Hi, the problem is I will have to add a belt transmission to increase the RPM of the permanent magnet alternator to achieve useable power at average wind speeds. I can fabricate the transmission. If there are wind gusts the input can exceed 450 volts.

Ok, thank you for explaining. Basically what you have is not a voltage problem it is a design problem. The first thing is you need to decide on what your setup will do in peak wind power situations;
A. Convert all the power to electricity and store in battery
B. Dump some or all excess power into a short or load
C. Draw only the power needed and let RPM and voltage rise

This is a standard problem in wind generators.

My suggestion would be to look at using the PWM to give you some control over the power drawn from the mill, which will give your controller more options. That would be option A but with some intelligent control;

For instance if it increases PWM duty during peak wind it will load the turbine down and reduce it's RPM significantly, which will lower its efficiency and reduce the problem of how you will deal with excess power. It also means the voltage from the generator will be much lower (compared to open circuit freewheeling in peak wind).

During lower wind conditions your controller can optimise the PWM using a MPPT system to give you the max possible power into your battery.

If the cap issue strill troubles you it is easy enough to pair two 450v caps in series to make a 900v cap. For switching devices many of the TV HOUT transistors and PSU FETs are rated for >1500v at a few amps and are very rugged in general.

 

I'm sure he's wrestling with the same problem all windmills suffer from: If you design for 5-10 mph wind, then you have a big problem at 50 mph. if you design for even just 20, you've got nothing at 5. It's just an unavoidable consequence of the physics involved, that the power available goes up with the cube of wind speed. That cube factor makes for an engineering challenge.

Greetings, yes this one problem that needs to be solved. The other reason I am searching for a solution is if the controller circuit is powered from the PMA side it would turn it self off when there is no wind.

 

	
	

		
		
		

			
			
			
			
			
		
	
	
	

		
I'm sure he's wrestling with the same problem all windmills suffer from: If you design for 5-10 mph wind, then you have a big problem at 50 mph. if you design for even just 20, you've got nothing at 5. It's just an unavoidable consequence of the physics involved, that the power available goes up with the cube of wind speed. That cube factor makes for an engineering challenge.
	
	
	

		
	

Situation you described could only be corrected aerodynamically! Wind turbine blade efficiency limit is 0,59 (so called Betz limit). Good airfoil based blades could achieve up to 0,53 efficiency. So if nominal wind speed is achieved (normaly 12-15 m/s) aerodynamical braking starts working to prevent rapid power rise. Large multimegawatt turbines have pitch control function to lower blade efficiency, smaller turbines tale furling to turn blades out of wind and this way lower wind area blades are directed into. Some windmill blade configurations have aerodynamical protection "built in" without any moving parts just like multiblade old West water pumping windmills.

 

Situation you described could only be corrected aerodynamically!

(emphasis added)
I agree that's a common and maybe even superior solution but it most certainly is not the only solution. Mechanical and electrical brakes are also used, at least in the DIY world.

 

Hi, I have two possible PMA’s that I can use. One is a F&P smart drive. The other is one I can fabricate myself. I plan on using the belt drive transmission. The F&P output is about 0.9 volts per revolution if the ratio of the transmission is to high the output can be over 400 volts at higher wind speeds. I know the blade design I am using is slow and has a max RPM of about 150 at higher wind speeds. But I have only been testing with 3 foot tall blades, if I increase the blade size or make slight changes to the configuration I do not what will happen. If I use the PMA that can fabricate it has a lower voltage output but higher current and I think it will not be a problem. Thank you for the ideas.

photos of circuit and PMA's

 

Progress is slow. I still have to route connections. I included standoffs for plexy-glass safety shields. Once a suitable inductor is found the foot print can be reduced.

 

Hi, tested system using hand crank on the stock F&P. Three out of the four Buck converters are working. With the duty cycle between 30 and 50 % the input voltage stayed at approximately 40 volts DC. The max output current was about 5 amps at about 12 volts. If the duty cycle was below 30% the input voltage quickly increased above the 400 volt input limit. I stopped spinning the hand crank and avoided damage to the circuit. As I added more buck converter the input voltage remained constant for the same RPM. Using 12 volt deep cell for a test load.

I have to trace down the problem with the bad buck converter , fix the F&P to be driven by the drill press and include input voltage limiting circuit. At this time it appears the circuit will work.

replaced the multi meter measuring the input voltage and the measured values are more realistic. At 20% duty cycle the max input voltage is about 100 volts DC under manual operation of the PMA

 

Hi, I have question regarding the inverted output of the buck converter when using it to charge a 12 volt battery. The scope shows the output is inverted. The current measured is positive going into the battery. So the battery is charging but I can not explain why this is so. Any help will be greatly appreciated.

 

So the battery is charging ...

If that's true, there's only one way that happens: The emf across the terminals is higher than that of the battery. Maybe you're having confusion over what "ground" is, or how you're measuring your signal? A schematic might help.

 

Hi, I am using just the positive tip of the scope probe to test with. If I test one buck converter or all of them together, the results are the same. Voltage at the input is high with a low current and the output is about 12 volt DC with a higher current. The converters are working but I do not understand why a inverted output is charging the battery. I am running multiple converters in parallel from one controller board. I also provided a drawing showing the same circuit for just one converter.

 

Hi, I am using just the positive tip of the scope probe to test with.

No you're not. You'll get no response unless there's a complete circuit, so you need to consider where the rest of the circuit is. Through the air? Through your hands?

 

I still stand by my idea that a ,buck-boost, Sepic, or Cuk converter would be a better choice for this type project.

You still would need to set the PMA up and record data though. Which for some reason you either don't want to do or you don't want to share the data with the rest of us. Running it down the road strapped to your car doesn't count, it tells you nothing about 'real world' data.

After getting the output data for your local winds and your PMA, THEN the design work would start. You or anyone needs that data to make a clear choice on a project.

With a buck-boost type converter, the average of the out put data would be the design point between "continuous" or "discontinuous" operation of the converter. When your getting a low voltage it would work in the boost mode. At high voltage it would be working in the buck mode. There would be no constant monitoring of the PMA output and switching from 1 to 5 converters, the design of the converter would do it automatically.

I do (I think) understand where you coming from with you original idea though. You want something to market. To anyone making a DIY PMA. But its just not going to be possible with all the variable's involved, local wind speed, the builders wind vanes/sails, the builders PMA output.

I know this comes across as a put down, or discouragement, but its not meant that way! Its just statement of how most projects/design work is done. You acquire data and design from that data.

 

Hi, the circuit is using a isolated power supply. The Source of the of the mosfet is connected to the ground of isolated power supply. I not sure where to connect the ground lead to measure that signal.

If the output of the buck converter is inverted and connected to a 12 battery, how should the scope leads be connected so the scope is not damaged?

I am now using a drill press to drive the PMA, stock F&P. At 100 RPM the input current is 1 amp DC @ 45 volts DC. The output current is 4 amps @ the battery voltage; around 12 volts; and increases as the battery charges.
Above 100 RPM the belt slips. I have to fix that.

I do provide all the data I have. The problem is the internal resistance of the PMA consumes most of the power and creates a braking effect. This circuit when working correctly should reduce the braking effect and the data for the PMA will change.

Under wind conditions the results will change because for a specific size blade can only extract a set amount power. So the turbine will either stall or over spin depending on the percentage of the duty cycle.

I am just starting with a basic Buck converter. After the basic circuit is working then other circuit configuration can be considered. All suggestions are welcome, getting the circuit to work is what is important, not my feeling, it is not a problem.

This is the first time using the Toroid inductor. I am wondering if the switching frequency should be different for the different duty cycles.

photos shows output of buck converter with not using the ground lead and drill press test fixture

 

Hi, I found the problem that was causing the test values to pulsate. The belt from the drill press was slipping and that was causing the pulsated measured values.
the overload on the drill press motor kick in at higher RPMs, but I broke 5 amp output barrier and measure 7 amps at the output and the circuit is still working. Happy day!

 

Hi, approximate measured values:
RPM = 280

Current in = .7 time 3 I can only measure the current at the input of one buck converter, I am using 3 buck converters. Input Current = 2.1 amps DC

Vin=58 volts DC

duty cycle = 30 %

Vout= 12 volts

Current output = 7 amps

 

The belt from the drill press was slipping and that was causing the pulsated measured values.

Same problem I've run into, as well as a hot motor on the drill press, and sagging rpm due to load. I realized I need good rpm data to make sense of the output data, and that I really can't move up without putting my drill press at serious risk. I was getting ready to use brake disks on a trailer axle bearing, but realized that the metal of a brake disk moving thru a magnetic field would induce an eddy current drag. Kind of stuck for now.

 

Hi, I am not sure what your design looks like. This is a photo of the test rig I am using. I had to reduce the RPM’s at the PMA because the drill press RPM range is to high. Maybe it will help give you a idea to solve the problem.

 

Thanks, that's very interesting. I hadn't really considered a belt-driven reduction but that would make my press a lot happier.

 

OK, I'll try one more time to get my point across. Not trying to be a troll but trying to really help.

Driving your (both of you) PMA with a electric motor is great to find the max output. But gives you no real information thats usable in design. The the PMA and its wind driven (non-electrical) power supply is what its going to be facing in the real world. Can you agree with that? If so that is the data that you need to work with. Not data gained from a motor driven situation.

This will tell you even more than the output of the PMA. It will give data on loads to the tower, drive shaft from the sails/vanes, and RPM that the wind will give. A wind gen is a total package, not just one item.

 

Driving your (both of you) PMA with a electric motor is great to find the max output. But gives you no real information thats usable in design.

I get your point, but you overstate the case. More data is never a bad thing. Studying and mapping the PMA output response to rpm and applied load supplies TONS of useful design data, such as the emf per pulse and the inductance of various winding configurations. Waiting to collect such data until you've built an entire installation would be foolhardy.