Wind turbine voltage splitter

[verytricky]

Hi,

I have a wind turbine which runs most of the time below 150 volts, connected to a windmaster inverter, which is grid tied. The windmaster is limited to 150 volts, so I have a device which shorts out the turbine when 150 volts is reached - this activates the break to slow the turbine.

I was thinking of another solution.

Voltage dividers exist, I am using one to log the voltage generated by dividing the voltage by 10 because my data logger was designed for a 24 volt system, not 150 volts.


How easy would it be to build a device that when the voltage reaches 145 volts, it 'adds' in a circuit that acts as a voltage divider, taking off say 30 volts from the circut, so that the break device does not activate. If the wind speed ever got to the point when it procuced 180 volts, then the break device would get its 150 volts and activate the wind turbine break.

Such a device could help produce more power, as on the few occasions the turbine produces over 150 volts, it takes up to 3 minutes for every thing to reset and start generating power. So a gust of wind taking the voltage from a steady 120volts to a few seconds of 160 volts would loose a significant amount of power in relation to the period of the gust.

 

[Pommie]

If you use a voltage divider you will loose a lot of power in the resistors. A more elegant solution would be a crowbar circuit (google electronic crowbar). A crowbar will start to conduct at 150V and will take as much excess current as the turbine will supply. Your inverter will still get it's maximum amount.

The biggest problem is the power requirements of a crowbar. It will have to dissipate the excess energy produced, that is the difference in output at 180V compared to 150V. What is the rating of the turbine?

BTW, I have made the assumption that the turbine produces DC.

Mike.

 

[verytricky]

The turbine is a WINDSAVE 1200 there are no stats I can find as to its rating.

I am modifying the energy it produces to suit a Mastervolt Windmaster inverter, as the original Plug n Save inverter uses more energy than it produces. For example, in a three week period it produced a nett -0.1 kwh of energy. The Windmaster inverter currently produces a nett 0.8 kwh per day, with the same turbine and the same blades!!! This value will improve as I sort out the DC produced by the turbine. The DC is currently a cross between a SawTooth and a sine wave shape, and this affects the Mastervolts ability to produce electricity.

 

[Pommie]

Just googled it and it is supposed to produce 1.25kW and so over a day it should produce a lot more than 0.8kWh, or are you saying it produced an average of 0.8kW per hour over the 24 hours? This would be around 19kWH per day. At 50% capacity it should produce 15kWH per day.

If it is producing 0.8kW per day then stick it on ebay as it is a complete waste of time. If it's producing 20 kWH per day then it will reduce your electricity bill by $2 (ish) per day and so be worthwhile.

Can you check what the 0.8kWH per day actually means? There is a huge difference between 0.8kW and 0.8kWH/day. If you have any current values that will help to figure out what is being produced.

Mike

 

[Pommie]

Just found **broken link removed** and it appears that this is a complete con. Sorry.

Mike.

 

[verytricky]

Mike,

The Windsave 1200 is a complete con. That is why I got it for free.

It does not generate the 1.2kw unless there is a full blown storm ( ie constant 12m/s wind, and it shuts down at 14m/s windspeed! The other problem is their inverter - the 'plug n save' draws quite a lot of current - about an amp from the 240v mains whilst in standby mode.


I have TWO electricity meters 'plumbed' into the output of the inverter. one is a 'one way only' meter, with a ratchet to stop reverse electricity moving the wheel backwards - this shows me electricily produced only. The other is one that does not have the ratchet, so show NETT electricity, ie when the power goes to the inverter, and the inverter is not producing power, it runs backwards.

From these two meters I am calculating the actual electricity generated from the turbine.

My aim is - To come up with a system that gets electricity from the turbine in the low wind areas that they are currently instaled in.

First thing was to ditch the 'Plug n Save' which is totally useless.

Next thing is to get electronics and stuff to let the turbine drive a Windmaster - a cheap grid tied inverter that runs from 42 to 150 volts.

Final step is to produce turbine blades that make the most use of lower wind speeds, and furl out when the wind speeds pick up. This is my actual background, and the thing I have many ideas on.


Then - I want to go about retro fitting the Windsave installed units with things that actually work!

There are about 2000 of them installed in the UK and the current thinking is that over half are no longer being used, as in switched off!

If a cheap retrofit would work - that would be of benefit to those poor people who were suckered into buying the rubbish in the first place.


For info:

Yes when I say I am getting 0.8 kw per day I mean 0.8 KWH per 24 hour period - approximately 1 electrical unit on the meter! The generation meter shows 1 unit or 1kwh per 24 hours, but I am loosing about 0.2 KWH per day driving the thing.

This is better than when I had the plug and save installed - then it actually COST money to work.


I am sure if I can stop the inverter switching -which is due to the voltage fluctuations - I can generate a much higher KWH.

My solar pannel uses a Mastervolt inverter - the same thing with slightly differing software, and it generates 2 units a day from a 600watt system and this is England in winter!





To finalise the electronics I need to fix this, I would like to get some device that will absorb any voltage over the 150 volts when it is generated, so that the inverter still gets the voltage ..

I am working in another thread to get some smoothing help for the DC current that will also help the inverter. The inverter can handle 0.7kw or 700w output so I would like to try to get the inverter as close to this as possible for as long as possible....

 

[Willbe]

You want continuity to 150v and a voltage limiter after that.

Assuming smooth DC at first, the equivalent circuit would be a 150v Zener with a dropping resistor that varies from zero up to whatever is necessary to dissipate the extra power.

One way is to have a comparator that senses the 150v and switches in series resistors using one or more relays.

This gets a little tricky, Very.

Let's say the invertor draws constant power over a range of input voltages. And, it "likes" voltages between 120v and 150v.

Is there a single value of resistance that, when switched in, drops the invertor voltage from 180v to 120v?
If not, you need more than one value of resistance.

You can also use this circuit to switch in energy storage that can use from zero to 30v.

You've given us some center values and some limits; what are reasonable limits for invertor input voltages?
I think the whole design can fall out of this single interval, once known.

 

[verytricky]

The upper voltage is supposed to be 240v DC. I got this by running the turbine against a car tire simulating the max RMP the turbine goes before it turns on its own breaks.

Thus far in all my logging, I have seen a single spike of 205 volts but the highest 'normal' value of the turbine when running during a storm was 180 volts, then the tail caused it to furl - ie the electronic break did not kick in, the tail furled the turbine way before the electronic breaker value.

Electronically, the final component in my circut, just before the actual inverter is this 150V limiting switch. It was designed to stop anything over 150V hitting the inverter, so I can continue to use that as my safety switch, and work the balance of the electronics to suit the 80% of the cases.


So it is possible to 'dump' voltage into a thing like a 24v water heater? I can get one of those. So when the electronics senses 145 volts, it opens a gate for the voltage to get dumped into this 24 volt water heater...?

I could use that as a 'pre-heater' - water heading to my boiler can get pre-heated with excess wind energy, reducing the amount of heating required in the actual boiler, so that would be an effective way of utilising that 'excess' energy.

 

[Willbe]

So it is possible to 'dump' voltage into a thing like a 24v water heater? I can get one of those. So when the electronics senses 145 volts, it opens a gate for the voltage to get dumped into this 24 volt water heater...?

I don't see why not, at this point.

Can you post a system level schematic and a theory of normal operation so I can print it out?

Any patchwork circuitry has to not mess up normal operation. Seems to me, things that draw constant power can latch up into undesirable states with this sort of switching circuitry.
There are probably several options here, and we should thrash them out before buying a single hardware component.

 

[verytricky]

Can you post a system level schematic and a theory of normal operation so I can print it out?

Ummmmmn - I dont think I understand the question.

 

[Pommie]

This is the circuit that you need,
**broken link removed**

However, without knowing the current available at 150V and 180V it's impossible to calculate any values.

You would also need some big smoothing capacitors.

Mike.

 

[verytricky]

Mike,

I can get the current ( amps ) at each voltage. What I have done is a first step towards getting this information...

I have a lot of data: Windspeed vs Voltage and this is fairly consistent. I have placed a coil of copper wire around a broom stick to make a coil which has some resistance, placed into the wind turbine circut, and I will measure the voltage drop accross this copper coil, measure the ohms of the copper coil and then be able to calculate the amperage. At the same time I will continue to measure windspeed. I will then overlay this data onto my existing windspeed/voltage graph, creating a windspeed/voltage/amperage graph.

I am hoping the amps will increase with the voltage in a consistent manner, and I will also test this observation by using my multimeter at set times to get an accurate amperage to confirm the setup works.

A bit of a strange way perhaps, But I do not have an ampmeter with logging...

Then I should be able to provide you with realistic amp/volt readings.


I have just ordered the capacitors to smooth the DC current from the turbine. Once these are installed, I will run some tests for a while, then test the amperage when I am happy with the smoothing.

 

[verytricky]

This is the circuit that you need,
However, without knowing the current available at 150V and 180V it's impossible to calculate any values.

OK, I have had a look at the circut diagram you provided, and I dont understand it. ( not your fault! )

How does it work in theory, and which resistances are the inverter and water heater respectivly? Or is this an offshoot circut, designed to switch the water heater on, and has nothing to do with the existing circutry.

 

[Willbe]

Mine would have the water heater in series with invertor input, but the heater input is shorted out by relay contacts until the voltage exceeds 150v, at which point a comparator opens the contacts, then having the heater absorb the extra power.

But, depending on impedance levels, this setup could oscillate. Invertors that draw constant power act strangely.

This is one candidate setup. There are probably others but I need to see a system schematic and owner's manual.

 

[Pommie]

The circuit works by conducting once the voltage exceeds 150V. This increases the load on the turbine and prevents the voltage going any higher. As the turbine further increases in speed the circuit will take more current to hold the voltage at 150V. Your inverter will see the full 150V and take whatever current it requires. The load resistor (R2) could be your water heater but it depends on how the other limiting circuit works.

Do you have any information on the circuit that operates the brake?

An alternative circuit that switches in an additional load would be,
**broken link removed**
This is probably easier to understand. (R4 is the heater)
The relay wouldn't chatter as hysteresis is inbuilt.
<edit>This has the disadvantage that when 150V is reached it reduces the load on the turbine and the turbine would speed up. Not really desirable.</edit>

Mike.

 

[verytricky]

There are probably others but I need to see a system schematic and owner's manual.

There is no owners manual. WINDSAVE has made everything propriotory, and the booklett they give contains zero information on the turbine. It is a 'how to' book on things like dont use water to clean the inverter, in a storm turn on the break switch, this is how to change the fuse etc.

I have in fact thrown out their inverter, and replaced it with a Mastervolt grid tied inverter.

The current circut is simple and shown in the following picture.

 

[verytricky]

A soon to be made change will insert two capacitors into the feed, one before and one after the 'Black Box' to try and smooth the 'saw-tooth' sine wave DC voltage into a smoother current, as the Mastervolt is more efficient when it has smooth voltage.

 

[verytricky]

Do you have any information on the circuit that operates the brake?

No information at all. I do know - by tracing their inverter wiring - that turning on the switch called 'Wind Break' disconnects the inverter from the DC input ( opens a relay ) and then almost immediately it shorts the two DC input wires via a second relay.

When this break is applied the turbine is very stiff to turn, and slows down dramatically in good wind and stops completely in average wind.

I have tested this myself, holding the DC wires in hand. The turbine spins and touching the two wires together brings it to a halt. The 'Black Box' was a device I bough off the internet. It shorts the two input wires at about 149 volts, and this causes the turbine to slow down. The output wires from the black box drop directly to zero volts when this occurs. It holds this short for about 8 seconds, then releases the short, allowing the turbine to start turning again.



Thought!

This alternate diagram would be able to replace the 'Black Box', as it does the same function! Except in place of shorting the turbine, it actually does something usefull with the current...

 

[Willbe]

Shorting a generator provides dynamic braking. I think this is set up this way to prevent damage to the turbine. Sounds like we can't take advantage of high wind speeds.

 

[verytricky]

Cant take advantage of high wind speeds due to the limit on the inverter for input. Could dump it into a battery array? Then use that to feed the turbine in low wind speed situations???

There is an idea...