Humming noise at cut in

[zvizdic]

Basically whats happening is the windmill is making a humming noise at cut in. Here are some specs on the turbine:

-standard 10 foot windmill
-wound for 48 volts with 130 turns per coil, 16 AWG

I want to know if anybody has experienced this humming noise right at cut in, Im pretty sure that it has nothing to do with noisy blades because I left them unloaded at the moderate winds and it never made any noise. So that eliminates blade shape and left me thinking it has to be something with the alternator so I experimented with the higher voltage bank and as I put the fifth battery, 60 volt nominal, the humming noise went considerably down. The windmill is close to home and the the sound bothers us at night. Any suggestions would be gladly appreciated.

Thanks!

[SparWeb]

Three things:  it could be normal.  All generators make at least a little bit of noise.  When the current flows in the coil it causes a magnetic field of its own which pushes on the magnets.  The force varies with each magnet passing a coil so the result is a vibration.  It's not usually large until a lot of current flows.
Then again, if the noise is strong and there is evidence of large vibration, then the noise could come from a shorted coil, crossed leads, or maybe a backward coil.
Another reason for noise could be that the stator isn't centered or has come loose.  Once the magnetic forces kick in when current flows, it makes the stator move.

All bad things but if it's turning and making useful amounts of power then you likely don't have the electrical problems.  Try this: measure AC voltage across each of the 3 phases.  If the numbers come out nearly the same, then you probably don't have a problem with shorts or flipped coils.  Try this below cut-in and above cut-in if you can.  If you find no electrical problems but the noise is quite loud and/or getting worse, take a pair of binoculars and look carefully at the thing, or take the tower down to inspect more carefully.

I wouldn't use 5 batteries.  Not much that you can hook up will be built to handle the 72+ volts you're going to see when they're fully charged.

PS:  Last year I had a little generator that made a lot of noise when the temperature was below -40C.  It turned out to be a bearing noise because the grease in the ball-bearing was too hard at that temperature.
It was a squeaking/scraping noise, but it had a cyclic frequency that didn't equal the rate of rotation.  It took 3 or 4 turns for the sound to repeat its cycle.  That's how I figured out it was a bearing problem:  The balls in bearings go around once for every 4 revolutions of the inner race.  Obviously the bearing was shot after a few months of skidding like that.

[freejuice]

LOL believe it or not is your tail a bit too heavy?
 The tail on my 17 footer is and at cut-in, or slightly above it makes a noise...but not very loud... it sounds like that  native Australian wind  instrument...I can't even begin to spell it.. The vibration is at the moment of cut in...It goes away with a bit higher wind speed.

[cdog]

My 10' makes noise when it first hit cut in, untill about 15 amps, it resonates down the tower, always has, three sets of blades two bearings and three stators, i think its the nature ov the beast?

[BruceDownunder]

Yesceramic magnets didn't have that noise..

Bruce.,,, I retrofitted Neo's to a twin F&P (fisher and Parkel washing machine permanent magnet nmotors() ,, and yes the growling noise was evident at low and take off speeds,.. After that , the growling went away  ,,but came back on slowing down .. Annoying ,, ..

The ordinary

[BruceDownunder]

Well,,, that last post got stuffed up a bit ,,,must be all the flood water in my lappie ,,,I'll take it ouside and give Eh   ashake ...

Drowned down undar....

[cdog]

I have wondered if filling the tower with foam or wrapping rubber or some sort of damper on the outside would work...

[Flux]

All alternators make some vibration, which equates to noise. Some are worse than others and working through rectifiers aggravates the situation. At cut in the windings are carrying short pulses of current and these cause noise. Problems are far worsde if this frrequency happens to hit a mechanical resonance.

If it was not as bad with the extra battery then you may be on or near a mechanical resonance. Sometimes changing things like stator mountings can move you away from a resonance. Not so easy to do unless you can get the thing on a bench test, trial and error lowering a machine amy be time consuming. You will never get rid of all noise but if it is only at one speed then it seems to indicate you may have a resonance.

You may be able to damp whatever is causing the resonance, it may even be something on the tower, but it will be very hit and miss.

Noamally the thing is far enough away for the usual noises not to be a nuisance and in the old days before neo and stalled operation blade noise masked virtually everything else.

The only electrical trick I can think of is to add a big choke in series between the rectifier and battery but few will have such a thing handy. it has to be big to have much inductance without adding excessive resistance. It certainly makes things much better on single phase machines but with 3 phase the issues are usually much less. You could check your 3 open circuit voltages for balance, a recersed coil would cause a big unbalance and your region near cut in may be in single phase mode. If phases are balanced there is not much else you can do except fit double glazing to keep the noise out.

Flux

[jlt]

And don't forget the tail,they seem to amplify the the noise.I have found that wood has less vibration than steel or aluminum.The 5 phase  machine i built was totally silent. But the three phase machines have made some noise right at cut  in speed.If all-else fails. you could make a new stator with ten coils. that is how the Hugh Piggot    . Machines were built. My house Is close to some railroad tracks.  but I can verily here the trains. I have triple pane windows. helps a lot with the sound . In the summertime. the sound is very loud with windows open.

[DanB]

Just to say lots of the things everyone else has said here...

- it's normal, but the hum from a 10' turbine in my experience is not loud or unpleasant.
- The tower design could enter into it - if couplers can rattle, or... if you do like me and build towers from thin walled large diameter tubing, that can make it worse.
- I would not play with higher voltage, 48V is useful - higher voltage won't work well with most inverters and stuff you need to have in your system.  Plus - higher voltage lets the blade run too fast and might mess with furling.

The tail can definitely pick up some of this noise and act as a sounding board.  Often times (I normally use thin wood for the tail) I caulk between the tail vane and the boom, that helps sometimes.

As flux said, you might experiment with ways of damping vibration at the stator mount.

It's normal though.. if you think your 10' turbine is bad, you should hear my 20' turbine with the 10" diameter thin walled tower...at cutin it sounds something like a distant WW2 bomber flying around!

[zvizdic]

All alternators make some vibration, which equates to noise. Some are worse than others and working through rectifiers aggravates the situation. At cut in the windings are carrying short pulses of current and these cause noise. Problems are far worsde if this frrequency happens to hit a mechanical resonance.
Flux

I am afraid that the phases are not balanced and that is causing it. 130 turns does not mean that each coil has the same amount of copper.
 Perhaps adding to the resistance of one leg or two to balance the phases and remove noise.

[zvizdic]

It's normal though.. if you think your 10' turbine is bad, you should hear my 20' turbine with the 10" diameter thin walled tower...at cutin it sounds something like a distant WW2 bomber flying around!

That would be a good description of the noise. But we are here to perfect this machine to be reliable and quiet as possible.
 It does not bother me,  I rather love that sound because I do not need to go to the garage to see whether is charging or not.
But when the wife does not like then you have to find, a solution or shut down at night.
It is winter and I have no desire to take off the alternator on this cold. I see that this is the case with many turbines and was kind of normal.
 In the spring I might try doing tests on lathe.
Here are a few pictures:



As you can see in the picture stator iron inserts, which allows me to tighten the stator very good. Inserts have several channels on it that keeps them well-fiberglasst.

[electronbaby]

Judging from the picture, it appears that your stator brackets are longer than normal. This may be allowing more torsional vibration induced into the bracket and therefore becoming audible from the ground. Most stator brackets that I have seen built, (or built myself) have been relatively short and support the stator from right behind the main bearing shaft. Your design looks like it supports the stator from near the vertical yaw tube. May not be a big deal, but I would think this would allow more torsion and vibration at the stator due to flexing of the mounts. They do appear to have good "stays" welded horizontally between brackets, but this will do nothing for reducing the torsion on the bracket (unless you add a 45 degree diagonal gussets between your original stator support brackets.

 I may be wrong and it may work fine for you,.....just my two cents :-)

RoyR

[Volvo farmer]

It might be an optical illusion, but the spacing of these coils appears a little off.

[zvizdic]

Good observation is the key to problem solving.This may be the reason.

 More eyes and brains are more likely to solve the problem.

Looks new stator will be my next project. But no more 9 coils.

[keithturtle]

it sounds like that  native Australian wind  instrument...I can't even begin to spell it..

The didgeridoo?  That's what my neighbors 5kw Bergey sounds like in 20 mph+ winds

It sound like watts to me

Turtle

[scoraigwind]

Alternators pretty much always make a slight hum or droning noise.  I usually like it.  It's a gentle music.  But occasionally it can become intrusively loud.  More often it gets loud on grid tied machines.

One option that has not been mentioned yet is to mess with the bearings a bit.  Tightening or loosening the bearings can alter the resonance of the alternator and alter the way it sounds.

If it's a low growl then you may have unbalanced phases.  If it's higher pitched then it is just the ripple from the 3 phases.  Using five phases will make this higher again and fainter.  But a little song is normal. 

In the old days when I used 'dynamos' which americans call 'generators' producing DC directly then there was no generator noise, but since then every alternator machine does have a song to sing, whether homebrew or manufactured.

Try adjusting your bearings.

[freejuice]

it sounds like that  native Australian wind  instrument...I can't even begin to spell it..

The didgeridoo?  That's what my neighbors 5kw Bergey sounds like in 20 mph+ winds

It sound like watts to me

Turtle

 Yes that is the instrument and it it happens at cut-in or slightly above it, after a few more RPMs it completely goes away.
Actually it is a pretty cool sound and not very loud to be a pain.


Since I need to reduce the tail weight a bit  I thought it would dissapper...oh well we shall eventually see.
 All the best,
 Gavin

[jlt]

I noticed your mill is very close to your house and has three guy wires. are any of the guys attached to your house? That would really amplify the noise. 

[poco dinero]

Mine don't just hum, they absolutely growl.  Sound like a deep-throated big block V-8 with glasspacks pulling a heavy load about a half mile away.  Sounds like money to me.

poco

[piglet2]

Poco, it might be the tin tail that vibrates?

/piglet

[TomW]

Mine don't just hum, they absolutely growl.  Sound like a deep-throated big block V-8 with glasspacks pulling a heavy load about a half mile away.  Sounds like money to me.

poco

Yeah, all 3 of my turbines sing their own song as Hugh mentioned earlier in the thread.

They are all different designs held on different structures from short 4 legged towers to tall  4 legged tower of a water pumper
lineage.

My 12 footer is on a 6 3/4" steam tube pipe type tower and is the most audible probably due to its size and the big resonating chamber created by 40 feet of tube holding it up. Generally, it is music to me but gets tedious occasionally.

I think of it as my audible power production monitor.

The sound of power being made as it were.

And, yes it can sound like a motor working at a distance especially if the wind is blowing the sound towards the listener. Only hear it inside if windows are open.

Just from here.

Tom

[zvizdic]

I noticed your mill is very close to your house and has three guy wires. are any of the guys attached to your house? That would really amplify the noise. 

Yes  is close to home and no cable is connected to the house.
Struck me this morning, with -20 C  the ground is rock hard and transmit sound.
It became louder as it went some colder. Another idea is to install vibration isolation.

[poco dinero]

Posted on: January 18, 2011, 08:43:53 AMPosted by: piglet2 

Poco, it might be the tin tail that vibrates?

/piglet

 

Can't imagine the tin tail making that deep-throated of a noise.  Besides, it doesn't growl seriously until the output reaches about 1500 watts.

No, I think it's the alternator growling.  It might be magnified by the steel shell of the 56 foot monopole tower.  Big steel tube, 3 inch diameter at the top and 24 inch diameter at the bottom.

I don't mind the sound.  It's 250 feet from the house, so you can't hear it there.

poco