Posted: 10:29am 14 Nov 2005

Copy link to clipboard

Print this post

I'm no wiz at these things, ask anyone in the forum and they'll tell you the same but, it sound like your trying to pour the generated power directly into an inverter.

Everything I've read about so far runs the power into rectifiers which converts it to a DC voltage. Because the ouputed DC voltage is variable, it is run into a battery charge controller which manages a 12/24/48V output that charges batteries which, you then attach your inverter. Doing it that way you can attach any old UK inverter.

You can make your own charge controller from a kit that suits the variable AC voltages produced by gennies.  Also known as a Shunt, shunt controller etc. Gizmo even has schematics for one on the DIY Windmill site or, you could look at a site like Xantrex.

Posted: 11:09am 14 Nov 2005

Copy link to clipboard

Print this post

I think what Paul is chasing is a MPPT. MPPT's are clever little devices that can increase the charging current from a solar panel by a few percent. They do this by using a buck/boost converter. Here's an example, dont rely on the figures, they are only approx....

We are trying to charge a 12v battery. The sun is low and the panel only makes 10 volts, not enough to charge the battery. But the solar panel can still supply a few amps, say 10 amps at 8 volts if we loaded it. The MPPT converts this 8 volts/10 amps to 14 volts/5 amps, enought to start charging.

Now in full sunlight, the panel makes 20 volts at 10 amps. If we put this across our battery and loaded it down to 14 volts, we might get 12 amps. The MPPT can convert 20 volts at 10 amps down to 14 volts at 15 amps.

So they can convert the panel voltage to a good charging voltage at the best current it can get from the panel. MPPT = Maxium Power Point Tracker. It tracks the available power from the panel and converts this to the best charging voltage/current. They are very clever, involve some fancy electronics and usually have a little microcontroller built in.

Paul is looking for a MPPT for a windmill. They would need to be built differently from a Solar MPPT, as windmills have different power curves - solar panels have a smooth power to sunlight ratio, where a windmills power increases expodentially with wind speed. A 300 watt solar panel will only ever make 300 watts max, but a 300 watt windmill can make several times that in wind gusts, so the MPPT needs to be pretty tough.

Phew, hope that made sense.

Glenn

Posted: 11:27am 14 Nov 2005

Copy link to clipboard

Print this post

Hmmm...I understood that too!.

Something like this might be the go.

http://www.oatleyelectronics.com/kits/k091a.html

Posted: 04:04pm 14 Nov 2005

Copy link to clipboard

Print this post

Hi Greg and Glenn,

Thanks for the info. This project is being done on a shoe string (not because I'm hard up but just to prove a point). So far about £17

I have considered a charge controller / shunt regulator and battery setup. I also have a UPS 1KWatt which I could use as an inverter.

Charge controllers are cheap and I as you say there are plenty of kits available if I didn't want to build from scratch.The only problem is I would need to get some batteries.

Therefore what I am ideally looking for is, a grid inverter to feed the rectified 3 phase into so it suppliments my household supply.

Most of these I have come across are expensive £500 + and as I posted previously only appear to support PV arrays.

Inverteres I have looked at SMA windy/sunnyboys, Soladin (matervolt) Xantrex, Siemans, Sunways,Atersa, Solartechnik, NK OK4

So the question is can I connect a wind generator straight into these if I condition the output, smoothing / filtering, overvolt protection etc.

Posted: 05:20pm 15 Nov 2005

Copy link to clipboard

Print this post

Just to let you know,

You can use an induction motor for your wind turbine.

The squirrel cage Induction Motor makes an excellent generator when it is driven above its synchronous speed. The same features that make this motor desirable over the other types of motors makes the Induction Generator desirable over other types of generators, namely the inherent ruggedness of the squirrel cage design and the simplicity of the control systems.

The Induction Motor becomes a generator when it is connected to an electrical power system and then driven above its synchronous speed by some prime mover. The prime mover may be a turbine, an engine, a windmill, or anything that is capable of supplying the torque and speed needed to drive the motor into the over-speed condition.

The performance characteristics as a generator will vary slightly from those as a motor. In general, the slip RPM and power factor will be lower and the efficiency will be higher. The differences may be so slight as to be undetectable by normal field measuring methods.

A major advantage of the Induction Generator is frequency regulation. The speed has to be tightly controlled with a synchronous generator so that its frequency doesn’t deviate from line frequency. The output frequency and volts are regulated by the power system in the Induction Generators and are independent of speed variations. The self-regulation effect minimizes control system complexity.

Induction Generator controls are very much like those of an Induction Motor, with some exceptions:

1. The system must be equipped with a speed limiting control. In the event that electrical load is lost, the torque of the prime mover will rapidly accelerate the system to potentially dangerous speeds. A brake, governor, or throttle shutoff is required to avoid dangerous speeds.
   
2. The electrical breaker must be equipped to limit fault current. In the event of a short circuit fault in the power system, the generator is supplying the fault current. Current limiting fuses are usually adequate.
   
3. The torque output of the prime mover must be limited to prevent overloading the generator.  In the extreme case, the prime mover could push past the pushover (breakdown) torque of the generator, causing runaway speed.
   
4. In some cases, wind speed may drop below the generator’s synchronous speed. If this happens, the generator will motorize to drive the system. use a anamometer that triggers a contactor to disengage the motor. 

Check out http://www.otherpower.com/otherpower_experiments.html

Posted: 06:01pm 15 Nov 2005

Copy link to clipboard

Print this post

Thanks Solarmike,

It sounds like a good idea but I am half way to finishing my generator. It is a single rotor 3 phase (9 coils 12 magnets). Made from scrap I found lying around at work. The body is made from a piece of a B747 aircraft 210mm dia towing arm (alluminium), bearings salvaged from the freight loading system  etc. Enamelled wire I scrouged of a mate along with the loan of a winding machine. Unfortunately I had to buy Neo magnets and some rectifiers. The blades I am making from 4"x2" timber which was lying around. So total investment so far £17.

Posted: 05:59pm 04 Dec 2005

Copy link to clipboard

Print this post

I am amazed at your resourcefullness! You sound like me. Turning junk into gold. if you are going to build another windmill that is going to be connected to the grid, Try an induction motor for your generator. If you supply it power it will spin like a motor. If the wind is blowing then the motor will overspeed and become a phase syncronized generator! you will never need a 'windy boy' inverter, and it cost's next to nothing. I would suggest using a anemometer to measure wind speed and have it trigger a contactor that closes the 'motor to grid' switch. That way your not going to have a big fan. 

15 Years ago I took a drill and oversped a 1/4 Hp 860 rpm induction motor while it was running and it pushed power back into the grid! I had to try it. This is how most large '30 Kw windmills and up' work.