do my pelton wheel spoons need modification??

[mab]

hello all,

it's been a while since I posed on my hydro project, but it's proceeding slowly.

I acquired a pelton wheel on ebay - there's not much info with it but I think it's not quite right as it is. I assume I should aim the jet at the approximate center of the spoons, but the spoons are quite thick and the cut-out section is angled such that a jet aimed for the center of the spoons would be deflected away from the wheel by the next spoon intersecting the jet.

If I angle the jet so that it's parallel to the cut-out then the jet barely hits the wheel at all (with a 1/2" jet, a fair portion of the jet would miss the wheel entirely).

I've tried to show the issue with the pics using the ruler to show the angle the jet would have to be to avoid deflection.

I'm thinking I should grind some materiel off the backs of the spoons but wanted some expert opinions before doing something so irreversible.

[XeonPony]

your jet should be at a slight angle, that is how an impulse wheel works is by deflecting the water. you seem to have yours really densly populated but I'll let other state their opinion whom have more functional knowledge, but from my view all looks good.

[Flux]

That is an inherent problem with a Pelton. The notch is an attempt to reduce the deflection from the approaching spoon.

The normal blades are made with the notch cast in, yours for simplicity seem to have been machined in afterwards and it has affected the front edge of the spoons.

I really don't think it is going to be that significant. Just aim the jet at the divider just below the machining. You may have to play with the angle of approach of the jet but you will only get one spoon active at a time and as the next one comes up the jet will transfer to it.

I think you are stuck with it, removing material is probably not what you want, it looks as though more has been removed than ideal already. THe notch is normally narrow and the front surface of the spoons normally maintains it's edge whereas your front edge has been machined off on either side of the divider rib.

[mab]

OK, thanks - I'll try it as is then.

XP I did have a thought that it might work better if I remove every other spoon (at least I could aim the jet in better, but then I'm just guessing TBH).

[hydrosun]

I remember reading that it is better to have the buckets close together to ensure that the water is hitting at close to right angles. But more than one jet is hit at a time. So your pelton is built right.  The pelton on my Harris unit has 17 buckets on a 4 inch diameter wheel. The nozzle is aimed
at the tips of the buckets as long as none of the stream misses the buckets.
Chris

[Flux]

Yes the bucket spacing looks normal. If you leave alternate ones out not only do you have the problem of not working at right angles to the jet but you will reach a situation where the jet will shoot through and miss the buckets at certain parts of the revolution. To overcome this you would have to angle the jet in but I think the Pelton design has been around long enough for its ideal form to be established. Yours looks fine except for the machining away of ther lip of the buckets but virtually all the change in momentum takes place at the sides so it won't matter.

The notch lets your bucket reach the right angled position without being intercepted by the approaching one. Just beyond this point the jet transfers to the approaching bucket as it comes nearly to the right angle position. As Isaid previously on a single jet rotor only one bucket can be active at any time.

Your buckets seem near enough to me, although perhaps lacking the precision of a Harris or  Gilkes.

Flux

[mab]

Thanks,

I guess I'm thinking up problems that don't exist again (I do that sometimes). I'll run it as is and see how I get on  - with winter approaching I really need to get it in without bogging down on efficiency issues anyway.

[Harold in CR]

 Any updates on this project ?

 I just scored a Pelton on ebay, and will be rigging it to an alternator for playing with set ups, after the 20th of Nov. I only have 20 GPM during dry season, but,it has been fairly steady at 45+ GPM for the past 3 months and 2+ months still to go.

 Have to start gathering piping and supports for it, so I can get things working and adjustments made.

[mab]

err.. well, I'm getting closer - but not yet tried it.

Since my last post I've taken the generator, wheel and a single nozzle assembly down the their place by the stream, made electrical connections to the capacitors and cable back to the house, and today I connected the nozzle up to 100meters of 90mm penstock and lashed the pipe to various trees/rocks on the way down.

I've still got to run another 12m or so of pipe at the top end and construct a suitable collector/strainer, and my homemade PWM voltage limiter/diversion controller is not working as it was supposed to (I can't get it to ignore the sinusoidal waveform (200ish volts, hopefully, 40ish Hz ac), so it's trying to regulate to a constant amplitude - ie clipping the tops off the sinewave.

ironically, progress is being hampered by all the recent rains - there's a lot of water about, and mud and mosquitos.

[Harold in CR]

 Thanks for the update. I hear you about the rain, and bugs. We always have to battle the mud.

 I am going to build a dustpan shaped inlet to the 2-4" pipes I am going to drop down 25' to my turbine. I will build a "V" shaped roof of screening over the pan, so the debris rises and gets flushed over the dam. The Coanda screening site is no longer functional, so, I have to figure how to keep as much fine grit as possible from going through the nozzle. I will converge the 2-4" pipes into a "Y" and from there reduce down to 2" then down to the nozzle. Trying to reduce the friction loss as much as possible, and, keep from having a runaway when the creek becomes a raging torrent.

 I would prefer 6" pipe, but, it's hard to locate here, and, connectors are VERY expensive.

 I too have to lay out the best route and fasten the pipes very well.

 Keep us posted. I am following your progress.

 Harold

[keithturtle]

I would prefer 6" pipe, but, it's hard to locate here, and, connectors are VERY expensive.

Might flex be an option for you, Harold?  I'm not sure the extra diameter will make much of a difference at low flows though.   May be able to run a single piece making connectors a moot point.

http://www.goodyearep.com/ProductsDetail.aspx?id=2274

You'll be nowhere near the pressure capacity, and the stuff weathers well, at least it does in the midwest USA

Turtle

[Harold in CR]

 Hi Keith
 My first 100' run needs to be nearly level. I have to run out of the jungle growth to a ditch I cut through a hill. From there, it's all down hill for 150' to the creek bed, at the 25' drop. I doubt the stuff you linked to is even available here. It;s amazing the things that are available in the states, that these people have never heard about.

 It would probably be OK for the drop but, I need to channel the water to the elevation change first.  When the creek (spring) has a lot of rain running over it, it goes from 4'wide X 6-8" deep, to 30' wide X 2' deep, and then drops, right before the hill I channeled through. IF I don't do
this right, I could have a major washout cut through that hill. My ditch is 10' away from the creek bed, and,  about 6' above where the drop is at present.

 I'm going to pour a bag mix worth of concrete on the pipes (1 bag cement 20 shovels of gravel) and cover that over with dirt and grass clumps, and hope it pegs down during the dry season.

[mab]

I still haven't got the top of the penstock to where it should eventually go, but I decided to stick the end of the pipe in the stream where it is and see what would happen.

got about 33psi static on the gauge and tried spinning it up - didn't generate anything except a phenomenal amount of noise - like a foghorn - could here it from 200yds away, but I noticed that if I stuck my finger slightly over then end of the nozzle (to deflect the water in toward the center of the wheel) it was much quieter, so readjusted nozzle for minimum noise.

still no power but initially I thought the motor was turning too slow (I got carried away greasing the bearings - so there was a noticeable resistance in the rotor when turning by hand). Left it running for 10 mins and the rear bearing got slightly warm - so there was too much grease.

Had a bit of a think and felt my initial guess of the speed was out and that it should be generating after all - went back to the house and back fed the motor with 4amps d.c. for about 30 secs and went down an tried again  - motor picked up then suddenly dropped in speed like it was loaded - plugged in a lamp and it lit up!  Success!!

I've got a couple of DPDT switches between the 3 100uF caps and the motor:- one swaps the 2C of the C-2C between leading or following the C phase - sure enough the lamp was brighter on one setting. The other switch swaps one of the 100uF caps so it's either in parallel with one cap (100uF/200uF) or in series with the other (50uF/100uF) - the lamp was brighter with the 50/100 setting so stuck with that.

So I went back to the house to check my meters:- with a (230v) 120W lamp plugged in I was getting 150v, 27Hz.

the light was going so I has to go and see to the animals - got back 40mins later and it was now showing 38Hz but the same voltage - not sure why it's changed but maybe some of the grease has melted out of the bearings.

After a while I noticed the frequency had dropped a little and decided to go down the the genny and check things out. Got down there and I could smell something was cooking - genny was OK, but the metal box with the caps in was HOT! as I stood there the genny speed went up like it wasn't loaded anymore and the glow had gone from the window in the house  .

turns out those cheap chinese motor run caps weren't a good bargain after all  even though with a rating of 450v 60Hz they should've been OK).

Oh-well, at lease I know the system is viable, so I can justify the cost of some decent caps and some more pipe to extend the penstock (and some bits n bobs to make another two nozzles)  .

[Harold in CR]

 Sounds good so far. 

[mab]

Well I got my new (and expensive) caps about 10 days ago - and the genny works much better with them - I'm getting about 250w now. I've ordered the plumbing for another two nozzles but am still waiting for it.

Seems to work best at about 120v, 25Hz ATM - which is handy as I can use a standard 240v, 50Hz transformer to change voltages - if I have one with a high enough output voltage.

Trouble is I've gotten used to solar power over the years -  turning things on in the morning and off in the afternoon - so coming in in the evening, turning on the lights and seeing the gauges saying the battery is still charging seems unnatural.

I expect I'll just be getting used to it just when it breaks down.