Another iced up axial flux alternator

[jmk]

 I'm in the freezing rain and the geny is all froze over. We are getting about 30 mph gust. My blades aren't moving. They normally would be spinning 10 rpm in a 30 mph gust. I have the grid power at the moment, but it might go down with the weather conditions. I don't need to use the machine yet and could wait for it to warm up and melt loose. What I am concerned about is that when it does start to melt, and start to spin that it's going to gouge  or crack the stator. The gap isn't perfect because the stator has a little bit of a warp to it. Do you think it would be better to let it melt on its own or boost it with some current when things start to get warmer?

 I was reading about Dan B and Bruce's iced up postings. Ed was saying to put a positive lead on one of the phase wires of a three phase and a negative  on one of the other two for about 20 seconds. I am wondering if the bridge rectifier needs to be disconnected when doing this. I think not, but I want to make sure. If not, can it just be jumped across the terminals of the rectifier with screw drivers?

[DanB]

Hmmm... I woke up this morning and tried to take my daughter to school and the front wheels of the volvo were so packed up with ice that they couldn't move!

About the wind turbine though...  Yes, I've had very good luck bridging the rectifiers for 20 - 60 sec.  I would do 1 phase for a bit - then another.  You don't need to remove the rectifiers.  Itll serve to both melt off the stator, and - if you do it to all three phases in turns, there will be lots of torque trying to 'break' it loose.

It's only happened to me here a couple times and I've always found it easy to melt them out.

[Nando]

Careful, if you have the diodes connected, do not apply reverse voltage to the diodes to warm up the stator, YOU are just making the diodes conduct.

You need to apply the power prior the diodes to warm up the stator.

Nando

[jmk]

 To my understanding I need to conect the positive terminal of the rectifier to the ac terminal. Then on another phase conect the negative terminal to an ac terminal. Is this right?  

[Flux]

yes that's right. Don't under any circumstance reverse the dc connection to the rectifier.

Flux

[jmk]

 Good that's what I did. Its spinning now. Thanks for the help again. It's hitting up to fifty amps 30 volt at the peak of the gusts.  

 Just to update you guys I lowered it pulled the leading edge tape off that was starting to peel at the tips. closed the air gap up to 5/8". The tracking was off on one blade by 1/2". I couldn't correct it by bolt pressure so I raised it up after rebalanceing it. The balance was weird I had to take off weight from where I had it and put it on the other side. After it was up it ran a lot slower, and power came on sooner. The rotor was noisy so I lowered it. I opened the air gap back up to 3/4". I had up to 1/8" thickness on my trailing edge, so I plained that down to a sharp edge. I painted it rebalanced and stuck some milk jug plastic in between the plywood hub and front rotor to get the tracking within 1/4". I liked the speed of the rotor when the air gap was tighter, but I could here it rub every now and then. After I raised back up it ran a lot quieter. Even though the power came on faster with the 5/8" air gap I believe that it gets to higher amps and holds them longer with a 3/4" air gap. It's hard to tell though because when I had the 5/8" gap it wasn't tracking good and was making noise. This was wasting power causing lower rotorperformance.I do believe though that a well balanced, quiet, good tracking rotor good gives an exceptional amount of better performance. It will put out power in light winds that it wouldn't before. I have seen it hit 60 amps the other day. It mostly is pushing just a couple of amps most of the time, but it's in turbulent air. I find it more fun to watch the amp meter, and scary to watch the rotor. That is when it's cranking amps out. It's really fun to watch it while it's powering my wood boiler, and pumps (275 watts)  when the dump load has to go off every now and then!  Well, thanks again and have fun JMK.

[jmk]

 I forgot to mention that I cut the tail down to seven foot from eight. I really cant tell the differance. It seems to have a hard time furling. I thinking six foot might be better. Not because of stator heat but because It's hard to get used to it spinning so fast. I wonder if it would furl better if I had the tail furl the other direction?  

[Flux]

Tail length doesn't affect furling much. Within reason a longer tail gives better stability. If the tail is too long you may have trouble keeping the moment low enough, but it is really the moment about the pivot that matters and reducing weight is better than reducing length.

You make it furl by leaving the tail anchored in space and it rotates about the yaw axis. You can make it crab at an angle to the wind if the tail is too short or too small but although it crabs, it may not furl.

I have a feeling that some of the burn outs have come from the mistaken belief that things are furling when in reality they are crabbing and running at a bit of an angle. It looks ok to see the tail at a  bit of an angle in modest winds but to be sure, you have to see it swing its tail to about 60 deg to be absolutely sure things are furling.

If you can't get it to furl properly with a lighter tail then you may have the alternator offset too small. If it is below a critical value it will never furl.

If you are running at higher speeds up towards runaway instead of near stall it may need more offset.

Flux