Spring Scale Fun

[vawtman]

The turbine will start spinning when the gauge reads 8lbs,windspeed~around 12 mph.

The pulley is 12in and the belt covers half of it.

 Am i getting any usefull info here?Fun to watch the gauge.

 If i let it freewheel to 120rpms the gauge reads over 30 before i can start slowing it.

 The scale and belt were set so that the reading was 0 and snug.

 Heres some pics.

 Thanks

[Flux]

I don't understand the first picture.

In the second and third you seem to be using the belt as a rope dynamometer. You need two spring scales, one in each side and the force you need is the difference between the two.

Taking your figure of 30 lb as a best case ( will be less when you extract the pull in the other side) that gives you about 250W. I am not sure if it is sustained or whether you are removing the inertial energy. you need the speed and load at the point that it sustains motion.

Certainly on the right lines, keep up the experiments. Try it with the second spring scale. I find a simple wooden brake clamped round the shaft infinitely easier to read under varying conditions but it can be done.

Flux

[vawtman]

Hi Flux

 The first pic is steel tubing attached from the tower to the blade in a attempt to measure startup torque.

 Back to walmart to get another.You realize this is gonna cost me another 5 bucks!!

 Kidding

 How could a wooden brake on the shaft stop it when i cant with 2 hands.

 Would you please do a drawing when you can.The shaft is 1 1/4in

 thanks.

[windstuffnow]

  This is what Flux meant by using a board as the brake, it's very controllable by tightening the thumb screws or loostening them which ever allows it to run continuous while getting a reading from the scale.   The double spring system works quite well also, just have to calculate the difference between the two springs and the arm length to get the torque.

Do you have a way to measure wind speed, rpm and torque at any given moment?  That information would make it easy to match an alternator to it.

.

[vawtman]

Hi Ed

 Thanks,I understand now

 At its current testing sight the wind is all over the place.Today probably 0-40mph.

 Windspeed i think im a good guesstimator at and would not overblow things.

 Rpms i just count since the blades are visible when dragged down.

 Torque is what im trying now,right.

 Thanks alot and gonna build your drawing.

[thefinis]

You are getting there but you are going to need a way to measure wind speed. Even with an anemometer if there is lots of turbulence and gusts you may have to guess at an average wind speed. I bought one they use for wind surfing pretty cheap. For my brake I used a 2x2x18 with a bolt on U mount from a car's suspension and cut out the bottom of the rubber bushing to about half the shaft diameter. At 1 ft out from center drilled a hole to attach my spring scale(needs to pull at 90 degrees from the board). Count rpms and watch scale keep adjusting bolts till you find the sweet spot where lbs of pull times rpms equals the biggest figure (at a given wind speed). Now you need to know the the wind speed this is taken at if you want to know what it will do at other wind speeds like 10 mph or how good a job it is doing of converting the wind power available. The difference in a 7 mph wind and a 11 mph one may be small on how it feels but have great effect on how the results show efficiency.

My setup worked fair but could not get a good enough reading on wind speed as I was too much in the trees and it tended to vary greatly every few seconds which of course makes the rpms vary with it especially when lightly loaded. Once the pull/lbs was set by tightening the bolts it tended to stay fairly constant between adjustments even with rpm variations. Quite a sight as the spring scale and rpm gage were about 10 ft up the tower and I was measuring wind speed by climbing on top of my pickup cab and trying to average the wind/rpm readings back and forth over and over. Ed's wings overpowered it. They would slow a little as I tightened the bolts and then roll the rubber up and spit it out. They did it no matter what I tried even stopping the turbine and tightening the bolts all the way down, that time it spit the rubber out in 3 pieces. They died in a wind storm before I ever got another brake set made.

I have been grounded till I finish spring planting and catch up on much needed paperwork.

Finis

[electrondady1]

 like vman i have struggled with matching the alt to  the mill.

 ok ,this is the best explanation i have seen so far .

this tester device will give ft.lbs of torque readings at motion( or at rest at specific positions).

if i can measure the windspeed and rpm and torque required to stop or what the mill is capable of resisting while turning.

i'm hopeing you could  carry it to the next step and with this data  explain how a alternator could be configured to match  

i don't understand how a second spring scale, as flux has  suggested could be hooked in.

[Flux]

Hope this works.

You need tension in the belt to give grip, that tension is common to both so you need the difference in scale readings to give the force due to torque.

In this case the torque arm is the RADIUS of the pulley.

Flux

[Flux]

Thanks, you confused me when you said that it started spinning when the gauge read 8lb, I thought you had some form of brake in the beam.

Thanks Ed, that is a far better drawing than I could have done.

flux

[Norm]

Here is the way I would do it, pick a day when

you have a nice steady wind or else use a wheel

from a car for a flywheel to average out the

wind speed, then use the 2 spring system,

(Prony brake)then gradually apply the brake, at

a point where you get the biggest differental

reading is your maximum torque at that average

wind speed.

   Now to duplicate that amount of torque per

minute.

   Take your alternator or whatever, hook it up

to the battery to be charged, put a 4 inch drum

on the alternator shaft ( Pi x 4=>1ft.), then an

adjustable weight...like a bucket or barrel of

water attached to a rope wrapped around the drum

that unwinds and turns the generator at a certain

speed, keep adding more water until it will

match the ft.lbs of torque per minute that you

got from the Prony brake.

         Spring and weight fun !

       (  :>) Norm.

[jimjjnn]

Flux. Souldn't that be DIAMETER instead of RADIUS of the pulley?

[windstuffnow]

  I believe the radius would be the correct value to use since the torque or pull is actually on one side.   The radius would be the "arm" length.   Some of the small ones I've built like this I've always used the radius for calculating output.  

.

[Flux]

No , it should be radius, that is why I put it in capitals.

I scrounged the picture from somewhere and I have no idea why the pulley has D on it, I thought it might confuse.

The force boils down to one acting on the radius of the wheel as in any other torque measurement.

Flux

[wdyasq]

I think it was a part label - "D: RPM guage" or similar.

Ron

[vawtman]

Hi Ed

 Could i make that out of hdpe?

 Love to play with the stuff. Is it too slippery to get a accurate reading?

[vawtman]

Thanks Flux

 Wondering something,if i use the 12in pulley with a belt matched for it,How does the friction of the belt and pulley factor in?If it was just on the shaft there would be less friction loss.Am i right or way off base has usual?

 

[windstuffnow]

  The idea is to add enough friction on the shaft to pull the spring scale to get a reading while its running at a specific rpm and load so you can calculate the output of the machine.  Either the belt/dual spring or tension arm type prony brakes are designed to add a force to the shaft to calculate this.  To much friction will simply stop the machine not enough and it will allow it to run free and you wouldn't get an accurate account of what the machine is doing.  

  The thumb screws allow you to apply a controlled amount of friction to the shaft while reading rpm and torque.   With the belt over pulley type you would need to be able to adjust the spring tension in an at rest stat as needed to get it dialed in.   It's best to use a flat belt ( a leather belt that holds your pants up works very well ).   In either case the resulting numbers would be the same.   In order to get it correct you'll still need a way to measure wind speed, rpm and torque at any given moment for an accurate accounting of what the machine is doing.

.

[vawtman]

Thanks Ed

 How did you know i needed a belt to hold my pants up.Your right im hipless.I understand that friction is what were measuring but if you apply friction over a small area(the shaft)or the 12in pulley(big shaft)struggling with the accuracy of measurements between the two.

 The v belt seemed to cog alot.

 Off to a new setup.

[RP]

The friction of the belt and pulley is what you want.  That's the load you are putting on the mechanism.  The friction from the slippage will cause heat thus dissipating power from the turbine.

You could use a greased belt but then you'd need a bunch of force on the spring scales to get friction or a dry sticky strap of leather in which case you'd need less force on the scales.  In either case you subtract the force on scale B from scale A leaving you zero... until you start turning the shaft.  

Let's say you have the shaft spinning in a stiff breeze at 100rpm with the belt slack.  You start tightening up the belt until your rpms fall to a reasonably steady 50 rpm.  You read the scales and find that one of them reads 8 pounds and the other reads 30 pounds.  30-8=22lbs. Multiply this by the radius of the wheel in feet and you have torque in pound feet.

Multiply the torque by the rpm and divide by 5252 to get Horse Power and divide HP by 746 to get watts.

Now try slacking up the belt some to drop the torque but the rpms increase.  If the torque drops by 10 % but the rpms increase by 30%, then your total power in watts has increased by 17%.  

On the other hand if your torque drops by 10% but your rpms only increase by 5% then your total power has dropped by 5.5%  Any given turbine will have an optimum torque and rpm for a given windspeed for maximum total power out.  This where Tip Speed Ratio comes in.

This is the heart of matching the alternator (and the load) to the turbine.  Part of the trick is trying to design things to be as max as possible over the full range of possible windspeeds and (usually) preferably in the most common windspeeds

Hope this helps.  I'm sure someone will jump in if I got this seriously wrong.

[rossw]

and divide HP by 746 to get watts


....


I'm sure someone will jump in if I got this seriously wrong.

I'm sure you meant "MULTIPLY horsepower by 746 to get watts"....

[Flux]

The  "V " belt is not ideal, it is intended to wedge rather than slip. It should work but may not be as smooth in action as you would wish. A piece of natural fibre rope that fits to the bottom of the pulley groove would work far better, especially with such a large diameter pulley.

Leather works well on a flat pulley, if you have a source of round leather belt as was used on Singer sewing machines that may work, but sisal or hemp rope is fine.

Flux

[thefinis]

I keep thinking of going to suspenders.

On one you use the radius of the shaft on the other you use the radius of the pulley.

1" shaft use .5 in on the 12" pulley you use 6 in when figuring the torque. It is basicly an arm or lever from the center of the shaft to the outside edge. The 1" shaft will take lots more tension and may try and burn the belt because of the small area of friction but both should be fairly accurate if you can get an even slippage. Try the smooth rope Flux suggested cotton if you have one.

Finis

[vawtman]

Howdy Finis

 Now that i understand how the formula works i may have had the perfect setup right under my nose.

 Remember i had that 24in exercise bike flywheel on it at one time.I still have it and and also the nylon band and the control lever from the bike.

 Gosh darn it

 Thankyou and everybody.LOVE THIS PLACE

[RP]

Dohh!  That was a big goof.  Thanks for catching that.  :-)

[thefinis]

That seems to be the way it goes. You go to all the trouble to build a part especially for a project and then find that you had something that would have worked in one of the piles of spare parts.

I still have a set of your wings that the wife wants me to put back up but if I do I am going to go to 8 ft diameter like your have. I am tower poor at the moment and a bigger tower is my next project.

Here is a link to a whole page of vawts from different companies with lots of different types and setups. I enjoyed looking and it gave me some ideas to try.

http://peswiki.com/index.php/Directory:Vertical_Axis_Wind_Turbines

Finis

[vawtman]

Finis,

 I think at 8ft diameter it will run much better.When you spread the blades out over a larger diameter(13ft) the turbine will be slower rpm wise(unless you increase the solidity) and more wind just blows through it.Sure the tsr is there but the speed to the alt isnt.In my opinion.

 By the way i sprung my spring scale the other day when the vbelt locked up somehow and snapped of the screw that held it and it went flying oh well it was cheap.

 What about 3 power poles if you can scavenge them up?Doesnt seem like you need to go that high from pics ive seen of your sight.

 Good luck with your planting.