El Cheapo mk2 - problems

[coldte]

Hello, since my last post i have reworked the alternator ,it is now 3 phase 12magnet 9 coils @ 275 turns each with a resistance of 4 ohms / coil and 24 ohms / phase to phase.Installed on tower it turns very well.Problem after reading the board and with help from several posts i worked it out that maximum speed at 10 mph around 100 rpm , seemed about right so connected up and attached multimeter and seemed ok starts generating immediately it turns and reaches 12-15 volts at around 30 rpm or so (i have no speed sensor , just a guestimate), wind at the time very gusty around 10 mph.Had a switch on battery connection and after switching on lost all power or at least it seems that way. checked all day in same conditions,always same even at 25 - 30 volts ( approx 80 rpm) as soon as connected a huge drop in voltage and reduction in speed

Am i expecting too much out of this machine at low revs or is it something i have overlooked ;example too much load.

Input / insight on problem greatly appreciated.

Regards

coldte

[s4w2099]

You dont give any info on the size of your prop but for a 12V machine thats too much resistance.

Also looks like its stalling, better Google search the board for the term "stall" and document yourself about the issue first.

[windstuffnow]

  I'm assuming the blades are about 2ft tall, I don't believe you said in your last post... Your expecting alot from a 6 sq ft turbine in a 10mph wind.  I'd say if your getting 3 watts from your rendition of the Lenz2 machine your doing good.  My 2ft x 2ft does 8 watts in a 10 mph wind and it has all the trimmings and fine tuned wing angles.  The 24 ohm stator is most likely eating up most of what the shaft is producing in power.  Something in the range of 1 to 2 ohm would be my goal for that small of machine running 12volts.

.

[s4w2099]

ohh, vawt, never mind me then.

[electrondady1]

what are the dimentions of your magnets?

why have you placed the concave side of your wings on the outside?

[coldte]

Hi ed ,

Thankyou for your prompt reply ,its appreciated .

The wings are approx 3ft long and i have added the winglets as you suggested ( not pretty but seem to function ok )It appears much as i suspected the stator resistance is to high,producing the volts but with little current.

If i doubled the size of wire to 0.75mm will i have to have the same number of turns or can i get away with less.

Unfortunately the average wind speed in this area is about 7.5 mph but we have the usual ups and downs, i am as you mentioned aiming for a small charge of about 1-2 amps if possible at 12v.

Dont know if you read my last posting about my venture into naca profiles for my boat rudder and the success i had with it at low speed ,i wondered what you thought of the fish like tail arrangement i used and if it would transfer across with any benefit.

Knowing you are into planes a bit ,i read somewhere  that on wings they sometimes raise or lower small obstructions to improve airflow over the wing ( i do not mean ailerons), any use to us?

thanks again

regards

coldte

[windstuffnow]

Hi Coldte,

  With a small machine and low wind your really dealing with an efficiency battle to extract any amount of power.  The machine itself has to extract energy fairly well to begin with and the alternator needs to be as efficient as possible to convert the mechanical energy to usable electric.  Unfortunately, this conversion process uses up a considerable amount of power from the shaft.  For instance, in a 10 mph wind with a 10 sq ft turbine there is about 30 watts available to be extracted.  If the turbine is running say 35% efficient in extracting the energy then you have 10.5 watts available at the shaft.  Now if you put an alternator on there that is say 50% efficient then you'll most likely get 5 watts not including wire run losses, bearings etc.  So the best thing we can do is make either the turbine or the alternator more efficient.   In your case, right now, the alternator would be the best place to start.  Once you get an alternator that will be fairly efficient you can tweak the turbine and measure the results.  

  In order to achieve the 1 or 2 amps you'll most likely need a taller turbine.  Get the alternator up and working well and you can always add taller blades or another identical turbine stacked on top of the one you have to increase collection area.  

  Some of the other mod's such as adding slats on the nose or flaps on the trailing edge may or may not help depending on the design of each.  I thing the gain, if any, would be very small.  The alternator would be the best attack for maximum output.  Keep the cut in speed at or around 50 rpm and the resistance in the alternator very low.  At 2 amps output 7 ohms would be the 50% point so you want to try for around 1 or 2 ohms to keep the efficiency in the 70% or above range for your expected output.

  .

[vawtman]

Hi Colte

 You seem to have the knack on how a vawt operates now and all thats needed is an improvement in the design of the blades.The only thing in my opinion that lets it spin is that little nosing.Not much power(torque) in that.

 Sorry if i seem a bit harsh.

My early turbines were less elcheapo than yours and didn't spin.

Hang in there.

Mark