Hi,

I have a wind turbine.....

And it does not do exactly what I want, and I am trying to build a few things to improve matters.

One issue I have is that from time to time the voltage from the wind turbine dropps to just below the 42 volts that the inverter needs, so the inveter switches off. It takes a few minutes of 'sensing' for the inverter to produce lectricity again.

I had an idea, and I wondered how I would go about making it work.


I have a series of 12v batteries wired up to produce 48 volts. I already have these batteries. When the wind drops and the turbine produces less than the 42 volts the inverter needs, the battery bank switches in for the period of time that the voltage is too low. If the batteries get drained to 42 volts, the inverter switches off anyway - so I cant draw the batteries down too far. When the wind speed is high, I get in excess of 150 volts, and I can use that excess voltage in a circut to charge the batteries up during that period.

Typically the wind speed drops below the 42 volt range for only a few seconds at a time, but I 'loose' the next few minutes of generation whilst the inverter 'sences' the voltage is back.


Design issues:

There should be no 'feedback' of voltage to the batteries when the turbine generates between 50 to 150 volts. This results in a popped battery! I want to avoid that.

The switching should be as seamless as possible. If there is a break whilst the voltage is applied then the inverter will 'drop out' and the time delay will kick in.

The batteries should kick in if the voltage drops below 46 volts, but kick out if the voltage reaches 50 volts.

We can assume that by the time I build this I will have a stable DC signal, and not the current saw tooth voltage! So the period from when it switches on or off will be seconds/minutes apart, and not several times a second...

 

Isn't this the same topic as your other thread?

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Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com/

 

The topic is getting the tind turbine to work.

I thought for clarity that there should be seperate threads for each idea, as I thought they were completely seperate items:

1) How to divide 300 volts by 10 so a 30v logger can work. DONE
2) Smoothing circut for sawtooth DC current using capacitors. DONE
3) Circut to utilise voltages over 150 V for other uses.
4) Circut to inject voltage from battery when turbine voltage goes below 42 volts

My understanding of how these threads work is to divide them up into segments that are distinct. I fear that an answer on a few posts back regarding the smoothing circut could be misunderstood if I had just posted about the overvoltage and then read the reply.

Although they are all one project, they are distinct and seperate bits of electronics.

 

This could be done automatically by using diode switching. Two diodes would be required.Both diode's cathode ends would wire to the positive input terminal of the inverter. The anode of one diode would wire to the positive lead from the wind generator's output and the other diode's anode would wire to the positive terminal of your +48vdc battery string. Of course the inventor, generator and battery's negative lead all wire together.

Whichever diode's cathode has the higher voltage would cause all the current to flow from that source, so as long as your batteries stay at 46vdc the invertor will run even if the wind generator is disconnected and once the generator is producing more the 0.6vdc higher then the battery voltage then the current will flow from the generator. Just be sure the diodes current rating is in excess of your maximum current possible. They make diodes in screw mount version that allow for heatsinking. This method is called diode isolation and it works very well, no moving parts and is real inexpensive. The diodes also prevent any kind of 'backflow' from one voltage source to the other, so no problem there.

Lefty

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Measurement changes behavior

 

So I would get something like this:

DIODE SCHOTTKY 150V 80A D61-8 - VS-89CNQ150APBF

 

Yes, if you need the 80amp rating. Schottky diodes are even better because they have a lower forward bias voltage drop 0.2vdc Vc 0.6 for regular diodes so at 80amps of current flow they waste 32 less watts of power. They do usually cost more then plain diodes of the same rating.

Lefty

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Measurement changes behavior

 

Actually this one looks better, it's a dual diode in one package with a common cathode and is a lot cheaper:

DIODE SCHOTTKY 150V 80A TO-247 - STPS80150CW

Lefty

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Measurement changes behavior

 

I think I know the maximum amperage the wind turbine can provide is 12 amps, as this is the input fuse on the original inverter. With my limiting circutry before it gets to the inverter I am guessing the maximum Amperage will be 7 amps. Quite an educated guess actually, based on some sampling.


I am hot sure in my mind how the diode knows which line has the higher voltage? In my brain I can only see one half of the circut working.

*Disclaimer: Ex computer programmer. NOT an electronics person!

I can see how it will stop the reverse flow of electricity into the batteries from the turbine.
I can see how if there is no electricity from the turbine then the batteries would work.
I see how if there is voltage from the turbine then that gets connected.

I dont see how the battery line gets disconnected when the turbine line exceeds the battery voltage?

Can you show me a diagram, or offer an explanation? Please type slowly.

 

"I dont see how the battery line gets disconnected when the turbine line exceeds the battery voltage?"

The battery line doesn't get disconnected, it's isolation diode just stops conducting because it is reverse biased when the generator voltage is higher then the battery voltage. Lets try an example with real values. Assume the generator is turning good and outputing 60vdc. The inverter is seeing that 60vdc (minus the diode drop of less then one volt) on it's positive input terminal. The battery's diode is also seeing that 60vdc on it's common cathode terminal and the battery diode is seeing 48v on it's anode terminal.

Because the battery diode's cathode terminal is at a higher voltage the it's anode, it is reversed biased, turned off and no current can flow through it.

It's the reason that a diode will only allow AC current to flow in one direction when used as a rectifier, current can only flow through a diode when it's forward biased and blocks flow when reversed biased.

So it will work just like you want, no muss no fuss.

That better?

Lefty

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Measurement changes behavior

 

You obviously did not play much with the slow kids....


I will sit with this a bit and try get it sorted in my head. I am looking up the specification sheet and looking on the internet for the way things work. I should have it in a day or two.

The first project, the /10 voltage for the logging initially burned my brain, but its obvious now...

 

No problem, I've learned to be patient with software people.

A diode is fundamentally a voltage sensitive switching device, turning on and off depending on the polarity of the voltage applied across their two terminals.

Have a great Christmas

Lefty

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Measurement changes behavior

 

OK,

A diode basically stops current going one directlion, but allows it to move in the other ( yes there are the long list of exceptions, but basically )

A schottky diode has a very low forward voltage drop, and is thus efficient.

Here is a link to a 150volt 20 amp Schottky with three legs: A common cathode, basically two schottky diodes packaged into one box. DIODE SCHOTTKY 150V 20A TO220AB - STPS20150CT

This is setup with the three legs being InputAnode1, CommonCathode, InputAnode2


So:

The Negative DC wires from both the batteries and the wind turbine will connect directly to the inverter.

The Positive DC wire from the Wind turbine will connect to InputAnode1.

The Positive DC wire from the Batteries will connect to InputAnode2

Then a new wire will connect from the middle leg - CommonCathode - to the inverter.


Then magic happens because Dopey is poisoned with arsenic and was growing geraniums, and when the Battery Voltage exceeds the Wind turbine voltage, the electricity flows from the batteries, and when the Wind Turbine voltage exceeds the battery voltage, then the electricity flows from the Wind Turbine.

For some reason - possibly witchcraft - only one of these input legs will conduct electricity at any one time.

Sound about right?

 

One error, maybe a typo: "The Negative DC wires from both the batteries..."

I thought you were going to wire two 12 (woops four) volt batteries in series to make one 48vdc battery? If so, then only one battery's negative terminal hooks to the inverter and generator ground connection. Then one positive and one negative of each battery wire together and finally the single positive battery terminal left wires to a diode anode connection. That make sense? How you will charge that is left up to you as additional homework. You can always disconnect both batteries and charge them as two separate 12vdc batteries.

You got the rest right and all that homework pays off. I bet you didn't think you would get off this simple and cheap for this function.

Oh you probably should mount that diode pack to a smooth metal surface, maybe 6" square as it will be dissipating around 5-6 watts of heat at max current. Also be sure you make a good mechanical as well as electrical connection to the diode pins as your wire size is probably fairly thick and not easy to work with, you want to avoid mechanical stress to the diode pins by stress reliving the wire with clamps or grommets, etc.

Be careful because all but a few of those kinds of pack have the metal mounting tab connected electrically to one of the pins, that makes it 'hot' to ground so either add a mica insulator between the pack and plate and be sure the bolt doesn't contact the plate and use heat sink paste if possible. Or just mount the whole plate without insulators inside of something and remember (label it!) it's hot to ground.

Good luck
Lefty

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Measurement changes behavior

 

Americans.... Sheeesh!

Translation:

The negative wires, one from the batteries and another one from the Turbine will be connected to the inverter directly. Both refers to the two negative wires, one from each source. No typo, just a huge ocean.


I am going to wire up FOUR 12 volt batteries in series to make a 48 volt super battery to fill in the 'holes'.



You are right - There was no way I expected this to work out this cheap! I was expecting a hell of a complicated very fussy circut!!!




For the ultimate laugh of the day perhaps?:
When I was initially experimenting with wind turbines, I had setup two cheap and nasty 24 volt turbines right next to each other, and played around with altering the blades, ie numbers, profiles, lengths etc. I still have these, and they are still mounted right near the new turbine. I am going to use these two wind turbines to charge the batteries! One turbine charging its own set of two batteries. So the 'filler' electricity from the batteries will also come from the wind, just from cheap and nasty 24 volt systems.

This is great because I then use all the equipment I have already and I dont waste anything.

I will be humping batteries from the garage to the shed tomorrow- they are very heavy and I cant use a wheel barrow due to the mud, so that will be my excercise for the month!

 

Arrived in the post this afternoon. Tomorrow will be the big test day!!!

All I need now is some wind!