Measuring RPM's up on the tower?

[MickS]

At the moment I have 3 differing gennys flying.

Even the one that destroyed the blades (500 watts with hard drive mags) when the tail blew off in a storm has been repaired and is running well.

My biggest hastle at the moment is that I do not have any accurate method of measuring RPM's up on the tower, so I am guesing when I make any mofification that there is any improvement of if I have made things worse.

I have a digital frequency meter which works well on electronic circuits but gives very confusing results whatever way I try to use it on my gennys.

If anyone has ideas on suitable test probes, connection methods I would be very grateful.

The attached pic fyi is my furling design that has been up and running for 2 years now and has not been dropped.

It is getting a bit ragged looking on the fins so it might come down some time in the next year or so and get some stainless fins instead of aluminium.

Mick S

[Flux]

If you have a true digital frequency meter then you are unlikely to make any sense of the speed of an operating wind generator.

Most of the multimeters with frequency range will do the job, but I suspect they are just f/v converters not digital time interval meters.

In almost every case you will need some sort of filter to have any chance of measuring frequency of an alternator connected to a rectifier. You may measure the thing on open circuit without a filter.

A filter consisting of 47k in series with .22uf across the meter terminals is usually enough to clean up the waveform so that you measure the fundamental, not the harmonics.

Flux

[ptitchard]

Sorry can not help much on measuring RPM but am interested in your furling mechanism.

I can not work out how it works . I am assuming that it is not a tilt back system and therefore must be based on turning moment being balanced by the rotors.

Is the other tube linked to the arm to act as a counterweight?

Any possibility of more pictures or diagram?

PS. There have been numerous posts with people using bicycle speedo's to measure RPM.

[Nando]

Though you request help, you do not indicate the equipment you have supplying the power.

I presume that when you mean up in the tower, you mean you down and the mill up.

;>0}

seriously, Flux remark with the low pass filter ( 10 milliseconds) may remove the charging spikes from the line, sometimes you may increase the time constant to have better results.

Another way is to use a current transformer, a home made is OK, like take a 20 or so watts transformer and place ONE turn in the core and place it in series with one of the 3 phase lines and load it ( using the 110 volts winding = 10 ohms resistor, wattage around 5 watts), the wave form may be distorted but you may be capable of reading the frequency and the current at the same time.

Nando

[MickS]

Thanks Flux and Nando for some ideas.

Yep Nando, its a 3 phase axial flux setup with it up in the air and me on the ground.

I like the suggestion of a transformer in series with one of the phases. I will give it a try.

To answer Pritchards question about furling here is some extre details.

I wanted to try something different other than the conventional 'tail' pointing out the back method so this is what I came up with and it seems to work quite well and handles storm force winds better than the usual furling method.

Basically it works like this.

The whole thing is mounted on a stub axle mounted vertically on the pole. A vehicle hub is mounted on the stub axle in the usual manner. Two brackets are bolted to the hub and sit up vertically.

I have installed slip rings onto the rear side of the hub. The brushes are mounted here also. Since it has been up I have not needed to replace any brushes.

The 3 phase is rectified at the genny so I only need 2 slip rings - I use 2 brushes per slip ring - for safety in case one of them breaks etc.

The genny sits between these two vertical brackets with a bolt passing through brackets and genny mount. This allows the whole geny to rotate in any direction around the mast pole and also lift up so that blades become horozontal to the ground (thus furled to the wind).

The stainless steel pole hanging down is the tail.

The side surfaces of the tail are pushed by the wind so that the blades always face into the wind. The fact that this is also a down wind setup also assists with pointing into the wind.

The front face of the tail surface is push harder and harder as the wind gets stronger and the whole genny pivots up and the blades become more side on to the wind, thus reducing the force on them.

The tips if the side fins are curved so that as the tail lifts, there is extra force sideways to stop the genny rotating out of the wind due to gyroscopic and other forces.

The pole on top is welded to the genny and acts as a counterweight - see even the roll of leas flashing on the knob on the end to finetune the balance.

This pole being long (i've experimented with its length also) seems to have a stabilising affect on any sudden motions of the genny in gusty weather.

I am very happy how the whole thing works and it is the only one I dont worry about when there are storms.

The stronger the wind gets the higher the tail lifts - it just sort of streams out behind, a bit like a kite tail.

All the movements up and down are quite gentle once you get the balance correct so there is no violent thumping or banging going on so the chance of breakage is reduced.

Sorry this is long winded, but I dont know how else to explain how it works.

Mick S

[ptitchard]

Thanks for the explaination of the furling system. I missed the fact it was a downwind, tilt up system. This seems an easier system to adjust and setup than the standard tail boom.I have my generator down at the moment converting to a duel rotor from single rotor I may consider a furling system change at the same time.

[A Ramon]

Don't know if this helps any, but I found this post with some informative wind turbine specifications.