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Discussion Starter #1
Why are so many wind turbines designed in DC as opposed to AC.
And in an area that has a pretty consistant wind can you build a generator using an AC electric motor?
I work with DC systems but I really don't want all the batteries, the inverter and converter.
Can this whole process be streamlined for a better residential application?
The answer is probably simple but it's just not coming to me at the moment.


does anyone use a residential solar or wind power system?
 

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I'm no expert (only a few EE classes before I decided I liked computers and digital systems better than analogue and switched majors) I suspect it's easier to tie a system based on DC and a bank of batteries (acting as a buffer) into the power grid with an inverter than it is to take the varying output from an AC generator.

Can it be done better for home systems? Possibly, but again, there's the issue interfacing it with an existing power grid that most people aren't willing to give up just to move to a finicky power system -- and if they do give up the grid, they're going to want the battery bank as storage for windless days, or heavier use, etc.
 

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I'm no expert (only a few EE classes before I decided I liked computers and digital systems better than analogue and switched majors) I suspect it's easier to tie a system based on DC and a bank of batteries (acting as a buffer) into the power grid with an inverter than it is to take the varying output from an AC generator.

Can it be done better for home systems? Possibly, but again, there's the issue interfacing it with an existing power grid that most people aren't willing to give up just to move to a finicky power system -- and if they do give up the grid, they're going to want the battery bank as storage for windless days, or heavier use, etc.
:shock: Yes. This. Wait...I'm an accountant. Never mined. :-D
 

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I'm no expert (only a few EE classes before I decided I liked computers and digital systems better than analogue and switched majors) I suspect it's easier to tie a system based on DC and a bank of batteries (acting as a buffer) into the power grid with an inverter than it is to take the varying output from an AC generator.
I too am not an EE, but do deal with AC and DC telecom power plants for work. I'm guessing it might have something to do with the cycles per second. For electronics to work properly, the AC CPS need to be kept at about 60Hz. With the constant wind speed variation, it may cause issues with keeping the CPS constant (don't know for sure, just guessing). The batteries act as a type of noise filter from the generator and the invertor allows a clean AC sine wave out to the AC grid.
 

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Discussion Starter #5
With out filtering you'd get a hum in com lines but I'm not sure if it would affect standard house hold electronics. It may well though. Homes have become almost as sensitive as central offices. a fluctuation in the hz might not have an effect on the microwave but could be catastrophic to a home computer.
I know AC can't be stored but I never thought about the ramifications of the wave fluctuations.
 

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It was said already: The reason is that you have to hold AC at exactly 60 cycles per second. That frequency is generated by the revolutions per second of the generator shaft. It's really hard to maintain that with the unpredictability of the wind.

It's much easier to generate straight DC and then let the batteries act as a buffer, and feed it into a frequency-controlled inverter to get the AC perfect.

--Justin
 

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It was said already: The reason is that you have to hold AC at exactly 60 cycles per second. That frequency is generated by the revolutions per second of the generator shaft. It's really hard to maintain that with the unpredictability of the wind.

It's much easier to generate straight DC and then let the batteries act as a buffer, and feed it into a frequency-controlled inverter to get the AC perfect.

--Justin
This seems odd to me, varying the pitch of the blades and heading of the prop could get you close to constant input shaft speed. With transmissions you could refine it.

-mechanically inclined, electrically noobtarded here.
 

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I'm no expert on wind generators but it seems to me that generating DC is unneccessarily complicated because you need a commutator and all that good stuff ie. brushes and sparking etc. That's one of the reasons cars changed over from generators to alternators.
Why not just go the automotive route with wind generators by producing 3 phase AC (just needs ordinary smooth slip rings) and then convert to DC through diodes, for battery storage ,which then can be sent to an inverter for precise frequency control.
Just saying :p
 

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Look at a Regular car alternator.Without a Rectifier/regulator circuit you produce AC Voltage but at Varying voltages.It reaks Havoc on Electrical components compared to the steady DC output of 12-14 VDC.The Battery part sucks when trying to make Free Power but helps our electronics live.
 

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Off the Net said:
AC has at least three advantages over DC in a power distribution grid:

  1. Large electrical generators happen to generate AC naturally, so conversion to DC would involve an extra step.
  2. Transformers must have alternating current to operate, and we will see that the power distribution grid depends on transformers.
  3. It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice.
Sadly, you cannot store a A/C 'charge' but can store D/C. This is the biggest reason most household grids run on D/C. you can store it up when windy/sunny to use when not. In an A/C system, you could run things when you have the ability, otherwise, you are back on grid.
 

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The wind turbines have to produce AC at some point. Although you could use big diodes to rectify it for a DC battery charge, I believe that all the big ones use electronics to control the current flow through the phases to get the most power out of a revolution. This is a lot more efficient than just diode rectification but still produces a DC output. It is a lot like hybrid cars using the electric motors for regeneration during breaking. My company makes the control systems for hybrid cars and we have had a number of companies work with us to use similar controls on the big wind generators. I don't know about the smaller home type ones though.
 

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Discussion Starter #14 (Edited)
It was said already: The reason is that you have to hold AC at exactly 60 cycles per second. That frequency is generated by the revolutions per second of the generator shaft. It's really hard to maintain that with the unpredictability of the wind.

It's much easier to generate straight DC and then let the batteries act as a buffer, and feed it into a frequency-controlled inverter to get the AC perfect.

--Justin
The shaft rpm affects the cycle per second? I always assumed that the rpm of the shaft only affected the power output.
So a regulator not only controls voltage output but the hz as well.
didn't know that.
cool
 

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Discussion Starter #15
I'm no expert on wind generators but it seems to me that generating DC is unneccessarily complicated because you need a commutator and all that good stuff ie. brushes and sparking etc. That's one of the reasons cars changed over from generators to alternators.
Why not just go the automotive route with wind generators by producing 3 phase AC (just needs ordinary smooth slip rings) and then convert to DC through diodes, for battery storage ,which then can be sent to an inverter for precise frequency control.
Just saying :p
Thats actually a slick idea. Still need batteris though.
 

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The shaft rpm affects the cycle per second? I always assumed that the rpm of the shaft only affected the power output.
So a regulator not only controls voltage output but the hz as well.
didn't know that.
cool

3,600 RPM = 60 hz

3,000 RPM = 50 hz

To further complicate the matter, all big generators that are tied together on the power grid not only turn at 3,600 rpm but they all hit top dead center at the exact time so they can all remain in phase.

When a power plant brings a generator online they will sync it with the real world using a sync scope and will throw in the " tie to the power grid " when their generator hits TDC at the same time as the other generators from around the grid.

If they do not, it will cause a bump throughout the grid. If it is a large power plant and they sync out of time they can actually knock smaller power plants offline.

Most inverters are modified sine wave. The pure sine wave inverters are much more expensive. My bus has a 2,000 watt modified sine wave inverter with a built in 3 stage converter. That is tied to a bank of 4 - 6 volt agm batteries for house power plus 2 - 12 volt batteries for the diesel engine. Everything is backed up with 50 amp shore power and a 8,000 watt diesel generator.

Chris
 
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