The big wind storm of PNW

[force9BOAT]

Well I'm back on-line for the first time since last Thursday night/Friday morning wind storm in the Pacific Northwest.  My house had no grid power for three and a half days.  I was able to keep lights on via my RE system.

A couple weeks ago Dave B posted a story about his machine hitting 800RPM in 60mph wind. (http://www.fieldlines.com/story/2006/12/4/15639/7575).  I was really worried my 10' machine might not fair was well as Dave's so before the storm hit I disconnected from the rectifiers and soldered all the output leads together.  Shorting the turbine thus, during the most saver wind my machine never turned any faster than about 30 RPM.   I was really happy about that considering large trees were falling all over my neighborhood and my house was literally shaking.

On Friday morning as the wind was dying down I reconnected to the rectifiers and starting producing power for all of about 30 minutes.  Naturally the wind dropped to ZERO and that's where it's been since Friday morning.  Cloud cover kept my solar panels from producing much as well not that they produce much this time of year anyway at 47 North so I had to be frugal about using my RE power when I needed it most.  Kind of disappointing in that regard but I'm happy to still have my turbine undamaged.

Rob

[DanB]

Sounds like you need a stop switch!  Unhooking the rectifiers and soldering all the leads together seems sort of inconvenient.

Nice to hear you survived and had lights!

[TomW]

DanB;

I agree on the switches. Only need 2 to fully short 3 leads. No need to disconnect the rectifiers just short the leads with switches on the turbine side. In case thats why you unhooked the rectifiers.

Just a thought.

Ditto on your survival of said storm.

Cheers.

TomW

[coldspot]

Glad it was not a wreck for you!

My Ametek lost a blade, No big deal, was

only adding to global warming with it anyway.

(fetched the other two extra blades from shop/shed

tonight for a repair maybe this week).

A question-

"just short the leads with switches on the turbine side"

Would this be for three phase only or would shorting

before the rectifier on a PM type also be advised???

I built a rectifier into my control box for maybe being able to hook up a couple of small mills of the

Ametek size, and put the "Pull to short" heavy duty switch after this.(this would connect pos and neg).

None of this has been actually hooked up to anything yet, due to girl friends house rules, the reason for the shop/shed!

LOL

[Ungrounded Lightning Rod]

"just short the leads with switches on the turbine side"

Would this be for three phase only or would shorting

before the rectifier on a PM type also be advised???

Huh?

Three-phase vs. single phase (vs. whatever phase) is one issue, PM versus excited is another entirely.

You need one switch to short single phase, two to short Y or delta three phase, N to short jerry-rigged N phase.

I built a rectifier into my control box for maybe being able to hook up a couple of small mills of the Ametek size, and put the "Pull to short" heavy duty switch after this.(this would connect pos and neg).  None of this has been actually hooked up to anything yet

Short UPstream of the rectifiers.  Very important.

First:  Shorting downstream of the rectifiers means the short-circuit current goes through the rectifiers.  If the mill was whirling away when you closed the switch you'll get a big, long pulse of overcurrent as you're converting the kenetic energy of the spinning mill into heat.  If the rectifiers are in that circuit they'll probably die.  If they die "shorted" your mill doesn't restart once the switch is turned off.  If they die "open" your mill runs away once the wind picks up - which is what you wanted to prevent.

Second:  The (+)/(-) output is connected directly to a battery once you're hooked up.  Short THAT and you'll have hundreds of amps through your switch and battery wiring, followed by the switch welding "on", follwed by a fire, maybe wires exploding like primacord, maybe the BATTERIES exploding and spraying acid all over everything.

[Shadow]

At the bottom of my tower I have a male and female 220 volt receptacle, (the type used on dryers or kichen range). I have them mounted on a small pedestal that is covered.When I see any signs of twists in the cable I can simple unplug it and sort it out and plug it back in. I also keep a spare rectacle there with all the inside connections soldered together so when I lay the tower down to work on it I simply use this plug to keep the turbine shorted out. This is all before the rectifiers so youre working with 3 wires, these kind of receptacles work great with 3 #10 gauge wires. And you can find them for a dime a dozen at garage sales. I have a knife switch in the power shed I use to stop the mill or keep it stopped. But I find this one at the base of the tower is real handy.

[Dave B]

Hi Rob,

  Dave B. here. Glad you anticipated the wind and had time to short out your alternator. My single phase with fairly thick coils and high resistance had previously shown it's ability to start and accelerate from a dead stop and shorted. Also, playing a big part was the minimal offset so furling was set too high from the start for the extra high winds. It's kind of bitter sweet but I knew the winds were on their way and I figured it was a rare but very good opportunity to find the weakest link so I left it up. Things could have been much worse if I did not leave a load on or would have tried to leave it shorted, you never would have known it was holding it back some at 800 RPM for 12' diameter. I am currently building an 18' dual disk which will furl early to run slow and easy. For the record West System Epoxy is amazing stuff, it still looks as if the initial failure was due to magnets scraping the face of a few coils and then knocking one loose. This caused by the rotor flexing during rapid yaw at high RPM (again minimal offset will not dampen the yaw as much either) All magnets and remaining coils remained rock solid and had been face glued with West System and fillets. Thanks for the reference to my story and yours, hope this helps others out there.  Dave B.

[Flux]

Perhaps a bit about brake switches would be useful.

If you have copied a design by DanB or Hugh, then you can use a brake switch to hold it stationary or stop it from speed. The alternators are efficient enough to do this.

With Hugh's normal design with rectifiers on top you need to short the dc. To do this without shorting the batteries you need a change over switch ( with or without a series blocking diode). Hugh has a diagram in his plans. It is a bit hard on the rectifier, but as the design uses lots of 35A bridges it copes with it. Diodes have a short time surge rating much above the average rating.

If you have the 3 phase available then it is far better to short the ac.

If you have done your own half baked version of an axial machine, you should find that a brake switch will hold it stopped in normal winds. You may or not be able to stop it in a high wind and you would need to satisfy yourself that it will remained stationary in very high winds. If it will not stop within a few seconds from speed then you had better turn the brake off or it will fry the stator. If the brake will not stop it from speed then you would need to prove to yourself that it will hold it stationary in a very high wind. If it does start up and you are not there to turn the brake off, bye bye stator.

It takes a lot of magnet and copper to be absolutely sure it can be totally reliable with a brake switch.

Many motor conversions may not stop from speed but may be safe when left stopped. This depends on the proportions of resistance and reactance in the windings and you will have to decide by experiment.

DC motors may stay braked with a short before the rectifier, but every case is different, if it gets away it will destruct.

With DC machines DONT try to stop them from any significant speed, the excess current will murder the commutator and brushes, they just can't be designed for gross overload.

You have to know your machine and act accordingly. Try to find out what happens in reasonable winds, even then a machine that seems as though it will always stay braked may get away in a severe storm.

Flux

[coldspot]

ULR-

"(this would connect pos and neg)"

This half baked self made setup I've done,

The switch unhooks the Pos from going to the

charge controller and hooks it to a Neg wire thats

diode blocked from doing anything but shorting just the wires going back to the bridge rec, (35A).

Was just wondering if maybe it would be better to place switch before the bridge.

Flux-

I also wondered about the brushes on DC motors when shorted out but didn't think about doing at speed, that would be very hard on them I'm sure.

Brake using more load sounds best for all types.

learning as I go, but glad to have opinions from people that have been there done that!

Thanks

[Nando]

Here is a classic reason why a Pitch controlled is much better than a furling unit.

At the stated high wind velocities the Furling type has to be stopped with emergency conditions and NO power is generated, in this time of need when the GRID goes away for several days.

The Pitch controlled at these high winds may be producing peak power supplying the emergency power.

Comments on this type of emergency shut down are common here and in other places, Pitch control allows power generation and wind mill protection during these specific troubled times.

Nando

[TomW]

flux;

Nice piece on electrical braking. May I suggest that you cut and paste it into the "newbies" section as a story with a title of "Electrical Braking Strategies" or something else descriptive? Or, if you prefer, I could copy it into a story there.

Valuable info I would like see not sink into the void.

Cheers.

TomW

[Flux]

Tom please feel free to copy it there, your computer skills are probably far better than mine, I get in a mess with files.

Flux