AX 300-3 & VLLR

Author Message


Joined: 10/02/2007
Location: Australia
Posts: 729
Posted: 09:24am 08 May 2012      

Hi All,

As I have been quiet over the past few months it has been for a few reasons , I think in one off my last
posts I gave a link to some video I took on a fairly windy day showing my mills furling and the logging system.

It did not stop there , well it did with both mills dead at the end of the day, it only started ...

So you don't have to go back over and find it in with a site search Here's the LINK

The list of events that happened later that day has lead me on a complete redesign and rethink on how I can control my mills.

1/ The wind continued to strengthen

2/ The Grid went down which took away 2.2kW of load

3/ Both mills were combining to output over 4kW in peaks

4/ 1kw dump load could not keep up, even with both mills furling as peaks still continued as the mills furled

In the pressure of the moment as a lull came through I threw the shorting switche’s , the AX300-2 did not stop, but instantly went into an unloaded state and as the gusts came the blades were reaching RPMs that were sphincter clenching.
The mill could not furl as gyroscopic force had taken over, and I could only watch on from a safe distance, and trust my engineering .
The blades and hub handled what I would think was in excess of 1200RPM peaks at times.
The sound from the blades resembled an aircraft doing propeller checks and a helicopter landing all at one time, anyway the blades and mill survived structurally .

The smaller mill also burnt the stator and windings, but due to the iron core and shorted windings eventually it came into a stalled state.

Below are a couple of pics of the destruction, but I do not want to dwell on it, or go into any lengthy debates on the “whys/what’s “ and in depth of that.

Ax300 Stator a bit worse for wear, smashed,chewed up, and bird nested .

500W Kit Stator Cooked- High Temp Silicon wire is crispy.

As This has now been my 2nd AX melt down / Blow up or whatever you want to call it, and also the 2nd 500W melt down, I needed to seriously reconsider how the mills are controlled in high wind situations.

The options considered for rebuilding the mills, so this doesn't continue to happen on a regular basis, which seems to be every year at the same time.

-Mechanical braking... eg Disc or band/drum brake

-Better Furling

-Mechanical assist furling

-Diversion Load resistor braking ..

-Combinations of all the Above

-Piss the mills of and get my kicks from watching solar panels.

The common denominator here is that the GOE222 Blades and the power that they develop in high wind , and the fact that once over a certain RPM mechanical furling becomes difficult , but in saying that the power they develop in light to moderate wind is well worth the trade off of having way to much power at the high wind speeds. This could be said with all blade profiles in strong wind, and burning up stators appears to be a fairly regular occurrence associated with the Axial Flux design, due to its resin encapsulated stators and the lack of heat dissipation.

The problem I also Identified with both mills, being basically low resistance windings.
The AX300 is wound for a 48V cut-in RPM of 200, and then uses a Cap/Doubler to bring the actual cut in down to 100rpm.
This enables the alternator to achieve higher efficiency with less copper windings needed to get the low end power, which equates to less heat in the windings with the AX300.

The 500W Kit @48v is a lot higher at 350RPM, and uses both a Cap/doubler and quadrupler in parallel to get a cut in of 130RPM.
This has enabled the 500W mill kit (which better suites 24V) to now be used at 48V.

But there is a downside to this. When the mills are shorted out to brake or stall the mills, the doublers are bypassed and causes the original wiring configuration to dissipate the heat generated from the power of blades, this means that when stalled using a shorting switch in high winds, the blade rpm can reach a point where a fair/large amount of power is being produced in stall which has to be dissipated as heat, due the GOE222 blade because of its high torque low RPM capability.
With shorting the phases the energy is dissipated internally in the stator, (with some additional loss with line resistance) causes the coils to overheat and expand rapidly, which is not good for epoxy encapsulated windings.

Another anomaly I picked up and is limited basically to this particular design of enclosed stator type AXFX, is that both times it has burnt a stator, the stator was forced in one direction towards the front magnets, I had not paid too much attention to this, but while I was assembling it for a clearance check I remembered that it have a slight misalignment
of about 10mm with the magnet plates, that happened due to a bit of a mistake when I originally built it, for the last 40mm when the two plates are lowered together it required alignment rods to align the bolt holes, this really is no different than decogging for an AxFx and the flux lines are angled as they cut the coils.
As Both Gordon and myself built these similar AXFX alternators 3 years ago it has always been a mystery to why mine was so quiet and barely makes any noise, as its quite common for AXFX designs to have a growl at cutin and while producing power.

This then identified another problem I think could be happening, being as the stator gets warmer and more flexible the force of the angled flux lines constantly forces the stator in one direction, and eventually causing contact with the magnets, and more so when shorted or loaded heavily.
Resulting in both burn outs having made contact to the same areas on the magnets

Contact on front Mags

I was going to re-align the holes so the flux lines are at 90deg to the windings to stop the flex under load but decided not to, and give the front air gap a little more clearance, as having a quiet generator is a good option, with the mill location being close to the house.

My main problems have always been with controlling my mills in high wind, when no more power is required. ( probably in reality it is common with all mills )
All power generated is feed back to the Grid by 2 x 1200W Latronics PVE grid inverters that feed off a 48v 225A/Hr flooded Lead Acid Battery Bank.

There is 2.3kw of solar feeding in to the batteries as well as the 2 Wind Generators, as the solar is only peaking for 4hrs a day, and allowing for losses with inverters etc. I only have a gap of 300 ~ 400w that the mills have during the peak solar period,
I installed a 25 X 3000Farad Cap bank in parallel with the batteries to absorb wind gusts and solar bursts, as there is very little A/hr absorption in the Batteries as they are constantly held @ 52.3V due to the cut off point for the inverters.
The Caps will absorb approx 8000W in 30sec, since they were added the spikes are slower and smoother.

25 X 3000F 2.7V Ultra Caps

In this situation it is very hard to size a dump load that dumps excess power from the batteries, so it is a better option to use a diversion load for the mills and use that to stop the power from the mills completely when the voltage is high, or the grid is down, or the inverters are lagging.
The solar will regulate its self through the MPPT Charger, but if the wind is fairly blowing and the sun is shining (which only happens a few days a year in my poor wind location) this is the time when a good control system needs to be in place, and more so for my next Axial Ax400 (which is under construction) goes up, increasing the power to almost twice the output of the AX300.

With all this to consider I have had an idea in the back of my mind, it has come from my present work place, where the machine I work on and operate uses a system called a "Liquid Start Resistor" to start Conveyor belts for a 12000TPH Crushing and Conveying system, that shifts overburden at the mine I work at.

Each of the two main belts , one which is 2.5km have 4 x 1200kW motors that need to start slow at high torque and slowly ramp up to full speed of 5.8m/s , this is done by the Liquid Resistors that basically have two sets of annodes in a tank, basicly one set are moved closer to the other by a drive motor untill there is no resistance.
The tank is filled with over 1000L of liquid with high Ph. Basically very salty water.
When starting under load over 1 megawatt @ 1200V x 4 is being passed through each
of the liquid resistors and excess power is dissipated into the fluid. These monsters have cooling pumps and fans and you only get 3 consecutive starts before having to go into a LRS cool down time out.

Below are a couple of pics of these units and what is being started .


2.5Klm Conveyor

High Voltage liquid start Resistor

So the thought I had was to use this concept but in reverse to control a windmill, buy dissapating the power into liquid when shuting down or controlling,instead of into the windings so I set up a bit of a test to see how well it would work, I did a bit of a video of the test to show the basic idea which was set up on my test stand.

The Basic components and operation .

-The Liquid load can directly connected to the Mill AC

-Infinately variable through liquid concentration or plate immersion

-The Anodes/plates are just S/S 1.5~2mm sheet cut to size

-The liquid is a solution of rain water and Sodium Carbonate " Ph Increaser" for pools/spars , other options .. Bicarb, Caustic Soda, Acids, Salts…………

The test shows only 3 plates with the 3 phases connected to them, this is only effectively acting on 2 phases a 4th plate is required to fully balance
the 3 phase loading.

Heres a link to a Vid I did of the doing a test LINK HERE

As you can see in the Video, the load can be infinitely controlled by the amount of surface area of the plates in solution , as the plates are immersed in the liquid the AC load comes on, and the DC output drops and the generator output is then being dissipated into the liquid as heat.
Also the Loading torque on the alternator is increased dramatically from what the load was at the set RPM as the plates are fully immersed, by having this type of diversion load it can be bought in smoothly and the loading increased to the point where the mill is stalled and stops producing power.

I started to then think about how to put in a control mechanism to lower the plates into and out of the liquid, and of course the options here are limitless and I could go on and on with every option that went through my head, from water pressure to air pressure, magnetic and the list goes on............

From here on is where the whole project started to take on another direction, as I keep in contact with Pete " Downwind " and Gordon Gw@PE who haven't been active on the forum for quite some time, I explained to Pete my thoughts and tests that I had done so far with the Liquid Resistor,

I also should say at this point, that this control system is nothing new , and the whole concept has been around for donkeys years, whether any one has gone down the same path as I am, I don't really know because haven't been able to find to much on the internet about Liquid Resistors as such in this application . As this is using AC it creates very little hydrogen, DC can do the same but creates a lot more hydrogen and will also get a deposit build up on one plate.

Anyway after talking to Pete he also decided to set up a bit of a test to see what I had explained, and from what he observed agreed that the idea had merit.

After my 2nd AX burn out we had been discussing ways to monitor stator temperature in axial flux alternators, and he had come up with a concept of using a infra red slip ring rather than wireless that would allow data to be sent around the yaw bearing using 3 infra red LEDs and one 38khz IR pick up sensor , this would not get affected by interference from the blades rotating or signal losses. With a DS18b20 temp sensor mounted in the stator, the data would then be recorded to my logging laptop to see what is going on with stator temp when the mill is hammering.

Sensor in stator

At this point the whole concept started to take on a whole new direction as with Pete involved and his wealth of knowledge and experience with circuit design and programming Picaxe, we started talking about what could be done with options (conditions) that the liquid resistor would be activated by, and what would be best to drive the probes, as I stated prior there are a whole lot of different options here, but first we decided to try using a stepper motor to drive the plates in and out of the liquid with a threaded rod. The idea did work but lacked enough speed.

I then sourced some fast acting linear actuators that could extend and retract 200mm in 1.25sec along with controller boards as well as a manual motor controller for testing , the only problem is the actuator voltage was 24V, so would have had to use a 48VDC-24VDc converter which luckily I have a few I picked up a few years back .

After sending down a linear actuator and solid state motor control to Pete he then put together a control board and I started on all the fabrication of the tank and plates etc.

Linear Actuator with S/S Plates mounted

Tank made from 300mm ABS Pipe

After probably much hair loss and probably a whole lot of cursing the whole system was tested and sent up to me to fit, and I must say as you can see from the pics Pete put together a very professional well finished control box that has all the circuitry which I mounted into the lower electrical box .

The controller triggers on...

* 1-Voltage Max and min ( Adjustable in Program)

* 2- Rpm - ( if over 340 Rpm Shutdown, if under 300 Rpm Restart ) Adjustable

* 3- Stator Temp ( If Temp over 80DegC Shutdown & If Under 60DegC Restart) Adjustable

* 4- Emergency Shutdown

* 5- Manual over-ride for in and out

The motor control board is also in the control box but not shown .

The infra red sender unit mounted into the nacell , and is powered
directly from the mill AC .

The 3 infra red senders are mounted in a 100mm pvc
pipe cap and the joiner screws up and holds the ring in
place and also shields the pick up from direct sun .

The "VLLR" (Variable Load Liquid Resistor)control box which is now mounted into the box front also has all the manual controlls for Emergency Shutdown / Stop and manual in and out .

The finished unit with the upper and lower limit switches to
tell the controller where the plates are , the actuator also is covered
by some 100mm pvc pipe for weather protection .

I had originally intended to mount the actuator on a S/S tank with the plates being rotated into and out of the fluid with the actuator connected to a suitable sized arm, as I had a heap of the large ABS pipe that was originally used for blades, I decided to go with a
vertical arrangement as shown in the pic, it was simple to build but setting up the limit switches was a little tricky.
I now think that it is a better concept to go back to my original plan of the rotating the plates with a purpose built S/S tank when the new Axial goes up .

This is also where I think the whole concept moved a bit more hi tech, (well it actually happened way before this point but I will slot it in here.)
I came across a program called “Team Viewer” and it enables access to computers connected to the net from anywhere, as well as from the latest Iphones and androids , basically I can log on to my Logging Laptop and check on the mills and solar from anywhere in Australia and I would think the world as long as you have internet access or phone service .

We basically thought it would be pretty cool to be able to control and shutdown the mill from thousands of miles away, Gordon put together a VB program with an on screen display and some activation buttons that would enable a shutdown and Restart as well as the ability to manually control the actuator.
The on screen keys send serial data to the controlling circuit, which in turn implements the commands.
The control circuit then sends information back that is displayed in a status window to show the instruction had been activated, it also records to a log record any info of what has been happening with temp and if it has shut down for any reason and the reason that triggered the shutdown.

Its not a really clear screen Dump Pic but thats what happened today and its not much to rave about in the wind side . The VB program can be seen in centre with the stator temps recorded at 2 deg increments during the day and a shutdown and restart at the top of the status screen , so whatever is on that computer can be controlled from a laptop / home computer or mobile phone as shown above

Anyway that’s about it , since installing it I have not had any real wind to rave about, but it has done its job quite a few times with the Grid going down and the solar pushing the battery voltage up past the shut down set point 59.5V, I did have one gusty day when high RPM activated the VLLR. It is also very interesting to watch what is happening with the stator temp, it is surprising how quickly temperature rises once it starts to produce over 500w, this is a bit of an eye opener and quickly jumped from ambient to 55deg a few times on a few 1kW + Bursts.
At present the Temp is set to shut down at 80DegC and now just a waiting game for the winter winds to arrive and give the whole system a good work out and at that time I hope to get some more Video of the system working at protecting the AX300-3 and hopfully this year is not a -4 .

I know this specific concept that has been put together as a team effort might not be everyones cup of tea, but there are other options, and could be simplified as a basic shutdown resistor and could even be used to capture excess power as stored heat with the use of a heat exchanger , the one trouble that does arise is with switching the low voltage AC with a SSR, and at present I have not found such a beast but it can still be done with conventional relay type AC rated types . Also there are many other options that could be used to actuate the plates into and out of the liquid.

I have just obtained a couple of nice S/S tanks and will be re-designing the way the actuator and plates are mounted along with the new AX that is taking shape at present, but that will be another thread.

Edited by fillm 2012-05-09
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