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HYDRO TURBINES => Hydro Turbines => Topic started by: jonesy on November 05, 2017, 10:01:21 AM



Title: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 05, 2017, 10:01:21 AM
A friend asked me to look at the electrical end of a home made hydro generator.
It was an installation in the mid 80's and appeared to work for a good while, but no longer works. The guy that designed/installed it cannot be contacted.
The alternator is 20kW/3 phase 230V and came as a lump requiring 1500rpm on a 20cm V pulley. This is driven by a 140cm pulley direct off the horizontal water wheel. The water wheel is best described as a series of spoons ~20x10cm, most of which are whole.
It was a flour mill, and the top rotating stone was originally removed. The rotating shaft terminates with a rectangular spigot approx 50mm x 30mm, and sticks up about 40mm. It's not clear how this was then attached and continued up to the 140cm pulley as there is a gap of about 20cm, but there are plenty of unused parts that almost fit lying around. The only broken and bent bits are M14 x 15cm bolts from a 30cm flange, that form what was most likely a flexible coupling to the spigot. The spigot is mainly clean and in good condition, and may have had something (badly) welded to it.
Any (fag packet) way to determine a likely maximum power that can be transmitted through a spigot of this size? It would be a shame to restore it to find that you can only run a kettle. A new water wheel and shaft will most likely be required. The flow is readily controlled, and is pretty consistent year round, so how likely will 50Hz be maintained?

I have no photos of the mechanical end.  I'll need to go back and take some.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: Philip R on November 05, 2017, 02:14:11 PM
20kW @ 1500 rpm equates to 127.3 newton meters. Approx 13 KG meters or approx 95 ft lbs.
The shaft diameter need not be large. Think of the cross sections of the half shafts of a car transmission. Less than an inch in diameter, and the torsional loads they endure at harsh accelerations!
Philip R
 


Title: Re: How big a shaft for driving a 20kW alternator
Post by: renewablejohn on November 05, 2017, 03:32:09 PM
This is just not on. Get us all excited about a new hydro project and then no pictures.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 05, 2017, 04:41:52 PM
This is just not on. Get us all excited about a new hydro project and then no pictures.
I can't quite believe that I didn't take any photos of the boring mechanical bits.  ;D Got lots of the control panels etc. There was a lovely museum piece from Compaq which turned out to be a UPS.
Thanks for the figures. Something must have gone wrong to shear/bend the 4 off M14 bolts on the flexible? coupling. I'd been thinking it could have been a large electrical load applied, but could it have been caused by the pelton jamming on a log and stored energy in the larger pulley (more like a large cart wheel) doing the damage?
I did try to spin up the alternator shaft on a cordless drill and it turned fine, just not fast enough to excite.
Would I be correct in saying the ratio is 1400/200 ie 7:1, so the large pulley spins about 3.6 times per second.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 14, 2017, 05:20:09 PM
I've been sent a picture. I'll try to get some more.
At the bottom is the drive from the water wheel, terminated in a rectangular spigot. The large pulley is above and stops at the flange with the bolts. This pulley is held up about 100mm, and needs to drop down to align with the alternator pulley. The spigot will end up supporting this.
Any ideas how to join the two in a flexible manner.

(https://s33.postimg.org/nbqbsgmnv/shaft.jpg) (https://postimg.org/image/nbqbsgmnv/)


Title: Re: How big a shaft for driving a 20kW alternator
Post by: offthegridandy on November 14, 2017, 05:31:58 PM
Is there any way you could bodge summat from a tractor PTO shaft? 


Title: Re: How big a shaft for driving a 20kW alternator
Post by: knighty on November 14, 2017, 05:58:36 PM
there's loads of flexible couplings around you can buy off the shelf which you could have machined/adapted to fit that

most are pretty much a bit of rubber between two steel plates

Google image search for flexible couplings to give you an idea (https://www.google.co.uk/search?q=flexible+coupling&num=100&source=lnms&tbm=isch&sa=X&ved=0ahUKEwin97LR0b7XAhUGrxoKHZC3BLUQ_AUICigB&biw=1280&bih=905)

or... are you aiming more for home made/cheap? - pretty much all rear wheel drive cars/vans have a flexible rubber part between the gearbox and propshaft - it would be pretty easy to adapt one of those

*

the square shaft - does it have a hole through it ?  it looks like it does but not 100% sure by picture - is that shaft removable ?

it looks pretty rough, it would be much much better if you could remove that and have it machined square again

the round bit below it... is that some sort of bearing/bush housing or does that turn too ?


Title: Re: How big a shaft for driving a 20kW alternator
Post by: Nickel2 on November 14, 2017, 09:15:12 PM
If the generator and the turbine each have their own full set of supporting bearings, perhaps a Granada/Transit/BMW prop-shaft coupling would do the job. They are suitably rubbery and would tolerate a reasonable amount of mis-alignment without problems.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: marshman on November 15, 2017, 08:06:37 AM
Use a Layrub coupling. Just google "layrub coupling" does exactly what you want. Lots of different sizes and data on max torque etc.

http://www.davidcornwallis.com/downloads.php

Click on layrub couplings to get datasheet of sizes etc.

Not sure on pricing.

Roger


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 17, 2017, 04:02:25 PM
Thank you all for the suggestions. As we haven't even got the water wheel turning, I think we'll need quick and dirty to see what other problems there are. The belt tension is made by steel ropes and tensioners back to the walls. Wear suggests that one belt was used, but both pulleys have 3 grooves. There are 2 belts ready to use.
To answer some of the questions.
There isn't a hole in the drive peg. The peg seems to be machined from the larger circular part - no obvious welding. Might be preferable to weld a sleeve over it, once we've worked out what type of metal it is.
The water wheel must be fixed at the base with some sort of thrust bearing. So the shaft could come out, but I'm guessing we'd need remove the lower mill stone, then hoist the shaft/water wheel clear of the water.
The generator has its own bearings and rotates freely.
There is one picture showing parts that have been made and not used. The OD is ~30cm. It looks like these parts relied on the mass of the large pulley and gravity to keep them together. There are no broken or worn parts.

(https://s7.postimg.org/ya7haolvr/IMG_20171117_140620.jpg) (https://postimg.org/image/ya7haolvr/)

(https://s7.postimg.org/tctwp49hj/IMG_20171117_141812.jpg) (https://postimg.org/image/tctwp49hj/)

(https://s7.postimg.org/egvdhk0nr/IMG_20171117_141848.jpg) (https://postimg.org/image/egvdhk0nr/)

(https://s7.postimg.org/hayiuzfon/IMG_20171117_141930.jpg) (https://postimg.org/image/hayiuzfon/)


Title: Re: How big a shaft for driving a 20kW alternator
Post by: Tinbum on November 17, 2017, 04:39:08 PM
Is it possible that the slotted new part with the 4 bolt holes goes on the bottom shaft and then you need a large thick rubber washer that sits between that and the top shaft. The two are then bolted together with the 4 bolts that are hanging down. ???

The rubber washer could be drilled with 8 holes so there is no fixed rigid connection. ???


Title: Re: How big a shaft for driving a 20kW alternator
Post by: rogeriko on November 17, 2017, 08:17:24 PM
This is off a mercedes propshaft you just need to find one the right size.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: knighty on November 18, 2017, 12:33:17 AM
the flexible joint is the easy bit, fixing something to that square pin is the tricky bit

are you sure the square pin and the round bit below it are one piece ?

the shaft would need some sort of bushing or bearing at the top of it ?

unless, there's a bushing there we just can't see in the photos ?

or, it relies on the bushing above, which makes the joint a lot more important and also means you don't want a flexible joint, it would need to be rigid



check for a bush/bearing below the square peg

and also check to see if the square peg and the round part are cast - because that'll make a big difference as to how you fix to it

(quick google/youtube search will show you hot to test for cast better than I can explain it)


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 18, 2017, 09:27:59 AM
Is it possible that the slotted new part with the 4 bolt holes goes on the bottom shaft and then you need a large thick rubber washer that sits between that and the top shaft. The two are then bolted together with the 4 bolts that are hanging down. ???

The rubber washer could be drilled with 8 holes so there is no fixed rigid connection. ???
There is a large piece of lorry tyre lying about, drilled as you suggest. The only bit I can't get is once the slotted piece is in place, there is a large part of shaft sticking up. This would require a stack of rubber washers to reach the upper flange, but webs have been welded on. There is a much heavier piece, no photo, that is basically flat (~30mm thick) with a slot and bolt holes which would work with a single rubber piece.

There is probably a bush/bearing under the peg. Plenty of grease has worked its way down to the wheel from the bearing. Looking at the remains of another mill stone (there were 3 stones originally) it looks like the peg used to be longer, with something that looks like a pickaxe fitted over the peg. I'm guessing this rotated the upper stone, so was height adjustable in some way to change the gap between the stones. So there must have been some sort of bearing originally.

You make an important point knighty, and the penny only dropped last night. The large pulley is standing on the mill stone, and is bolted in a few places. The alternator is similar. You might be able to see the ropes holding the large pulley go via a bearing. I'm beginning the think the large pulley, belt and alternator (tensioned off the opposite wall) all work together to ensure alignment onto the main shaft.

That joint off a mercedes propshaft looks good.



Title: Re: How big a shaft for driving a 20kW alternator
Post by: Tinbum on November 18, 2017, 09:48:13 AM

There is a large piece of lorry tyre lying about, drilled as you suggest. The only bit I can't get is once the slotted piece is in place, there is a large part of shaft sticking up. This would require a stack of rubber washers to reach the upper flange, but webs have been welded on. There is a much heavier piece, no photo, that is basically flat (~30mm thick) with a slot and bolt holes which would work with a single rubber piece.


I imagined the webs on the slotted piece being on the underside. ie the flat part with the slot being the top. The circular tube being to locate the part on the lower  shaft.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: longstroke on November 22, 2017, 04:32:33 PM
It sounds like someone has previously tried to repair the coupling.

The picture makes the top of the drive pin look like a part above it was fractured off previously - can you post a close up?

Then someone has tried to make up adapter pieces to be able to reconnect to the vertical shaft above.

It would appear that you could try running the wheel as is without damaging the top of the shaft - after trying to see how good the bearing under the wheel is, which presumably incorporates a thrust bearing to support the weight of the wheel and shaft, and the reaction force due to the water.
Have you been able to turn this by hand?

This is a really exciting project - I'd personally love a place with a water turbine, or potential for!

With regards to frequency stability - what was previously done with the generated power as this will influence the possibilities?
I'm guessing this is in France, so I've no idea on the regs for connecting to the grid?


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on November 23, 2017, 09:05:51 AM
I imagined the webs on the slotted piece being on the underside. ie the flat part with the slot being the top. The circular tube being to locate the part on the lower  shaft.
Hadn't thought of that. It makes sense.

There are quite a few broken bolts, but no worn or broken flanges etc. My gut feeling is that the drive pin has fractured, but the current collection of bits will work with a pin shorter than it currently is.

As you say, the next job is to open the sluice and spin the wheel. From there it should be quick enough to fit the 'new' coupling, the tyre and bolt it up.
It is an exciting project, however, it takes 2nd place to getting a house comfortable. It was it a real state, having been abandoned for many years. It's in good shape now, but plenty still to do.
The mill is in France, not far from Lourdes. Despite being close to a main road, there are no services near by. IIRC, the cost for a small supply was around Ä60k (after a substantial grant) and more if you want to  inject. That gets the supply to the boundary, then there would be the costs for 100m or so to the mill.
There is what looks like a sluice control system on the wall. However, there are no actuators, just limit/open/close switches. If restored, this could control the frequency, but manual tweaking will be required to see how the system copes under load. The current electrical installation is basic, so it's not obvious what was previously connected. There are a lot of halogen lights around.
If I can drag my friend away from building, I'll go back over and we'll spend some time trying to get it spinning.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on February 15, 2018, 02:43:47 PM
A quick update. Opened the sluice and the water wheel turned.
https://1drv.ms/u/s!AjwyWSZbtvVcugz2aic36flbT_2P
Not the most exciting video, but you can see how out of true it all is. Internally, the spigot was running oval - about 5mm per revolution.
The speed is hugely down on the required 3.6 rev per second. Getting about 0.8 rev per second, which works out to ~11Hz. The race could have been more full - maybe another 30cm.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: knighty on February 15, 2018, 11:51:53 PM
I get a "sorry there was a problem playing the video" message


Title: Re: How big a shaft for driving a 20kW alternator
Post by: Westie on February 16, 2018, 09:19:44 AM
I can't get it to play online but it does download and play with VLC, it's an mp4 video.

The whole thing looks under bodgeengineered to me.  The main drive shaft looks undersized, if it had a bearing support just above the wheel it would be a lot more stable. Have you looked at the bearing arrangement under the wheel as it looks knackered to me or the shaft has bent.

 


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on February 18, 2018, 09:26:18 AM
I despair of onedrive. Even as the owner I can't get the darn thing to play. As Westie says, it can be downloaded (28M) and played as mp4, but to cut to the chase, you'll see a 1m diameter horizontal wheel with ~100mm run out, on a long vertical shaft moving side to side. The noise and vibration was impressive inside, but probably normal for a mill!
The wheel and shaft weighs a good amount and could be hoisted up, down and out. The thrust bearing is on a concrete pad and does seem to be knackered. I hadn't thought about a bent shaft.

The wheel is pretty worn too from use. It's not known whether this was from leccy generation or milling.
Anyone got any good suggestions on new suitable products. We get a 1.4m head and a flow of ~300 l/s. Can improve the head by maybe 100mm, and there is scope to improve the flow by widening the current overflow channel from ~200mm wide. The race is ~3m wide.


Title: Re: How big a shaft for driving a 20kW alternator
Post by: knighty on February 18, 2018, 10:40:09 PM
downloaded it (can't believe I didn't see the download link!)

watched it on repeat, it's hard to tell, but I think your bottom bearing could be causing a lot of your problems, if the problem was at the top of the shaft you'd expect the shaf to be constantly off to the same side/position - also if the problem was inside at the top it would (probably) be pretty obvious when you were standing next to it

does it have a bearing or a bush ?  a bush would be more fitting with the age

and I think water could be used for lubrication in some old bushs ?


Title: Re: How big a shaft for driving a 20kW alternator
Post by: jonesy on February 19, 2018, 12:45:08 PM
I see what you mean - it could well be a bush. It was lightly seized. It's not possible to see the bush/bearing with the wheel in place.

There was plenty of wobbling inside, so I did even wonder if there was a top bearing.



Title: Re: How big a shaft for driving a 20kW alternator
Post by: guydewdney on February 21, 2018, 08:15:53 PM
I think itís time for a low head turbine from our sponsors....