where the generator speed will be 1500 RPM. And if 45:1 Gear Box is used, then 8 number of poles will be required and the generator speed will be 750 RPM.

Thanks pswagh, I think you have pretty much answered my query. I'm not sure of the frequency here in Ireland but I can easily find out. I know that the generator engines in the trawlers had to be governed at 1,800rpm. You seem to be saying that I will need 360magnets, Does that mean 360 coils also? I have lots of torque! If I put two rows of magnets, would that double the output and if it did would that mean increasing the copper. What sort / size of magnets nd copper would I need? If you would rather send any Info you might like to give, by e-mail I think you can do so through the site. I wouldn't like to put my e-mail here on the open site. I appreciate the trouble you have gone to already in responding. Your explanation seems logical, is convincing and confirms my, not very well informed, thinking. Regards, and appreciation, from Gerry D.

Thanks for your response HiTekRedNek, and you make a lot of sense. If I had as much sense I wouldn't be even thinking about direct drive but I haven't and I am. If it finally proves too difficult, fair enough. If not, the rig will be everlasting! The commercial windmills turn at all sorts of speed and they are connected to the grid and I am assuming that if my wheel can produce enough electricity, the technology already exists to sort out the cycles. I have experience of marine controllable-pitch propellors and I think that the commercial windmills must have computer controlled pitch control becase that technology has been in use for years now. But there is new technology in the pipeline which will do it in a better way. However, I am retired and have the time, D.V., to take a one fence at a time approach. Producing torque was the first fence and we have that sorted out better than I could have hoped for. I have two close friends, one builds grp trawlers and the other has an engineering workshop and services ships. So I have useful backup. The practicalities of building a big P.M.generator is the fence I am facing now. Controlling the sync will be the next fence whether I gear up or whether I pole down. I wasn't sure if it was possible to pole down to my speed but apparently it is, and in any case it is an interesting subject and judgeing by your response you are interested also and obviously knowledgeable. So thanks for your response, I am very much a learner in these matters electrical! Regards from Gerry D.

Please think about, what you want. But, there are constraints, as you know from practical experience.

1,. Direct drive. The magnetic fluxes need a closed circuit. Never mind the colossal size, the 1 degree or so pole separation. You need colossal magnetic sheet metal stampings to close simply the nearest few poles. You ready for that? Permanent magnet or excited, who cares?

2,. Previous notes detailed in depth and width the gearing needed to a 4(?) pole off-the-shelf generator with maintenance support. Permitting me being impolite, duh.

3,. Unless you are independently rich, forget about synchronizing your wonderful setup to the grid. For yourself, it is not needed, nor desirable. My generator isn't.

4,. Voltage control? Reasonably. Frequency control? Reasonably. In standalone, reasonable is somewhere under 5%. K.I.S.S.

Best regards