start up wind speed: 4' vs 10'

[defed]

it would seem to me that a 10' would start turning in slower wind than a 4' due to more blade area catching the wind...is this the case?  not talking about power generation, necessarily, just any old lazy blade spinning.

[DanB]

Yes, it does seem that typically, larger machines start turning in lower winds.

[Flux]

It's probably true to say that the bearing friction and grease drag loss has less effect on start up of larger machines but so much depends on the design.

Typically any ironless  machine will start below the wind speeds at which it produces power. This may not be true even for bigger iron cored machines and most small iron cored ones will not start to turn in winds much less than 10 mph. They won't very likely make any power in these lighter winds so it is not a big issue.

Blade tsr and design also is a big factor in the start up speed so it is hard to genaralise.

Flux

[defed]

i was just messing w/ my 4' piggott style, and even tho ppl recommended i not do it, i propped it up on a 7' stand to see what happens.  initially, i just put the blades on the bearing, thinking less weight to turn...but found that it turned better w/ the magnet disc on.  wouldn't even sag to the heavy side w/o the disc, and spins well w/ the disc and drops the heavy side.  i have gotten it to spin in moderate wind, at 7' height which is not GOOD wind, just curious how hard it is to get the 4' going initially.





 

[Rover]

Also depends on the number of blades, obviously. My 6' iron core has 3 blades and starts about the same time my 4'  6 bladed iron core does. (diferent pma's, different blade styles).

For both .. startup is a nice to see, cut-in takes a bit longer...with the smaller one.. quite a bit

[defed]

got all of the welding done today.  basically just need to make the 8x20 tail and then figure out how to mount it to a 20' test tower.  then maybe i can get some better wind and see what happens.

[ChrisOlson]

When my anemometer says 5.0 mph I can expect that both of my machines will be turning.  But the bigger one (13 foot) will stay turning even when the anemometer drops off to 2.2 mph while the smaller one (10 foot) will come to a stop.  So I'd say, generally speaking, that bigger rotors will start turning with less wind.

Both of them cut-in at around 7.5 mph but if the wind is fairly constant at about that speed it seems the bigger one will put out 1/2 amp or so pretty consistently while the smaller one fades in and out of cut-in.  So, once again, that indicates that the bigger rotor spins more consistently in very light wind.
--
Chris

[jlt]

My water pumper style mill starts at a much lower wind speed than my three blade wind turbines do.

[jberango10]

Hello every one, I'm Julius and I'm newbie here,..
I just want to ask if wind-turbine is a synchronous speed?

many thanks...


DamonHD note: potentially SPAMmy link removed.  Please don't post commercial links or keywords or links anywhere in your messages or profile until you've established yourself here.

[defed]

after having the 4' up on the test tower (still only 16' high), i've noticed that it seems to take alot of wind to get it going, but once it IS going, it seems to stay running in lower winds.  i just got my anemometer up so i can't say what wind speed it will start to turn at and what wind speed it reaches cut-in, but today in 8mph winds it didn't budge.

if i recall, Hugh says in his book that cut-in is 7mph.  i'm guessing that it DOES charge at 7mph, but only if it has a 15mph wind to get it spinning (speeds only a guess until i get some wind again).  is it 'normal' for a small 4' turbine to need more wind to start than actually charge?

i noticed in some of Hugh's old info, his blade specs for the 4' are wider.  seems like this would start up in less wind, so not sure why he changed them.  maybe the slimmer blades are better in higher winds?  i'm going to draw out the old and new blades and see how different they are...maybe i need to make another set.

[97fishmt]

Hello defed,

4' is not a lot of swept area.
Is it possible to build a 6'er
to match your alternator?

I tested my latest 6'er last
week and it started in lite winds
and put out some serious power
just on my small test stand (8' off
the ground).  I felt it was a good
match to the alternator.  I need to
get it up into clean air now and it
will be a good performer.

[defed]

i am going to make a 10' if i get my permits thru for a 50' tower.  the 4' is just a test/practice model.

i know it is a small swept area, which is why i am curious to hear the performance of others who have built Hugh's 4'.  i don't mind if it takes some extra wind to get going, as long as that is 'normal'.  i just don't know if i did something wrong or not!  with this model, i'm not using the power for anything, it will just be wasted.  i'm thinking that the blade area to weight of magnet disk ratio might be lower as well, which could make it start a little hard.  ie 4' blades sweep 13 sq ft for a magnet disk that weighs 5 lbs, where a 10' sweeps 80 sq ft for a magnet disk that weighs 15 lbs (don't know exact weights here, just making an example for my theory).

it was performing well last wkend when we had some good wind, but my anemometer wasn't up so i can't say what it was doing at what wind speed.  the wind hasn't blown a lick since! 

[defed]

97fish,

where did you get the specs for those blades?  the shape looks a bit different than the ones i made.

[97fishmt]

Hi

I just wing it now that I have had some practice
at building blades.  What ever wood is laying around
or I come home with.  Plan out a game plan and go for
it and see how it comes out.

I am doing just the opposite of most folks, I'm matching
a blade set to motors with different power curves.  So
I some times try for a compromise to work on more than
one motor.  I built that one with the pine I had laying
around and knew I needed more torque and less speed
for a few motors like this.



It works great. I have over a dozen different blade sets
with different sizes and profiles.  So I know what will
work for the different motor power curves.  Or at least
I play around and find out what doesn't work and what
works better.

[scoraigwind]

The amount of wind needed to start up a set of blades depends on the size and shape of the blades in relation to the friction.  It's meaningless to speak of the blades except in the context of what they are turning.  Obviously the 4 foot blades will have about 1/6 of the torque of the ten foot blades, and the bearings and seals don't have a huge lot less friction, so hence the 4 footer does not start quite so easily.  If there's enough wind to produce useful power it should start but if not then try removing the seal and using lighter/less grease.