windmill noise

[hall99m]

I have been running for some time a hugh piggot type 1kw axial flux windmill and have noticed it make a 'whine' when load it applied to it.  This whine gets louder as more load is applied.

What causes this noise?

Is it possible to reduce this noise?

Hall99m.

[TomW]

hall;

My first question would be has it done this from the beginning?

The several small units I have flown, including Zubbly conversions and Tape Drive units all of them produce this "buzz" or "hum" and it seems to be normal. I figured it is just part of producing power in the coils. In my case it is not loud enough to be heard at any distance. Something like a tower resonance may make it louder when the unit is at a certain speed.

Just some real world observation. Perhaps the engineer types can explain the in depth reasons for it.

Cheers.

TomW

[mikeyduk]

Hi Hall

I'll take a stab at this.

It is an effect known as "back EMF"

In short as you generate power the return current attempts to magnetise the coils.

This produces a resonating field acting on the rotor.

It's the reason why the more current demanded by the load tends to try and slow the alternator.Increasing Back EMF.

Conversely when controlling a motor using PWM at low speeds the armature can be heard to "sing" at the pulse frequency.

On the other hand I could talking out of my rear ,but I think it's basically right.Go here http://www.newton.dep.anl.gov/askasci/phy00/phy00351.htm For a read.

 Mike

[hall99m]

I use triacs to switch heating elements in sequence as the power from the wind varies.  The machine made this noise from the beginning, when the machine starts up and the first element is switched on the alternator starts to whine, this gets louder as more elements are switched on.  would some rubber washers applied to the stator mountings reduce this noise?

Hall99m

[Flux]

There is always some noise from the alternator but if it is at a reasonable hight it is normally only audible close to the tower ( noise transmission through the tower).

You have an unusual load condition and there may be some problem with unbalanced load or with turn off of the triacs chopping the waveform. Unless you have a scope I don't know how you can check for this.

If it is bothering you I suspect it is noisier than normal.

Flux

[hall99m]

If I was to connect up an ammeter to each of the three phases would that show any imbalance?

Hall99m.

[David HK]

One aspect that may deserve some consideration is the blade arrangement.

Are they homemade? If so, how well and careful was the sculpting of the blades done to follow the pencil lines? How accurate were the pencil lines to create the aerofoil shape? Are they aerofoils or something else?

Having done that, how careful and how much time was taken to set the blade tips up in follow-through alignment and then balance them?

This may come into the equation somewhere.

David HK

[hall99m]

When the windmill is running with no load there is no whine, when the first element is switched on the whining starts.

I have put an ammeter in each phase at a time and watched as the controller switches through each element in sequence.  All I can really tell is that one phase sometimes seems to be switching at a slightly different time and sometimes it seems to 'half' switch on.

Although having said this the windmill still gives a continous tone of a whine.

[tecker]

As the magnets pass over the coil under load the coil bucks as  higher voltage sinks into the lower voltage load and transmutes into  high current drive. It could be likened to a rock tossed into a pond.

You get the same noise if two like polls are driven in opposite directions . I 've measured the flex on the stator and can see no real movement .( a rough measure made with a stainless wire) . I would have to say that the noise is air expanding and collapsing around the approaching like poles . I don't want to seem like a flake ( even though I am ) but it's an unavoidable part of the process . You can lessen the noise by matching the voltage of your load ie impedance matching .

[Shadow]

I'm interested in your setup.Is this a hard system to build? What size elements etc? How much water can you heat? Lots of questions. Thanks

[Ungrounded Lightning Rod]

You have an unusual load condition and there may be some problem with unbalanced load or with turn off of the triacs chopping the waveform. Unless you have a scope I don't know how you can check for this.

You can check for waveform chop by putting a bypass switch across the triacs.  Turn on the switches across the activated triacs, shorting them out and hooking the heaters directly to the power source.  If the noise is the result of the triac turning on after the voltage has climbed significantly during each half-cycle, producing a steep current rise, this will substitute a purely resistive load for the triac-chopped one and the whine will disappear.

If that solves it, look into your triac's trigger generator to see why they're turning on late.  Or use relays.

Capacitors across the GENNY output may also help, by bypassing the high frequency components of the waveform so they don't rattle the coils.  But if big enough to mitigate the problem they may also load the mill enough to delay startup in light winds and/or increase I2R losses and heating, requiring earlier furling.  Hooking capacitors across the LOAD side of the trics or across the triacs themselves will fry the triacs.

[Ungrounded Lightning Rod]

The current in the wire produces a force between the (electrons in the) wire and the (electrons in the) magnet.

The current varies with the stage of the cycle, producing a varying force that results in a twice-line-frequency hum, and because it's not a pure sine wave it also has harmonics.

If your triacs are switching on a resistive load after the voltage has climbed significantly in each half-cycle, this produces a sudden rise in current, and thus in drag force.  This sudden rise represents energy at significant multiples of the line voltage.  Thus it produces a "whine" rather than a "rumble" when it yanks sharply on the coils and the magnets.

[Flux]

Yes, bypassing the triacs will be the best test you can do without a scope.

You may be able to add some form of resilience to the stator mounts but you will have to be very careful not to make it too flexible. I am convinced you have a chopped waveform problem but if the controller is doing what you want other than the noise then you could try mechanical means of reducing noise transmission to the tower. I doubt that the direct noise radiation from the alternator will be objectionable.

Triacs are not without their problems and you may have much more activity than you think. Snubbers of about .22uf and 47 ohms across the triacs may be worth a try but without a scope it is total guesswork.

Flux

[hall99m]

What are snubbers?

[hall99m]

What do you mean by impedence matching?

[hall99m]

I use the heat control circuits on hugh piggot's website.  I use ordinary mains storage heaers as loads for the generator, the controller switches on each element in sequence as the wind varies.

[Flux]

Capacitor and resistor in series used to limit the rate of change of voltage across electronic devices. In the case of thyristors and triacs they also hold the current above latching value momentarily in the presence of inductance and sometimes produce turn on when the device may not normally do so,

Flux

[hall99m]

I have tried directly connecting the alternator to the loads and there is no whine, only a slight hum.  I will try snubbers on the triacs and see if it helps.

[Flux]

You have confirmed my suspicions, If you can borrow a scope I think you will find that the triacs are switching rapidly at audio frequency. They are dreadful things and back to back thyristors work far better, but the drive circuits are even more demanding than for triacs.

You likely have a problem due to the source inductance of the load and also you likely have rather ineffective drive, those diacs, ujts and cheap short pulse drives are not totally effective. Usually you can get round the limitations near enough. Using snubbers for this is not standard practice but it often works well enough to get the stupid things on.

All this is simple at first sight, but detailed solutions are a bit more tricky.

Flux

[veewee77]

Does the whine increase with turbine RPM? If it does, then it is likely just the magnets passing the coils causing vibrations that are being transmitted through the tower, blades and other things.

If the whine stays at the same frequency, it is your controller making the turbine "sing" due to the PWM loading and unloading at it's operating frequency.

If your controller is just turning on and off (not PWM) the elements, the frequency should vary with RPM and that will be normal, but if it is excessive, I would look for several things.

Loose bolts, or weak (ie. lightweight) mountings.  Heavier mountings for the stator and etc will be harder to vibrate and radiate noise.  Lightweight ones will vibrate much easier and transmit that vibration through.

Hope you get it resolved. . .

Doug

[hall99m]

My controller is not PWM, it just switches the elements on and off.  It starts to whine when the first element is switched on and increases in pitch and loudness as the windmill speed increases.

I have tried directly connecting the windmill to the elements, bypassing the triacs and there was no whining, I could try putting snubbers across the triacs and see if it helps.

Hall99m.

[Flux]

If you are using Hugh's circuit at least you have decent drive to the triacs, the opto device keeps the gate drive on.

Very difficult to check any of this without a scope but first make sure the speed signal from the 2917 is clean, the 2917 is easily false triggered by spikes, the triacs may be messing up its output.

Also the comparator circuits may not be switching cleanly in the presence of interference.

Try the snubbers first. Not sure of your system voltage, the snubber resistors may need to be 3 or 5 watt rating if you have fairly high volts. The capacitors need to be polypropylene pulse types for long term use, polyester or similar may do for a trial.

Flux

[hall99m]

I have two triacs per load control circuit, I will include a file from my previous discussion on altering my load control circuits, could this be giving me problems?

My system starts to produce power at around 100vac, max of around 150vac.  I would need at least this value of capacitor and resistor wouln't I?

I have an ammeter in series in one phase to monitor current, could this be causing problems?

Hall99m.

[hall99m]

I'm sorry that didnt work, if you can look at my previous posting 'altering my load control circuits' this shows how I have my circuits configured.  Alternatively I could email the file to you.

Hall99m.

[kurt]

here is the link http://www.fieldlines.com/story/2006/1/21/192149/711

[Flux]

Feeding the opto coupler diodes in series should be perfectly ok.

Yes the snubber capacitors need to be at least 400v dc rating.

In the optocoupler data sheet I see that in the typical triac driver circuit the triac has a snubber, triacs are notorious for the lack of dV/dT rating so I would try the snubber route first.

If you can solve the problem with the first stage load then the same trick will likely work for each step.

Flux

[hall99m]

I will try the snubbers, I will let you know what happens.

Hall99m.