Author Topic: Air gap  (Read 3211 times)

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NeilMan

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Air gap
« on: March 27, 2009, 12:30:16 PM »
 If one reduces the air gap on the 10' home brew genny, will it make it harder for it to start up in low winds, Only asking because most of the time I have to kick start mine with a 9v battery. I have mine up around 30ft, open fields all around so there's lot's of wind.


24 volt machine

#14 70 +- turns

1x2x1/2 n42


Thanks

« Last Edit: March 27, 2009, 12:30:16 PM by (unknown) »

luv2weld

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Re: Air gap
« Reply #1 on: March 27, 2009, 08:43:20 AM »
There could be several reasons----

Bolts vibrated loose on stator causing rubbing

Nuts holding rotors vibrated loose causing rubbing

Bearing on hub adjusted too tight

Grease in hub frozen

Ice build up on rotor/stator


Has it ever self started??? Is this something new that just developed????

Have you checked the rectifiers to make sure one is not shorted???

Does it work properly after you jump start it???

What tests have you done???

Please give us all the info you can.


Ralph

« Last Edit: March 27, 2009, 08:43:20 AM by luv2weld »
The best way to "kill time" is to work it to death!

mbeland

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Re: Air gap
« Reply #2 on: March 27, 2009, 09:02:31 AM »
I am relatively a newbie concerning wind generators but as I understand it, reducing air gap will increase voltage and power you could get at given rpm, but it won't make it turn more easily. Is the prop well balanced?


Martin

« Last Edit: March 27, 2009, 09:02:31 AM by mbeland »

mbeland

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Re: Air gap
« Reply #3 on: March 27, 2009, 09:07:09 AM »
Sorry, I got the question wrong. Yes I think it may in some situations make it harder to turn in the way that it increases the power of the gen which could lower the speed at which the thing reaches stall. However, it should not limit it from turning from the start unless, it is shorted or something is rubbing. My two cents.


Martin

« Last Edit: March 27, 2009, 09:07:09 AM by mbeland »

NeilMan

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Re: Air gap
« Reply #4 on: March 27, 2009, 10:34:50 AM »
It has started on it's own in heavy winds, and the blades are out of balance, I'm going to cut up a new set and make sure they are all the same weight, the one thing I noticed is when I do kick start it, the hole machine then moves a foot counter clock wise, so if it's facing south when I kick start it, it then moves towards the

east maybe a foot.


I'm going to check the rectifier for a short.


Regards

« Last Edit: March 27, 2009, 10:34:50 AM by NeilMan »

TomW

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Re: Air gap
« Reply #5 on: March 27, 2009, 11:02:06 AM »
NeilMan;


Every dual rotor I have ever seen turns freely in the lightest of breezes. There should be no "cogging" or other resistance to turning caused by the magnets / coils until it starts hitting charge voltage.


Having said that, do understand I am far from an expert, but have seen several in use and have 2 here.


I suspect your balance is a bigger issue than any magnetic / electrical problem unless of course the bridge is fried to a short. Might try removing it from the circuit and see if it can start with no connection on the ground? If it runs up to speed then you can be pretty sure the bridge is junk. Be ready to short it out as soon as it gets going so it doesn't get going crazy fast.


The seeking a specific spot on the pole is an indication either the pole is not plumb or the cutoff on the end is not true / level or something. Combined with a heavy on one side prop this would kill startup it seems?


Bottom line is you have something wrong of a mechanical nature up on the tower, either balance or being plumb?


Good Luck with it.


Tom

« Last Edit: March 27, 2009, 11:02:06 AM by TomW »

ghurd

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Re: Air gap
« Reply #6 on: March 27, 2009, 11:15:52 AM »
The 9V kick start thing has me wondering.  Like a smoke alarm battery, or a 12V with 2 dead cells?


I took the twisting to be gyroscopic related, like a motor with heavy unbalanced flywheel being powered up in your hand.

Or maybe wind seeking prop force balancing with the tail.

Interesting stuff.


But my bet is on the blades being Way out of balance.

That is a fixable problem.

G-

« Last Edit: March 27, 2009, 11:15:52 AM by ghurd »
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KEG

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Re: Air gap
« Reply #7 on: March 27, 2009, 11:56:27 AM »
What kind of hard ware is holding the stator on is it stainless or steel, steel will make it have a cogging affect, balance the blades you've got as well and that will make a big differance.
« Last Edit: March 27, 2009, 11:56:27 AM by KEG »

NeilMan

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Re: Air gap
« Reply #8 on: March 27, 2009, 03:02:43 PM »
Thanks everyone for the help, I will cut the new blades soon and let you know if that was the problem.


Regards

« Last Edit: March 27, 2009, 03:02:43 PM by NeilMan »

Ungrounded Lightning Rod

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Re: Air gap
« Reply #9 on: March 27, 2009, 05:20:46 PM »
It has started on it's own in heavy winds, and the blades are out of balance,


That's your problem.  Get the blades into static balance and it should start on its own.


Static balance is easy.


one thing I noticed is when I do kick start it, the hole machine then moves a foot counter clock wise, so if it's facing south when I kick start it, it then moves towards the east maybe a foot.


Another sign that it's out of static balance.  WAY out.  (And that you've got a really good yaw bearing.  B-) )


I'm going to cut up a new set ...


Just balance the ones you've got.


As for gap, it should not matter at all (unless it results in the stator and rotor rubbing).  An alternator without iron cores (and without magnetic metal screws near the rotor magnets) has no cogging.  So the only things keeping it from starting when it's dead-stopped are bearing/seal friction and static imbalance.


I'm going to check the rectifier for a short.


Won't hurt.  Two shorted diodes - one to (+) one to (-) - could put current through a coil and hold the prop in a preferred position.  Just one will put drag on the mill like a shorted coil for part of the rotation.  But drag from a shorted coil or diode doesn't happen until the mill is actually moving.


(Drag might keep it slow enough to exacerbate the startomg problem from the imbalance.  On the other hand, enough of an imbalance that "kick-starting" the mill yaws it by a FOOT is a LOT of imbalance.  So I'd deal with that first, and just check the diodes for completeness and because it's easy.)

« Last Edit: March 27, 2009, 05:20:46 PM by Ungrounded Lightning Rod »

Ungrounded Lightning Rod

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Re: Air gap
« Reply #10 on: March 27, 2009, 05:22:21 PM »
Prediction:  When you give it a kick start the bottom blade moves one way and the front of the mill moves the other.
« Last Edit: March 27, 2009, 05:22:21 PM by Ungrounded Lightning Rod »

Ungrounded Lightning Rod

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Re: Air gap
« Reply #11 on: March 27, 2009, 05:25:03 PM »
Just static-balance the ones you've got.  Why cut new blades just for balance?  (You'd have to balance THOSE anyhow or you'd be back where you started.)


Save cutting blades for changing size/shape or fixing a major problem.

« Last Edit: March 27, 2009, 05:25:03 PM by Ungrounded Lightning Rod »

NeilMan

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Re: Air gap
« Reply #12 on: March 27, 2009, 06:11:07 PM »
One of the blades is 6oz's lighter then the other two and I also noticed that one blade is chipping bad on the leading edge. Need to use better wood and maybe coat the edge with resin.
« Last Edit: March 27, 2009, 06:11:07 PM by NeilMan »

TomW

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Balance it, Don't remake it
« Reply #13 on: March 27, 2009, 07:31:50 PM »
Just a "fer instance""


My 8 foot basswood set that I just balanced needed about 250 grams of lead screwed to the area between 2 blades plus an 8" length of 3/8" ready rod, 4 nuts and a bit of 1" angle to attach the rod to. One blade always stopped on the bottom. I figure, all told, I have about a pound of weight on it to balance it.


It runs sweet now but was pretty unusable before I balanced it.


Don't be too concerned if it takes a fair bit of weight to do it. I balance it on the machine on the mast while its horizontal. spin it and watch where it settles keep tweaking the weight til it works. I use anything handy like nuts bolts washers hunks of steel etc to get it "close", then attach lead decoy weights to the hub area between blades. Then use the rod and nuts to fine tune it.

Lots easier to balance a set than build a set.


We really need a balancing tutorial. Zubbly [RIP] taught me how to do it with a ready rod like I do it now. I try to keep the added weight close to the hub and close to the center between front and rear of prop thickness.


Good Luck with it.


Tom

Just FYI.


Tom

« Last Edit: March 27, 2009, 07:31:50 PM by TomW »

jmk

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Re: Air gap
« Reply #14 on: March 30, 2009, 03:02:09 PM »
 You will be surprised how easily a balanced rotor spins in the slightest breeze! Just make sure it's calm when you balance it. The better you fine tune it the more it spins when you give it a whirl to see where it stops. Also when balanced it wont stop in the same position. Make sure that the tips track too. You don't want to pack your bearings full of grease either. Just so they are covered with grease. That makes a huge difference in start up.
« Last Edit: March 30, 2009, 03:02:09 PM by jmk »